WELDABILITY OF TANTULUM ALLOYS.

The factors which might affect the ductility of fusion welds in Ta alloys include interstitial impurities, welding parameters, alloying elements, and weldment microstructure. Studies showed that base-material alloy content and interstitial-impurity content are most important. In general, machine fusion welds in Ta alloys with a total alloy content Hf, Mo, W, Re greater than 13 atomic will have a room-temperature minimum bend radius greater than 2t in the as-welded condition. The interstitial content of Ta alloy sheet should be less than 100 ppm by wt total of O2, N2, and H2 with a C content of about 50 ppm or less if fusion welds are to be ductile at room temperature. The 2t bend transition temperature of fusion welds in Ta-5W-2.5Mo and Ta-10W-2.5Mo is less than -320 F if the welds are stress relived 1 hr at 1500 F. Tensile joint efficiencies of from 86 at room temperature to 88 at 3500 F can be obtained with fusion welds in Ta-5W-2.5Mo and Ta-10W-2.5Mo, but the joint efficiencies of welds in Ta-17W are lower. A severe exposure of 10 hr at 3500 F impaired the ductility of both base material and welds in the Ta-10W-2.5Mo alloy. Author