Effects of Homogenization Treatment on the Microsegregation of a Ni-Co Based Superalloy Produced by Directional Solidification

• 作者: Zijian Zhou Rui Zhang Chuanyong Cui Yizhou Zhou Xiaofeng Sun
• 来源期刊: 金属学报（英文版）
• 年，卷（期）: 2021,（7）
• 页码范围: 943-954
• 页数: 12页
• 语种: 英文

摘要

To reduce microsegregation,a series of homogenization treatments were carried out on a Ni-Co based superalloy prepared through directional solidification (DS).The element segregation characteristics and microstructural evolution were inves-tigated by optical microscopy (OM),scanning electron microscopy (SEM),and electron probe microanalysis (EPMA).The results show that the elements are non-uniformly distributed in the solidified superalloy,in which W and Ti have the greatest tendency of microsegregation.Furthermore,severe microsegregation leads to complicated precipitations,includ-ing η-Ni3Ti and eutectic (γ+ γ').EPMA results show that A1 and Mo are uniformly distributed between the eutectic (γ+ γ')and γ matrix,whereas Ti is segregated in the eutectic (γ + γ') and η phases.The positive segregation element Ti,which is continuously rejected into the remaining liquid during γ matrix solidification,promotes the formation of eutectic (γ+ γ') and the transformation of the η phase.According to the homogenization effect,the optimal single-stage homogenization process of this alloy is 1180 ℃ for 2 h because of the sufficient diffusion segregation of the elements.In the present study,a kinetic diffusion model was built to reflect the degree of element segregation during homogenization,and the diffusion coefficients of W and Ti were estimated.