Thermal Barrier Coatings Explained

THERMAL BARRIER COATINGS
STC/SPRT/ME/2017-18 Page 1
CHAPTER. 1
1. INTRODUCTION
Thermal Barrier Coatings, as the name suggests are coatings which provide a barrier to the flow of
heat. Thermal Barrier Coatings (TBC) performs the important function of insulating components such as
gas turbine and aero engine parts operating at elevated temperatures. Thermal barrier coatings (TBC) are
layer systems deposited on thermally highly loaded metallic components, as for instance in gas turbines.
TBC’s are characterized by their low thermal conductivity, the coating bearing a large temperature
gradient when exposed to heat flow. The most commonly used TBC material is Yttrium Stabilized
Zirconia (YSZ), which exhibits resistance to thermal shock and thermal fatigue up to 1150°C. YSZ is
generally deposited by plasma spraying and electron beam physical vapour deposition (EBPVD)
processes. It can also be deposited by HVOF spraying for applications such as blade tip wear prevention,
where the wear resistant properties of this material can also be used. The use of the TBC raises the
process temperature and thus increases the efficiency. 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. In conjunction with active film cooling, TBCs permit working
fluid temperatures higher than the melting point of the metal airfoil in some turbine applications. Due to
increasing demand for higher engine operation (efficiency increases at higher temperatures), better
durability/lifetime, and thinner coatings to reduce parasitic weight for rotating/moving components, there
is great motivation to develop new and advanced TBCs.

1.1 Thermal Barrier Coating
Thermal Barrier Coating are designed to protect metal structural components from extreme elevated
temperatures, thereby reducing stress and fatigue and increasing the part’s lifespan. In order to provide
such a high level of protection, thermal barriers incorporate several key components. Every coating
consists of four distinct layers, with each layer adding to the protective thermal properties and enabling
the coating to form a unique thermal barrier.
Fig 1.1 Thermal barrier coatings (TBCs).

1.2 Thermal Barrier Coating Composition.
A typical thermal coating simply consists of a metallic layer paired with a ceramic layer. The
mismatched thermal expansion coefficients, however, can cause the bond to be compromised where it
adheres to the substrate. Sometimes, a “bond coat” is used between the metal substrate and the ceramic layer
to aid in adhesion. These types of thermal barrier coatings have four different layers. The first part of the
thermal coating is the metal substrate itself. Usually the metal that thermal coatings work well with is a
single or polycrystalline cobalt or nickel alloy mixed with other elements depending on the desired
properties of the end-product. The first layer of the coating is called the bond coat—it’s what enables the
coating to bond to the substrate and therefore plays an integral role in forming a thermal barrier. The bond
coat is typically a metallic layer made of a nano-structured ceramic-metallic composite that adheres the layer
to the metal substrate and is responsible for generating the second coating layer of thermally grown ceramic
oxide, which occurs when the coating is subjected to a high temperature. When nano-particles of aluminum
oxides and nitrides are distributed throughout the bond coat or along its surface, the formation of thermally
grown oxides is catalyzed. This ceramic layer is responsible for forming a uniform, thermally protective
barrier by acting as an oxygen diffuser which prevents the substrate from becoming thermally oxidized. The
last layer of the coating is the ceramic top coat, which is made of yttria-stabilized zirconia (YSZ). The top
coat protects the substrate by keeping the other coating layers at a lower temperature than the surface.

