Direct diffusion bonding of immiscible tungsten and copper at temperature close to Copper's melting point

In this study, a direct diffusion bonding method is designed to bond tungsten (W) and copper (Cu) without using an interlayer metal at a temperature close to themelting point of copper (T-mCu). The results show that the direct diffusion bonding method is feasible and the key point to a successful connection is that bonding temperatures should be controlled in an effective temperature range 0.81T(mCu)-0.97T(mCu). The most appropriate bonding parameters are that the bonding temperature is 980 degrees C, the bonding time is 180 min and the bonding pressure is 106 MPa. The maximum tensile and bending strengths of the as-obtained W/Cu joints are similar to 172 and similar to 232 MPa, respectively, which reach a very high level compared to pure copper. The corresponding fractures are ductile. The micro-tests for the W/Cu joint show that diffusion occurs between W and Cu and the thickness of the W/Cu diffusion layer is similar to 22 nm. Through the diffusion, a metallurgical bonding interface has been successfully constructed, which is the essential reason for the high strengths of the W/Cu joint. The diffusion between W and Cu when the bonding temperature is close to T-mCu may be induced by the high-temperature structure of Cu, which needs further investigation. (C) 2017 Elsevier Ltd. All rights reserved.