Fabrication of NiTi intermetallic compound by a reactive gas laser atomization process

We attempted to synthesize NiTi intermetallic compound from two types of stranded wires, pure Ti wire (with a diameter of 300 μm) and pure Ni wire (with diameters of 300 and 250 μm). The stranded wire was melted and reacted using a laser, and the melted metal was gas-atomized using high-pressure Ar gas or coated on an aluminum base material. The particle size of the obtained powder ranged from 10 to 125 μm. Thickness of the coating layer was 3 mm. The compositions of the powders and coating layer could be adjusted by changing the wire diameter of Ni of the stranded wire. In other words, the compositions of the powders and coating layer could be controlled by adjusting the Ti to Ni ratio of the stranded wire. Consequently, we produced NiTi intermetallic compound with the purposive composition. Sintered compact with a relative density of 99.9% or more could be produced by sintering the powders by pulsed electric-current sintering device. The defects of the coating layer were reduced to 0.1% or less by the hot press treatment. The sintered compact of the powders with a Ti–Ni composition ratio of one to one and the molding compact of the coating layer produced in a similar manner were a single NiTi martensite phase. By this manufacturing method, NiTi intermetallic compound with an Mf temperature of 320 K and Af temperature of 365 K could be produced.