Experimental investigation of the mechanical properties and microstructures of Ti–6Al–4V solid-state diffusion bonding joint under high temperature conditions

The mechanical properties and related mechanisms of the Ti–6Al–4V alloy solid-state diffusion bonding (SSDB) joint under elevated temperature conditions have been experimentally investigated in this study. Tensile tests with temperatures (298 K–1173 K) and strain rates (0.001 s⁻¹, 0.1 s⁻¹) of the joint and base metal (BM) were carried out. The microstructural evolutions were characterised by optical microscope, scanning electron microscope combined with backscatter diffraction. The results show that the tensile strength and elongation of the joint are slightly lower than the BM at 298 K, which is attributed to the higher Schmid factor and unbonded areas of the joint. However, at elevated temperatures from 1023 to 1123 K, the tensile strength of the joint turns to be higher than the BM, while the elongation of the joint is much lower than the BM. Grains with relatively high Taylor factors cluster at the DB interface. The larger number fraction of high angle grain boundaries (HAGBs−88%) and a higher inclination of strain hardening at DB interface, cause a higher strength of the joint at high temperatures. No significant plasticity variation of the joint is revealed because of primitive remnant holes and new straight HAGBs at DB interface. While when the temperature further increases to 1173 K, the difference of properties between the joint and BM become negligible. Corresponding reasons are characterized as dynamic recrystallization occurs at the interface of the joint at 1173 K, which is 50 K higher than that of BM, and the interface is eliminated.