Materials Technology for Engineers pre-test 1 notes

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SUMMARY NOTES + 200 QNS
musadoto
AE 217
LATEST WORLD’S MULTIPLE
CHOICES

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Course objectives
Upon completion of the course, students will be able to:
(i) Identify internal structure and behavior of metallurgical materials.
(ii) Identify internal structure and behavior of timber.
(iii) Identify behaviors of mineral binders, composite materials and plastics.
PART I
Metallurgy: Materials classification: ferrous and non-ferrous materials. Single phase
materials: internal structure, inter atomic bonding; crystallography; defects in crystals;
structure of metals. Multi-phase materials: microstructure of alloys (phase diagrams);
precipitation hardening; thermo-mechanical treatment of steel, case hardening,
tempering, annealing, normalizing. Mechanical properties: elastic and plastic behavior
of crystalline solids, dislocation, work hardening and annealing; time dependent
behavior; fracture mechanism. Testing of materials: destructive and non-destructive
methods, tensile, hardness, notched bar, creep and fatigue tests. Corrosion:
electrochemical corrosion, construction materials, strength and corrosion resistance,
corrosion-prevention techniques, materials selection.
PART II
Timber:
Wood structure, defects, grading, physical and mechanical properties, durability and
preservation, joints.
Mineral binders:
Gypsum, lime, cement: production processes, chemical backgrounds, technical
properties. Concrete: constituents; properties of fresh and hardened concrete, mix
design and quality control, light-weight concrete.
Composite materials; sintered products
Plastics: Types, characteristics and their use in agriculture.
Practicals: Practicals will be conducted on analysis of internal structure and
behaviour of building materials under different environment
COURSE CONTENTS
SUMMARIES ARE BASED ON CLASS NOTES AND CALLISTER BOOK 7Th
edition

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TOPIC 1: INTRODUCTION
After careful study of this chapter you should be able to do the following:
1. List six different property classifications of materials that determine their applicability.
2. Cite the four components that are involved in the design, production, and utilization of
materials, and briefly describe the interrelationships between these components.
3. Cite three criteria that are important in the materials selection process.
4. (a) List the three primary classifications of solid materials, and then cite the distinctive
Chemical feature of each.
(b) Note the other three types of materials and, for each, its distinctive feature(s).
THE HISTORY OF MATERIAL TECHNOLOGY
Materials are probably more deep-seated in our culture than most of us realize.
Transportation, housing, clothing, communication, recreation, and food production virtually
every segment of our everyday lives is influenced to one degree or another by materials.
Historically, the development and advancement of societies have been intimately tied to the
members’ ability to produce and manipulate materials to fill their needs. In fact, early
civilizations have been designated by the level of their materials development (i.e., Stone
Age, Bronze Age). The earliest humans had access to only a very limited number of
materials, those that occur naturally: stone, wood, clay, skins, and so on. With time they
discovered techniques for producing materials that had properties superior to those of the
natural ones; these new materials included pottery and various metals. Furthermore, it was
discovered that the properties of a material could be altered by heat treatments and by the
addition of other substances. At this point, materials utilization was totally a selection
process, that is, deciding from a given, rather limited set of materials the one that was best
suited for an application by virtue of its characteristics. It was not until relatively recent
times that scientists came to understand the relationships between the structural elements of
materials and their properties. This knowledge acquired in the past 60 years or so, has
empowered them to fashion, to a large degree, the characteristics of materials. Thus, tens of
thousands of different materials have evolved with rather specialized characteristics that
meet the needs of our modern and complex society; these include metals, plastics, glasses,
and fibers. The development of many technologies that make our existence so comfortable
has been intimately associated with the accessibility of suitable materials. An advancement
in the understanding of a material type is often the forerunner to the stepwise progression of
a technology. For example, automobiles would not have been possible without the
availability of inexpensive steel or some other comparable substitute. In our contemporary
era, sophisticated electronic devices rely on components that are made from what are called
semiconducting materials.
Stone→Bronze→Iron→AdvancedMaterials

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MATERIALS SCIENCE AND ENGINEERING
 ―materials science‖ involves investigating the relationships that exist between the
structures and properties of materials.
 “materials engineering” is, on the basis of these structure–property correlations,
designing or engineering the structure of a material to produce a predetermined set of
properties.
From a functional perspective, the role of a materials scientist is to develop or
synthesize new materials, whereas a materials engineer is called upon to create
new products or systems using existing materials, and/or to develop techniques for
processing materials. Most graduates in materials programs are trained to be both
materials scientists and materials engineers.
The structure of a material usually relates to the arrangement of its internal
components. Subatomic structure involves electrons within the individual atoms
and interactions with their nuclei. On an atomic level, structure encompasses the
organization of atoms or molecules relative to one another. Structural elements that
may be viewed with the naked eye are termed as ―macroscopic.‖ (no need of
microscope).
A property is a material trait in terms of the kind and magnitude of response to
a specific imposed stimulus. Generally, definitions of properties are made
independent of material shape and size.
In addition to structure and properties , two other important components are
involved in the science and engineering of materials—namely, ―processing‖ and
―performance.‖ With regard to the relationships of these four components, the
structure of a material will depend on how it is processed. Furthermore, a material’s
performance will be a function of its properties. Thus, the interrelationship between
processing, structure, properties, and performance is as depicted in the schematic
illustration shown in Figure below. Throughout this text we draw attention to the
relationships among these four components in terms of the design, production, and
utilization of materials.
Structure→ Processing →Properties→ Performance

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WHY STUDY MATERIALS SCIENCE AND ENGINEERING?
Why do we study materials? Many an applied scientist or engineer, whether mechanical,
civil, chemical, or electrical, will at one time or another be exposed to a design problem
involving materials. Examples might include a transmission gear, the superstructure for a
building, an oil refinery component, or an integrated circuit chip. Of course, materials
scientists and engineers are specialists who are totally involved in the investigation and
design of materials.
1. Many times, a materials problem is one of selecting the right material from the many
thousands that are available. There are several criteria on which the final decision is
normally based. First of all, the in-service conditions must be characterized, for these
will dictate the properties required of the material. On only rare occasions does a
material possess the maximum or ideal combination of properties. Thus, it may be
necessary to trade off one characteristic for another. The classic example involves
strength and ductility; normally, a material having a high strength will have only a
limited ductility. In such cases a reasonable compromise between two or more
properties may be necessary.
2. A second selection consideration is any deterioration of material properties that
may occur during service operation. For example, significant reductions in mechanical
strength may result from exposure to elevated temperatures or corrosive
environments.
3. Finally, probably the overriding consideration is that of economics: What will the
finished product cost? A material may be found that has the ideal set of properties but
is prohibitively expensive. Here again, some compromise is inevitable. The cost of a
finished piece also includes any expense incurred during fabrication to produce the
desired shape.
The more familiar an engineer or scientist is with the various
characteristics and structure–property relationships, as well as processing
techniques of materials, the more proficient and confident he or she will be
to make judicious materials choices based on their criteria.
APPLICATION OF ENGINEERING MATERIALS IN OUR DAILY LIFE.
1. Housing 2. Communication 3. Clothing 4. Recreation 5. Transportation
Material properties that observed at subatomic level, atomic level,
microscopic level, macroscopic level.

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Our role in engineering materials then is to understand the application and specify the
appropriate material to do the job as a function of:
a. Strength (yield and ultimate)
b. Ductility, flexibility
c. Weight/density
d. Working environment
e. Cost: Lifecycle expenses, Environmental impact.
CLASSIFICATION OF MATERIALS
Solid materials have been conveniently grouped into three basic classifications: metals,
Ceramics and polymers. This scheme is based primarily on chemical makeup and atomic
structure, and most materials fall into one distinct grouping or another, although there are
some intermediates. In addition, there are the composites, combinations of two or more of
the above three basic material classes. Another classification is advanced materials-those
used in high-technology applications, Semiconductors, biomaterials, smart materials, and
Nano-engineered materials.
1. METALS
Materials in this group are composed of one or more metallic elements (such as iron,
aluminum, copper, titanium, gold, and nickel), and often also nonmetallic elements
(for example, carbon, nitrogen, and oxygen) in relatively small amounts.3 Atoms in
metals and their alloys are arranged in a very orderly manner. Metals have the
following characteristics;
a) Strong
b) Ductile
c) High thermal & electrical conductivity
d) Opaque and reflective.

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2. CERAMICS
Ceramics are compounds between metallic and nonmetallic elements; they are most
frequently oxides, nitrides, and carbides. For example, some of the common ceramic
materials include aluminum oxide (or alumina, Al2O3), silicon dioxide (or silica,
SiO2), silicon carbide (SiC), silicon nitride (Si3N4), and, in addition, what some refer
to as the traditional ceramics-those composed of clay minerals (i.e., porcelain), as
well as cement, and glass. Have the following characteristics of ionic bonding
(refractory)-compounds of metallic & non-metallic elements (oxides, carbides,
nitrides, sulfides), Brittle, glassy, elastic, hard: non-conducting(insulators);high
resistive to temperature and harsh environments. e.g glass, porcelain.
3. POLYMERS/PLASTICS
Polymers include the familiar plastic and rubber materials. Many of them are organic
compounds that are chemically based on carbon, hydrogen, and other nonmetallic
elements ( O,N, and Si). Furthermore, they have very large molecular structures, often
chain-like in nature that have a backbone of carbon atoms. Some of the common and
familiar polymers are polyethylene (PE), nylon, poly(vinyl chloride) (PVC),
polycarbonate (PC), polystyrene (PS), and silicone rubber. These materials typically
have low densities , whereas their mechanical characteristics are generally dissimilar
to the metallic and ceramic materials-they are not as stiff nor as strong as these other
material types However, on the basis of their low densities, many times their
stiffnesses and strengths on a per mass basis are comparable to the metals and
ceramics. In addition, many of the polymers are extremely ductile and pliable (i.e.,
plastic), which means they are easily formed into complex shapes. In general, they are
relatively inert chemically and unreactive in a large number of environments. One
major drawback to the polymers is their tendency to soften and/or decompose at
modest temperatures, which, in some instances, limits their use. Furthermore, they
have low electrical conductivities and are nonmagnetic. Characteristics are
summarized below as
a. Soft
b. Ductile
c. low strength
d. low density
e. Thermal & electrical insulators
f. Optically translucent or transparent. E.g. Plastics rubber

