Diffusion bonding of Ti–6Al–4V alloy using superplastic titanium alloy insert material

Ti–6Al–4 V alloy was diffusion bonded in a vacuum using β rich α–β titanium alloy SP-700 insert material sheet which shows larger superplastic elongation at lower temperatures with larger elongation than Ti–6Al–4 V alloy. The bonding was carried out for 0·3–3·6 ks at 973–1173 K at which temperature the insert material is reported to show superplastic deformation. Pressures of 1·9–9·5 MPa were applied to the bond interfaces during bonding. Effects of bonding temperature, pressure, and time on the soundness of bonding interface and strength were examined. The soundness and bonding strength increased with increases in bonding time, temperature, and pressure. The insert material led to good bonding at lower temperature with smaller pressure than direct bonding without insert material. TEM observation suggested that the insert material kept a microduplex structure consisting of equiaxed fine α–β grains and deformed superplastically during bonding.