Precipitation behavior and strengthening mechanism of the interfacial nano-O phase of Ti2AlNb diffusion welded joints with high-entropy interlayer during aging process

This study designed a post-weld aging experiments to improve the room and high-temperature strength in Ti2AlNb diffusion welded joints with high entropy interlayers. Firstly, the interfacial microstructure of the Ti2AlNb diffusion welded joints under different aging processes was investigated, followed by room and high-temperature mechanical property tests to establish the aging process window for the joints. Finally, the precipitation mechanism of the nano-O phase in the diffusion reaction interface (DRI) between Ti2AlNb and high entropy interlayers was analyzed, and the strengthening/toughening mechanisms of the aged joints were elucidated. The results indicate that with the aging temperature increasing, the B2 phase in DRI decomposes into a disordered β phase and nano-O phase, with the nano-O phase uniformly distributed in DRI and maintaining a specific Burgers vector relationship, i.e., (001)_O // (1¯01¯)_β，[1¯10]_O // [1¯11]_β. The size of the O phase increases gradually with the rise in aging temperature and time, while the volume fraction decreases gradually. But the tensile strength of the joint decrease with aging temperature and time increasing, whereas the elongation increases gradually. The aging process window for the joint is determined as 770 to 800 °C for a time period of 1 to 6 h. The nano-O phase at the DRI not only impedes dislocation movement, but also undergoes slip and twinning deformation, thereby strengthening and coordinating the plastic deformation of the joint. This research provides design guidelines and theoretical support for diffusion bonding of Ti2AlNb alloy.