Effect of solid solution temperature on microstructure of Hf-containing K416B Ni-based superalloy with high W-content

Abstract

By means of microstructure observation on Hf-containing K416B Ni-based superalloy with high W-content after solid solution heat treatment at different temperatures, the effect of solid solution temperature on microstructure of the alloy was investigated. The results show that with the increasing of solid solution temperature, the size of secondary dendrite increases slightly by element diffusion, and the eutectic content decreases gradually to promote the densification of alloy microstructure. In addition, the γ′ phase is dissolved into the matrix, and its size is decreased. During high temperature solid solution heat treatment, the primary strip MC phase in the inter-dendrite is decomposed to form granular M6C carbides, while the morphology and quantity of large sized block M6C phase in eutectic have no obvious change. The solid solution treatment causes that the element W is segregated in the dendrites to diffuse into inter-dendrites, and elements of Hf，Nb，Ti and Cr diffuse into the dendrites, the segregation degree of each element of the alloy is greatly reduced. The results of microstructure research indicate that the optimal solid-solution heat treatment process for the alloy is 1220 ℃ × 4 h.

Keywords

• K416B Ni-based superalloy
• solution temperature
• microstructure