CHAPTER.2
2.1 LITERATURE REVIEW.
This paper reviews the role of ceramic coatings technology in the hot sections of modern gas turbine
engines by contrasting the role of surface engineering and coatings away from secondary reliance (i.e. the
coating extending the life of the component and when the coating is lost or fails there is still an appreciable
remnant life of the component) to prime reliance where the failure of the coating would result in a rapid
failure of the component. To illustrate this change in design philosophy, the coating systems deployed in the
HP turbine module in both shrouded and un shrouded configurations are discussed by comparing the
performance of first and second generation coating systems. Following the introduction of electron-beam
physical vapour deposited (EB-PVD) zirconia partially stabilised with yttria (PYSZ) on the high pressure
turbine blade in the early 1990’s, a second generation low thermal conductivity coating was developed
which successfully reduced the thermal conductivity of the coating by blocking electro-magnetic radiation in
the infrared region and introducing mass and strain scattering centres in the lattice, reducing the amount of
cooling flow to achieve a given component life.
These ceramic alloying developments and optimisation of the low thermal conductivity coating are
discussed along with a detailed understanding of the degradation and failure mechanisms in a range of
laboratory/engine environments which included foreign object damage, CMAS simulation, erosion and
probabilistic lifing.In the development of future shroudless turbines, the adoption of advanced coating
systems have successfully overcome the limiting factors associated with first-generation PYSZ materials of a
relatively low sintering temperature (1200C) and elevated surface temperatures driven by the low thermal
conductivity associated with thick coatings when used as abradable seals. The process optimisation and
failure mechanism work on these new coating systems is discussed which combine an improved high
temperature capability and a high resistance to thermal cyclic loading with good erosion behaviour,
abradability and rubcompatibility with the abrasive tip coating. Looking forward, one of the key roles for
surface engineering will be in supporting the integration of composite materials into the high pressure
turbine by designing the ultimate in prime reliant protective coating systems. This paper concludes by briefly
reviewing some of the strategies and technologies that will need to be developed to manage the protection of
composite components in advanced engines.

CHAPTER. 3
3.1. Construction and Working.
A thermal barrier coating is generally composed of two layers:
Fig 3.1: Construction of (TBC).


3.1.1. Metallic Bond Coat
with a thickness of about 0.004” (0.1 mm). The alloy of the bond coating is MCrAlY, where M is Ni,
Fe or Co. The bond coat is an intermediate layer providing strong adhesion of the outer ceramic layer to
the substrate surface. The bond coat also inhibits the diffusion of the substrate and the ceramic coating
components. Aluminum in the amount of about 10% in the bond coat is required for a formation of an
oxide barrier (thermally grown oxide) on the interface between the bond coatand the ceramic layer. The
thermally grown oxide form as a result of oxidation of the bond coat with Oxygendiffusing from the
combustion gases throghout the ceramic layer. The oxide laye riscomposed of α-Al2O3.

.3.1.2. Outer ceramic layer (Top Coat).
Commonly 6-9%yttria (Y2O3) stabilized zirconia (ZrO2)with tetragonal crystal structure is used for
building the outer ceramic layer. Yttria is added to zirconia in order to stabilize the tetragonal structure.
Without a stabilizing agent tetragona lzirconia transforms to monoclinic allotrope stable at low
temperatures. The volume change (about 8%) resulting from the tetragonal-monoclinic transformation
causes internal stresses and cracking. Monoclinic zirconia isalso undesirable because of its low
Coefficient of Thermal Expansion and poor mechanical properties. Tetragonal zirconia is characterized
by:
1. Low thermal conductivity.
2. High Coefficient of Thermal Expansion which allows reducing thermal stresses at the boundary with the
metallic substrate.
3. Relatively high Fracture Toughness.
4. High thermal shock resistance.
3.2.APPLICATIONS OF TBC.
1 . Direct vapour deposition is mainly used for producing coatings on complex surfaces.
2 . It is capable of producing coatings on internal surfaces of machine parts which cannot be attained by
other methods.

CHAPTER. 4
4.1 Material Selection On TBC.
Yttria stabilized zirconia has become the preferred TBC layer material for gas turbine engine
applications because of its low thermal conductivity, k and its relatively high thermal coefficient of
expansion (compared to many other ceramics). This reduces the thermal expansion mismatch with the
high thermal expansion coefficient metals to which it is applied. It also has good erosion resistance which
is important because of the entrainment of high velocity particles in the engine gases. The low thermal
conductivity of bulk YSZ results from the low intrinsic thermal conductivity of zirconia and phonon
scattering defects introduced by the addition of yttria. These defects are introduced because yttria addition
requires the creation of O2? vacancies to maintain the electrical neutrality of the ionic lattice. Since both
the yttrium solutes and the O2– vacancies are effective phonon scattering sites the thermal conductivity is
decreased as the yttria content is increased. YSZ has a room temperature, grain size dependent, thermal
conductivity of 2.2-2.6 W/mK in the densest form. Adding porosity further reduces k and can improve the
in-plane compliance.

