Microstructure evolution and mechanical properties of a high-strength Ti2AlNb alloy processed by large-strain two-pass hot extrusion

Abstract

The microstructure evolution and tensile behavior of Ti2AlNb alloy (Ti-22Al-23Nb-1Mo-1Zr) processed by two-pass hot extrusion and two-step heat treatment were investigated. After extruding deformation in the B2 phase field, the B2 grains were refined from about 1500–50 µm through dynamic recrystallization. The microstructures subjected to solution treatment in the B2 + α2 phase field and aging treatment in the B2 + O phase field include B2 matrix, lamellar O, rim O and lamellarα2/O phases. The microstructure and tensile properties are sensitive to aging temperature. As the increase of the aging temperature, the content of the B2 phase and the size of the lamellar O phase increase, resulting in low strength and high ductility. The alloy aged at 800 °C has a good match of strength and ductility. It has an elongation of 6.3% with a tensile strength as high as 1225 MPa due to the precipitation strengthening of numerous lamellar O phase and fine grain strengthening. The tensile fracture mode predominantly shows quasi-cleavage characteristics with typical cleavage facets and massive dimples, which is consistent with the good balance of tensile strength and ductility. An in-depth understanding of the relationship between microstructure and tensile properties in this study can be helpful for the engineering application of the Ti2AlNb alloy.