Effects of HIP temperature on the microstructural evolution and property restoration of a Ni-based superalloy

The effects of hot isostatic pressing (HIP) temperature on the evolution of microstructural characteristics around the creep cavities were investigated using five different soaking temperatures during HIP. The restoration of microstructural and material properties under these HIP schedules followed by the same rejuvenation heat treatment (RHT) procedure was then evaluated. The results showed that HIP temperature played a dominant role in the cavity healing process, determining the evolution features of cavities and hence the extending ratio of rupture life. With gradually increasing the adopted HIP temperature, the cavity healing behaviors were revealed. Concentrically oriented N-type γ′ rafting structure in the vicinity of the healing cavity was observed at an appropriate soaking temperature. The driving force for the cavity healing was considered to be the chemical potential gradient induced by the stress gradient field around the cavity. The appropriate HIP schedule followed by RHT process significantly improved the rupture life of damaged alloy, and the extending ratio varied with the adopted HIP temperature.