4.2 TBC coating in ic engines and coating methods.
With various methods, combustion chamber elements are coated with coating materials in internal
combustion engines. Leading method among these is thermal barrier coating. Thermal barrier coatings are
used in order to increase reliability and strength of hot parts of metal components, increase yield and
performance of engines. Engine parts which are coated with thermal barrier are; piston, cylinder head
cylinder sleeve and exhaust valves. Engines with thermal barrier coating are called low heat loss engines.
Different methods are used in order to coat the surface of metals. In industry, thermal barrier coatings are
produced in a number of ways.
1. Electron Beam Physical Vapor Deposition (EBPVD).
2. Air Plasma Spray (APS).
3. Electrostatic Spray Assisted Vapors Deposition (ESAVD).
4. Direct Vapor Deposition.
5. ELECTRON BEAM PHYSICAL VAPOR DEPOSITION.
4.2.1) Purpose: In this research, Cerium Stabilized Zirconia is coated on the I.C engine cylinder liner using
Plasma Spray Coating technique. The coating system has effects on the fuel consumption, the power
and the combustion efficiency, pollution contents. Their performance characteristics and results are
studied and tabulated.
4.2.2) Design/methodology/approach: Thermal Barrier Coating (TBC) are used to achieve the
reduced heat rejection in engine cylinders. It is known that the efficiency of internal combustion
diesel engines changes 38-42%. It is about 60% of the fuel energy dismissed from combustion chamber.
4.2.3) Practical implications: To save energy, combustion chamber component is coated with low thermal
conduction materials. In this paper, we are giving idea to thermal barrier coating and ceramic materials
which are used for making low heat released engines. It reduces the excessive heat transfer to the coolant
and exhaust system, thus improves the mechanical and thermal efficiency.

4.3 Materials used for thermal barier coating in ( IC ENGINE ).
1) Zirconates: The main advantage of zircontes are their low sintering activity, low thermal
conductivity, high thermal expansion coefficient and good thermal cycling resistance. The main
problem is the high thermal expansion coefficient which results in residual stress in the coating, and
this can cause coating delamination.
2) Yittria Stabilized Zirconia:7-8% yittria stabilized zirconia has high thermal expansion coefficient,
low thermal conductivity and high thermal shock resistance.[3]
3) Mullite: Mullite is an important ceramic material because of its low density, high thermal stability,
stability in severe chemical environments, low thermal conductivity and favourable strength and creep
behaviour. Compared with yittria stabilized zirconia, mullite has a much lower thermal expansion
coefficient and higher thermal conductivity, and is much more oxygen resistant than yittria stabilized
zirconia. The low thermal expansion coefficient of mullite is an advantage relative to yittria stabilized
zirconia in high thermal gradients and under thermal shock conditions.[4]
4) Alumina: It has very high hardness and chemical inertness. Alumina has relatively high thermal
conductivity and low thermal expansion coefficient compared with yittria stabilized zirconia. Even
though alumina alone is not a good thermal barrier coating candidate, its addition to yittria stabilized
zirconia can increase the hardness of the coating and improve the oxidation resistance of the substrate.[4]
5) Spinel: Although spinel has very good high temperature and chemical properties, its thermal
expansion coefficient prevents its usage as a reliable choice for thermal barrier coatings.
6) Forsterite: The high thermal expansion coefficient of forsterite permits a good match with the
substrate. At thicknesses of some hundred microns, it shows a very good thermal shock resistance.

4.4 EFFECT OF TBC ON IC ENGINES.
A major breakthrough in diesel engine technology has been achieved by the pioneering work done by
Kamo and Bryzik since 1978 to 1989 as the first persons in introducing TBC system for engines.They
used thermally insulating material silicon nitride. Recent trend of coating on diesel engine is to providing
a thin ceramic (about 2mm top layer) coating on parts like piston and cylinder head resulting in reduction
of fuel consumption, emission, oil consumption, engine noise, Components temperature and cost, while
increasing engine life, engine power,valves lifetime, reliability.describe that efficiency of most
commercially available diesel engine ranges from 38% to 42%. Therefore, between 58% and 62% of the
fuel energy content is lost in the form of waste heat. Approximately 30% is retained in the exhaust gas
and the remainder is removed by the cooling, etc. More than 55% of the energy, which is produced during
the combustion process, is removed by cooling water/air and through the exhaust gas. In order to save
energy, it is an advantage to protect the hot parts by a thermally insulating layer. This will reduce the heat
transfer through the engine walls, and a greater part of the produced energy can be utilized, involving an
increased efficiency .

