This presentation describes the thermal barrier coating process, its anatomy, types, material selection, failure, and characterization. Thermal barrier coatings (TBCs) were introduced to protect the external surface of gas turbine engine components from thermal resistance and thereby decrease the temperature of the metal surfaces. Yttria stabilized zirconia (YSZ) is one of the most popular and widely used TBC materials as it provides the best performance in high-temperature zones such as diesel engines and gas turbines. The columnar microstructure of YSZ coating provides excellent strain tolerance and adhesion to the coating. Gas turbines are used to power aircraft, trains, ships, electrical generators, pumps, gas compressors, and tanks.

1. Seminar and Technical Writing (CR798)
THERMAL BARRIER COATING
FOR
GAS TURBINE ENGINES
1
Presented by: Nelson Kandulna (519CR6009)
Course Instructor: Prof. Debasish Sarkar
Department of Ceramic Engineering
NIT Rourkela, Odisha, India-769008

2. Contents
 What is a gas turbine engine ?
 Applications of gas turbine engine
 What is Thermal barrier coating(TBC) ?
 Why we need TBCs?
 Advantages and disadvantages of TBCs
 Anatomy of TBC
 Material Selection for TBCs
 TBC Failure
 TBC Characterization
 Summary
2
National Institute of Technology, Rourkela

3. Gas turbine engine
 A gas turbine is a machine delivering mechanical power or thrust.
 Gas turbine engines are mainly used for two purposes first for power production
and second for generating thrust force in an aircraft in order to move it forward.
3
National Institute of Technology, Rourkela

4. Applications of gas turbine engine
1. For power generation in thermal power plants.
2. For propulsion in fighter or civilian get
4. In battle tank
3. In marine fields
4
National Institute of Technology, Rourkela

5. 5. In Aero get trains, concept cars, racing cars, superbikes.
5
Contd.
National Institute of Technology, Rourkela

6. Thermal barrier coatings (TBCs)
 TBCs are refractory-oxide ceramic coatings applied to the surfaces of hot metallic parts.
 The function of a TBC system is to allow higher temperature operating conditions than
would be allowed by the metals used to make the engine.
 TBC’s are used in hot section components of the engine; these include the combustor, turbine
inlet guide vanes, turbine blades, turbine stator blades and afterburners.
6
National Institute of Technology, Rourkela

7.  Gas turbines operate under the
Brayton cycle.
 Overall efficiency of the turbine
will increase if the pressure ratio
is increased.
 However, a consequence of
increasing the pressure ratio is a
higher compressor outlet
temperature, leading to higher
turbine temperatures.
Why we need TBCs ?
7
National Institute of Technology, Rourkela

8.  The main barrier to this upward trend has been the development of materials capable
of withstanding the increased turbine inlet temperatures required.
 Present developments of single crystal nickel alloy blades with film and internal
cooling have reached the limit of capability.
 There are presently no immediate replacements for the nickel blades used in the
high pressure turbine section, though a number of composite (SiC-SiC) and
intermetallic (Nb-Si, Mo-Si, Ti-Al) options are under development.
8
Contd.
 It can be seen that higher turbine temperatures will also raise the efficiency of the
process combined with an increased specific power output. The trend in both aero
turbines and industrial power turbines is a need for greater efficiency and specific
power.
National Institute of Technology, Rourkela

9. Graphical representation for the growth of TBC
9
National Institute of Technology, Rourkela

10. Development of upper operating limit of turbine materials
with time
10
Adapted
from Stöver et al.
National Institute of Technology, Rourkela

11. Advantages
 It does not require the use of any vacuum electron beam or
plasma so reduces the manufacturing costs.
 It also uses less power and raw materials making it more
environmentally friendly.
Disadvantages
 Operating cost is very high
11
National Institute of Technology, Rourkela

12. Anatomy of TBC
TBC’s consist of at least three component layers.
The first layer is the bond coat applied onto the base component.
 An intermediate layer is formed during operation called the
thermally grown oxide (TGO).
The final layer is the ceramic top coat that provides the operating
temperature increase.
12
National Institute of Technology, Rourkela

13. Anatomy of TBC
13
National Institute of Technology, Rourkela

14. TOP COAT
 Low thermal conductivity to prevent heat transfer to the component from
the combustion gas.
 High thermal expansion coefficient to allow the ceramic to expand and
contract with the component without cracking.
 Phase stability at high temperatures to prevent any changes in volume that
would cause failure.
 6-8% yttria partially stabilised zirconia (YSZ) has become the material of
choice for this application.
 This material is used due to its relatively high coefficient of thermal
expansion and very low thermal conductivity of around 2.25 W m-1 K-1 in
bulk form and the region of 1 W m-1 K-1 for a standard TBC coating. YSZ
is also stable up to 1200 °C.
14
National Institute of Technology, Rourkela

15. BOND COAT
Bond coats are commonly of two types. Diffusion based aluminide
coatings or MCrAlY (Metal-Chromium-Aluminium-Yttrium) overlay
coatings.
The M can be Fe, Co, Ni or a mixture of more than one element.
Present standard coatings are mixtures of nickel and cobalt depending
on the environmental requirements.
High nickel content coatings are more suitable for oxidation resistance
and high cobalt content suitable for high corrosion environments.
15
National Institute of Technology, Rourkela

16. Contd.
Bond coats are commonly of two types. Diffusion based aluminide
coatings or MCrAlY (Metal-Chromium-Aluminium-Yttrium) overlay
coatings.
The M can be Fe, Co, Ni or a mixture of more than one element.
Present standard coatings are mixtures of nickel and cobalt depending on
the environmental requirements.
High nickel content coatings are more suitable for oxidation resistance
and high cobalt content suitable for high corrosion environments.
16
The bond coat provides a number of functions to the system:
National Institute of Technology, Rourkela