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COMPOSITE MATERIALS
A composite is composed of two (or more) individual materials, which come from the
categories discussed above i.e metals, ceramics, and polymers.The design goal of a
composite is to achieve a combination of properties that is not displayed by any single
material, and also to incorporate the best characteristics of each of the component
materials. A large number of composite types exist that are represented by different
combinations of metals, ceramics, and polymers. Furthermore, some naturally
occurring materials are also considered to be composites-for example, wood and bone.
However, most of those we consider in our discussions are synthetic (or man-made)
composites. One of the most common and familiar composites is fiberglass, in which
small glass fibers are embedded within a polymeric material (normally an epoxy or
polyester).The glass fibers are relatively strong and stiff (but also brittle), whereas
the polymer is ductile (but also weak and flexible). Thus, the resulting fiberglass is
relatively stiff, strong, flexible, and ductile. In addition, it has a low density.Another
of these technologically important materials is the ―carbon fiber-reinforced
polymer‖ (or ―CFRP‖) composite-carbon fibers that are embedded within a polymer.
These materials are stiffer and stronger than the glass fiber-reinforced materials, yet
they are more expensive.The CFRP composites are used in some aircraft and
aerospace applications, as well as high-tech sporting equipment (e.g., bicycles,
golf clubs, tennis rackets, and skis/snowboards).
Note Fiberglass is sometimes also termed a ―glass fiber-reinforced
polymer‖ composite, abbreviated ―GFRP.‖
MATERIAL PROPERTIES AND QUALITIES
Properties are the way the material responds to the environment and external forces.
1. Physical Properties: Density, Melting Point, Hardness.
2. Mechanical Properties: Response to mechanical force( yield, tensile, compressive
and torsional strength, Ductility, Fatigue Strength, Fracture, Toughness).
3. Manufacturing Properties: Ability to be shaped by Moulding, Casting, Plastic
Deformation, Powder processing, Machining, Ability to be joined by adhesives,
Welding etc
4. Chemical Properties: Resistance to oxidation, corrosion, solvents and environmental
factors.
5. Electrical and Magnetic Properties: Response to electrical and magnetic fields,
conductivity etc
6. Thermal Properties: related to transmission of heat and heat capacity.
7. Optical Properties: Include absorption, transmission and scattering of light.
8. Economic Properties: Raw material and processing costs, availability.
9. Aesthetic Properties: Appearance, texture and ability to accept special finishes .

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FUTURE OF MATERIALS SCIENCE
Design of materials having specific desired characteristics directly from our
knowledge of atomic structure.
Miniaturization: ―Nanostructured" materials, with microstructure that has length
scales between 1 and 100 nanometers with unusual properties. Electronic components,
materials for quantum computing.
Smart materials: airplane wings that adjust to the air flow conditions, buildings that
stabilize themselves in earthquakes.
Environment-friendly materials: biodegradable or photodegradable plastics,
advances in nuclear waste processing, etc.
Learning from Nature: shells and biological hard tissue can be as strong as the most
advanced laboratory-produced ceramics, mollusces produce biocompatible adhesives
that we do not know how to reproduce.
TERMINOLOGIES TO KNOW
1. Alloy: Metallic material consisting a mixture of two or more metals/ or A mixture of
metallic and non-metallic.
2. Deformation: Loss of original figure and shape without falling apart (rapture).
3. Ductility: Ability of a material to sustain large deformation without fracture.
4. Fatigue: Failure of material caused by repeated load (cyclic loading/alternating
stresses, vibrations).
5. Hardness: Resistance of surface of a material to penetration, indentation, scratches.
6. Toughness: Ability of a material to be worked, hammered or shaped under pressure
or blows without falling/breaking.
7. Brittleness: Ability of the material to fracture (fail) with minimum deformation.
8. Stress: The ratio of applied force/cross sectional area upon which it acts.
9. Strain: Deformation brought about by stress; ΔL/L
10.Ultimate Tensile Strength: Minimum stress to cause failure under standard
conditions.

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TOPIC 2:METALLURGY
MATERIALS CLASSIFICATION
Choice of materials for a machine element depends very much on its properties, cost,
availability and such other factors. It is therefore important to have some idea of the
common engineering materials and their properties before learning the details of design
procedure.
Common engineering materials are normally classified as
1. METALS (cast iron , steel and wrought iron).
2. NON METALS
a. Light metal group such as aluminum and its alloys, magnesium and
manganese alloys.
b. Copper based alloys such as brass (Cu-Zn), bronze (Cu-Sn).
c. White metal group such as nickel, silver, white bearing metals eg.
SnSb7Cu3, Sn60Sb11Pb, zinc

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FERROUS METALS
Metallic materials are inorganic substances which are composed one or more metallic
elements and also contain some nonmetallic elements. Metals are usually found in the form
of ores which are raw or crude form impurities includes oxides, sulphides, nitrites, sulphates
and traces elements like inert gasses. Ferrous materials are usually refers to the materials that
have a high content of iron in them. Iron is the one of the most common element in earth
crust making 5% of earth crust. Ferrous compounds are usually garnished in color
OCCURRENCE OF IRON:
Iron is never available in pure form it is available in the form of different ores the most
common ore is hematite various form of iron and steel are obtained by purifying and
adjusting the composition of pig iron by suitable methods.
Types of Iron Ores (on the basis of Iron Content):
Magnetite (72%-75%) Fe3O4
Hematite (70%) Fe2O3
Iron pyrite (47%) FeS
Siderite (40%) Fe2Co3
The reduction of hematite is easy so we prefer it. Iron is extracted from hematite or the
separation of iron by reduction with carbon is very reactive. This process takes place in a
blast furnace at 20000
c.
TYPES OF FERROUS METALS:
Pig iron
Cast iron
Wrought iron
steel
QN. The basic difference between iron and steel???
Main difference
Many people consider iron and steel to be similar and get confused about the differences. It
is safe to say that they are similar and that actually is the main difference as well. Iron is a
pure substance that exists on its own WHILE steel is considered an alloy of iron.The other
difference between them is that iron is regarded as brittle materials WHILE steel is viewed
as an active material .

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COMPARISON CHART
Key Differences
Iron is considered a real element that has properties which are true in nature. On the
other hand, steel is an alloy of iron which does not have pure features.
Iron can easily get oxidized and then result in rust and therefore does not have a shiny
surface, while steel, on the other hand, has different elements that protect it from
rushing, hence providing it with shine.
Iron is made up of itself while steel is made up of iron and carbon.
The iron itself is not as sturdy and is considered as a brittle material. Steel, on the
other hand, has carbon in it which makes it one of the most powerful metal to exist.
Iron was initially used for building purposes, but now steel is utilized for that purpose.
Iron is used for making tools and instruments and automobiles while steel is used in
making buildings, rails, and other architecture.
There are different types of steel which include carbon steel and alloy steel. While the
types of iron are many, but the most famous ones include cast iron, wrought iron and
steel.
Types of Ferrous Metals:
1. Pig iron
2. Cast iron
3. Wrought iron
4. steel

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PIG IRON
It is most impure and crudest form of iron. To remove the impurities from the ores some
treatments are necessary. Pig iron contains (3.5%-5%) carbon content. Carbon is added by
melting it the product obtained is called pig iron.
Properties of Pig Iron:
It is neither ductile nor malleable.
It melts easily.
It is difficult to bend.
Its fusion temperature is 1200o
c.
It can be hardened but cannot be tempered.
It cannot be magnetized.
It does not rust easily.
It cannot be welded.
It has very high compression strength but very small in tension and shear.
It is low in cost.
Uses of Pig Iron:
It is use in the manufacturing of cast iron.
It is use in the manufacturing of wrought iron.
It is use in the manufacturing of different forms of steels.
It is use to make wheels and iron pipes.
Because of its high compression strength it is use in column boxes and plates.
CAST IRON
When we melt the pig iron in the presence of coke and calcium carbonate the product
obtained is called cast iron. It has gray white color its gray color is due to the presence of
graphite and white due to the presence of carbon (carbides).It can be transferred into
different molds of desired shapes and size. It contains (1.5%-4%) carbon content and a small
amount of manganese.
Properties of Cast Iron:
It is available in two colors gray and white.
Its structure is crystalline and fibers.
It is brittle in nature.
It cannot with stand shocks and impacts.
It cannot be welded.
It cannot be magnetized.
It is not ductile.

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It is not malleable.
It cannot be crust easily.
Its melting point is (1175%-1290%) CO.
It can be hardened and tempered.
Its specific gravity is 7.5
It becomes soft in salt solutions.
It is weak in shear and tension.
It is strong in compression.
Very good casting characteristics.
Low cost High compressive strength
Good wear resistance
Excellent machinability
Uses of Cast Iron:
It is used for making grain water pipes.
It is used for making columns.
It is used for making storage tanks.
It is used to support for heavy machinery.
It is used for making wheel and railway tracks.
It is used for making wrought iron.
The varieties of cast iron in common use are:
a. Grey cast iron
b. White cast iron
c. Malleable cast iron
d. Spheroidal or Nodular graphite cast iron
e. Chilled cast iron
f. Alloy cast iron
g. Austenitic cast iron
A. GREY CAST IRON
It is the iron which is most commonly used in foundry work. If this iron is machined or
broken, its fractured section shows the greyish colour, hence the name ―grey‖ cast iron.
The grey colour is due to the fact that carbon is present in the form of free graphite.
A very good characteristic of grey cast iron is that the free graphite in its structure
acts as a lubricant. This is suitable for those components/products where sliding
action is desired.
The other properties are:
good machinability,
high compressive strength, low tensile strength and
no ductility.

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In view of its low cost, it is preferred in all fields where ductility and high strength
are not required.
The grey cast iron castings are widely utilized in machine tools bodies (lathe) and
slideways, automobile cylinder blocks and flywheels, etc.
Some examples of grey cast iron are ;
FG20,
FG35 or
FG35Si15.
The numbers indicate ultimate tensile strength in MPa and 15 indicates 0.15% silicon.
B. WHITE CAST IRON
It is so called due to the whitish colour shown by its fracture. White cast iron contains
carbon exclusively in the form of iron carbide Fe3C (cementite) which is HARD and
BRITTLE.
From engineering point of view, white cast iron has limited applications. This is
because of poor machinability and possessing, in general, relatively poor mechanical
properties.
It is used for inferior castings and places where hard coating is required as in outer
surface of car wheels.
Only crushing rolls are made of white cast iron. But it is used as raw material for
production of malleable cast iron.
It is very hard. Therefore it is suitable for making surfaces that resist abrasion, such as
brake drums, clutch plates and sliding parts of machinery
C. MALLEABLE CAST IRON
The malleable cast iron is produced from white cast iron by suitable heat treatment, i.e.,
annealing.
The white cast iron is brittle and hard. It is, therefore, unsuitable for articles which are
thin, light and subjected to shock and vibrations or for small castings used in various
machine components.
The malleable cast iron is ductile and may be bent without rupture or breaking the
section. Its tensile strength is usually higher than that of grey cast iron and has
excellent machining qualities and is inexpensive.
Malleable cast iron components are mainly utilized in place of forged steel or parts
where intricate shape of these parts creates forging problem (or where forging is
expensive). This material is principally employed in rail, road automotive and pipe
fittings etc.

