Friction Welding of Pure Tungsten to Oxygen Free Copper with Intermediate Layer

Abstract

In order to improve the friction weldability of tungsten to copper, a commercially pure tungsten was friction-welded to an oxygen free copper with the aid of intermediate layers of various metals. Intermediate layers employed were foils of Ti, Al, Nb, Ni, Fe and Ag of thickness 20-30μm. Burn-off rates during friction welding with intermediate layers except Ag were greater than that observed without an intermediate layer. Especially, intermediate layers of Ti, Nb and Fe increased the burn-off rate remarkably. Intermediate layers except Ag became finer or thiner particles during friction process and was mixed with Cu forming stratified microstructures. When intermediate layers of Ti and Al were applied, intermetallic compounds of Ti-Cu and Al-Cu systems were formed in the mixed layer. As the friction time was increased, the tensile strength of joints was increased, and reached almost saturated values depending on the intermediate layers. The tensile strength of joints with intermediate layers of Ti, Nb and Fe was increased rapidly than that of the direct welding without an intermediate layer, and reached higher levels. Especially, joints with the intermediate layer of Nb were fractured in the HAZ of copper at friction times of 4 s or more, while joints with the other intermediate layers were fractured at weld similarly to the case of the direct welding. Friction torque and heat input during welding with the intermediate layers of Ti, Nb and Fe were much greater than those of friction welding without an intermediate layer, suggesting that the increases in friction torque and heat input accelerated the burn-off and the rise in tensile strength of joints.