Effects of different microstructures of near-α titanium alloys on interfacial voids evolution and bonding mechanisms produced by hot compression bonding

Abstract

In this study, we investigated interfacial void healing, dynamic recrystallization, and the mechanical characteristics of the near-α titanium alloys bonding joints by hot compression bonding with different microstructures. The evolution of microstructure at bonding interfaces was investigated using SEM, EBSD and TEM. Molecular dynamics simulations were used to investigate evolution of interfacial voids. As for the bonding interface of equiaxed to equiaxed microstructure (E-E interface), most interfacial voids are found at the α-α interface, with fewer at the β-β interface. While for the bonding interface of Widmanstätten to Widmanstätten microstructure (W–W interface), interfacial voids are randomly distributed, notably with the β phase growing into these interfacial voids. This observation suggests a higher healing propensity of the β phase during bonding, which is due to that the diffusion rate of the body-centered cubic (BCC) β phase is 1.5 times higher than that of the hexagonal closed-packed (HCP) α phase, as verified by molecular dynamics simulations. Moreover, the characteristics of interfacial dynamic recrystallization indicate that continuous dynamic recrystallization characterized by progressive sub-grain rotation occurs at both the E-E interface and the W–W interface, with subsequent rotational dynamic recrystallization further refining the interfacial dynamically recrystallized grains. However, the further growth of interfacial recrystallization grains in W–W interface is hindered by the lamellar of the Widmanstätten microstructure. Notably, the mechanical properties of the joints are found to be comparable to the base material, highlighting the effectiveness of HCB in maintaining the integrity and strength of near-α titanium alloys bonding joints.