Microstructural changes of 22Cr-9Mo-3Fe-4Nb Ni-Base Superalloy during Creep

Abstract

A new Ni based superalloy is considered as bucket material because of high fatigue resistance with fine grain. However a bucket is usually exposed to high temperature for a long time, so creep rupture tests were conducted to understand the microstructure evolution during creep deformation under various stresses at temperatures of 566, 593, 621, 649 and 670 °C. The hardness applied to the crept specimen of these alloys increased until the value of LMP reached 25, and decreased while the value of LMP exceeded 25. The microstructure analysis with TEM, SEM and OM were conducted on ruptured specimen to observe the changes of γ" morphology, carbides, and fracture mode. As a result of investigating microstructural changes and creep properties, it can be concluded that the effect of grain size on creep properties is dominant regardless of the size of γ".