Advanced Welding and Joining of Corrosion Resistant Nb-W Alloy

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Weldability of Nb-5%W alloy was investigated using GTA and EB welding. The HAZ softening occurred in GTA welds and joint strength was reduced to approx. 300MPa. The HAZ softening was inhibited and joint strength was improved in EB welds, while toughness of EBW joint was much less than that of base metal.Dissimilar diffusion bonding of Nb-5%W alloy to SUS304ULC stainless steel was conducted. The reaction layers of Fe-Nb intermetallic compounds were formed at the bond interface and growth kinetics of them were followed by the parabolic law. Tensile strength of joint attained the maximum value of approx. 200MPa at the reaction layer thickness of 8μm..Diffusion bonding of Nb-5%W alloy to SUS304ULC stainless steel using Ta insert metal was conducted. An obvious reaction layer was not formed at the Nb-W/Ta interface, while reaction layer consisted of TaFe2 and TaCr2 could be observed at the Ta/SUS304ULC interface. Tensile strength of Ta-inserted joint (Nb- W/Ta/SUS304ULC joint) was a maximum of approx. 250MPa.Explosive bonding of Nb-5%W alloy to SUS304ULC stainless steel was examined. The characteristic wavy interface and very few reaction products were formed at the bond interface, and hardening of bond interface hardly occurred in the explosive bonded joint. Explosive bonding of Nb-5%W alloy to SUS304ULC stainless steel using Ta insert metal was conducted in order to improve the joint properties. Although a solid solution forcibly mixed Ta with Nb-W was formed at the Nb-W/Ta interface, hardening of bond interface was very slight. Shear test of explosive bonded joints of Nb-W/SUS304ULC, Nb-W/Ta and Ta/SUS304ULC revealed that every joint was fractured in the Nb-W or Ta base metal, and that shear strengths of the joints were almost comparable to those of base metals.