Fabrication of TiNi Shape Memory Alloy by a Pulse Current Sintering Process

Titanium-nickel shape memory alloys were fabricated by a pulse current sintering process from two types of starting powders prepared through different processes: mechanical alloying of TiH and Ni powders mixture and dehydrogenation (MA powder), and pre-mixed of Ti and Ni powders (mixed powder). The MA powder was composed of mainly TiNi phase and a small amount of Ti sub 2 Ni and TiNi sub 3 phases. The composition of this powder remained unchanged after the pulse current sintering at 973-1173K for 300 s, while the relative density of 100% was attained for the sintering body. On the contrary, the pulse current sintering of the mixed powder at 1273K for 60-300 s, led to a distingusihed compositional change and the relative density of 100%. The TiNi sub 3 phase in the sintered body could be removed on the condition of longer sintering period or by heat treatment at 1273K for 18 ks; however, the Ti sub 2 Ni phase could not be removed. The composition and the thermal characteristics (Ms=318K) of these sintered bodies were found to be almost the same as those of commercially available Ti-Ni shape memory alloys.