Study of TLP bonding of Ti-6Al-4V alloy produced by vacuum plasma spray forming and forging

Abstract

Due to the nature of the near-net-shape formed of Ti-6Al-4V alloy produced by vacuum plasma spray forming (VPSF), post-deposition heat treatment is necessary to achieve to the superior mechanical and physical properties. In this study, transient liquid phase (TLP) bonding of VPSF and forging Ti-6Al-4V alloy were investigated. Simultaneous joining process under equi-axed α phase heat treatment cycle was performed to achieve to a suitable microstructure and mechanical properties of both bonding area and parent metal. Different thicknesses of 2, 5, 10, and 25μm copper interlayer were used and the effect of the interlayer thickness was evaluated. Results showed that the joint region was wider in the TLP bonded VPSF alloy compared to the forged alloy under the same bonding conditions because of the higher diffusion rates in the VPSF alloy. The highest bonding shear strength was achieved for 2μm interlayer thickness. It was 452 and 492MPa for the TLP bonded VPSF and forged alloy, respectively. Increasing the interlayer thickness resulted in decreasing the bonding strength and increasing the hardness of the joint area due to the existence of Ti2Cu intermetallic compounds. The fracture analysis showed the brittle behavior due to the existence of the intermetallic compounds.