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D. NODULAR CAST IRON
It is also known as ―spheroidal graphite iron‖ or Ductile iron or High strength ―Cast iron‖.
This nodular cast iron is obtained by adding magnesium to the molten cast iron.
The magnesium converts the graphite of cast iron from flake to spheroidal or nodular
form. In this manner, the mechanical properties are considerably improved. The
strength increases, yield point improves and brittleness is reduced. Such castings can
even replace steel components.
Outstanding characteristics of nodular cast iron are high fluidity which allows the
castings of intricate shape. This cast iron is widely used in castings where density as
well as pressure tightness is a highly desirable quality.
The applications include hydraulic cylinders, valves, pipes and pipe fittings, cylinder
head for compressors, diesel engines, etc.
They are designated as, for example,
 SG50/7,
 SG80/2 etc
where the first number gives the tensile strength in Mpa and the second number indicates
percentage elongation.
E. CHILLED CAST IRON
Quick cooling is generally known as chilling and the iron so produced is ―chilled iron‖.
 The outer surface of all castings always gets chilled to a limited depth about (1 to 2
mm) during pouring and solidification of molten metal after coming in contact with
cool sand of mould
 Chills are employed on any faces of castings which are required to be hard to
withstand wear and friction. Chilled castings are used in producing stamping dies and
crushing rolls railway, wheels cam followers, and so on.
F. ALLOY CAST IRON
Alloying elements are added to cast iron to overcome inherent deficiencies in ordinary cast
iron to provide requisite characteristics for special purposes.
The alloy cast iron is extremely tough, wear resistant and non-magnetic steel about 12
to 14 per cent manganese should be added.
They are also known as Abrasion resistant cast iron.

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A typical designation is ABR33 Ni4 Cr2 which indicates a tensile strength in kg/mm2
with 4% nickel and 2% chromium.
G. AUSTENITIC CAST IRON
They are used for making automobile parts such as cylinders, pistons, piston rings, brake
drums etc.
(More details click the title ).
WROUGHT IRON
It is the purest form of iron. It contains 99% iron and 1% impurity( traces of carbon,
phosphorus, manganese, silicon, sulphur and slag). In wrought iron corrosion will be
large. It is the most common type of iron used in engineering.
Properties of Wrought Iron:
Its structure is fibers.
It is ductile and malleable.
It can be welded
It is tough.
It can withstand shocks and impacts.
Its melting point is 1500o
c.
It is softening at 900o
c.
It can rust easily.
It is unaffected from any salt solution.
It can be magnetized.
It is a good conductor of heat and electricity.
Uses of Wrought Iron:
It is used for making sheets due to its malleability.
It is used for making rods.
It is used for making gas pipes.
It is used for making boiler tubes.
It is used for making window frames.
Produced by re-melting pig iron.

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STEEL
Steels are the large family of metals which consists mostly of iron and other elements
usually carbon ranging (0.2%-2.1%) depending upon the grades carbon is the most common
alloying material for iron but various other alloying metals may also be used such as
manganese, chromium, tungsten, vanadium etc…Difference between cast iron and steel is
due to its carbon contents. Steel goes harder and tougher with an increase in carbon content
up to 1.7%.This carbon will not combine with iron and will be present as a free graphite.
TYPES OF STEEL
Plain Carbon steel
Alloy steel
Stainless steel
PLAIN CARBON STEEL
Steel containing (0.2%-1.5%) carbon content is called carbon steel it is further classified into
3 types.
Low carbon steel (dead mild steel)
Medium carbon steel (mild carbon steel)
High carbon steel
Types Carbon content Use in making
Low carbon steel 0.2% Sheets, wires, pipes ,screws
Medium carbon steel (0.3%-0.7%) Wheels, axels, boilers, blades
High carbon steel (0.7%-1.5%) Surgical instruments, blades, sprigs, cuttlry
The properties of plain carbon steel depend mainly on the carbon percentages and other
alloying elements are not usually present in more than 0.5 to 1% such as 0.5% Si or 1% Mn
etc. There is a large variety of plane carbon steel and they are designated as C01, C14, C45,
C70 and so on where the number indicates the carbon percentage.
Properties of Medium Carbon Steel:
Its structure is fibers.
It has dark blue color.
It is ductile and malleable.
It is more tuff and elastic.
Its corrosion rate is high.
It can be magnetized permanently.

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It can with stand with shocks and impacts.
It can with stand shear.
It can be welded.
It is difficult to harden and tempered.
Uses of Medium Carbon Steel:
It is extensively used to reinforce the concrete structures.
It is used in construction works. Like angle iron, rods, e-sections etc…
It is used in the manufacturing of various tools. Like machine parts and railway tracks
etc…
Properties of High Carbon Steel:
It has granules structure.
It is more tuff and elastic then medium carbon steel.
It is easy to harden and tempered.
It is more difficult to weld.
It can be magnetized easily.
It can withstand shocks and impacts.
Uses of High Carbon Steel:
It is used in surgical instruments.
It is used in cutlery.
It is used in making springs.
It is used in tools for drilling.
It is used in making blades.
It is used in machine parts with good hardness, toughness and durability.
ALLOY STEEL
Alloy steel can be made by adding small quantities of other elements to carbon steel, for
example, boron, chromium, cobalt, copper and nickel. The different elements added are able
to improve the physical and mechanical properties of steel such as wear resistant, corrosion
resistance, electric or magnetic properties. Some examples of alloy steels are 35Ni1Cr60,
30Ni4Cr1, 40Cr1Mo28, 37Mn2.
Alloy steel has also three types
1. Manganese steel (10%-18% manganese)
2. Silicon steel (1%-5% silicon)
3. Nickel steel (2%-04% nickel)

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The carbon content of high speed steel is approximately 0.75%. It also contains small
quantities of chromium, vanadium and tungsten. It is harder than carbon steel, and can even
retain its hardness while being cut at high speed. Therefore it is suitable for manufacturing.
various cutting tools such as turning tools and drill bits .
STAINLESS STEEL
Stainless steel contains chromium and a small quantity of nickel. It is very resistant to
corrosion, and does not easily undergo oxidation or rusting. As it does not rust easily, its
surface can usually remain smooth. It is shiny and silvery white in colour. Stainless steel is
often used in the manufacturing of products with a high degree of resistance to rust, such as
cutlery, kitchen utensils, sinks and moving blades of steam turbines. One important type of
stainless steel is often described as 18/8 steel where chromium and nickel percentages are 18
and 8 respectively. A typical designation of a stainless steel is 15Si2Mn2Cr18Ni8 where
carbon percentage is 0.15.
Note: If carbon content is greater than 1% then steel is called as cast steel .
EFFECTS OF ALLOYING ELEMENTS IN STEEL

1. Nickel - ferrite strengthener; increases the hardenability and impact strength of steels.
2. Chromium- for hardness and strength
3. Tungsten- for hardness at elevated temperature.
4. Vanadium- for tensile strength
5. Manganese – strength and hardness; decreases ductility and weldability; effects
hardenability of steel.
6. Silicon – one of the principal deoxidizers used in steel making. In low-carbon steels,
silicon is generally detrimental to surface quality.
7. Copper – detrimental to hot-working steels; beneficial to corrosion resistance
(Cu>0.20%).
8. Molybdenum- increases the hardenability; enhances the creep resistance of low-alloy
steels. For extra tensile strength.
9. Phosphorus – increases strength and hardness and decreases ductility and notch
impact toughness of steel.
10.Sulfur- decreases ductility and notch impact toughness Weldability decreases. Found
in the form of sulfide inclusions.

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NON-FERROUS METALS
Ferrous materials are usually refers to the materials that have a low content of iron in them.
Some important nonferrous metals are aluminum, copper, lead, tin and zinc. Non-ferrous
metals are those which do not contain significant quantity of iron or iron as base metal.
These metals possess low strength at high temperatures, generally suffer from hot shortness
and have more shrinkage than ferrous metals.
They are utilized in industry due to following advantages:
1. High corrosion resistance
2. Easy to fabricate, i.e., machining, casting, welding, forging and rolling
3. Possess very good thermal and electrical conductivity
4. Attractive colour and low density
 The various non-metals used in industry are: copper, aluminum, tin, lead, zinc, and
nickel, etc., and their alloys.
THE ARBITRARY CLASSIFICATION OF NON-FERROUS METALS
1 Light metals: Aluminum, Magnesium, Titanium, Beryllium, and so on.
2 Heavy metals: Copper, Zinc, Lead, Tin, and so on.
3 Refractory metals: Tungsten, Nickel, Molybdenum, Chromium, and so on.
4 Precious metals: Gold, Silver, Platinum, and so on.
Aluminum is the highest ranking material in use next to steel. Copper and its alloys (brass
and bronze) rank second while Zinc ranks third in consumption. Light weight of certain
nonferrous materials are of special importance in aircraft and space industry. Zinc, tin and
lead (with low melting points) are used in special applications. Tungsten, molybdenum and
chromium are used in products that must resist high temp. Nickel and cobalt are also suitable
as heat resistant alloys. Precious metals (with high cost) are not only used in jewelry, but
also in many applications requiring high electrical conductivity and corrosion resistance
ALUMINUM
Aluminum found its maximum use in every field of engineering due to its particular
properties softness, lightweight it has become very useful metal in all over the world.
Modified metallurgical processes have improved strength and durability of different metals
to such an extent that it has made maximum use of aluminum in engineering processes.

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Properties Aluminum:
It is highly ductile.
It is malleable.
It is light in weight.
It can withstand corrosion.
It is the good conductor of heat and electricity.
It is very soft in nature.
It can be melted easily.
Its melting point is 6600C.
It has good strength and durability.
Uses:
It is use in making door and windows.
It is use in making pipes.
It is use in making electrical cables.
It is use in making panels.
It is use in making air craft’s.
It is use in making automobile parts.
It is use in making alloys
LEAD
Lead is the heaviest of the common metal. Lead is extracted from its ore known as galena. It
is bluish grey in colour and dull lusture which goes very dull on exposure to air.
Properties and Uses
Its specific gravity is 7.1 and melting point is 360°C.
It is resistant to corrosion and many chemicals do not react with it (even acids).
It is soft, heavy and malleable, can be easily worked and shaped.
Lead is utilized as alloying element in producing solders and plumber’s solders.
It is alloyed with brass as well as steel to improve their machinability.
It is utilized in manufacturing of water pipes, coating for electrical cables, acid tanks
and roof covering etc.

