Titanium Powders via Gas-Solid Direct Reaction Process and Mechanical Properties of Their Extruded Materials

抄録

In the present study, titanium (Ti) powders containing some nitrogen (N) atoms were prepared by a gas (N₂)-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. Ti₂N layers were formed at Ti powder surfaces via the above gas-solid reaction, however, no formation of Ti₂N compounds was found in the extruded Ti materials. That is, the solid solution of N atoms in α-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 Ti-6Al-4V alloy with the standard specification of ASTM B348-00-GR5 (0.2%YS: 918 MPa, UTS: 1047 MPa, elongation: 16.6%).