Controlling grain size via dynamic recrystallization in an advanced polycrystalline nickel base superalloy

Abstract

Controlling grain size in polycrystalline nickel base superalloy is of paramount importance in optimizing hot-working process and achieving the desirable mechanical properties. Typically, a uniform and fine grain size is required throughout forging process to realize the superplastic deformation. Unfortunately, the forging processing window is very narrow and needs to be synergistically controlled by deformation temperature, strain rate, as well as strain amount, and the failure would lead to the non-uniform grain size, abnormal grain growth and even cracking. During superplastic deformation, dynamic recrystallization (DRX) is the governing mechanism to be adopted to maintain the required grain size. Previous literature have extensively documented the separated effect of deformation parameters using monotonic-pass compression test. Herein, we perform the multi-pass compression experiments to investigate the flow stress behavior and grain size evolution. By conducting multi-pass tests over a range of deformation parameters, it was demonstrated that the flow stress and grain size response differed from that in single-pass tests. The multi-pass compression tests unambiguously uncover the roles of DRX and static recrystallization (SRX) in regulating grain size and affecting flow stress. The experimental results further show, comparing to the monotonic-pass compression, the multi-pass approach can provide versatile routes to attain the desirable grain size distribution by means of utilizing DRX and SRX principles.