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ZINC
The chief ores of zinc are blende (ZnS) and calamine (ZnCO3). Zinc is a fairly heavy,
bluish-white metal principally utilized in view of its low cost, corrosion resistance and
alloying characteristics. Melting point of zinc is 420°C and it boils at 940°C. Zinc is
commonly use as a protective metal or in making alloys.
Properties of zinc
High corrosion resistance: Widely used as protective coating on iron and steel.
Coating may be provided by dip galvanizing or electroplating.
High fluidity and low melting point: Most suitable metal for pressure die casting
generally in the form of alloy.
When rolled into sheets, zinc is utilized for roof covering and for providing a damp
proof non-corrosive lining to containers.
The galvanized wires, nails, etc. are produced by galvanizing technique and zinc is
also used in manufacture of brasses.
Uses of zinc:
It forms important alloys like brass and German silver etc…
It is use in making fertilizers.
It is use in making printing blocks in textile industry.
It is use in making alloys making.
It is use as a base in paints.
It is use in making pipes.
It is use in making nuclear weapons.
TIN
Tin is very common metal in the family of nonferrous metals. It is mostly use as a protection
layer for the protection of different metals. It is a brilliant white metal with yellowish tinge.
Melting point of tin is 240°C.
Properties:
It has silver white color.
It is ductile.
It is malleable.
It is the good conductor of heat.
Its melting point is 2300C.
It can withstand with corrosion in a better way.
It becomes brittle at 2000C.

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Uses of Tin:
It is use to give coating to iron and steel sheets.
It is used in making different alloys.
It is extensively in electroplating.
COPPER
It is probably the first engineering metal to be used. Unlike other metals, it can occur in
nature in the metallic form as well as an ore. It has very good heat and electrical
conductivity and resists to corrosion when alloyed with other metals. Copper is a corrosion
resistant metal of an attractive reddish brown colour.
Properties
High Thermal Conductivity: Used in heat exchangers, heating vessels and
appliances,etc.
High Electrical Conductivity: Used as electrical conductor in various shapes and
forms for various applications.
Good Corrosion Resistance: Used for providing coating on steel prior to nickel and
chromium plating
High Ductility: Can be easily cold worked, folded and spun. Requires annealing after
cold working as it loses its ductility.
Copper alloys consist of the following general categories:
1. Coppers (minimum 99.3% Cu)
2. High coppers (99.3-96% Cu)
3. Brasses (Cu-Zn alloys with 5-40% Zn)
4. Bronzes (mainly Cu-Sn alloy, and also alloys of Cu- P, Cu-Al, Cu-Si)
5. Copper Nickels (Cu-Ni alloys, also known as cupro-nickels)
6. Nickel Silvers (Cu-Ni-Zn alloys which actually do not contain silver)
Copper alloys widely used in practice
Brasses :Brass is highly corrosion resistant, easily machinable and therefore a good
bearing material.
Bronzes :This is suitable for working in cold state. It was originally made for casting
guns but used now for boiler fittings, bushes, glands and other such uses.

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GENERAL DESCRIPTION OF COPPER
Properties:
It is crystalline in nature.
It has reddish brown color.
It is highly ductile.
It is highly malleable.
It can be welded when red hot.
It is the excellent conductor of heat and electricity.
Its corrosion rate is low.
It is soft and flexible.
It is light in weight.
It turns to the greenish color when expose to atmosphere.
Uses of copper:
It is use as base in paint.
It is used in lead batteries.
It is used in lead joints in sanitary fittings.
It is used for cable covering.
It is used in lead alloying bullets.
It is used in lining the instruments in metallurgical instruments.
 Copper is one of the most widely used metal but due to its high price we use it with
some limitations in engineering work.
CADMIUM
It is obtained commercially as a by-product in the metallurgy of zinc and to some extent
of lead
Properties and Uses
1. White metal with bluish tinge, capable of taking a high polish.
2. Its specific gravity is 8.67 and melts at 321°C.
3. It is slightly harder than tin but softer than zinc.
4. It is malleable and ductile and can be readily rolled and drawn into wires. It is chiefly
utilized in antifriction alloys for bearings. It is also used as rust proof coating for iron
and steel. Components of automobiles and refrigerator such as nuts, bolts and
trimmings, locks and wire products are plated with it.

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DURALUMIN
This is an alloy of 4% Cu, 0.5% Mn, 0.5% Mg and aluminum. It is widely used in
automobile and aircraft components.
Y-ALLOY
This is an alloy of 4% Cu, 1.5% Mn, 2% Ni, 6% Si, Mg, Fe and the rest is Al. It gives large
strength at high temperature. It is used for aircraft engine parts such as cylinder heads, piston
etc.
MAGNALIUM
This is an aluminium alloy with 2 to 10 % magnesium. It also contains 1.75% Cu. Due to its
light weight and good strength it is used for aircraft and automobile components.
NICKEL
About at least 85% of all nickel production is obtained from sulphide ores.
Properties and Uses
1. Pure nickel is tough, silver coloured metal, harder than copper having some but less
ductility but of about same strength.
2. It is plated on steel to provide a corrosion resistance surface or layer.
3. Widely used as an alloying element with steel. Higher proportions are advantageously
added in the production of steel such as monel or in conel.
4. It possesses good resistance to both acids and alkalis regarding corrosion so widely
utilized in food processing equipment.
TITANIUM (TI)
It is used in corrosive environments or in applications of light weight, high
strength and nonmagnetic properties. It has good high temperature strength as
compared with other light metals.
BERYLLIUM (BE)
Beryllium is a recently emergent material having several unique properties of low density
(one-third lighter than aluminum), high modulus-to-density ratio (six times greater than
ultrahigh-strength steels), high melting point, dimensional stability, excellent thermal
conductivity and transparency to X-rays. However, it has serious deficiencies of high cost,
poor ductility, and toxicity. It is not especially receptive to alloying.

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All conventional machining operations including some nontraditional processes (e.g.
EDM and ECM) are possible. However, it must be machined in specially equipped
facilities due to its toxic effect. In addition, surface of beryllium is damaged after
machining, and hence secondary finishing operations must be carefully conducted. It
is typically used in military aircraft brake systems, missile guidance systems, satellite
structures, and X-ray windows.
MAGNESIUM (MG)
It is the lightest “engineering” material available. The combination of low density and
good mechanical strength has made it one of the most specified materials in aircraft, space,
portable power tools, luggage and similar applications as competing with the aluminum
alloys. Alloys of magnesium are the easiest of all engineering metals to machine. They are
amenable to die casting, and they are easily welded. Also, magnesium parts can be joined by
riveting and adhesive bonding. Other notable characteristics are high electrical and thermal
conductivity as well as very high damping capacity. On the down side, it is highly
susceptible to galvanic corrosion since it is anodic. Under certain conditions, flammability
can be a problem as it is an active metal. Magnesium alloys are best suited for applications
where lightness is of primary importance. When lightness must be combined with
strength, aluminum alloys are better material alternatives.
NON-METALSNon-metallic materials are also used in engineering practice due to principally their low
cost, flexibility and resistance to heat and electricity. Though there are many suitable non-
metals, the following are important few from design point of view:
1. Timber This is a relatively low cost material and a bad conductor of heat and
electricity. It has also good elastic and frictional properties and is widely used in
foundry patterns and as water lubricated bearings.
2. Leather This is widely used in engineering for its flexibility and wear resistance. It is
widely used for belt drives, washers and such other applications.
3. Rubber : It has high bulk modulus and is used for drive elements, sealing, vibration
isolation and similar applications.
4. Plastics :These are synthetic materials which can be moulded into desired shapes
under pressure with or without application of heat. These are now extensively used in
various industrial applications for their corrosion resistance, dimensional stability and
relatively low cost.

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TYPES OF PLASTICS
1. Thermosetting plastics- Thermosetting plastics are formed under heat and pressure.
It initially softens and with increasing heat and pressure, polymerisation takes place.
This results in hardening of the material. These plastics cannot be deformed or re-
moulded again under heat and pressure. Some examples of thermosetting plastics are
phenol formaldehyde (Bakelite), phenol-furfural (Durite), epoxy resins, phenolic
resins etc.
2. Thermoplastics- Thermoplastics do not become hard with the application of heat and
pressure and no chemical change takes place. They remain soft at elevated
temperatures until they are hardened by cooling. These can be re-melted and
remoulded by application of heat and pressure. Some examples of thermoplastics are
cellulose nitrate (celluloid), polythene, polyvinyl acetate, polyvinyl chloride ( PVC)
etc.
Mechanical properties of
common engineering
materials

1. Elasticity: Physical or mechanical property of metals which makes it to able to return
in to its original shape after it has been deformed. Elasticity is the ability of the
materials to return in to its original shape after the load is removed theoretically the
elastic limit of a material is the limit to which material is loaded and still recovers its
original shape after the load is removed.
2. Plasticity: It is the ability of the material to deform permanently without breaking or
rupture by carefully alloying of metals then combine the combination of plasticity and
strength is used to manufacture the large structures.
3. Ductility: It is the physical and mechanical property of metals that allows the metals
to deform, drawn, bends or twists in to different shapes by applying the tensile forces
without fracture or breaking. Ductile metals are vitals in creating wires or tubes
because of its easy of forming. For example platinum, copper and steel etc…

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4. Malleability:It is the property of the materials that enables the materials to be
deformed by compressive forces without developing the defects like breaking
cracking etc… malleable material is one of that stress hammer forget rolls into thin
sheets. The sheets of metals are then used to form shapes for structures mechanically
need for example gold, manganese and copper etc…
5. Brittleness: Brittle metals are one that breaks shatters before it deformed. While cast
iron and cast aluminum very hard steel and glass is the one of the best example of the
brittle materials. Generally a brittle metal are very high in the compression strength
and in tensile strength. Brittle metals are not suitable for the heavy loads as they could
break easily and can cause the damage.
6. Fusibility: It is the mechanical property of the metals to be liquefied by heating this
process is called welding. Here metals are liquefied and then joined together when it
becomes harden it becomes one piece. Steel liquefy at 2500o
F while aluminum alloy
at 1110o
F.
7. Creep: Creep is the tendency of metal to moves slowly or deform permanently under
the influence of stresses. It occurs as the result of the long term exposure to a high
level of stress that are below the yield point of the material. Creep is more swear in
materials that are subjected to heat for the long periods and near the melting points.
Creep is always increases with the temperature the rate of this deformation is a
function of materials properties exposure times’ exposure temperature and applied
structural loads. Creep deformation is the time dependent deformation. The
temperature ranges in which the creep deformation may occur is different in various
metals. As a rule of thumb the effects of the creep deformation generally becomes
more noticeable at approximately 30% of melting points of the metals and 40%-50%
of the melting points of ceramics.
8. Resilience- This is the property of the material that enables it to resist shock and
impact by storing energy. The measure of resilience is the strain energy absorbed per
unit volume. For a rod of length L subjected to tensile load P, a linear load-deflection
plot is shown in figure.

