Secondary γ′ evolution and relationship to hot deformation behavior of a supersolvus-treated superalloy with high precipitate volume fraction

Abstract

This paper presents results from a research initiative aimed at the evolution of secondary γ′ and its effects on hot deformation behavior by using compression tests of a supersolvus-treated superalloy at 1080–1200 °C and 0.001–1 s−1. Secondary γ′ in deformed regions and in dynamic recrystallization (DRX) regions have different evolution behaviors during hot working. In deformed regions precipitates have a noteworthy coarsening tendency depending on strain rates. At high strain rates, e.g. at 1 s−1, γ′ is elongated along strain direction by plastic deformation. Whereas, directional coarsening takes place at low strain rates, e.g. 0.001 s−1, owing to the severe plastic deformation and the high concentration level of γ′-forming element induced by supersolvus treatment. And thus secondary γ′ evolution in deformed regions can be attributed to two competing factors: (a) plastic flow and (b) directional coarsening induced by diffusion. In contrast, γ′ in DRX regions always dissolves following grain boundary migration and almost re-precipitates at boundaries. Only a small number of re-precipitated γ′ can be found in the interior of new grains. Abnormal phenomenon of sharp stress decline appears at low strain rates and low deformation temperatures, which is related to DRX, γ′ directional coarsening and γ′ dissolution.