This study compares the deposition and oxidation behavior of two oxide-dispersed CoNiCrAlY powders, one commercially obtained, the other prepared in a high-energy attrition ball mill using CoNiCrAlY and nanosize α-alumina powders. The custom powder was deposited by HVOF spraying using two sets of parameters, one optimized for CoNiCrAlY powder, the other for fine alumina. Coatings produced under the latter conditions were found to be porous, which can be attributed to a low degree of melting in the dispersed alumina. Isothermal oxidation testing at 1373 K for up to 1000 h in air caused oxidation not only at the surface, but also inside the coatings due to the movement of oxygen through the pores. The coatings deposited under the other set of parameters, i.e., at higher power levels, were free of pores. Isothermal oxidation tests were also carried out on coatings produced from the commercial powder, in this case, by HVOF and as well as vacuum plasma spraying. The coatings obtained by HVOF spraying were found to have a thinner thermally grown oxide layer than not only the VPS coatings, but also conventional metallic bond coats. Internal oxidation in the HVOF coatings is due to insufficient cohesion of the spray particles. Furnace cycling tests were conducted on specimens with an additional ceramic thermal barrier coating. Specimens with VPS bond coats produced from commercial oxide-dispersed powder achieved almost same number of cycles to delamination as specimens with conventional metal bond coats.

In this work, plasma spray-physical vapor deposition (PS-PVD) is used to create oxygen transport membranes, consisting of gastight LaSrCoFeO thin films on porous MCrAlY metallic supports. During spraying, a protective layer of alumina forms at the interface between the membrane and support preventing interdiffusion. Surface roughness of the metallic support is shown to play a critical role in limiting microstructural defects. Phase composition, growth rate, and microstructure buildup are also investigated along with the annealing behavior of LSCF films at different temperatures. Initial results are promising and further improvements are expected by optimizing process parameters.

Processing of powder feedstock materials often influences the deposition behavior and ultimately, the properties of the atmospheric plasma spray (APS) deposited coatings. The necessity of materials design and the control of deposition parameters are therefore, of high importance. Feedstock from promising ceramic thermal barrier coating materials with Ba(Mg 1/3 Ta 2/3 )O 3 and La(Al 1/4 Mg 1/2 T 1/4 )O 3 perovskite structures (λ~ 2 W/m-K and α~11x10-6 /K at 1473 K) were prepared through solid state and conventional spray drying techniques. The powders were then deposited on metallic substrates by APS process. Monitoring of in-flight particle characteristics and splat formation as well as characterization of deposited coatings, were conducted. It was found that these types of perovskite materials tend to lose constituents during deposition by atmospheric plasma spraying. This paper reports on the challenges of powder feedstock design and the control of critical deposition parameters to prevent or minimize the non-stoichiometric deposition of decomposition-prone perovskite coatings by APS process.

In this investigation, two complex perovskite powders, Ba(MgTa)O and Ta(AlMgT)O, are deposited by atmospheric plasma spraying and evaluated for use as thermal barrier layers. Process parameters are optimized to provide sufficient melting without causing the formation of secondary phases. Deposited coatings are assessed based on composition, morphology, porosity, and thermal cycling lifetime. It is shown that the nature of the starting powders has a significant effect on the lifetime and performance of perovskite-based thermal barrier coatings.

Advanced ceramic materials of perovskite structure have been developed for potential application in thermal barrier coating systems, in an effort to improve the properties of the pre-existing ones like yttria stabilized zirconia. Yb 2 O 3 and Gd 2 O 3 doped strontium zirconate (SrZrO 3 ) and barium magnesium tantalate (Ba(Mg 1/3 Ta 2/3 )O 3 ) of the ABO 3 and complex A(B’ 1/3 B” 2/3 )O 3 systems respectively, have been synthesized using ball milling prior to solid state sintering. Thermal and mechanical investigations show desirable properties for high temperature coating applications. On atmospheric plasma spraying, the newly developed TBCs reveal promising thermal cycle lifetime above 1300°C.