CHAPTER. 5
5.1.Methods of depositing thermal barrier coatings.
Fig 5.1 : Air Plasma Spray

Most of thermal barrier coatings are deposited by one of the two techniques:
5.1.1. Air Plasma Spraying (APS)
The method utilizes an electrical arc ionizing Argon flowing through it and converting into hot
plasma at a temperature of about 15,000°F (8,300°C). The ceramic material in powdered form is injected
into the plasma jet where the ceramic grains melt and move in the stream of the hot gas towards the substrate
surface. When the molten particles impact the substrate surface they solidify in form of splats (flattened
discs). The resulting microstructure is composed of the grains and elongated pores stretched in the direction
parallel to the substrate surface.
5.1.2. Substrate and Surface Cooling during Thermal Spraying.
Cooling of the substrate from the back or at the spray surface is an important tool to control the
morphology of the ceramic coating. Surface cooling i.e. allows to realize tailored segmented structures
depending from the surface temperature kept. The higher the temperature the finer the segmentation. At low
temperatures some porosity without any segmentation is the normal morphology. Cooling also is an
important means to optimize the residual stresses in the ceramic coating. So it is reported, that surface
cooling reveals an almost stress free condition [25]. However, too low surface temperatures can lead to
unfavorable spreading behavior of the molten particles and accordingly to low adhesion conditions. Too high
substrate temperatures can lead to compressive stresses during cooling and thereby, depending on the
bondcoat roughness and surface conditions, to crack formation in the interface and near the bond coat
respectively.

5.2. Advantages.
1. There is a wide range of coating materials that meet a wide variety of different needs, with nearly all
materials available in a suitable powder form.
2. Higher quality coatings such as flame or electrical arc spraying.
3. Many types of substrate material, including metals, ceramics, plastics, glass, and composite materials can
be coated using plasma spraying.
4. The high temperature of a plasma jet makes it particularly suitable for spraying coatings of refractory
metals and ceramics, including ZrO2, B4C and tungsten.
5. A broader powder particle size range can be used, typically 5-100µm, compared with HVOF spraying.
6. Plasma spraying is a well-established coating process that is widely available and well understood.
5.3. Disadvantages.
1. Air plasma spraying equipment is generally very expensive to buy and use.
2. It is a line-of-sight process, similar to all other thermal spraying processes, making it difficult to coat
internal bores of small diameters or restricted access surfaces.
3. The plasma spray gun usually experiences rapid deterioration of the inner gun electrodes and other
internal components. This leads to frequent replacement of gun electrodes, and the need for quality
control to maintain coating consistency.
4. The high temperatures associated with the plasma jet can result in carbide decomposition or excessive
oxidation when spraying in air, giving carbide coatings with lower hardness or metallic coatings with
higher oxide levels compared with HVOF sprayed coatings.
5. The equipment is not suitable for manual operation and requires use of automated gun manipulators.

CHAPTER. 6
6.1. Electron Beam Physical Vapor Deposition (EB-PVD).
In EB-PVD technique an electron beam is directed to the target made of the ceramic material. The
electrons bombard the target and vaporize the material, molecules of which are accelerated towards the
substrate surface. The ceramic material deposits on the surface in form of parallel columns oriented
perpendicualar to the substrate surface.
Because of its columnar structure the coatings produced by the method of electron beam physical vapor
deposition have the thermal conductivity 30-40% higher than that of the coatings deposited by Air Plasma
Spraying. On the other hand the columnar structure is more tolerant to the stresses generated by thermal
expansion of the coating.
Fig 6.1: Electron-beam physical vapor deposition (EB-PVD).

CHAPTER. 7
7.1 Advantages of EBPVD.
1. . The material utilization efficiency is high relative to other methods.
2. This process has potential industrial application for wear-resistant and thermal barrier coatings in
aerospace industries
3. Due to the very high deposition rate.
7.2 Disadvantages of EBPVD.
1. This process cannot be used to coat the inner surface.
2. Performed at a low enough pressure.

