Effect of beam offset on the microstructure and properties of a dissimilar tungsten/kovar electron beam weld

Butt joints of tungsten and Kovar were prepared by different electron beam welding processes. This study investigates the effect of beam offset on the microstructure and mechanical properties of the joins. Infusion zone (FZ), subcrystals precipitated in coarse austenite grains transformed from columnar subcrystals at the boundary to equiaxed subcrystals in the middle of the FZ. The microhardness of the tungsten heat-affected zone (HAZ) reduces to 420HV because the cold-rolled structure disappeared due to melting and recrystallization. Because of fine-grain strengthening, the microhardness in FZ increases to 170HV. In direct welding, brittle intermetallic compounds and ductility dip cracks generated around the fusion line are responsible for poor mechanical properties. Beam offset welding inhibits such defects, and the tensile strength increases by 36% compared to direct welding.