TiNi化合物の相変態に及ぼす熱処理の影響

抄録

In order to clarify the effect of heat treatment on the martensitic transformation in the TiNi compound, the electrical resistivity vs temperature curves of TiNi containing hyper-stoichiometric concentration of nickel which were heat-treated under various conditions were obtained. TiNi containing more than 51 at%Ni showed a remarkable quenching effect. The Ms temperature of water-quenched specimens decreased with increasing nickel concentration. The Ms temperature of Ti-50 at%Ni was constant regardless of the change in quenching temperature, whereas that of Ti-51 and 52 at%Ni decreased with increasing quenching temperature above 500°C. The Ms temperature of Ti-51 at%Ni, however, became constant by quenching from a temperature above 600°C. In Ti-52 at%Ni the Ms temperature decreased below liquid nitrogen temperature by quenching from a temperature above 750°C. The Ms temperature increased up to −5°C by aging at 500°C after water quenching from 1000°C in both Ti-51 and −52 at%Ni. In Ti-49.5, 50.0 and 50.4 at%Ni the appearance of a peak in resistivity-temperature curve was observed after some complete thermal cycles. The Ms temperature decreased during initial five cycles and then became constant. From the results obtained by electrical resistivity measurement and X-ray diffraction, it is concluded that the TiNi compound has a CsCl-type ordered structure and order-disorder transformation or peritectoid transformation does not exist in the temperature range from the Ms temperature to 1000°C. It is also found that the nonstoichiometric range of the compound becomes narrower with decreasing temperature and the maximum nickel concentration at 500°C is 50.8 at%Ni.