Original paper(Vol.46 No.6 pp.684)

Basic study on high temperature protective coating design of single crystal Ni based super alloy

Itoh Yoshiyasu; Tamura Masataka; Takahashi Yasuo

Abstract:A computer aided interactive system for coating design has been developed, which enables to analyze conveniently the reaction diffusion of bonded materials. The object of this study is the overlay coatings of MCrAlY alloy sprayed by a low pressure plasma spray (LPPS) process for protection against high temperature corrosion and oxidation in the field of gas turbine components. However, the reaction diffusion behavior at the interface between the MCrAlY coating and the substrate, which has an important effect on coating degradation, has not been fully clarified. Four kinds of low pressure plasma sprayed MCrAlY alloys, namely CoCrAlY, NiCrAlY, CoNiCrAlY and NiCoCrAlY, and single crystal CMSX 2 were selected for the experiments.
The experimental results showed that the reaction diffusion layers consisted of aluminum compound layer and low aluminum layer. In case of the NiCoCrAlY and CoNiCrAlY coatings, the aluminum compound layer could not be observed clearly. It was also indicated that each diffusion thickness could be expressed by the parabolic time dependence. The order of reaction diffusion rate was NiCrAlY greater than CoCrAlY greater than CoNiCrAlY greater than NiCoCrAlY. It was also clarified by the simulation analysis that the diffusion distance during heating process cannot be ignored in comparison with the total diffusion distance, and the estimation of long time diffusion was made.

Key Words:coating design, low-pressure spray, MCrAlY coating, single-crystal CMSX-2, traction diffusion, parabolic time low, diffusion rate constant