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

Abstract

The recycling process of the coarse machined chips from the commercial Ti-6%Al-4%V (Ti-64) alloy products to ne powders available for powder metallurgy (PM) components was established. The brittle TiH 2 compounds formation in Ti chips via heat treatment in hydrogen gas atmosphere signi cantly improved their milling ability. TG-TDA and XRD analysis suggested the hydration and dehydration behavior of pure Ti and TiH 2 powders. The suitable hydration temperature over 873 K in H 2-Ar mixed gas successfully caused TiH 2 compounds synthesis in Ti-64 chips, and resulted in reproduction of ne 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 satis ed 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.

Fabrication of Boronized Ti6Al4V/HA Composites by Microwave Sintering in Mixed Gases

“…When sintering was performed in the mixed gas of Ar + H 2 , another phase, TiH 2 , was observed with weakened reflections from the main components of the composite. This hydriding reaction is expressed as follows 28 Ti H TiH…”

“…During cooling, a part of TiH 2 was decomposed to Ti and H 2 . 28 As a result, the reflection from the titanium matrix phase was lowered. Another reason for the change in the peak intensity could be related to the transition from β-Ti to α-Ti during cooling because of the higher hydrogen diffusion rate in β-Ti atoms than that in α-Ti atoms, which will broaden the stability region of the β-Ti phase.…”

“…When sintering was performed in the mixed gas of Ar + H 2 , another phase, TiH 2 , was observed with weakened reflections from the main components of the composite. This hydriding reaction is expressed as follows TiH 2 is brittle and thermally stable at low temperatures. The sintering of titanium could be accelerated by the diffusion of hydrogen atoms from TiH 2 , along the α-Ti grain boundaries.…”

“…The sintering of titanium could be accelerated by the diffusion of hydrogen atoms from TiH 2 , along the α-Ti grain boundaries. During cooling, a part of TiH 2 was decomposed to Ti and H 2 . As a result, the reflection from the titanium matrix phase was lowered.…”

From Machining Chips to Raw Material for Powder Metallurgy—A Review

“…Some authors revealed the success of applying a pre-heat treatment on a Ti alloy, heating in an H 2 -Ar mixture atmosphere, on decreasing particle size, the production of fine particles was attributed to the formation of brittle TiH 2 compound during the pre-heat treatment step [ 26 ]. Another study evaluated the effect of chemical composition on fragmentation, the application of similar milling conditions on two steels, an extra low carbon steel and a low carbon type, the former type faced with agglomeration formation caused by cold welding.…”