Effect of Solution Treatment on Microstructure Evolution of a Powder Metallurgy Nickel Based Superalloy with Incomplete Dynamic Recrystallization Microstructure

Abstract

In this paper, the powder metallurgy (P/M) Ni-based superalloy FGH4096 with an incomplete dynamic recrystallization structure was treated by a solution treatment at different temperatures, cooling methods, and holding times. The size, morphology, and distribution of grains and γ′ precipitates were characterized by an optical microscope (OM) and a scanning electron microscope (SEM). Research results showed that with the increase of solution temperature from 1060 °C to 1100 °C, the degree of recrystallization increased continuously, the distribution of grain became uniform, and a large number of annealing twins were found. At the same time, the degree of redissolution of the primary γ′ precipitates at the grain boundary increased, and the size of secondary γ′ phase reprecipitated within the grain decreased. The morphology of the secondary γ′ precipitates is mainly spherical with a single distribution under air cooling (AC), while the morphology is near-spherical, cuboids, octets, petaloid, and dendrites with a bimodal distribution under furnace cooling (FC). The size of the γ′ precipitates decreased and the volume fraction increased with the extension of holding time at a higher solution temperature (1100 °C).