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9. Toughness- This is the property which enables a material to be twisted, bent or
stretched under impact load or high stress before rupture. It may be considered to be
the ability of the material to absorb energy in the plastic zone. The measure of
toughness is the amount of energy absorbed after being stressed up to the point of
fracture.
10.Hardness- Property of the material that enables it to resist permanent deformation,
penetration, indentation etc. Size of indentations by various types of indenters are the
measure of hardness e.g. Brinnel hardness test, Rockwell hardness test, Vickers
hardness (diamond pyramid) test. These tests give hardness numbers which are related
to yield pressure (MPa).
SINGLE PHASE MATERIALS (topic 3)
Materials scientists and engineers have developed a set of instruments in order to
characterize the structure of materials at various length scales.
We can examine and describe the structure of materials at five different levels:
1. atomic structure;
2. short- and long-range atomic arrangements;
3. nanostructure;
4. microstructure; and
5. macrostructure.
 The features of the structure at each of these levels may have distinct and profound
influences on a material’s properties and behavior.
ATOMIC STRUCTURE
Atomic Structure determines:
1. Physical Properties
2. Chemical Properties
3. Biological Properties
4. Electromagnetic Properties
The arrangement of atoms and the bonds between the atoms are primary means by which
materials carry loadings and resist deterioration. Steel alloys that have more free
electrons are more likely to corrode, metal alloys with interstitial alloying elements melt
at lower temperatures than pure metals, but may be substantially stronger and tougher
than pure metals. The properties are highly dependent on the structure type, cooling
environment, size and nature of the alloys and the temperature they are formed.

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Electrons and protons are negative and positive charges of the same magnitude being
1.60x10-19
coulombs. Neutrons are electrically neutral. Protons and neutrons have
approximately the mass, 1.67x10 27
kg, which is larger than that of an electron,9.11x10-31
kg. Atomic number (Z)-is the number of protons per atoms. Atomic mass (A)-is the sum
of the masses of protons and neutrons within the nucleus.
Atomic mass is measured in atomic mass unit (amu) where 1amu=(112) the mass of
most common isotope of carbon atom, measured in grams. A =Z+N, where N is
number of neutrons.Isotopes-atoms with same atomic number but different atomic
masses. A mole is the amount of matter that has a mass in grams equal to the atomic
mass in amu of the atoms. Thus a mole of carbon has a mass of 12 grams.
The number of atoms or molecules in a mole of substance is called the Avogadro’s
number, Nay. Nay=1gram/1amu = 6.023x1023
.E.g. Calculating the number of atoms per
cm3
, n, in a piece of material of density δ(g/cm3
) n = Nav δ / M, where M is the
atomic mass in amu. Thus, for graphite (carbon) with a density δ = 1.8 g/cm3
and
M=12, n =6.023x1023
atoms/mol x 1.8 g/cm3
/ 12 g/mol) = 9 x1022
atoms/cm3
.Most
solid materials will have atomic density in the order of 6x1022
, that’s about 39 million
atoms per centimeter. Mean distance between atomsis in the range of 0.25 nm. It gives
an idea about scale of atomic structures in solids.
TYPES OF ATOMIC BONDING
1)Primary Bonding:
Ionic bonding
Covalent bonding
Metallic bonding
2)Secondary bonding:
Fluactuating Induced Dipole
Polar Molecule-Induced Dipole
Permanent Dipole Bonds
IONIC BONDING (ceramics, e.g., salt and clay)
Non directional Forms when an atom that has a strong tendency to give up
electrons (a metal) is in close proximity to an atom that has a strong tendency to
accept electrons (nonmetal).Transfer of one or more electrons from the outer shell
of one atom to the outer shell of the other atom depending on the valence of the
atoms.Results in an electron arrangement when many ions (+ and -) are in close

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proximity, e.g., NaCl, that has a polar arrangement of the ions similar to a magnet.
Forms crystalline structure
COVALENT BONDING (most important for plastics)
Occurs when two non-metal atoms are in close proximity. Both atoms have a
tendency to accept electrons, which results in shared outer electron shells of the
two atoms. Number of shared electrons is usually to satisfy the octet rule.
Resulting structure is substantially different that the individual atoms, e.g., C and
H4 make CH4, a new and distinct molecule. Atoms is covalent bonds are not ions
since the electrons are shared rather than transferred as in ionic or metallic bonds.
Covalent bonds are very strong. As a result, covalently bonded materials are very
strong and hard. For example, diamond (C), silicon carbide (SiC), silicon nitride
(Si3N4), and boron nitride (BN) all have covalent bonds. These materials also
exhibit very high melting points, which means they could be useful for high-
temperature applications. On the other hand, the high temperature needed for
processing presents a challenge. The materials bonded in this manner typically
have limited ductility because the bonds tend to be directional. The electrical
conductivity of many covalently bonded materials (i.e., silicon, diamond, and
many ceramics) is not high since the valence electrons are locked in bonds between
atoms and are not readily available for conduction.
METALLIC BONDING
Occurs when two metal atoms are in close proximity. Both atoms have tendency to
give up electrons. Electrons are free to move about entire atoms structure
Releasing electrons yields a lower energy state. The metal atoms approach each
other and give up electrons when in close proximity to a sea of electrons. Charged
metal ions cancel the repulsive forces due to the electron movement. Crystal
structures can form in some atoms but the forces are not as strong as ionic bonds
in ceramics. Metallic alloys can form when each gives up electrons and form a
positively charged ion. Because their valence electrons are not fixed in any one
position, most pure metals are good electrical conductors of electricity at relatively
low temperatures (T ˂ 300 K). Under the influence of an applied voltage, the
valence electrons move, causing a current to flow if the circuit is complete. Metals
show good ductility since the metallic bonds are non-directional.

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Secondary bonding: weaker than ionic, metallic, covalent
– Hydrogen bonding
• Occurs between the positive end of a bond and the negative end of
another bond.
• Example, water the positive end is the H and the negative end is O.
– van der Waals
• Occurs due to the attraction of all molecules have for each other, e.g.
gravitational. Forces are weak since masses are small
– induced dipole
• Occurs when one end of a polar bond approaches a non-polar portion of
another molecule.
BINDING ENERGY AND INTERATOMIC SPACING
 Interatomic Spacing: The equilibrium distance between atoms is caused by a balance
between repulsive and attractive forces. In the metallic bond, for example, the
attraction between the electrons and the ion cores is balanced by the repulsion
between ion cores. Equilibrium separation occurs when the total interatomic energy
(IAE) of the pair of atoms is at a minimum, or when no net force is acting to either
attract or repel the atoms The minimum energy is the binding energy, or the energy
required to create or break the bond. Consequently, materials having a high binding
energy also have a high strength and a high melting temperature. Ionically bonded
materials have a particularly large binding energy because of the large difference in
electronegativities between the ions.Metals have lower binding energies because the
electronegativities of the atoms are similar.

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Binding energy levels for different bonding regimes are listed below
Strong Primary Bonds
 Ionic Bond ..625 to 1550 kJ/mol
 Covalent Bond ..520 to 1200 kJ /mol
 Metallic Bond..100 to 800 kJ /mol
Weaker Secondary Bonds
 Van der Waals ..0,02 to 40 kJ/mol
 Hydrogen Bond ..10 to 40 kJ /mol
 Dipole-dipole ..0 to 20 kJ /mol
The Modulus of elasticity is related to the slope of the force distance curve

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CRYSTAL STRUCTURES
Fundamental Concepts
Atoms self-organize in crystals, most of the time. The crystalline lattice, is a periodic array
of the atoms. When the solid is not crystalline, it is called amorphous. Examples of
crystalline solids are metals, diamond and other precious stones, ice, graphite. Examples of
amorphous solids are glass, amorphous carbon (a-C), amorphous Si, most plastics.To discuss
crystalline structures it is useful to consider atoms as being hard spheres, with well-defined
radii. In this scheme, the shortest distance between two like atoms is one diameter.
Unit Cells
The unit cell is the smallest structure that repeats itself by translation through the crystal. We
construct these symmetrical units with the hard spheres. The most common types of unit
cells are the faced-centered cubic (FCC), the body-centered cubic (FCC) and the hexagonal
close-packed (HCP). Other types exist, particularly among minerals. The simple cube (SC)
is often used for didactical purpose, no material has this structure.
Metallic Crystal Structures
Important properties of the unit cells are
The type of atoms and their radii R.
cell dimensions (side a in cubic cells, side of base a and height c in HCP) in terms
of R.
n, number of atoms per unit cell. For an atom that is shared with m adjacent unit
cells, we only count a fraction of the atom, 1/m.
CN, the coordination number, which is the number of closest neighbors to which
an atom is bonded.
APF, the atomic packing factor, which is the fraction of the volume of the cell
actually occupied by the hard spheres. APF = Sum of atomic volumes/Volume of
cell.
ATOMIC PACKING FRACTION
Atomic packing factor (APF) or packing efficiency indicates how closely atoms are packed
in a unit cell and is given by the ratio of volume of atoms in the unit cell and volume of the
unit cell. Metals typically have relatively large atomic packing factors to maximize the
shielding provided by the free electron cloud.
APF= Volume of Atoms/ Volume of Cell
Volume of Atoms = n (4π/3) R3
Volume of Cell = a3

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Unit Cell n CN a/R APF
Simple Cubic SC 1 6 4/√ 0.52
Body Centered Cubic BCC 2 8 4/√ 0.68
Face Centered Cubic FCC 4 12 4/√ 0.74
Hexagonal close packed HCP 6 12 0.74
The closest packed direction in a BCC cell is along the diagonal of the cube; in a FCC cell is
along the diagonal of a face of the cube.
THE 14 CRYSTAL (BRAVAIS) LATTICES

