Effects of hydrogen on diffusion bonding of hydrogenated Ti6Al4V alloy containing 0.3 wt% hydrogen at fast heating rate

The diffusion bonding of hydrogenated Ti6Al4V alloy containing 0.3 wt% hydrogen was carried out. The effects of hydrogen on diffusion bonding at fast heating rate were investigated by SEM, EPMA, XRD, TEM and TG/DSC. According to the experimental observations, the featheriness α′α′ martensite and βHβH phase disappeared after bonding, and the fine needle α′α′ martensite and lamellar (α+β)(α+β) structure were formed. Moreover, the FCC δδ hydride translated into metastable hydride containing low hydrogen content with a crystal structure of TiH. Only the voids were observed in the interface, and the quantity of voids gradually decreased with the increase of bonding temperature, holding time and joining pressure. When bonded at 810∘C for 8 min under a pressure of 6 MPa, the voids were closed and the room temperature shear strength of this joint reached 450 MPa. The fast heating prevented the most hydrogen escaping during rise in temperature, avoided the oxidation of joining surface and caused more phase transformation, which helped to improve the diffusion bonding quality.