This presentation is about wear of metals and its different types with the prevention methods

1. 1

2. Wear of Metals
2

3. What is Metallic Wear?
The deterioration of metal surfaces is
known as the Metallic Wear.
Wear is the result of erosion, abrasion,
impact, metal-to-metal contact,
oxidation,
oxidation and corrosion or a
corrosion,
combination of these.
3

4. Introduction to Wear
Plastic deformation at the interface often leads to
wear, i.e., deformation induced wear.
Wear can also be caused by chemical p
y processes.
There are many different kinds of wear
mechanisms
We have to analyze these wear mechanisms
using mechanics, thermodynamics, etc. Tribology
is a multi-disciplinary subject
4

5. Types of Wear:
There are generally 12 Types of Metallic
Wear:
1 Mild Adhesion
1.
2. Severe Adhesion
3. Abrasion
4. Erosion
4 E i
5. Polishing
g
5

6. Types of Wear:
6 Contact Fatigue
6.
7. Corrosion
8. F tti
Fretting Corrosion
C i
9. Brinelling
10.Electro-Corrosion
11 Electrical Discharge
11.
12.Cavitation Damage
6

7. Mild Adhesion:
Mild Adhesion:
Generally, removal of surface film material
due to adhesion and subsequent loosening
during relative motion. Mild Adhesion
transfer and loosening of surface films only
only.
7

8. Example:
8

9. Other names Susceptible Machine Parts
Normal/Common All
Mild Adhesion - How to detect it :
Unaided Eye
U id d E Microscopically
Mi i ll
Smooth micro plateaus among
Low rates of wear
original grinding marks
No damage Slight coloration due to films
Deeper original grinding
Slight coloration due to films
marks still visible 9

10. Mild Adhesions Solutions:
Prevention
Mechanical None
LUBRICANT None
10

11. Severe Adhesion:
Severe Adhesion:
Cold welding of metal surfaces due to intimate
metal to metal contact.
Mechanism:
when two surfaces are brought together under loadload,
asperities of the two surfaces adhere to each other.
The conditions at the interface of these junctions are
j
similar to those of a cold weld. A strong bond is
formed but without much interdiffusion of atoms and
recrystallization as would occur i a h t weld.
t lli ti ld in hot ld
11

12. 12

13. Detection:
Severe Adhesion - How to detect it :
Unaided Eye Microscopically
Rough, torn,
Rough torn melted or plastically
Rough, irregular surface
deformed metal, bands or streaks
Metal from other surface adhering
High temperature oxidation to other surface by spot tests or
microprobe analysis
High friction, high rates of wear
Possible seizure 13

14. Conditions Promoting Wear:
Conditions:
1. High loads, speeds and/or temperatures
2. Use of stainless steels or aluminum
3. Insufficient lubricant
4. Lack of anti-scuff additives
5. No break in
6. Abrasive wear interrupting film allowing
adhesion
14

15. Severe Adhesion Solutions:
1 Reduce load, speed and temperature
1.
2. Improve oil cooling
3 Use compatible metals
3.
4. Apply surface coatings such as phosphating
5 Modify surface, such as ion implantation
5. surface
LUBRICANT:
Use more viscous oil to separate surfaces
Use "extreme pressure" (anti-scuff) additives such as
a sulfur-phosphorous or borate compounds
sulfur phosphorous
15

16. Abrasion:
Abrasion is the wearing of surfaces by rubbing,
grinding, or other types of friction.
It usually occurs due to metal-to metal contact. It
y
is a scraping, grinding wear that rubs away metal
surfaces and can be caused by the scouring
action of sand, gravel, slag, earth, and other gritty
material.
16

17. Example:
17

18. Detection:
Abrasion - How to detect it :
Unaided Eye Microscopically
Scratches or parallel furrows in the
d ec o o o o , s
direction of motion, similar to
o Ce
Clean furrows, bu s, c ps
u ows, burrs, chips
"sanding"
High rates of wear Embedded abrasive particles
In sliding bearings with soft overlay
embedded particles
b dd d i l
18

19. Conditions Promoting Wear:
Conditions:
1. Hard particles contaminating oil
2. Insufficient metal hardness
3. Hard metal with rough surface against soft metal
19

