Interfacial voids, microstructure and shear strength of TC4/TC17 bond

TC4 (Ti-6Al-4V) and TC17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr) were solid-state bonded at the bonding temperatures ranging from 780-840℃ the bonding pressures ranging from 10 to 30 MPa and a bonding time of 30 min. Quantitative analysis of void size and bonding ratio was obtained based on scanning electron microscopy observation in the bonding interface of TC4/TC17 bonds. Electron backscatter diffraction examination in the bonding interface showed that the curved bond line due to the interpenetration between TC4 and TC17 driven by plastic flow occurred. Interfacial voids generally occurred on TC4 side or on the α(TC4)/α(TC17) interface grain boundary, which was due to faster material flow from β phase to interfacial voids than that from α phase under the effect of diffusion and plastic flow. The disappearance of large sized voids with the increasing of bonding pressure from 10 MPa to 20 MPa at 820℃ 30 min and the increasing of bonding temperature from 780℃ to 820℃ at 30 MPa, 30 min resulted in significant increase in shear strength of TC4/TC17 bonds. Besides, the TC4/TC17 bond at 840℃ 30 MPa and 30 min showed evidently deformed bond line and high shear strength of 756 MPa, which was due to enhanced interpenetration between TC4 and TC17 influenced by significant of α→β phase transformation on TC17 side.