Preparation of Nb-silicide based alloy powder by hydrogenation-dehydrogenation reaction

Nb-16Si-25Ti-8Hf-2Cr-2Al alloy powders were prepared by a hydrogenation-dehydrogenation reaction. The Nb alloy ingot, which was prepared by vacuum arc melting, was composed of a (Nb, Ti) solid solution, (Nb, Ti, Hf)5Si3, and (Nb, Ti, Hf)3Si phases. For hydrogenation, the ingot was annealed in the hydrogen atmosphere and it underwent self-crushing. After hydrogenation, the hydrogen concentration increased from 0.003% to 1.30% and the (Nb, Ti) solid solution phase was completely transformed into the (Nb, Ti)H2 hydride phase. The hydrogenated ingot could be easily pulverized by milling due to its brittle nature. For dehydrogenation, the hydrogenated powders were annealed in a vacuum atmosphere, whereby the hydrogen concentration decreased to 0.002% and the (Nb, Ti)H2 hydride phase was transformed back to the (Nb, Ti) solid solution phase. By using this method, Nb alloy powders having sizes less than 20 μm could be easily fabricated.