Improving the thermal cycling lifetime of thermal barrier coatings with an atmospheric plasma-sprayed carbon-alloyed MCrAlY bond coat

The manufacturing of high-quality MCrAlY bond coats is crucial for the durability of thermal barrier coatings (TBCs). Although atmospheric plasma spraying (APS) offers a flexible and efficient deposition route, it has traditionally been considered unsuitable for MCrAlY bond coat deposition due to the high oxide content. In this study, NiCoCrAlY bond coats with low oxygen content were successfully prepared via APS by adding carbon as a deoxidizing agent to the feedstock powder. The effect of carbon content in the powders on the thermal cycling lifetime of TBCs, comprising yttria-stabilized zirconia (YSZ) top coats and APS-deposited NiCoCrAlYC bond coats, was systematically investigated through isothermal thermal cycling tests, with comparisons made to TBCs using low-pressure plasma-sprayed (LPPS) NiCoCrAlY bond coat. The results indicate that the APS-processed NiCoCrAlYC bond coat exhibits a dense microstructure with low oxide content. TBCs with the APS bond coat displayed the same failure mechanism as those with an LPPS bond coat. Remarkably, despite slightly lower Al content, TBCs with the APS bond coat achieved a 16 % longer thermal cycling lifetime than those with an LPPS bond coat. The formation of a continuous, dense α-Al₂O₃ scale, coupled with the precipitation of Cr₇C₃ carbide particles in the bond coat, led to this improvement by alleviating the thermal expansion mismatch between the top coat and the superalloy substrate. This work demonstrates the feasibility of using APS as a substitute for LPPS in producing high-performance MCrAlY bond coats for TBCs with enhanced thermal cycling resistance.