Properties of Plasma Sprayed Functionally Graded YSZ/NiCoCrAlY Composite Coatings

2000 ◽  
Author(s):  
K.A. Khor ◽  
Y.W. Gu ◽  
Z.L. Dong
Keyword(s):  
Thermal Expansion ◽  
Elastic Modulus ◽  
Bond Strength ◽  
Thermal Barrier Coatings ◽  
Coefficient Of Thermal Expansion ◽  
Composite Coatings ◽  
Functionally Graded ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Plasma Sprayed

Abstract Plasma sprayed thermal barrier coatings often face the problems of spallation and cracking in service owing to their poor bond strength and high residual stresses. Functionally graded thermal barrier coatings with a gradual compositional variation from heat resistant ceramics to fracture resistant metals are proposed to mitigate these problems. In this paper, functionally graded Y2O3 stabilized ZrO2 (YSZ) / NiCoCrAlY composite coatings were prepared using pre-alloyed and spheroidized composite powders. The mechanical and thermal properties of graded YSZ/NiCoCrAlY composite coatings, such as elastic modulus, bond strength, coefficient of thermal expansion, thermal cycling and oxidation resistance were investigated. Results showed that the bond strength and thermal cycling resistance of FGM coatings were much better than that of the duplex coatings. The coefficient of thermal expansion and elastic modulus changed gradually through the 5-layer functionally graded coating.

Evaluation of CeSZ Thermal Barrier Coatings for Diesels

2000 ◽  
Author(s):  
P.J. Huang ◽  
J.J. Swab ◽  
P.J. Patel ◽  
W.S. Chu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Barrier Coatings ◽  
Coefficient Of Thermal Expansion ◽  
Fuel Efficiency ◽  
Atmospheric Plasma ◽  
Thermal Barrier ◽  
Mechanical And Thermal Properties ◽  
Barrier Coatings ◽  
Spray Process

Abstract The development of thermal barrier coatings (TBCs) for diesel engines has been driven by the potential improvements in engine power and fuel efficiency that TBCs represent. TBCs have been employed for many years to reduce corrosion of valves and pistons because of their high temperature durability and thermal insulative properties. There are research programs to improve TBCs wear resistance to allow for its use in tribologically intensive areas of the engine. This paper will present results from tribological tests of ceria stabilized zirconia (CeSZ). The CeSZ was applied by atmospheric plasma spray process. Various mechanical and thermal properties were measured including wear, coefficient of thermal expansion, thermal conductivity, and microhardness. The results show the potential use of CeSZ in wear sensitive applications in diesel applications. Keywords: Thermal Barrier Coating, Diesel Engine, Wear, Thermal Conductivity, and Thermal Expansion

scholarly journals Thermal Shock and Oxidation Stability Tests to Grade Plasma Sprayed Functionally Gradient Thermal Barrier Coatings

2019 ◽  
Vol 1 (1) ◽  
pp. 1-11
Author(s):  
Pasupuleti Kirti Teja ◽  
Parvati Ramaswamy ◽  
Narayana Murthy S.V.S.
Keyword(s):  
Thermal Barrier Coatings ◽  
Inconel 718 ◽  
Oxidation Stability ◽  
Ceramic Coatings ◽  
Functionally Graded ◽  
Yttria Stabilized Zirconia ◽  
Thermal Barrier ◽  
Stabilized Zirconia ◽  
Barrier Coatings ◽  
Plasma Sprayed

Functionally graded layers in thermal barrier coatings reduce the stress gradient between the overlaid ceramic coatings and the underlying metallic component. Introduced to alleviate early onset of spallation of the coating due to thermal expansion mismatch, this facilitates improvement in the life of the component. Conventional thermal barrier coatings typically comprise of duplex layers of plasma sprayed 8% yttria stabilized zirconia (ceramic) coatings on bond coated (NiCrAlY) components/substrates (Inconel 718 for example). This work highlights the superiority of plasma sprayed coatings synthesized from blends of the intermetallic bond coat and ceramic plasma spray powders on Inconel 718 substrates in three-layer configuration over the duplex layered configuration. Assessed through (a) thermal shock cyclic tests (at 1200oC and 1400oC) in laboratory scale basic burner rig test facility and (b) oxidation stability test in high temperature furnace (at 800oC and 1000oC) the functionally graded coatings of certain configurations exhibited more than double the life of the conventional 8% yttria stabilized zirconia duplex (double layer) coatings. Micro- and crystal structure analysis support the findings and results are detailed and discussed.

Thermomechanical Evaluation and Thermal Expansion Behavior of Plasma-Sprayed Thermal Barrier Coatings

2009 ◽  
Vol 631-632 ◽  
pp. 85-90 ◽  
Author(s):  
Kenta Takagi ◽  
Akira Kawasaki ◽  
Yoshio Harada ◽  
Masakazu Okazaki
Keyword(s):  
Thermal Expansion ◽  
Thermal Barrier Coatings ◽  
Preliminary Investigation ◽  
Thermomechanical Analysis ◽  
Thermal Barrier ◽  
Continuous Change ◽  
Free Standing ◽  
Barrier Coatings ◽  
Plasma Sprayed ◽  
Thin Samples

