Microsegregation in Ni Base Alloy

Abstract

In Ni base alloys, the precipitates resulting from the segregation of alloy elements often harm the quality of the material. The experiments of solidification and solution treatment with Hastelloy were done. The formation and elimination of precipitates were investigated, and the following results were obtained.
1) The equilibrium distribution ratio of Mo is 0.77 and Mo is easy to segregate.
2) The precipitates are formed in the interdendritic region at final solidification stage and their size is determined by the cooling rate during solidification.
3) The effect of cooling rates on the precipitate size can be explained by the solidification model referred to the segregation of Mo.
4) The precipitates are fully eliminated by the solution treatment for 24 h at 1 250°C. The elimination of precipitates can be described by the model where the diffusion of Mo is a rate controlling step.