Characterization of the martensitic transformation in Ni 50-xTi50Cux alloys through pure thermal measurements wire

The addition of a third element to the Ni-Ti system often changes the product and the path of the martensitic transformation of the alloy, which is a direct B2-B19? transformation for the NiTi alloy in the fully annealed state. In this study we investigate the martensitic transformation of fully annealed Ni50-xTi50Cux (x = 3-10 at%) shape memory alloy (SMA) samples using differential scanning calorimetry (DSC) and the four-probe electrical resistance (ER) measurements under stress-free conditions. DSC and ER data show that the ternary alloy goes through a direct B2-B19? transformation for Cu content between 3 and 7 at% and through the two-stage B2-B19-B19? transformation for Cu content between 8 and 10 at%. We find good agreement between the two techniques as regards the detection of the phase transformation temperatures. B19? starting and finishing temperatures decreases with the increases of Cu content and show a significant reduction starting from 7 at%; the range of temperatures in which B19 is stable increases with increasing Cu content.