Dissimilar transient liquid phase bonding of Ti–6Al–4V and Co–Cr–Mo biomaterials using a Cu interlayer: Microstructure and mechanical properties

Abstract

In order to construct a bimetallic device for the medical application, the selection of the joining process is essential. Transient liquid phase (TLP) bonding of two biomaterials of Ti–6Al–4V and Co–Cr–Mo (ASTM F-75) alloys with a Cu interlayer was investigated at the bonding time of 5, 15, 30, and 45 min at the bonding temperature of 920 °C. To evaluate the microstructure, the interfacial brazing zone (IBZ) was studied using an optical microscope (OM), field emission scanning electron microscope (FE-SEM), and energy dispersive spectroscopy (EDS). The results showed that the microstructure of Ti–6Al–4V/Cu/Co–Cr–Mo was composed of CoCr(Ti, Mo), Ti(Cu, Co), Ti2Cu, α-Ti, and β-Ti. By raising the bonding time and increasing the diffusion of Cu into base metals, the transformation of Ti(Cu, Co) into Ti2Cu was done. Then, the thickness of the Ti(Cu, Co) intermetallic compound (IMC) reduced. With increasing bonding time from 30 to 45 min, the morphology of Ti2Cu IMC changed from tiny to blocky. Shear strength, microhardness, and fractographic assessment were used to investigate the mechanical properties of the bonding zone. It is found that with increasing the bonding time, the shear strength of the brazed joints increased. The maximum shear strength of 316 MPa occurred at 45 min. The microhardness test also demonstrated that the CoCr(Ti, Mo) in the diffusion layer with the hardness value of 839 HV was the hardest phase. The formation of IMCs changed the fracture mode.