Effect of heat treatment on the formation of serrated grain boundary and secondary γ′ phase in a high γ′ phase superalloy

Abstract

The influence of various heat treatment conditions on the microstructure was studied systematically for a new Ni-based deformed superalloy with a high γ′ phase in this paper. The effect laws of cooling rate, holding temperature, and holding time on the amplitude and wavelength of serrated grain boundaries (SGBs), as well as the morphology and size distribution of the secondary γ′ phase, were analyzed and summarized. The evolution process of secondary γ′ phase was discussed, and the formation mechanism of SGBs was revealed. The results show that the growth and migration of large primary γ′ phase at grain boundaries (GBs), along with their pinning effect on the boundaries, can lead to the formation of SGBs Additionally, the small-sized primary γ′ phase can also pin the GBs to form a SGBs. The critical cooling rate for the morphology transformation of the secondary γ′ phase is 5.3 ℃/min. During the isothermal holding process, the secondary γ′ phase undergoes aggregation growth, while excessively high holding temperature can result in abnormal growth.