Three types of phases, the CsCl(B2) type, the rhombohedral (R) type and the monoclinic (M) type, are recognized in near-equiatomic Ti-Ni alloys. The effect of the heat treatment (633 K-933 K) after cold work on the phase transformations among these three phases in three Ti-Ni alloys (49.7, 50.2 and 50.6 at%Ni) has been investigated by D.S.C. measurement.
The results are summarized as follows:
(1) The phase transformations are classified into the following three types according to the heat treatment temperature; (a) B2→R→M during cooling and M→R→B2 during heating for lower heat treatment temperatures; (b) B2→R→M during cooling and M→B2 during heating for intermediate heat treatment temperatures; and (c) B2→M during cooling and M→B2 during heating for higher heat treatment temperatures.
(2) The more the Ni content increases, the larger the temperature range for the R-phase to exist becomes and the more the R-phase transformation temperature decreases with the increase of the heat treatment temperature. But the R-phase transformation of the alloys heat-treated at 633 K starts at about 330 K, which is almost independent of the Ni content.