Powder forming process from machined titanium chips via heat treatment in hydrogen atmosphere

Abstract

The recycling process of the machined chips from the commercial Ti-6%Al-4%V (Ti-64) alloys to raw powders was established through the combination of brittle TiH₂ compounds formation via heat treatment in hydrogen gas atmosphere and fragmentation by ball milling technique. TG-TDA and XRD analysis obviously suggested the hydride and dehydride behavior of pure Ti and TiH₂ powders. The suitable heat treatment temperature at 873 K or more in H₂-Ar mixed gas successfully caused the formation of TiH₂ compounds, and resulted in the fragmentation of Ti-64 machined chips to powders with a median particle size of 120 μm, which were completely consolidated by pressing. In addition, the original machined chips never remained in the ball-milled machined chips after heat treated over 873 K. The green compact 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 powders.