The γ′ precipitate rafting and element distribution during hot isostatic pressing in a nickel-based superalloy

Abstract The γ′ precipitate rafting and the element distribution in the vicinity of creep cavities for a service-damaged nickel-based superalloy during hot isostatic pressing (HIP) were investigated. The concentrically oriented γ′ rafting-like structure near the creep cavities was formed under the HIP condition of 1150 °C/50 MPa/2 h, together with the primary γ′ denuded zone present between the creep cavity and the γ′ rafting zone. When increasing the hydrostatic pressure, the γ′ rafting structure became more and more remarkable. The wavelength-dispersive X-ray spectroscopy (WDX) results show that, the γ′-forming elements migrated from the primary γ′ denuded zone towards the γ′ rafting zone but the solutes in the γ matrix diffused in the opposite direction onto the creep cavity surface during HIP processing, With the increase of the hydrostatic pressure, the amount of γ′-forming elements which were driven by the atomic concentration gradient and diffused towards the γ′ rafting zone was continuously increased and the amount of solutes in the matrix that migrated in the opposite direction was also increased, indicating that the hydrostatic pressure can promote the atomic diffusion and heal creep cavities more effectively. It can be considered that the atomic diffusion mainly dominates pore closure.