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FACE-CENTERED CUBIC CRYSTAL STRUCTURE
The crystal structure found for many metals has a unit cell of cubic geometry, with atoms
located at each of the corners and the centers of all the cube faces. It is aptly called the face-
centered cubic (FCC) crystal structure. Some of the familiar metals having this crystal
structure are copper, aluminum, silver, and gold.
The spheres or ion cores touch one another across a face diagonal; the cube edge length a
and the atomic radius R are related through √ .For the FCC crystal structure, each
corner atom is shared among eight unit cells, whereas a face-centered atom belongs to only
two. Therefore, one-eighth of each of the eight corner atoms and one-half of each of the six
face atoms, or a total of four whole atoms, may be assigned to a given unit cell, where only
sphere portions are represented within the confines of the cube. The cell comprises the
volume of the cube, which is generated from the centers of the corner atoms as shown in the
figure. Corner and face positions are really equivalent; that is, translation of the cube corner
from an original corner atom to the center of a face atom will not alter the cell structure.
For face-centered cubics, the coordination number is 12, the front face atom has four corner
nearest-neighbor atoms surrounding it, four face atoms that are in contact from behind, and
four other equivalent face atoms residing in the next unit cell to the front, which is not
shown. For the FCC structure, the atomic packing factor is 0.74, which is the maximum
packing possible for spheres all having the same diameter.
Number of atoms per unit cell, n = 4.
FCC unit cell:
– 6 face atoms shared by two cells: 6 x 1/2 = 3
– 8 corner atoms shared by eight cells: 8 x 1/8 = 1

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BODY-CENTERED CUBIC CRYSTAL STRUCTURE

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This is Another common metallic crystal structure also has a cubic unit cell with atoms
located at all eight corners and a single atom at the cube center. This is called a body-
centered cubic (BCC) crystal structure. Center and corner atoms touch one another along
cube diagonals, and unit cell length a and atomic radius R are related through
√
Chromium, iron, tungsten,exhibit a BCC structure.Two atoms are associated with each BCC
unit cell: the equivalent of one atom from the eight corners, each of which is shared among
eight unit cells, and the single center atom, which is wholly contained within its cell. In
addition, corner and center atom positions are equivalent. The coordination number for the
BCC crystal structure is 8; each center atom has as nearest neighbors its eight corner atoms.
Since the coordination number is less for BCC than FCC, so also is the atomic packing
factor for BCC lower—0.68 versus 0.74.
Number of atoms per unit cell, n = 2
– Center atom not shared: 1 x 1 = 1
– 8 corner atoms shared by eight cells: 8 x 1/8 = 1

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HEXAGONAL CLOSE-PACKED CRYSTAL STRUCTURE

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Not all metals have unit cells with cubic symmetry; the final common metallic crystal
structure to be discussed has a unit cell that is hexagonal. Figure above shows a reduced-
sphere unit cell for this structure, which is termed hexagonal closepacked (HCP). The top
and bottom faces of the unit cell consist of six atoms that form regular hexagons and
surround a single atom in the center. Another plane that provides three additional atoms to
the unit cell is situated between the top and bottom planes. The atoms in this midplane have
as nearest neighbors atoms in both of the adjacent two planes. The equivalent of six atoms is
contained in each unit cell; one-sixth of each of the 12 top and bottom face corner atoms,
one-half of each of the 2 center face atoms, and all 3 midplane interior atoms. If a and c
represent, respectively, the c/a ratio should be 1.633; however, for some HCP metals this
ratio deviates from the ideal value.
The coordination number and the atomic packing factor for the HCP crystal structure
are the same as for FCC: 12 and 0.74, respectively.The HCP metals include cadmium,
magnesium, titanium, and zinc.
CN = 12
APF = 0.74

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ATOMIC RADII AND CRYSTAL STRUCTURES FOR 16 METALS

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EXAMPLES
1. Calculate the volume of an FCC unit cell in terms of the atomic radius R.
SOLUTION
In the FCC unit cell illustrated
the atoms touch one another across a face-diagonal the length of which is 4R.
Since the unit cell is a cube, its volume is where a is the cell edge length. From
the right triangle on the face,
, √
The FCC unit cell volume VC may be computed from
VC = a3
= √ = √
2. Show that the atomic packing factor for the FCC crystal structure is 0.74
SOLUTION
The APF is defined as the fraction of solid sphere volume in a unit cell, or
both the total atom and unit cell volumes may be calculated in terms of them
atomic radius r. the volume for a sphere is and since there are four atoms per
FCC unit cell, the total FCC atom (or sphere) volume is
= , the total unit cell volume is √
Therefore, the atomic packing factor is
√

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Some summaries.
 Atoms may assemble into crystalline or amorphous structures.
 We can predict the density of a material, provided we know the atomic
weight, atomic radius, and crystal geometry (e.g., FCC, BCC, HCP).
 Material properties generally vary with single crystal orientation (i.e.,
they are anisotropic), but properties are generally non-directional (i.e.,
they are isotropic) in polycrystals with randomly oriented grains.

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Topic 4
TESTING OF MATERIALS
Testing is an essential part of any engineering activity. Inspection and testing must take
place at many stages in the complex process of producing engineering materials, be they
metals, polymers, ceramics or composites and during the forming of these materials into
components and assembling the components to create an engineering product to satisfy some
specific requirement. The requirement for testing does not automatically cease when the
product has been manufactured. It is frequently necessary to check and test the article during
its service life in order to monitor changes, such as possible development of fatigue or
corrosion damage.
TYPES OF MATERIALS TESTING
1 Destructive Testing
2 Non-destructive Testing
DESTRUCTIVE TESTING
Are the kind of tests performed on samples of a material and a test-piece is damaged or
broken in the process. If the sample test-piece is correctly chosen and prepared, the results
should be indicative of the properties of the bulk material represented by the sample. These
tests are generally much easier to carry out, yield more information, and are easier to
interpret than non-destructive testing. Destructive testing is more suitable and economic for
objects which will be mass-produced, as the cost of destroying a small number of specimens
is negligible. It is usually not economical to do destructive testing where only one or very
few items are to be produced.
TYPES OF DESTRUCTIVE TESTING
1 Tensile Testing
2 Hardness Testing
3 Notch Impact Testing
4 Creep Testing
5 Fatigue Testing

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BENEFITS OF DESTRUCTIVE TESTING
1. Verifies properties of a material
2. Determines quality of welds
3. Helps you to reduce failures, accidents and costs.
4. Ensures compliance with regulations
HARDNESS TESTING
HARDNESS – Is the resistance to indentation or abrasion. The hardness of a material may
be determined by using either a scratch test or by making a surface indentation. Indentation
type hardness tests are widely used for checking of metal samples as they are easy to make
and yield information on heat treatment condition.
The various types of indentation test available for the hardness testing of metals the
most commonly used are:
1 The Brinell Test
2 The Vicker’s Diamond Test and
3 The Rockwell test
THE BRINELL TEST
Dr. J. A. Brinell invented the Brinell test in Sweden in 1900. The oldest of the hardness test
methods in common use today, the Brinell test is frequently used to determine the hardness
of forgings and castings that have a grain structure too course for Rockwell or Vickers
testing. Therefore, Brinell tests are frequently done on large parts. By varying the test force
and ball size, nearly all metals can be tested using a Brinell test. Brinell values are
considered test force independent as long as the ball size/test force relationship is the same.
In the USA, Brinell testing is typically done on iron and steel castings using a 3000 Kg test
force and a 10 mm diameter carbide ball. Aluminum and other softer alloys are frequently
tested using a 500 Kg test force and a 10 or 5mm carbide ball. Therefore the typical range of
Brinell testing in this country is 500 to 3000kg with 5 or 10mm carbide balls. In Europe
Brinell testing is done using a much wider range of forces and ball sizes. It's common in
Europe to perform Brinell tests on small parts using a 1 mm carbide ball and a test force as
low as 1kg. These low load tests are commonly referred to as baby Brinell tests.
STANDARDS
Brinell Test methods are defined in the following standards: ASTM E10 ; ISO 6506

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BRINELL TEST METHOD
All Brinell tests use a carbide ball indenter. The test procedure is as follows:
i. The indenter is pressed into the sample by an accurately controlled test force.
ii. The force is maintained for a specific dwell time, normally 10 - 15 seconds.
iii. After the dwell time is complete, the indenter is removed leaving a round indent in the
sample.
iv. The size of the indent is determined optically by measuring two diagonals of the round
indent using either a portable microscope or one that is integrated with the load
application device.
v. The Brinell hardness number is a function of the test force divided by the curved
surface area of the indent. The indentation is considered to be spherical with a radius
equal to half the diameter of the ball. The average of the two diagonals is used in the
following formula to calculate the Brinell hardness.
where: HB = the Brinell hardness number , F = the imposed load in kg , D = the diameter of
the spherical indenter in mm d = diameter of the resulting indenter impression in mm .The
Brinell number, which normally ranges from HB 50 to HB 750 for metals, will increase as
the sample gets harder. Tables are available to make the calculation simple.
Applications
Because of the wide test force range the Brinell test can be used on almost any metallic
material. The part size is only limited by the testing instrument's capacity.
Strengths
1. One scale covers the entire hardness range, although comparable results can only be
obtained if the ball size and test force relationship is the same.
2. A wide range of test forces and ball sizes to suit every application.
3. ―Nondestructive‖, sample can normally be reused.

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Weaknesses
1. The main drawback of the Brinell test is the need to optically measure the indent size.
This requires that the test point be finished well enough to make an accurate measurement.
2. Slow. Testing can take 30 seconds not counting the sample preparation time.
The Vicker’s Diamond Test
Vickers hardness test uses a square-base diamond pyramid as the indenter with the included
angle between opposite faces of the pyramid of 136o
. The Vickers hardness number (VHN)
is defined as the load divided by the surface area of the indentation.
Where
 P is the applied load, kg
 L is the average length of diagonals, mm
 θ is the angle between opposite faces of diamond =136o
.
One advantage of the Vicker’s test over the Brinell test is that the square impressions
made are always geometrically similar, irrespective of size. The plastic flow patterns,
therefore, are very similar for both deep and shallow indentations and in consequence, the
hardness value obtained is independent of the magnitude of the indenting force used.

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The Rockwell Test
The Rockwell test machine is a rapid action direct reading machine. This provides a very
convenient method for speedy comparative testing. The depth of impression is measured and
directly indicated by a pointer on a dial calibrated, inversely, into 100 divisions ( 1 scale
division=0.01mm of impression depth). A low scale number indicates a deep impression,
hence a soft material, and viceversa. The indentors used are hardened steel balls of various
diameters or a diamond cone with an included angle of 1200
.
Stanley P. Rockwell invented the Rockwell hardness test. He was a metallurgist for a large
ball bearing company and he wanted a fast non-destructive way to determine if the heat
treatment process they were doing on the bearing races was successful. The only hardness
tests he had available at time were Vickers, Brinell and Scleroscope. The Vickers test was
too time consuming, Brinell indents were too big for his parts and the Scleroscope was
difficult to use, especially on his small parts.
To satisfy his needs he invented the Rockwell test method. This simple sequence of test
force application proved to be a major advance in the world of hardness testing. It enabled
the user to perform an accurate hardness test on a variety of sized parts in just a few seconds.

