On the rejuvenation of crept Ni-Base single crystal superalloys (SX) by hot isostatic pressing (HIP)

In the present work, we study the effect of HIP rejuvenation treatments on the creep behavior and residual life of a pre-crept single crystal Ni-base superalloy of type CMSX-4. The present work combines miniature creep experiments of precisely oriented [001] tensile creep specimens with HIP treatments and quantitative analysis of scanning and transmission electron micrographs. A HIP-rejuvenation treatment after 5.0% creep pre-strain significantly improves creep strength. However, the microstructural damage induced by the creep pre-deformation could not be fully removed. In a series of sequential creep/HIP/creep-experiments, increasing levels of pre-deformation result in increasing levels of creep rates even after identical HIP-rejuvenation treatments. The memory effect, which causes this phenomenon, is related to an accumulation of permanent microstructural damage, which is not associated with rafting or cavitation. The mechanical results obtained in the present work are interpreted based on microstructural results on the gamma/gamma'-microstructure (gamma-channel widths and gamma'-size), on the pore population (number density of pores, pore size distributions and pore area fractions) and dislocation substructures which have formed during creep. The results are discussed in the light of previous results reported in the literature.