Abstract
The effect of heat treatment in the range 633 K–933 K on the phase transformations among three types of phases, i.e. the CsCl (B2)-, rhombohedral (R)- and monoclinic (M)-phases in Ti-49.7, 50.2 and 50.6 at%Ni alloys have been investigated using the differential scanning calorimetry (DSC) method. It has been confirmed that the phase transformations that occur during heating and cooling can be classified into the following three types depending on 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. It is also shown that the temperature range in which R-phase is stable becomes wider with increasing Ni content. The transformation temperature of R-phase was found to decrease with increasing heat treatment temperature. The starting point of the R-phase transformation in these alloys heat-treated at 633 K was estimated approximately at 330 K, which was almost independent of Ni content.
