Investigation and Simulation of the Effects of nm-Scale γ′ Precipitates on the Recrystallization of Ni-based Superalloys

Abstract

Superalloys are critical materials for the hottest sections of stationary gas turbines and aircraft engines. Homogeneously fine-grained microstructures are essential to unlock their superior high-temperature strength but are challenging to achieve in γ′-containing Ni-based superalloys. Such microstructures are achieved by recrystallization through hot working and grain boundary pinning viaμm-scale second phase particles. Discontinuous dynamic recrystallization is the predominant restoration mechanism, where grain growth is restricted by Zener pinning. Nanometer-scale γ′ precipitates may exercise similar pinning during the nucleation stage and thus delay recrystallization. While the effects of coarse, μm-scale, precipitates during recrystallization and grain growth are well-known, descriptions for fine coherent precipitates are currently lacking. To address this scarcity of knowledge, both γ′-rich and -lean microstructures of the γ′-containing Ni-base superalloy René 41 underwent identical uniaxial hot compression tests. Flow stress and microstructural analyses reveal the inhibition of recrystallization by nm-scale γ′ precipitates during both nucleation and growth stages. This effect is successfully described using thermo-kinetic modeling through application of a driving-force based model. These unique insights provide a novel pathway to unlock homogeneously fine-grained microstructures in γ′-containing Ni-based superalloys via advanced thermo-mechanical processing routes, required for applications in future generations of gas turbines and aircraft engines.