Multi-scale influences of as-cast microstructure heritability on intermediate/high temperature stress rupture behaviors of [111]-oriented Ni-based single crystal superalloy

Abstract

This study challenges the generally accepted principle that some degree of as-cast microstructure heritability (CMH), marked by <001> -oriented dendrite-associated inhomogeneity, is tolerable in conventional [001]-oriented Ni-based single crystal (SX) superalloys. Our findings reveal that this principle does not hold for newly developed [111]-oriented SX superalloys, where <001> -directed dendrites experience significant resolved shear stress under [111] applied loads. This work examines the stress rupture behaviors of a [111]-oriented low-Re Ni-based SX superalloy under various CMH conditions at 1100 °C/160 MPa and 760 °C/800 MPa. In the absence of CMH, the alloy achieves rupture properties comparable to fourth-generation SX superalloys. However, the presence of CMH drastically shortens rupture life and alters multi-scale deformation behaviors. High-temperature damage involves submicroscopic dislocation shearing, microscopic crack initiation, mesoscopic inter-dendritic crack connections, and macroscopic fractures. Intermediate-temperature damage is marked by submicroscopic stacking fault shearing, microscopic shear zone deformation, mesoscopic crack propagation, and macroscopic lattice rotation. Moreover, this research investigates the degradation mechanism of stress rupture property when the CMH is combined with slow cooling and reveals unique deformation behaviors, such as high-temperature subgrain formation and intermediate-temperature isolated micro-twins. This work provides new insights into the influence mechanism of the CMH.