CHPATER. 8
8.1.High Velocity Oxygen Fuel (HVOF).
8.1.1 Principle and Working.
The High Velocity Oxygen Fuel (HVOF) process is a subset of flame spray process. There are two
distinct differences between conventional flame spray and HVOF. HVOF utilizes confined combustion
and an extended nozzle to heat and accelerate the powdered coating material. Typical HVOF devices
operateat hypersonic gas velocities, greater than MACH 5. The extreme velocities provide kinetic energy
which help produce coatings are very dense and very well adhered in the as-sprayed condition.
Fig 8.1.1. High Velocity Oxygen - Fuel (HVOF).

8.1.2 Equipment.
The HVOF gun has three different inlets for the fuel gas, ceramic powder and for oxygen. The three
components are mixed in the mixing chamber and subjected to combustion in the combustion chamber.
This combustion product is made to flow through a nozzle and directed on to the substrate to form the
coating.
8.1.3. Process.
In High Velocity Oxygen Fuel process, oxygen and a suitable fuel (acetylene, propylene, propane or
hydrogen) is fed into a gun where it undergoes combustion to produce a high pressure flame. Ceramic
powder is also fed into it axially. This melts the powder, which is then passed through a nozzle to increase
it's velocity. This process produces dense strong coatings.
8.1.4 Features.
HVOF is commonly used to produce very wear resistant coatings such as cermets (ceramic and metal
mixes) like tungsten-carbide cobalt. Coatings of this type have wear resistance similar to sintered carbide
materials. Since HVOF produces very dense coatings (porosity levels less than 0.5%), it can be used to
produce very good corrosion resistant coatings from materials such as Inconel, Stellite, stainless steel and
ceramics.

8.1.5 Applications.
1 .H VOF coatings can be incorporated into the design of complex components such as high-tech medical
devices used for performing complex surgeries.
2 . To simple components such as bolts used in agricultural combines.
8.1.6 Advantages.
1. produces layers with low porosity, high density and homogeneous structure;
2. low residual tensions in the decanted layers;
3. recommended for carbide cermet, compared to the classic systems;
4. it allows decanting thick layers;
5. low roughness of the obtained surfaces;
6. excellent for wear and corrosion resistance;
7. enables Coating of complex geometries;
8. the process can be fully automatized.
8.1.7 Disadvantages.
1. lower temperature than plasma spray. There are certain materials that are more suitable to the plasma
spray;
2. the use of pure oxygen requires special protection measures;
3. more complex installation than the ones used for the classic spray.

CHAPTER. 9
9.1. Electrostatic Spray AssistedVapour Deposition (ESAVD).
Fig:9.1 Electrostatic Spray Assisted Vapour Deposition (ESAVD).
9.1.1 Principle and Working.
ESAVD is the process of producing coating on a heated substrate by spraying chemical precursors
through an electric field. It is a non- line-of-sight-process. The electric field helps to direct the chemicals
on to the substrate and initiate the chemical reaction.This leads to the formation of an adherent coating
with the correct chemical and physical characteristics, together with the desired microstructure.[3]

9.1.2 Process.
The ESAVD process involves the spraying of atomized, charged droplets containing carefully
formulated mixtures of coating precursor material through an electric field ,in an otherwise ambient
environment, towards a mildly heated substrate. Careful control of process conditions in the sprayer
action zone (i.e. zone between spray nozzle and substrate) allows the appropriate chemical reactions to
occur. These include evaporation/decomposition of aerosol droplets and formation of intermediate
reactants that undergo chemical reactions inthe vicinity of the heated surface of the substrate. This leads
to the formation of an adherent coating with the correct chemical and physical characteristics, together
with the desired microstructure. ESAVD enables the use of a simple aerosol type precursor delivery
system to be combined with the vapour phase based coating of Chemical Vapour Deposition. ESAVD is a
non-line-of sight process, and therefore able to coat complex geometries, the electric field helps to ensure
that a very high proportion of the precursor ends up on the substrate via electrostatic attraction. (
Boehman A L, 1997) The unique spray reaction zone is a distinct environment that enables the chemical
vapour deposition to occur unhindered. This means that coatings normally applied in dedicated reactors
using moderate to high vacuums ,and hence expensive vacuum systems, can now be applied in open
atmosphere. There sulting deposition equipment is simple to construct and can be maintained easily with
minimum equipment downtime, requiring arelatively low capital investment.

