Powder Forming Process from Machined Titanium Chips via Heat Treatment in Hydrogen Atmosphere

抄録

The recycling process of the coarse machined chips from the commercial Ti-6%Al-4%V (Ti-64) alloy products to fine powders available for powder metallurgy (PM) components was established. The brittle TiH₂ compounds formation in Ti chips via heat treatment in hydrogen gas atmosphere significantly improved their milling ability. TG-TDA and XRD analysis suggested the hydration and dehydration behavior of pure Ti and TiH₂ powders. The suitable hydration temperature over 873 K in H₂-Ar mixed gas successfully caused TiH₂ compounds synthesis in Ti-64 chips, and resulted in reproduction of fine Ti-64 powders with a median particle size of 120 µm from the machined spiral chips by mechanical milling process. The green compact of reproduced Ti-64 powder after vacuum sintering at 1273 K showed a relative density of about 93%, larger than that of the sintered material in using the commercial Ti-64 powder. The hydrogen and oxygen contents of the sintered specimen using reproduced Ti-64 powder were satisfied with JIS-60. Accordingly, the machined Ti alloy chips were directly recycled as valuable starting materials to reproduce PM components via combination of hydration-milling-dehydration process.