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Rockwell test methods are defined in the following standards:
 ASTM E18 Metals, ISO 6508 Metals , ASTM D785 Plastics
Types of the Rockwell Test
There are two types of Rockwell tests:
1. Rockwell: the minor load is 10 kgf, the major load is 60, 100, or 150 kgf.
2. Superficial Rockwell: the minor load is 3 kgf and major loads are 15, 30, or 45 kgf.
In both tests, the indenter may be either a diamond cone or steel ball, depending upon the
characteristics of the material being tested.
Rockwell Scales
Rockwell hardness values are expressed as a combination of a hardness number and a scale
symbol representing the indenter and the minor and major loads. The hardness number is
expressed by the symbol HR and the scale designation. There are 30 different scales. The
majority of applications are covered by the Rockwell C and B scales for testing steel, brass,
and other metals. However, the increasing use of materials other than steel and brass as well
as thin materials necessitates a basic knowledge of the factors that must be considered in
choosing the correct scale to ensure an accurate Rockwell test. The choice is not only
between the regular hardness test and superficial hardness test, with three different major
loads for each, but also between the diamond indenter and the 1/16, 1/8, 1/4 and 1/2 in.
diameter steel ball indenters.
For soft materials such as copper alloys, soft steel, and aluminum alloys a 1/16" diameter
steel ball is used with a 100-kilogram load and the hardness is read on the "B" scale. In
testing harder materials, hard cast iron and many steel alloys, a 120 degrees diamond cone is
used with up to a 150 kilogram load and the hardness is read on the "C" scale. There are
several Rockwell scales other than the "B" & "C" scales, (which are called the common
scales). A properly reported Rockwell value will have the hardness number followed by
"HR" (Hardness Rockwell) and the scale letter. For example, 50 HRB indicates that the
material has a hardness reading of 50 on the B scale.
If no specification exists or there is doubt about the suitability of the specified scale, an
analysis should be made of the following factors that control scale selection:
 Type of material
 Specimen thickness
 Test location
 Scale limitations

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Principles of the Rockwell Test
1. The indenter moves down into position on the part surface
2. A minor load is applied and a zero reference position is established
3. The major load is applied for a specified time period (dwell time) beyond zero
4. The major load is released leaving the minor load applied
The resulting Rockwell number represents the difference in depth from the zero
reference position as a result of the application of the major load.
The Rockwell hardness test is the most widely used hardness test and generally accepted
due to:
1. Its speed
2. Freedom from personal error.
3. Ability to distinguish small hardness difference
4. Small size of indentation.
Notch Impact Testing
In this type of test a bar specimen with a milled notch is struck by a fast moving hammer,
and the energy absorbed in fracturing the test-piece is measured. One major use of the notch
impact test is to determine whether heat treatment of a material has been carried out
successfully, as this type of test gives the most information on this.
The types of notched bar impact test that are most widely used are:
1. The Charpy and
2. The Izod test
In both types of test, a heavy pendulum is released and is allowed to strike a test-piece at the
bottom of its swing. A proportion of the energy of the pendulum is absorbed in fracturing the
test-piece. The height of the follow-through swing of the pendulum is measured, and the
energy absorbed in fracture determined.
In the Charpy Test, the test-piece is tested as a simply supported beam and the sharp edge
of the pendulum strikes at mid-span directly behind the milled notch.
An Izod Test, specimen is tested in a cantilever mode. The test-piece is firmly clamped in a
vice with the prepared notch level with the edge of the vice. The impact blow is delivered on
the same side as the notch.

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Creep Testing
Under normal conditions, engineering design is based on yield stress (or UTS). However, at
elevated temperatures the material may fail by stretching at a much lower stress, over a long
time. The process of slow but progressively increasing strain is called creep. Creep happens
slowly, and at an elevated temperature (for most engineering materials).
A creep test measures strain as a function of time at a constant stress and temperature. The
purpose of the creep test is to record strain for a period of over time - at a certain stress and
temperature. This data can be used to make predictions for the material in service.
A typical creep test has 3 stages:
a. Primary (transcient)
b. Secondary (linear)
c. Tertiary (to rupture) For a part subject to creep, the strain is monitored during
the linear stage (secondary creep), and taken out of service when approaching
the final stage (tertiary)
.

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Fatigue Testing
A component or structure in service may be subjected to fluctuating or alternating cycles of
stress, but rarely can it be found that one constant type of loading cycle applies during the
whole of the life of a component. Fatigue is gradual crack growth caused by alternating
loads. The crack propagates from an initiating point such as a sharp corner, indent, flaw or
other stress raiser. From a designer’s point of view, fatigue can be a particularly dangerous
form of failure because:
a. it occurs over time
b. it occurs at stress levels that are not only lower than the UTS, they can even be
lower than the yield strength.
The cyclic stress causes small cracks to form and grow until they are large enough to cause
fast fracture.
FATIGUE TESTING: WOHLER MACHINE
Specimens are subjected to bending as they revolve, alternating full tension and compression
each revolution. Starting with a high load with few revolutions, the load is reduced with each
subsequent test until a specimen survives ten million reversals without breaking. This stress
is referred to as the fatigue limit. The Fatigue Limit is the maximum stress that a material
can endure for an infinite number of cycles without breaking. It is also referred to as the
Endurance Limit.
Ten million cycles is considered a good enough approximation for infinite.

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 Many ferrous (iron-based) materials exhibit a Fatigue Limit (Endurance Limit , below
this stress amplitude, they will not fail by fatigue.Most non-ferrous materials do not
have a fatigue limit. Their fatigue strength is usually expressed as the maximum stress
for no failure after some specific number of cycles.
NON-DESTRUCTIVE TESTING
Defects such as cracks, porosity and inclusions, which may be potentially damaging may be
introduced into materials or components during manufacture, and other defects, such as
fatigue cracks, may be generated during service. It is necessary to be able to detect and
identify such defects and to ascertain their position and size so that decisions can be taken as
to whether specific defects can be tolerated or not.
 Non-destructive Testing (NDT) is a wide group of analysis techniques used to
evaluate the properties of a material, component or system without causing damage.
Non-destructive Examination (NDE)
Non-destructive Inspection (NDI)
Non-destructive Evaluation (NDE)
IMPORTANCE OF NDT
1 Does not permanently alter the article being inspected
2 Save both money and time in product evaluation, troubleshooting and research.
3 Can be used to detect flaws in an in-process machine part
COMMON NDT METHODS
NDT methods rely upon use of electromagnetic radiation, sound, and inherent properties of
materials (such as thermal, chemical, magnetic etc) to examine samples. A range of non-
destructive test methods is available for the inspection of materials and components and the
most widely used techniques are as shown in picture below.

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USES OF NDE METHODS?
1 Flaw Detection and Evaluation
2 Leak Detection
3 Location Determination
4 Dimensional Measurements
5 Structure and Microstructure Characterization
6 Estimation of Mechanical and Physical Properties
7 Stress (Strain) and Dynamic Response Measurements
8 Material Sorting and Chemical Composition Determination
WHEN ARE NDE METHODS USED?
There are NDE application at almost any stage in the production or life cycle of a
component.
–To assist in product development
–To screen or sort incoming materials
–To monitor, improve or control manufacturing processes

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–To verify proper processing such as heat treating
–To verify proper assembly
–To inspect for in-service damage
SIX MOST COMMON NDT METHODS
1. Visual Inspection
2. Liquid Penetrant / Dye Penetrant Inspection
3. Magnetic Particle Inspection
4. Ultrasonic
5. Eddy Current
6. X-ray (Radiographic testing)
SYSTEM FEATURES APPLICABILITY
Visual Inspection Probes Detection of defects which break the
surface, surface corrosion, etc
Interior of ducts, pipes
and assemblies
Liquid Penetrant Detection of defects which break the
surface
Can be used for any
metal, many plastics,
glass and glazed
ceramics.
Magnetic Particle Detection of defects which break the
surface and sub-surface defects close
to the surface
Can only be used for
ferro-magnetic materials
(most steels and irons)
Electrical Methods (Eddy
currents)
Detection of surface defects and some
sub-surface defects. Can also be used
to measure the thickness of non-
conductive coatings, e.g. paint on a
metal
Can be used for any
metal
Ultrasonic Testing Detection of internal defects but can
also detect surface flaws
Can be used for most
materials
Radiography Detection of internal defects, surface
defects and to check correctness of
assemblies
Can be used for most
materials but there are
limitations on the
maximum material
thickness
All these NDT systems co-exist and depending on the application, may either be used singly
or in conjunction with one another. There is some overlap between the various test methods
but they are complementary to one another. The fact that, for example, ultrasonic testing can
reveal both internal and surface flaws does not necessarily mean that it will be the best
method for all inspection applications. Much will depend upon the type of flaw present and
the shape and size of the components to be examined.

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1. VISUAL INSPECTION
Often the first stage in the examination of a component is visual inspection. Examination by
naked eye will only reveal relatively large defects which break the surface but the
effectiveness of visual inspection for external surfaces can be improved considerably
through use of a hand lens or stereoscopic microscope. Optical inspection probes, both rigid
and flexible, which can be inserted into cavities, ducts and pipes have been developed for the
inspection of internal surfaces.
2. LIQUID PENETRANT INSPECTION
Liquid penetrant inspection is a technique which can be used to detect defects in a wide
range of components, provided that the defect breaks the surface of the material. Liquid
penetrant inspection is an important industrial method and it can be used to indicate the
presence of defects such as cracks, laminations, laps and zones of surface porosity in a wide
variety of components. The method is applicable to almost any component, whether it be
large or small, of single or complex configuration, and it is employed for the inspection of
wrought and cast products in both ferrous and non-ferrous metals and alloys, ceramics,
glassware and some polymer components. The obvious major limitation of liquid penetrant
systems is that it can detect surface breaking defects only. The method is not suitable for use
with naturally porous materials such as unglazed ceramics but is used to detect glazing
defects. Some thermoplastics may be affected by the penetrant fluid, an organic solvent.
FIVE ESSENTIAL STEPS IN THE PENETRANT INSPECTION METHOD
1. Surface preparation
2. Application of penetrant
3. Removal of excess penetrant
4. Development
5. Observation and inspection
The surface of the component has to be thoroughly cleaned. Any surface to be examined
must be free from oil, water, grease or other contaminants if the successful indication of
defects is to be achieved. A liquid with high surface wetting characteristics is applied to the
surface of the part and allowed time to seep into surface breaking defects. The excess liquid
is removed from the surface of the part. A developer (powder) is applied to pull the trapped
penetrant out the defect and spread it on the surface where it can be seen. Visual inspection
is the final step in the process. The penetrant used is often loaded with a fluorescent dye and
the inspection is done under UV light to increase test sensitivity. The range of applications
of liquid penetrant testing is extremely wide and varied. The system is used in the aerospace,
automotive, and general manufacturing industries for the quality control of production and
by users during regular maintenance and safety checks. Typical components which are
checked by this system are turbine rotor discs and blades, pistons, cast cylinder heads,
wheels, forged components and welded assemblies.

