High strength-ductility synergy of Inconel 625 alloy with a layered bimodal grain-structure

The mechanical properties and deformation behaviors of a bimodal grain structured Inconel 625 alloy were systematically investigated over a wide temperature range from 25 degrees C to 900 degrees C. As compared with conventional Inconel 625 alloys, the heterogeneous Inconel 625 alloy exhibits superior strength-ductility synergy until 600 degrees C. The yield strength, ultimate tensile strength and elongation at room temperature reach 617 MPa, 1057 MPa and 56.9%, respectively. The grain boundary strengthening and twin boundary strengthening introduced by numerous fine grains result in high yield strength. Electron backscattered scattering diffraction and transmission electron microscopy results reveal different densities of geometrically necessary dislocations between coarse grains and fine grains. The strain gradients induced by incompatible deformation of bimodal grains produce large back stress work hardening, which not only significantly increases the ultimate tensile strength but also prevents early necking during tensile testing, improving tensile ductility. When temperature exceeds 600 degrees C, stress relaxation induced by dynamic recrystallization significantly decreases the strength of alloys but increases its ductility. This study demonstrates the strength and ductility of Inconel 625 alloy can be simultaneously improved by introducing heterogenous lamella structure and the great mechanical properties can retain until 600 degrees C.