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In the present study, titanium (Ti) powders containing some nitrogen (N) atoms were prepared by a gas (N 2 )-solid (Ti starting powder) direct reaction process, and consolidated as an extruded rod with high strength and ductility at ambient temperature. Nitrogen content of the Ti powders via the gas-solid direct reaction process dramatically increased as the treatment time increased while no change in the oxygen content. Ti 2 N layers were formed at Ti powder surfaces via the above gas-solid reaction, however, no formation of Ti 2 N compounds was found in the extruded Ti materials. That is, the solid solution of N atoms in ¡-Ti was complete, and expected to enhance the mechanical strength of Ti materials. 0.2% yield strength (YS) and ultimate tensile strength (UTS) of wrought Ti-N materials were proportional to the additive nitrogen content, and the decrease of elongation was very limited. For example, the extruded Ti powder material with nitrogen content of 0.74 mass% revealed 974 MPa in 0.2%YS, 1120 MPa in UTS and 21.7% in elongation. These tensile properties were superior to those of the conventional Ti6Al-4V alloy with the standard specification of ASTM B348-00-GR5 (0.2%YS: 918 MPa, UTS: 1047 MPa, elongation: 16.6%).

Ubiquitous light elements (ULEs) like oxygen (O), nitrogen (N), carbon (C) and hydrogen (H) can be the key additive elements to achieve the high specific strength and cost-effectiveness of powder metallurgy (PM) titanium (Ti) materials. They have high potential to be employed as promising useful reinforcements of conventional expensive alloying elements like vanadium (V) and Niobium (Nb). In this study, two ULEs, oxygen and hydrogen, were induced into pure Ti matrix via the PM route, and then the processed Ti powders were consolidated into the extruded Ti-O-H materials. The additive ULEs' contribution to the microstructures and strengthening behaviour of Ti wrought materials was investigated in detail. The extruded Ti-0.97O-0.11H specimen exhibited an excellent combination of ultimate tensile strength (UTS) of 1158 MPa and tensile elongation of 23.9%, which were superior to those of Ti-6Al-4V alloy (UTS: 1047 MPa, elongation: 16.6%).

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.