β-transus controlled microstructural transition in diffusion-bonded Ti-10V-3Al-2Fe alloy

This study investigates the effect of diffusion bonding temperature on the microstructural evolution and mechanical behavior of Ti-10V-3Al-2Fe alloy joints. Bonding was performed below, within, and above the reported α+ β → β phase transformation temperature range to clarify the relationship between phase transformation and joint performance. At sub-transus temperatures (650 – 750 °C), the joints exhibited incomplete interfacial bonding characterized by microvoids and spheroidized α phases. At a near-transus condition (775 °C, corresponding to the lower bound of the reported transformation range), an interlaced α+ β structure developed, while the precipitation of acicular secondary α phases was associated with a reduction in ductility. At super-transus conditions (800 – 850 °C), grain boundary migration and coarsening of α phases further suppressed elongation. Mechanical properties exhibited a temperature-dependent evolution up to 725 °C, with simultaneous improvements in strength and ductility. Beyond this range, strength gains were limited, whereas elongation declined sharply due to phase transformation and grain growth. These findings highlight the complex interplay between bonding temperature, microstructural evolution, and mechanical response, providing practical guidelines for optimizing diffusion bonding parameters of near-β titanium alloys.