Effects of thermal exposure on microstructure deformation and evolution of shot peened nickel-based single crystal superalloy

Microstructure deformation and thermally activated microstructural evolution of nickel-based single crystal (NBSC) superalloy subjected to shot peening (SP) were investigated. SP induced high-density dislocations and activated the octahedral slip system {111} 〈110〉 of NBSC superalloy. Under 0.25 mmA SP intensity, there appeared a severely deformed layer with a depth of 2.5–3.0 μm beneath the surface. High SP intensity resulted in rougher surface morphology, more dense slip bands, deeper cold work layer and larger mean geometrically necessary dislocation (GND) density. However, the deformed microstructure was thermodynamically unstable. Dislocation annihilation and rearrangement were the main thermally activated mechanism of microstructural evolution, and high temperature promoted dislocation movement and consumption. Under 0.25 mmA SP intensity after 24 h thermal exposure, GND density decreased from 4.86 × 10¹⁴ m⁻² to 2.72 × 10¹⁴ m⁻², and the depth of cold work layer decreased from 67 μm to 62 μm. In addition, SP treatment provided rapid diffusion channels for alloy elements, while thermal exposure further aggravated element diffusion.