The influence of bonding time on microstructure and mechanical properties of vacuum diffusion bonded joints between commercial pure titanium and medium carbon steel

Abstract

We used vacuum diffusion bonding to join commercial pure titanium (CPT) and medium carbon steel (MCS). Bonding was performed at 850 °C, 5 MPa, and bonding times (BTs) of 1, 2, 3 and 4 h. The BT effects on the microstructure and mechanical properties of the joints were investigated. The results confirmed the bonding between CPT and MCS at 850 °C and 5 MPa. Although incomplete fusion zones were found for BTs of 1 and 2 h, the interface was connected for BTs of 3 and 4 h. The grains of the CPT and MCS matrix increased with longer BT. The microstructure of the diffusion layer was composed of TiC, TiFe, and Fe2Ti at the bonding interface. The fracture mode of the samples was a ductile fracture, and testing results showed that the tensile strength first increased and then decreased, reaching the maximum for BTs of 3 and 4 h. The tensile test results showed that tensile fractures were formed of TiC with lamellar microstructure, and the content of TiC grew with increasing BT. Hardness test results showed that with increasing BT, the hardness of matrices decreased and the bonding zone widened.