FEA Based Level 3 Assessment of Deformed Tanks with Fluid Induced Loads
Thermal barrier coatings (TBC)
1. Advanced coating materials used on Turbine blade surface
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Naveen chandra
17MTRAP013
Source/Reference : “Thermal barrier coatings: characteristics of microstructure
and properties, generation and directions of development of bond”, Journal of
achievement in Materials & Manufacturing Engineering, Vol. 37.
2. 1. Thermal barrier coatings (TBC) are highly advanced
material systems usually applied to metallic surfaces, such
as gas turbines or aero-engine parts, operating at elevated
temperatures, as a form of Exhaust Heat Management.
2. These coatings serve to insulate components from large
and prolonged heat loads by utilizing thermally insulating
materials which can sustain an appreciable temperature
difference between the load bearing alloys and the coating
surface.
3. In doing so, these coatings can allow for higher operating
temperatures while limiting the thermal exposure of
structural components, extending part life by reducing
oxidation and thermal fatigue.
4. In conjunction with active film cooling, TBCs permit
working fluid temperatures higher than the melting point
of the metal airfoil in some turbine applications.
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3. Much number of factors are affecting for the material selection. They
are properties of materials, performance requirements, material’s
reliability, safety, Physical attributes environmental conditions,
availability, disposability and recyclability, and finally economic
factors.
1. The material of which a part is composed must be capable of
performing a part’s function (always it must be possible or not)
with out failure.
2. A material in a given application must also be reliable.
3. A material must safely perform its function.
4. Physical attributes such as configuration, size, weight, and
appearance sometimes also serve functional requirements that can
be used in
5. The environment in which a product operates strongly influences
service performance 3
5. TBC coating systems must possess a combination of properties
to be effective.
These include :
1. Low thermal conductivity
2. High resistance to spallation,
3. Good erosion resistance
4. Phase stability
5. Pore morphological stability &
6. Low Sintering activity
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6. Yttria stabilized zirconia (YSZ) is the most used TBC material.
The following are materials have been proposed as possible
alternative to YSZ.
Zirconates:
Zirconates have drawn the attention of several research groups as a
promising alternative to YSZ. The main advantages of zirconates are
their low sintering activity, low thermal conductivity, and good
thermal cycling resistance. The main problem is the high thermal
expansion coefficient (TEC) which results in residual stress in the
coating, and can cause coating delamination
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7. Garnets:
Polycrystalline garnet ceramics are used in different applications due to
Their unique properties. Particularly YAG (Y3Al5O12) is a good choice
for many High temperature applications, due to its excellent high
temperature and phase stability up to its melting point (1970°C). Other
advantages which make YAG a candidate as a TBC are their low thermal
conductivity and its low oxygen diffusivity.
Forsterite:
The high thermal expansion coefficient of forsterite (2MgO.SiO2),
11x10-6 /k, permits a good match with the substrate. At thicknesses of
Some hundred microns, it shows a very good thermal shock resistance
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8. Mullite:
Mullite is applied on SiC as an oxidation resistant layer to form an
environmental barrier coating (EBC). Its low oxygen diffusivity, low
creep rate at high temperatures, high thermo-mechanical fatigue
resistance and close thermal expansion coefficient match with SiC
makes it the ideal choice for this application.
Cordierite:
Cordierite (2MgO.2Al2O3.5SiO2) has a very low thermal expansion
coefficient but, for certain applications, could be an alternative for
TBCs. However, after plasma spraying, the cordierite deposition is
amorphous. While heating, two phase transformation occur, at
830°C and 1000°C, which produce a volume change and cause
Cracking.
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10. The main disadvantages are :
1. Ceramic bond coat interface region which was determined to be
the weakest link in the ZrO2-12Y2O3 / NiCrAlY system
2. Adhesive plus cohesive failure of the ceramic layer in this region
occurred when the coating was subjected to a normal tensile load
at room temperature as well as when applied on bars subjected to
axial tension or compression at elevated temperature
3. On prolonged high-temperature exposure in air, thermal barrier
coatings (TBCs) on bond-coated super alloys fail by spalling
4. Scientists discovered a new TBC failure mode, one in which
failure is associated with moisture-enhanced sub-critical crack-
growth along the bond-coat/ thermally grown oxide interface.
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11. Investigation of the current state-of-the-art in TBC
technology has indicated that opportunities exist to
significantly improve upon modern TBC systems. One
such opportunity is the tailoring of pore morphologies to
improve the insulative properties of the coatings. In doing
so an increase in the spallation life of the coating may
also be expected provided the in-plane compliance is not
compromised. To accomplish this, however, it appears
that improved TBC deposition approaches must be
developed which exhibit improved control over the
coating morphology.
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