Microstructural investigation of CoNiCrAlY coated Ni-based single crystal superalloy prepared by LPPS

Recent demand in increasing the efficiency of gas turbines has led the component materials to be exposed at much higher operating temperatures, which accordingly accelerates the microstructural deterioration of the coated materials, mainly caused by the interaction between the coated layer and the substrate. Therefore, controlling the chemistry of interfaces by the coating process is one of the most important keys to minimizing the microstructural changes during service. In this study, effects of surface treatments and coating conditions on microstructure changes of Ni-based superalloy substrates were investigated. CoNiCrAlY (AMDRY 9954) powder was coated on Ni-based single crystal superalloy TMS-82+ by low pressure plasma spraying (LPPS). It was found that grit-blasted treatment drastically distorted the coherent γ/γ′ microstructure of substrates, which accordingly promoted the uniform and accelerated precipitation of topologically close-packed (TCP) phases by the post heat treatment at 1273 K for 30 min. On the other hand, specimens without the grit-blast treatment had less amount of TCP precipitates, but showed preferred precipitation orientation along 〈011〉{100} direction. Surface preheating and surface sputter cleaning seemed to have less influences on microstructure change compared to the grit-blast treatment.