Refining Micron-Sized Grains to Nanoscale in Ni-Co Based Superalloy by Quasistatical Compressive Deformation at High Temperature

Compressive deformation was carried out in an Ni-Co-based superalloy with relatively low stacking fault energy (SFE) at 725 °C and a strain rate of 10−2 s−1; the underlying micromechanisms were investigated under true compression strains varying from 0.1 to 1.0. It was found that dislocation slipping accompanied by stacking fault (SF) shearing dominated the compressive deformation under the strain of 0.1 and 0.2. As the strain increased to 0.3 and 0.4, microtwinning was activated and then interacted with dislocations, leading to the formation of dislocation tangles or blocky distorted region. When true strain was further increased to 0.6, abundant subgains (SGs) with polygonous shape appeared and then transformed into nanograins as true strain increased to 1.0. It is demonstrated that high strain and microtwinning are the prerequisites for the evolution of nanograins in the deformed Ni-Co-based superalloy. High strain can produce plentiful dislocations and distorted micro-sized SGs; then the microtwins sheared these distorted regions and refined the micro-sized SGs into nanoscale, which subsequently transformed into nanograins with further deformation.