On the high-temperature creep and fatigue behaviours of an advanced hot-extruded nickel-based superalloy
Xingyu Pan, Chonglin Jia, Chunlei Qiu
Abstract
In this study, the high-temperature creep and fatigue behaviours of a hot-extruded nickel-based superalloy, GH4151, have been systematically studied. The alloy shows excellent creep and fatigue properties at 750 ∼ 800 °C, which is mainly due to dislocation slip and the formation of superlattice stacking faults (SSFs) being the dominant deformation mechanism. Segregation of Co and Cr occurs at SISFs which may have led to local γ′ → γ transformation while Co and Nb segregate along SESFs which results in local γ′ → η transformation. That different species of atoms segregate to different types of SSFs is mainly due to that there exists a concentration threshold for each solute element to be capable of segregating to a specific type of SSF. The elemental segregation at SSFs and the potential local phase transformation are beneficial to the creep resistance. Oxidation in the surface and subsurface regions is the main cause for crack initiation during high-temperature creep and fatigue testing. Oxidation along the grain boundaries (GBs) in the subsurface regions embrittles the material and leads to intergranular cracking. Inside the material where oxidation cannot reach, creep damage occurs mainly by forming micro-voids and microcracks along GBs.