We are investigating the feasibility of measuring thermal expansion coefficient (CTE) of free-standing thermal barrier coatings with a practical thickness of several hundred micrometers by mean of a widespread thermomechanical analysis toward its industrial standardization. First of all, this study conducted the preliminary investigation for the accurate measurement of thin samples with dense yettria-stabilized zirconia (YSZ) ceramics. With a sample supporting jig and proper conditions, even the usual thermomechanical analysis could give the accurate CTE values of thin samples down to 0.3mm thick. Also it showed good reproducibility with small measurement error less than 5%. In actual, this modified method could provide the reasonable CTE values of plasma-sprayed YSZ samples with thickness of >0.3mm. Further investigation with this method found a slight monotonic decrease in the CTE with annealing. This decrease was estimated to arise from the continuous change of microstructure which still went on even after saturation of sintering shrinkage. All the results demonstrated the present method to be available for the industrial standard.

scholarly journals The Evaluation of Durability of Plasma-Sprayed Thermal Barrier Coatings with Double-layer Bond Coat

Coatings ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 241 ◽  
Author(s):  
Li ◽  
Peng ◽  
Dong ◽  
Zhou ◽  
Wang ◽  
...  
Keyword(s):  
Thermal Barrier Coatings ◽  
Double Layer ◽  
Bond Coat ◽  
Coefficient Of Thermal Expansion ◽  
Type A ◽  
Thermal Barrier ◽  
Type B ◽  
Barrier Coatings ◽  
Oxidation Layer ◽  
Plasma Sprayed

The durability of atmospheric plasma-sprayed thermal barrier coatings (APS TBCs) with a double-layer bond coat was evaluated via isothermal cycling tests under 1120 °C. The bond coat consisted of a porosity layer deposited on the substrate and an oxidation layer deposited on the porosity layer. Two types of double-layer bond coats with different thickness ratios of the porosity layer to the oxidation layer (type A: 1:2 and type B: 2:1, respectively) were prepared. The results show that the porosity layer was oxidation free, the oxidation layer included a fraction of well-distributed α-Al2O3. The coefficient of thermal expansion of the oxidation layer was about 11.2 × 10−6 K−1, which was rather lower than that of the porosity layer. Thus, the oxidation layer can be regards as a secondary bond coat between ceramic topcoat and traditional bond coat. The thermal cyclic lifetime of type A TBCs was about 60 cycles, which exceeded 1.2 times the durability of type B TBCs. The delamination cracks in both TBCs all propagated in the ceramic topcoat, which were all identical to those in traditional TBCs. Therefore, the design of the double-layer bond coat affected the stress level rather than the stress distribution in TBCs.

Properties of ZrO2-7wt%Y2O3 Thermal Barrier Coatings in Relation to Plasma Spraying Conditions

1997 ◽  
Author(s):  
C. Funke ◽  
B. Siebert ◽  
D. Stöver ◽  
R. Vaßen
Keyword(s):  
Elastic Modulus ◽  
Plasma Spraying ◽  
Thermal Barrier Coatings ◽  
Bond Coat ◽  
Free Edge ◽  
Ceramic Coatings ◽  
Thermal Barrier ◽  
Normal Stresses ◽  
Barrier Coatings ◽  
Plasma Sprayed

Abstract Superalloy samples were coated with thermal barrier coatings (TBC). This TBC-system consisted of two layers. The first layer was a vacuum-plasma sprayed, corrosion resistant layer (MCrAlY) which also acted as a bond coat. The ceramic top layer was atmospheric-plasma sprayed Y2O3-stabilized ZrO2. In order to produce different microstructures, the plasma-spraying parameters for the production of the ceramic coatings were varied. The different ceramic coatings were characterized in terms of porosity and mean elastic modulus. The porosity distribution was also investigated due to its influence on the measured elastic modulus. To record the changes of the plasma sprayed Zirconia due to sintering, the mean elastic modulus of selected coatings was measured as a function of annealing time. One series of TBC-coated specimens was cyclically oxidized at a maximum temperature of 1100°C. After 500 h of thermal cycling, creep within the MCrAlY-bond coat led to a coating failure at both the internal beveled edge and free edge around the specimen. A finite element analysis study of the cyclic oxidation experiment was performed to gain insight into the stress redistributions within the bond coat as a function of time. During the initial temperature increase, critical tensile normal stresses developed above the MCrAlY-Zirconia interface at the free edge. However, these normal stresses became compressive for all following cooling cycles. On the other hand, large tensile normal stresses developed above the MCrAlY-Zirconia interface at the beveled edge during all the cooling cycles. Therefore, high normal stresses responsible for debonding were present within the ceramic coating during all cooling cycles with the most critical stresses occurring at the free edge during the first cooling cycle and near the beveled edge for all the following cooling cycles.

Initiation of Surface and Interface Edge Cracks in Functionally Graded Ceramic Thermal Barrier Coatings

1997 ◽  
Vol 119 (2) ◽  
pp. 148-152 ◽  
Author(s):  
Klod Kokini ◽  
Michael Case
Keyword(s):  
Thermal Barrier Coatings ◽  
Thermal Stresses ◽  
Functionally Graded ◽  
Thermal Barrier ◽  
Barrier Coatings ◽  
Surface And Interface ◽  
Probability Of Survival ◽  
Edge Cracks ◽  
Plasma Sprayed ◽  
Interface Edge

The initiation of surface and interface edge cracks in functionally graded ceramic thermal barrier coatings resulting from the application of a thermal load is studied. For a given specimen configuration, the singular behavior of the thermal stresses is analytically determined in terms of a singularity power β and pseudo-stress intensity factors K1 and K2. Crack initiation at the surface at the interface is related to the surface temperature and the temperature difference between the surface of the coating and the substrate. The experimental results are used to provide Weibull curves for the probability of survival of plasma sprayed mullite and CoCrAlY coating systems.

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