Vapor Deposition and Characterization of Tungsten-Rhenium Alloys

Deposition of tungsten-rhenium alloys by the simultaneous hydrogen reduction of tungsten and rhenium hexafluorides has been studied over the temperature range 450 to 700°C using a total system pressure of 10 torr and a H2/(WF6 + ReF6) ratio of about 20. Deposits formed on the inner wall of heated copper deposition tubes through which the reacting gases passed. Under these conditions the greater ease of reduction of ReFe6 compared to WF6 resulted in nonuniform deposits having a higher rhenium content near the inlet to the reaction zone than farther downstream. Deposits containing up to 46 wt% Re have been prepared. The use of argon with the reacting gases was found to improve homogeneity. The deposits were found to contain total interstitial impurities as low as 50 parts/106. The grain structure was typically columnar. X-ray diffraction revealed the presence of two phases that coexisted throughout part of the composition range: an alpha-tungsten (bcc) structure, which was the principal phase in low rhenium deposits, and a previously unreported beta-tungsten phase, which was favored by high rhenium contents.