Subgrains of γ′ phase in a single-crystal superalloy induced by ultrahigh temperature creep

A new type of γ′ phase subgrain has been found in a single-crystal superalloy after exposure to 360 hours of creep at 1200 °C and 60 MPa. This signifies the capacity of dynamic recrystallization (DRX) of γ′ phase, overturning the widely accepted idea that it is incapable of undergoing DRX. The remarkable plasticity of the γ′-precipitate, activated at ultrahigh temperature, is likely due to the slip/rotation and cracking of the γ′-subgrains. Microstructural evidence of the subgrain boundary originating from γ′-shearing dislocations and their associated walls was obtained, which explains the subgrain formation dependence on plastic deformation accumulation. These findings help us understand the γ′-deformation mechanism and guide to improve creep resistance.