Microstructures and interfacial quality of diffusion bonded TC21 titanium alloy joints

Diffusion bonding of TC21 titanium alloy was carried out at temperature ranging from 780 degrees C to 980 degrees C for 5-90 min. The interfacial bonding ratio, deformation ratio, microstructures and microhardness of the diffusion bonded joints were investigated. Results show that joints with high bonding quality can be obtained when bonded at 880 degrees C for 15-30 min. The microhardness increases with increasing the bonding temperature, while it has a peak value (HV367) when bonding time is prolonged up to 90 min. Fully equiaxed microstructures, bi-modal microstructures and fully lamellar microstructures were observed when bonded in temperature range of 780-880 degrees C, at 930 degrees C or 980 degrees C, respectively. The volume fraction of alpha. phase first increases and achieves the maximum when bonded at 880 degrees C for 60 min, and then descended.