The elemental uphill diffusion with micropores reduction during HIP treatment for a solution-treated nickel-based superalloy

Micropores and elemental segregation are detrimental to the high-temperature properties of nickel-based single-crystal (SX) superalloys and hot isostatic pressing (HIP) treatment has been considered as an appropriate method to reduce micropores and elemental segregation. In this study, the effect of a two-step HIP treatment on the solution-treated nickel-based SX superalloy was investigated. An elemental uphill diffusion with the micropores reduction was discovered during HIP treatment and caused the elemental segregation of Al, Cr and Ta at the dendritic scale. It indicates that the HIP treatment is not always beneficial for alloy homogenization. The results show that the first-step HIP treatment could promote the uphill diffusion and cause the elemental segregation with the significant micropores reduction. The second-step HIP treatment could decrease the elemental segregation with further micropores reduction. During subsequent heat treatments, the elemental segregation caused by HIP treatment could be basically eliminated with a slight increase of micropores. During HIP treatment, the micropores reduction and elemental segregation were correlated with the HIP temperature and pressure. This study will provide the supports for controlling micropores and homogenization of nickel-based SX superalloys.