20. Prevention:
MECHANICAL
Remove abrasive by improved air and oil filtering, clean oil
handling practices, improved seals, flushing and frequent
oil changes
il h
Minimize shot peening, beading, or sand blasting of
surfaces because abrasives cannot be completely
removed
Increase hardness of metal surfaces
LUBRICANT
Use oil free of abrasive particles
Use
U more viscous oil
i il
20

21. Erosion:
Definition:
Cutting of materials by hard particles in a high
velocity fluid impinging on a surface
Occurrence:
This type of wear results from sharp particles
impinging on a surface such as the cutting of
materials by hard particles in a high velocity fluid
impinging on a surface. This action is very much
like that of sandblasting.
21

22. Mechanism:
22

23. Erosion - How to detect it:
Unaided Eye Microscopically
1
Smooth, broad grooves in direction Short V-shaped furrows by
of fluid flow scanning electron microscopy
Matte texture, clean metal
, Embedded hard particles
p
Similar to sandblasting
23

24. Example:
24

25. Erosion – Solutions:
Prevention:
MECHANICAL:
Remove abrasive b i
R b i by improved air and oil filt i
d i d il filtering, clean oil
l il
handling practices, improved seals, flushing and frequent
oil changes
g
Increase hardness of metal surfaces
Reduce impact angle to less than 15 degrees
LUBRICANT:
Use oil free of abrasive particles
Use
U more viscous oil
i il
25

26. Contact Fatigue:
Definition:
Metal removed by cracking and pitting, due to
cyclic elastic stress during rolling and sliding
sliding.
Occurrence:
This type of wear is produced when repeated
sliding or rolling occurs over a track. The most
common example is the action of a ball or roller
bearing race. As the rolling element passes over
a given spot on the raceway it is stressed as the
raceway,
load is applied and released. 26

27. Contact Fatigue - How to detect it:
Detection:
Unaided Eye Microscopically
Combination of cracks and pits
Cracks, pits and spalls
with sharp edges
p g
Subsurface cracks by
y
metallographic cross-section.
Numerous metal inclusions
27

28. Example:
28

29. Prevention:
MECHANICAL:
Reduce contact pressures and frequency of cyclic
stress
Use high quality vacuum melted steels
Use less abusive surface finish
LUBRICANT:
Use clean, dry oil
clean
Use more viscous oil
Use oil with higher pressure viscosity coefficient
higher-pressure
29

30. Corrosion Wear:
Corrosion wear is the gradual deterioration of
unprotected metal surfaces, caused by the effects
of the atmosphere, acids, gases, alkalies, etc.
This type of wear creates pits and perforations
and may eventually dissolve metal parts.
30

31. Mechanism:
31

32. Corrosion - How to detect it:
Detection:
Unaided Eye Microscopically
Co oded e a su ace us ,
Corroded metal surface rust,
Scale, films, pits containing
l fil i i i
Fe²O³H²O (hydrated iron oxide) is a
corrosion products
common iron corrosion product
Dissolution of one phase in a 2-
phase alloy
32

33. Example:
33

34. Corrosion – Solutions:
Prevention
MECHANICAL
1.
1 Use more corrosion resistant metal (not stainless)
2. Reduce operating temperature
3. Eliminate corrosive material
LUBRICANT
1. Remove corrosive material such as too chemically active
additive and contaminates
2. Use improved corrosion inhibitor
3.
3 Use fresh il
U f h oil
34

35. Fretting:
Definition:
Wear between two solid surfaces experiencing
oscillatory relative motion of l
ill t l ti ti f low amplitude.
lit d
Occurrence:
Fretting wear occurs where there is oscillatory
motion with a small displacement ( ~1 micron) of
1
the contacting surfaces under load. Small wear
particles are formed through the mechanism of
adhesive wear 35

36. Mechanism:
36

37. Fretting - How to detect it
Unaided Eye Microscopically
Corroded stained surfaces
Thick films of oxide and
where damage on one
metal. Red and black for
surface is mirror image of
steel
mating surface
Loose colored debris around
real contact areas
l t t
Rouge (Fe?O?) colored
films, debris, grease or oil
37
for steel

38. Example:
38

39. Fretting - Solutions
Prevention
MECHANICAL
1 Reduce or stop vibration by tighter fit or higher load
1.
2. Improve lubrication between surfaces by rougher
(then honed) surface finish
LUBRICANT
1 Use oil of lower viscosity
1.
2. Relubricate frequently
3 Use oxidation inhibitors in oil
3.
39

