Creep anisotropy behavior, deformation mechanism, and its efficient suppression method in Inconel 625 superalloy

Mill products, such as sheets, usually show obvious anisotropy in their mechanical properties, which greatly affects both their applications and workability. In this study, the orientation-dependent tensile and creep behaviors of Inconel 625 alloy sheets with weak local textures were systematically investigated at 650 °C. The results showed that Inconel 625 superalloy exhibits nearly isotropic tensile properties; however, obvious creep anisotropy appears when loading along different directions. Creep life in the rolling direction (150 ± 5 h) was approximately 4.5 times longer than in the transverse direction (33 ± 1 h). Severe creep anisotropy was found to be determined by two aspects: (i) the change in deformation mechanisms along the rolling direction (a combination of boundary sliding, dislocation slipping, and twinning) and the transverse direction (dislocation slipping). Stronger impingement of slip bands on grain boundaries accelerated intergranular crack initiation and propagation during loading along the transverse direction, which resulted in a short creep life. (ii) The differences in strain compatibility at grain boundaries (i.e., creep loading along the transverse direction resulted in the initial grains forming strong Brass, Cu, and S textures). Creep cracks preferentially nucleated at the junctions between Cu/Brass texture grains, as these interfaces exhibit the worst strain compatibility (Luster–Morris parameter m′ ≤ 0.22). Furthermore, pre-stress aging (PSA) treatment is proposed as an efficient method to suppress creep anisotropy. The discrepancy rate of creep life was found to be reduced by nearly 50% after PSA treatment.