Influence of cooling strategy on microstructure, deformation mechanism and mechanical properties of a nickel-based superalloy

Abstract

In this study, the influence of cooling strategy after solution treatment on microstructure and mechanical properties of a novel cast and wrought nickel-based superalloy is studied. It was found that continuous oil cooling (CC) from the solution temperature led to formation of large primary γ' and ultrafine tertiary γ'. Interrupted cooling (IC), which involves furnace cooling from the solution treatment temperature (1080 °C) to a lower temperature (such as 1010 °C, 980 °C or 950 °C) first followed by an interrupted oil cooling, shows significant influence on microstructure. Owing to a short-period furnace cooling, secondary γ' started to form in these interrupted cooled samples and their volume fraction and size increased continuously with decreased IC temperature. In contrast, the volume fraction of tertiary γ' decreased with decreased IC temperature. The CC sample was found to deform mainly by dislocation glide/climb and extension of stacking faults at 650 °C/950 MPa. With increased volume fraction of large secondary γ' in the interrupted cooled samples, deformation became increasingly planar, i.e., the formation of stacking faults and nanotwins increasingly became the dominant deformation mechanisms. The cooling strategy shows no obvious influence on tensile properties and impact toughness but shows significant influence on stress rupture properties. With decreased IC temperature and coarsened microstructure, the stress rupture lifetime continues to decrease.