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3. MAGNETIC PARTICLE INSPECTION
The part is magnetized. Finely milled iron particles coated with a dye pigment are then
applied to the specimen. These particles are attracted to magnetic flux leakage fields and will
cluster to form an indication directly over the discontinuity. This indication can be visually
detected under proper lighting conditions.

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MAGNETIC PARTICLE CRACK INDICATIONS
4. RADIOGRAPHY
Radiography involves the use of penetrating gamma or X-radiation to examine parts and
products for imperfections. An X-ray generator or radioactive isotope is used as a source of
radiation. Radiation is directed through a part and onto film or other imaging media. The
resulting radiograph shows the dimensional features of the part. Possible imperfections are
indicated as density changes on the film in the same manner as a medical X-ray shows
broken bones.

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5. EDDY CURRENT TESTING
Eddy current testing is particularly well suited for detecting surface cracks but can also be
used to make electrical conductivity and coating thickness measurements. Here a small
surface probe is scanned over the part surface in an attempt to detect a crack.

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6. ULTRASONIC INSPECTION (PULSE-ECHO)
High frequency sound waves are introduced into a material and they are reflected back from
surfaces or flaws. Reflected sound energy is displayed versus time, and inspector can
visualize a cross section of the specimen showing the depth of features that reflect sound.
ULTRASONIC INSPECTION
Ultrasonic techniques are very widely used for the detection of internal defects in
materials, but they can also be used for the detection of small surface cracks.
Ultrasonics are used for the quality control inspection of part processed material, such
as rolled slabs, as well as for the inspection of finished components.
The techniques are also in regular use for the in-service testing of parts and
assemblies.
COMMON APPLICATION OF NDT
Inspection of Raw Products
Inspection Following Secondary Processing
In-Services Damage Inspection

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TOPIC 5
HEAT TREATMENT OF STEEL
DEFINITION
•Heat treating is a group of industrial and metalworking processes used to alter the physical,
and sometimes chemical properties of a material. Heat treatment involves the use of heating
or chilling, normally to extreme temperatures, to achieve a desired result such as hardening
or softening of a material.
HEAT TREATMENT TECHNIQUES
Depending on the rate of cooling, one can be performing the following heat treatments:
1. Annealing
2. Normalizing
3. Quenching
4. Tempering
ANNEALING
Annealing involves heating the material to a predetermined temperature and hold the
material at this temperature and cool the material to the room temperature slowly. The
process involves
1. heating of the material at the elevated or predetermined temperature
2. holding the material (soaking) at the temperature for longer time
3. very slowly cooling the material to the room temperature.
ANNEALING PURPOSES
1. Relieve internal stresses developed during solidification, machining, forging , rolling
or welding
2. Improve or restore ductility and toughness
3. Enhance machinability
4. Refrain grain size
NORMALIZING
The normalizing of steel is carried out by heating above the UCT ( Upper Critical
Temperature) to a single phase austenitic region to get homogeneous austenite, soaking there
for some time and then cooling it in air.

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AIMS OF NORMALIZING
1. To produce a harder and stronger steel than full annealing
2. To improve machinability
3. To modify and/or refine the grain structure
4. To obtain a relatively good ductility without reducing the hardness and strength
5. Produce a homogeneous structure
6. Provide a more consistent response when hardening or case hardening
COMPARISON OF ANNEALING AND NORMALIZING
1. The metal is heated to a higher temperature and then removed from the furnace for air
cooling in normalizing rather than furnace cooling.
2. In normalizing , the cooling rate is slower than that of a quench and temper operation
but faster than that used in annealing.
3. As a result of this intermediate cooling rate, the parts will possess a hardness and
strength somewhat greater than if annealed.
4. Fully annealed parts are uniform in softness ( and machinability) throughout the entire
part, since the entire part is exposed to the controlled furnace cooling. In the case of
the normalized part, depending on the part geometry, the cooling is non-uniform
resulting in non-uniform material properties across the part.
5. Internal stresses are more in normalizing as compared to annealing
6. Grain size obtained in normalizing is finer than in annealing
7. Normalizing is a cheaper and less time-consuming process.
ADVANTAGES OF NORMALIZING OVER ANNEALING
1. Better mechanical properties
2. Lesser time consuming
3. Lower cost of fuel and operation
ADVANTAGES OF ANNEALING OVER NORMALIZING
1. Greater softness
2. Complete absence of internal stresses which is a necessity in complex and intricate
parts

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QUENCHING (Hardening)
Quenching is a process of rapid cooling of materials from high temperature to room
temperature or even lower. In steels, quenching results in transformation of austenite to
martensite ( a non-equilibrium constituent).
QUENCHING MEDIUMS
1. Water
2. Brine (Sodium chloride aqueous solutions of about 10% by weight are widely used
and are called brines)
3. Oils
4. Polymer Quenchants
5. Salt Baths
TEMPERING
Hardened steels are so brittle that even a small impact will cause fracture. Toughness of such
a steel can be improved by tempering. Tempering ( formerly called drawing), consists of
reheating a quenched steel to a suitable temperature below the transformation temperature
for an appropriate time and cooling back to room temperature. This treatment will remove
internal stresses set up during quenching, remove some or all, of the hardness and increase
the toughness of the material. For most steels, cooling from the tempering temperature may
be either cooling in air or quenching in oil or water.
OXIDATION OF METAL
Metals possess affinity for oxygen, as they react with oxygen to form oxidise.The
amount of oxidation that takes place at ordinary temperatures is not serious.The rate of
oxidation reaction is temperature dependent – increases rapidly with an increase in
temperature. In many instances, the oxide layer that rapidly forms on a freshly exposed
metal surface tends to protect the metal from further oxidation.
The reactivity of a metal with oxygen varies very considerably from one metal to
another.Some metal showing low reactivity (eg. Cu, Pb). Other metal possessing very
high reactivities with oxygen (eg. Al, Mg)
• The rate at which oxidation occurs at the surface of a metal is largely controlled by the
nature of the metal, in which case:
1. It can act as a protection against further oxidation (non-porous)
2. It may form a porous layer, allowing oxygen relative free access to an exposed
metal surface allowing oxidation to continue at a constant rate.

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Molybdenum metal(the chemical element of atomic number 42 , a brittle silver-grey
metal) experiences worse phenomenon , at a temperature of 900o
C there is a
catastrophic oxidation of metal since at that temperature Molybdenum oxide is a
vapour hence NO surface Oxide layer can be formed.The Oxide layers that forms on
the surface of a metal is termed as FILM (Thin layer) or SCALE (Thick layer)
Film ≤ 10-3
mm thickness
Scale > (Film ≤ 10-3
mm thickness)
The Pilling – Bedworth (P-B) ratio defines the characteristics of an oxide layer on a
metal surface and is expressed as:
P-B ratio =
where
1. , are the atomic mass numbers of oxide and metal respectively.
2. , are the volumes of oxide and metal respectively .
3. are densities of oxide and metal respectively.
4. is number of metal atoms in the oxide molecule.
INTERPRETATION FROM THE P-B RATIO EQUATION
1. if P-B ratio < 1 , then the oxide occupies a smaller volume than volume
of a metal formed ( porous film).
2. If P-B ratio , then the volume of oxide and metal are nearly equal (
non-porous film which is protective (tenacious))
3. If P-B ratio > 1 , then the oxide film formed is protective at initial stage
but as the thickness of the oxide layer increases can cause it to flake off
fom the surfaces due to some stresses developed
Porous oxide films are non-protective as there is free access of oxygen to metal
surface. In such cases oxidation will continue at constant rate at any given
temperature and thickness of the oxide layer will increase linearly with time
according to the expression: y = Kt where K =A ,T is temperature in K
according to Arrhenius relationship.
The variation of the film thickness with time follows the parabolic law
y2
=Kt ,some metals shave highly protective oxide films expressed as
y=K log(at +1) follows parabolic law example zinc and chromium.

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CORROSION OF METALS
1. Corrosion is defined as the destructive and unintentional attack of a metal; it is
electrochemical and ordinarily begins at the surface. The problem of metallic corrosion is
one of significant proportions; in economic terms, it has been estimated that approximately
5% of an industrialized nation’s income is spent on corrosion prevention and the
maintenance or replacement of products lost or contaminated as a result of corrosion
reactions.The consequences of corrosion are all too common Corrosion processes are
occasionally used to advantage.
2.Corrosion is the disintegration of a material into its constituent’s atoms due to chemical
reaction on it by its surroundings. In the most common use of the world this means
electrochemical oxidation of the metals with an oxidant such as oxygen formation of oxide
of iron due to oxidation of the iron atoms it is a well known example of electrochemical
corrosion commonly known as rusting. This type of damage typically produces
oxides salts of organic metals corrosion can also refer to other materials than
metals such as ceramics and polymers etc… but usually the term degradation is
used.
TYPES OF CORROSION
1. Uniform General Attack Corrosion
2. Galvanic Corrosion
3. Pitting Corrosion
4. Crevice Corrosion
5. Intergranular Corrosion
6. Stress Corrosion
7. Erosion Corrosion
8. Cavitations Damage
9. Fretting Corrosion
10. Selective Leaching
1. UNIFORM GENERAL ATTACK CORROSION
Uniform general attack corrosion is characterized by corrosive attack proceeding
evenly over the entire surface area of a large surface area of the total area. It is simply
oxidation and reduction occurring uniformly over the surface it results from the direct
chemical attack and involve majorly the metal surface in natural environment. Oxygen
is the primary cause of the uniform general attack corrosion of steel and other metal
alloys general thinning takes place until failure. It is the most important form of the
corrosion however the uniform general attack corrosion is relatively easily measured.

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