Microstructure and properties of electron beam welded joints of tantalum and tungsten

Electron beam welding of tantalum/tungsten was carried out. The results showed that the main defects of the joints were cracks and unfused holes with poor connection. The microstructure of the heat affected zone on the tungsten side was coarse equiaxed grains and a little amount of small equiaxed grains with straight grain boundaries near the weld. The weld only consisted of the A2 phase of tantalum-tungsten replacement solid solution. Hardness of fusion line was considerably high, and there was a great hardness gradient in the heat affected zone as well. Tensile strength of welded joints was only 56 MPa. Fracture occurred near the fusion line on the tantalum side. Besides, the fracture was a mixture of intergranular fracture, cleavage fracture, and quasi-cleavage fracture, which was the typical characteristic of brittle fracture. Welding with 0.3 mm deflection to Ta was carried out to optimize the fusion state of welded joints. Hardness of the joint was lower than that with no deflection especially of the fusion line. Tensile strength of welded joints was improved to 86 MPa.