40. False Brinneling:
Definition:
Localized wear spots made by rolling elements on
raceways due to limited rolling/repeated impact
impact.
Occurrence:
Localized wear spots formed by rolling elements on
raceways due to limited rolling/repeated impact. False
Brinelling is typically characterized by indentations on the
inner or outer raceway of a rolling element bearing. The
indentation corresponded to the position of the rolling
elements.
l t
40

41. Example:
41

42. False Brinelling - Solutions
Detection:
Unaided Eye Microscopically
Indentations on raceway Indentations on raceway
Prevention
MECHANICAL
Reduce or eliminate impact
Rotate bearings occasionally
g y
LUBRICANT
Change viscosity
Consider additives
42

43. Cavitation:
Definition:
Removal of metal by vapor cavity implosion in a
cavitating liquid
liquid.
Occurrence:
Cavitation happens, for example, in high-pressure
pumps adjacent to the intake ports and on the
blades of a ship's propellers When a sudden
propellers.
local reduction in fluid pressure occurs, a vapor
cavity is formed When the vapor cavity later
formed.
collapses near a solid surface it produces a 43
mechanical shock.

44. Cavitation - How to detect it
Detection:
Unaided Eye Microscopically
Clean frosted or rough Clean, metallic bright rough
appearing metal
pp g metal, p
, pits
Removal of softer phase
from 2-phase metal
2 phase
Deep, rough pits or grooves
(graphite phase in cast iron
is susceptible)
44

45. Cavitation - Solutions
Prevention:
MECHANICAL
Use hard, tough metals, such as tool steel
Reduce vibration, flow velocities and pressures
Avoid restriction and obstructions to liquid flow
LUBRICANT
Avoid low vapor pressure, aerated, wet oils
Use noncorrosive oils
45

46. Polishing:
Definition:
Continuous removal of surface films byy
very fine abrasives.
Polishing wear is characterized by very
shiny, very smooth, mirror like metal
surfaces. Fine abrasives wear away the
surface films as they form and reform
46

47. Mechanism:
47

48. Polishing - How to detect it
Detection:
Unaided Eye Microscopically
Featureless surface except
High wear but a bright scratches at high
mirror finish magnification by electron
microscopy
Wavy profile
48

49. Example:
49

50. Polishing - Solutions
Prevention
MECHANICAL
None
LUBRICANT
Choose less chemically active additive
Remove corrosive contaminant
Remove abrasive
50

51. Electro-Corrosion
Definition:
Dissolution of a metal in an electrically
conducive li id b l
d i liquid by low amperage currents. t
51

52. Mechanism:
52

53. Electro corrosion
Electro-corrosion - How to detect it
Detection:
Unaided Eye Microscopically
Featureless surface except
F l f
High wear but a bright mirror
scratches at high magnification
finish
by electron microscopy
Corrosion pits, films, dissolution
Local corroded areas
of metals
Black spots such as made by a
small drop of acid
p
Corroded, worn metering edges 53

54. Example:
54

55. Electro corrosion
Electro-corrosion – Solutions:
Prevention
MECHANICAL
Decrease liquid velocity and velocity gradients
Use corrosion-resistant metals
Eliminate stray currents
y
Use nongalvanic couples
LUBRICANT
Decrease or increase electrical conductivity of lubricants
or hydraulic fluids
Highly compounded oils can act as electrolytes and be
electrolytes,
conductive. Phosphate ester hydraulic fluids are 55
conducive

56. Electrical Discharge
Electrical Discharge:
Removal of metal by high amperage electrical
discharge or spark between two surfaces
g p
56

57. Electrical Discharge - How to detect it
Unaided Eye Microscopically
Metal surface appears Pits, near edge of damage,
etched. In thrust bearings, showing once molten state,
sparks make tracks like an such as smooth bottoms,
electrical engraver rounded particles, gas holes
Rounded particles welded to
surface near pits
57

58. Example:
58

59. Electrical Discharge - Solutions
Prevention
MECHANICAL
Improve electrical insulation of bearings
Degauss magnetic rotating parts
Install brushes on shaft
Improve machine grounding
LUBRICANT
Use of oil of higher electrical
59

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