17.  Material selected for TBC should have following properties:-
1. Low thermal conductivity
2. High thermal expansion coefficient
3. Good erosion and corrosion resistance
4. High Thermal shock resistance
5. High temperature withstandibility
6. Low density
Therefore 7YSZ, HfO2, YAG, mullite, MgAl2O4, Silicates of Zr, Hf, Y, Gd,
aluminosilicates of (Ba, &Sr), Ba etc. are used as TBC.
Material Selection for TBC
17
National Institute of Technology, Rourkela

18. TBC Failure
 Thermal cycle is the main cause of TBC failure
 Thermal stress between top coat and substrate
 Oxidation
 Erosion due to CMAS (Calcium-Magnesium- Alumina-Silica)
TBC Deposition Methods
 Electron Beam Physical Vapour Deposition (EBPVD)
 Air Plasma Spray (APS)
 Electrostatic Spray Assisted Vapour Deposition (ESAVD)
 High velocity oxygen fuel (HVOF)
18
National Institute of Technology, Rourkela

19. 19
TBC Characterisation
Techniques for Investigating lifetime
Thermo-cyclic Fatigue
Thermal Shock
Measurement of Thermal Properties
𝜆 = 𝛼 ∙ 𝐶𝑝 ∙ 𝜌
Where α is thermal diffusivity (m²/s), Cp is specific heat capacity
(J/(kg·K)), ρ is density (kg/m³) λ is thermal conductivity (W/(m·K).
 It can be seen that a material with a high thermal conductivity will
have a high thermal diffusivity.
National Institute of Technology, Rourkela

20. 20
Contd.
Laser Flash Analysis
Where α is the thermal diffusivity (m²/s), L is the sample
thickness (m) and t(0.5) the time corresponding to the half
maximum increase in temperature at the back face of the sample
(s).
National Institute of Technology, Rourkela

21. 21
Contd.
Laser Flash Analysis
Figure: Schematic of the
laser flash analysis
equipment
National Institute of Technology, Rourkela

22. Summary
22
 Thermal barrier coatings (TBC’s) are used to provide both thermal
insulation and oxidation protection to high temperature components
within gas turbines.
 TBCs have been commonly used in gas turbines, both stationary and
jet turbines, for 20 years. Combustion chambers and combustion liners
and vanes are protected by parts. The heat exchangers rocket motor
nozzles, exhaust collectors, jet engine parts and nuclear energy
components can also be used for thermal-barrier coatings on furnace
components, heat processing equipment.
 7YSZ, HfO2, YAG, mullite, MgAl2O4, Silicates of Zr, Hf, Y, Gd,
aluminosilicates of (Ba, &Sr), Ba etc. are used as TBC for high
temperature gas turbine engines.
National Institute of Technology, Rourkela

23. Contd.
23
 The focus is to design thermal barrier coatings with lower conductivity
and longer lifetime than those coatings used in industry today. Greater
lifetime in Thermo Cycle Failure testing was demonstrated relative
to dense vertically cracked APS coatings.
 Performance improvements in both lifetime and thermal properties
for TBC systems can be achieved through designed microstructures.
National Institute of Technology, Rourkela

24. [1] Sonntag, Richard E.; Borgnakke, Claus (2006). Introduction to engineering thermodynamics (Second ed.). John
Wiley. ISBN 9780471737599.
[2] R. Miller, “Thermal barrier coatings for aircraft engines: history and directions,”Journal of thermal Spray
Technology, vol. 6, no. 1, pp. 35–42, Mar. 1997.
[2] D. Stöver, R. Vassen, G. Pracht, H. Lehmann, M. Dietrich, and J.-E. Döring, “New Material Concepts for the Next
Generation of Plasma-Sprayed Thermal Barrier Coatings,” Journal of Thermal Spray Technology, vol. 13, no. 1, pp. 76–
83, 2004.
[3] B. P. Bewlay, M. R. Jackson, P. R. Subramanian, and J.-C. Zhao, “A review of very-high-temperature Nb-silicide-
based composites,” Metallurgical and Materials Transactions A, vol. 34, no. 10, pp. 2043–2052, Oct. 2003.
[4] C. Brandt and O. T. Inal, “Mechanical properties of Cr, Mn, Fe, Co, and Ni modified titanium trialuminides,” Journal
of Materials Science, vol. Volume 37, no. Number 20, Oct. 2002.
[5] C. Leyens, R. Braun, M. Fröhlich, and P. Hovsepian, “Recent progress in the coating protection of gamma titanium-
aluminides,” JOM Journal of the Minerals, Metals and Materials Society, vol. 58, no. 1, pp. 17–21, Jan. 2006.
[6] A. Bennett, F. C. Roriz, and A. B. Thakker, “A philosophy for thermal barrier coating design and its corroboration by
10 000 h service experience on RB211 nozzle guide vanes,” Surface and Coatings Technology, vol. 32, no. 1–4, pp. 359–
375, Nov. 1987.
[7] S. Bose and J. DeMasi-Marcin, “Thermal barrier coating experience in gas turbine engines at Pratt & Whitney,”
Journal of Thermal Spray Technology, vol. 6, pp. 99–104, Mar. 1997.
[8] Z. Mutasim and W. Brentnall, “Thermal barrier coatings for industrial gas turbine applications: An industrial note,”
Journal of Thermal Spray Technology, vol. 6, pp. 105–108, Mar. 1997.
[9] I. Taymaz The effect of thermal barrier coatings on diesel engine performance J Surf Coat
Technol, 201 (2007), pp. 5249-5252
[10] Design of thermal barrier coatings N Curry - A Modeling Approach, 2014.
References
24
National Institute of Technology, Rourkela

25. THANK YOU
25
National Institute of Technology, Rourkela