9.1.3 Features.
[1]. The equipment is simple to construct and can be maintained easily with minimum equipment
downtime, requiring a relatively low capital investment.
[2]. This coatings which were normally applied in dedicated reactors using moderate to high vacuums,
and hence expensive vacuum systems, can be applied in open atmosphere.
[3]. The use of electrostatics also ensures that ESAVD is a ‘non-line-of-sight’ process and can therefore
be used to coat either flat surfaces or complex 3D geometries, e.g. hip implants, engine components and
curved windscreens.
[4]. Produces coatings with variable thickness at variable deposition rates depending on the conditions.
[5]. Uniformity and microstructure can be precisely controlled to produce very high standard coatings,
whether involving a dense coating onto a porous substrate or a porous coating onto a dense substrate.
[6]. The electric field directs the precursor to the substrate, thereby minimizing
losses to the surroundings, unlike other Chemical Vapour Deposition process.
When ESAVD is optimized over 90% of the precursor will end up on the substrate.

9.1.4 Applications.
1. Thermal barrier coatings for jet engine turbine blades.
2. Various thin layers in the manufacture of flat panel displays and photovoltaic panels, CIGS and CZTS-
based thin film solar cells.
3. Electronic components.
4. Biomedical coatings.
5. Glass coatings (such as self-cleaning).
6. Corrosion protection coatings.
9.1.5 Advantages.
1. it does not require the use of any vacuum, electron beam or plasma so reduces the manufacturing costs.
2. It also uses less power and raw materials making it more environmentally friendly.
3. Also the use of the electrostatic field means that the process can coat complex 3D parts easily.
9.1.6 Disadvantages.
1. Operating cost is very high.

CHAPTER. 10
Conclusion
Thermal barrier coating is actually a ceramic coating, which is having a layer structure. It not only
reduces thermal fatigue but also protects the underlying metal from oxidation and corrosion. It helps to
increase the operating temperature and also improves the engine performance. The life of the coated part
is increased to a great extent. The currently used coating material (yttria stabilized zirconia) is capable of
providing considerable protection for the existing engines, but in future, more powerful engines will be
developed and there is a need for a better coating material (Chan S H and Khor K A, 2000). Various
methods like plasma spray technology, electron beam physical vapour deposition etc. have significantly
improved the reliability of TBC turbines, diesel engines and other heat engines. Processing improvement
in the control and development of TBC are required. Further study on the mechanisms controlling coating
adherence and degradation in clean and dirty environments, the effects coating properties and correlation
of models of engine tests are necessary to obtain thermal barrier coating that have even better tolerance to
high temperature and thermo mechanical stresses.

CHAPTER. 11
Future scope
1. Thermal conductivity and thermal expansion co-efficent to be conduct at a various tempretures for
different compositions and zirconate material.
2. Scratch indentation test required on bond and top coat.
3. High tempreture corrosion and wear test required both top and bottom coat.
4. Performance test can conduct on zirconate thermal barrier coating (TBC) by using various other coating
techniques.

REFERENCES
[1]. H.W. GRUNLING and W. MANNSMANN, “JOURNAL DE PHYSIQUE IV Colloque C7,
supplkment au Journal de Physique 111, Volume 3, novembre 1993” Plasma sprayed thermal barrier
coatings for industrial gas turbines.
[2]. Sanket Shikhariya1, Bhushan Shimpi2, Abhishek Shinde3, Swapnil U. Deokar4, “Review on
Thermal Barrier Coating in IC Engine”.
[3]. Vishnu Sankar1, ‘Thermal Barrier Coatings Material Selection, Method of Preparation and
Applications – Review’,International journal of mechanical engineering and robotics research,vol.3.
[4]. Christoffer Blomqvist, “Thermal barrier coatings for diesel engine exhaust application”
[5]. T. Sadowski and P. Golewski, “Loadings in Thermal Barrier Coatingsof Jet Engine Turbine Blades’
Springer Briefs in Computational Mechanics.
[6]. V. Guruprakash *, N. Harivignesh, G. Karthick, N. Bose’ “Thermal barrier coating on I.C engine
cylinder liner”.

Thermal Barrier Coatings Explained

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Thermal Barrier Coatings Explained

Similar to Thermal Barrier Coatings Explained (20)

Recently uploaded

Recently uploaded (20)

Thermal Barrier Coatings Explained