WELDABILITY OF TUNGSTEN BASE ALLOYS.

The weldability of unalloyed tungsten and two tungsten alloys was evaluated.The alloys were W-25Re (wt %) and W-25Re-30Mo (at.%).These were evaluated as a r c cast material and for tge ternary alloy also as a powder metallurgy product.The most important aspect of welding unalloyed tungsten was that i t is very sensitive to thermal shock.High preheat temperatures (to 1400' F) alleviated this problem.W-25Re had improved thermal shock resistance but was shown to be basically hot tear sensitive in gas tungsten a r c welding.Preheat temperatures of 1400' F were again beneficial.The powder metallurgy W-25Re-30Mo alloy displayed excellent weldability, whereas the a r c cast material displayed extensive hot tearing and, hence, poor weldability.The anomalous hot tearing behavior of the a r c cast W-25Re-30Mo alloy was ascribed to a very high sensitivity to oxygen contamination.The effects of postweld annealing, joint preparation, and aging for 1000 hours at temperatures to 3000' F were evaluated.The high temperature tensile strength of base metal, gas tungsten a r c welds, and electron beam welds in W-25Re-30Mo was determined.*Based on work conducted under NASA contract NAS 3-2540.TWestinghouse Astronuclear Laboratory, Pittsburth, Pennsylvania.