Short study on mechanism of morphology change of γ′ precipitates in IN718 Plus

Abstract

γ′ Ni3Al phase (L12 structure) strengthened superalloy has become an important strengthening phase in Ni based superalloys because of its excellent high-temperature service performance, and has been widely used. The process of γ′ phase precipitation has also received a lot of attention and research. However, most studies focused on its growth rate. There were few studies on the morphology transformation of γ′ phase, and the morphology transformation process is complex. The mechanism of γ′ phase transformation process was systematically analyzed in this paper. Firstly, through molecular dynamics calculation, the most stable morphology of the γ′ phase in the nickel matrix was obtained under ideal conditions. The stability of spherical precipitates is higher than that of cubic precipitates. When the temperature is greater than 800 K, the stability is more obvious.Then through the micro EDS analysis of the γ′ phase in the morphology transformation process, it was shown that the soft impingement phenomenon exists in the nickel base alloy with high γ′ phase volume fraction. Further, by the derivation of the formula of solid-state phase transformation, it was found that the growth rate of precipitate is directly proportional to the concentration gradient of Al in the matrix at the interface, while increases with the rising of the Al concentration in the matrix at the interface. Finally, the way and mechanism of soft impingement affecting the morphology transformation were analyzed. The precipitates formed by soft impingement are nearly cubic precipitates with rounded edges and corners.