3. Introduction
3
TBCs are refractory-oxide ceramic coatings applied to the
surfaces of hot metallic parts.
TBCs perform the important function of insulating components
operating at elevated temperature.
Coatings can allow higher operating temperatures beyond the
limiting temperature of metal parts.
TBC not only consist of oxide ceramic coating (topcoat) itself but
also the underlying superalloy engine part, and two other layers
in between.
7. 7
Material Selection
Material selected for TBC should have following properties:-
Low Thermal Conductivity.
High Thermal Expansion Coefficient.
Good Erosion Resistance.
Therefore we use Porous Zirconia (ZrO2) partially stabilized with yttria
(Y2O3) popularly known as YSZ.
9. 9
TBC Failure
Spallation: It is a process by which the TBC peels off of the substrate; and
naturally, after the coating has spalled, the continuous thermal protection
layer no longer exists.
Thermal cycle is the main cause of TBC failure due to Thermal mismatch.
11. EBPVD
11
Electron Beam Physical Vapour Deposition or EBPVD is a form of
physical vapour deposition in which a target anode is bombarded
with an electron beam which causes atoms from the target to
transform into the gaseous phase.
These atoms then precipitate into solid form, coating everything in
the vacuum chamber (within line of sight) with a thin layer of the
anode material.
12. APS(Air Plasma Spray)
12
In plasma spraying process, the material to be deposited
(feedstock) is introduced into the plasma jet, emanating from
a plasma torch.
In the jet, where the temperature is of the order of 10,000 K,
the material is melted and propelled towards a substrate.
There, the molten droplets flatten, rapidly solidify and form a
deposit.
13. TBC on Turbine Blades and
Engines
13
Aircraft Gas Turbine:-
As we know that increase in turbine inlet temperature results in increased
thermal efficiency.
TBC can be applied on both Turbine
blades and combustion chambers.
Earlier calcia and magnesia stabilized
zirconia were used for coating (less durable).
Various tests were done at NASA on
Turbine blades for various temperature and
all coated blade were in good conditions.
15. Diesel Engines:-
15
TBC can allow higher working temperature which increase efficiency and
decrease CO and NOx emission.
Increase in engine power by 8% and decrease in fuel consumption by 15-
20% is noted by applying TBC.
Although not yet met with wide success.
16. Conclusion
16
TBC is a very useful technique and has a wide application in industries as well
as in automobile manufacturing.
Detailed analysis of coating stresses and controlled process, plasma spray
technology has significantly improved the reliability of TBC turbines, diesel
engines and other heat engines.
Thermal barrier coating allows engineers to improve product and
performance, reduce maintenance time, cost, save energy and reduce production
cost.
Application of TBC on Turbine blades made dramatic change in increasing
efficiency of Engine.
17. References
17
Materials Research Society (MRS) Bulletin, Thermal Barrier Coatings for
more efficient Gas Turbine Engines; October 2012 Vol. 37 No. 10.
Thermal Barrier Coating,
http://en.wikipedia.org/wiki/Thermal_barrier_coating
Plasma Spray, http://en.wikipedia.org/wiki/Plasma_Spray
A.G. Evans, D.R. Mumm, J.W. Hutchinson, G.H. Meier, F.S. Pettit.
Mechanism controlling the durability of Thermal Barrier Coatings: Progress
in Material Science 46 (2001) 505-553.
Carlos G. Levi. Emerging materials and processes for thermal barrier
systems: Current Opinion in Solid State and Materials Science 8 (2004) 77–
91.