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Investigation of the Physical Metallurgy of Joining Tungsten and Columbium
The metallographic analysis of 14 new braze alloys for miobium was completed. Studies on the effect of brazing parameters and testing variable on joint re-melt temperature have been continued. Applied stress during testing was the most important variable in control of failure temperature. New braze alloys for tungsten were evaluated for melting range. Electron beam melted ingots of W-Hf and W-Hf-C alloys were successfully worked to sheet. Gross thermal response characteristics were established and tests to determine transition temperatures in the wrought, fully recrystallized, and fusion welded conditions were initiated. No evidence of significant grain boundary hardening was observed in traverses of symmetrical randomly oriented indenters. The results demonstrate that earlier indications of grain boundary hardening were in fact related to a large hardness anisotropy. Annealing of unalloyed tungsten in a carbon-free, utra-high vacuum environment improves the low-temperature ductility. The tensile shear strength of lap joints diffusion bonded between Nb-1Zr and 316 SS, Nb-1Zr to Cu, and Cu to 316 SS was determined. Additional experiments confirmed the actual bonding between Be and 316 SS. Diffusion of Be into 316 SS, however, results in a brittle joint. The effect of Cr as a diffusion barrier in the Mo-0.5 Ti/R-41 and Mo0.5 i/L-605 systems was investigated.
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