Impacts of different designed microstructures on creep performance of a Ni-based wrought superalloy

The creep behavior of a novel Ni-based wrought superalloy with varying aging states, classified as large underaged (UA), little UA, and little over -aged (OA) states, was investigated at a temperature higher than the intragrain/grain-boundary iso-strength temperature (750 degrees C/250 MPa). In the samples before creep test, there are spherical gamma' precipitates homogeneously dispersed within the gamma matrix and carbides precipitated at grain boundaries (GBs). After creep tests, precipitate -free zones (PFZs) appear on grain boundaries, with a large blocklike gamma' phase present between carbides and PFZs, potentially serving as initiation sites for cracks. Little UA state samples exhibit the strongest creep resistance and intergranular fracture. The dominant creep deformation mechanism in the intra-grain is a combination of Orowan process involving slip and climb of matrix dislocations and shearing of gamma' precipitates. The results indicate that the optimizing the grain boundary microstructure may be more important than the change of intragranular microstructure when the creep temperature exceeds the isostrength temperature.