Shape memory characteristics and mechanical properties of high-density powder metal TiNi with post-sintering heat treatment

Through the use of fine titanium and nickel elemental powders and persistent liquid phase sintering, a high density powder metal Ti51Ni49 with a high phase transformation temperature and enthalpy, and narrow transformation hysteresis, which are comparable to those of wrought TiNi alloys, are produced. However, due to the presence of a semi-continuous Ti2Ni network, the shape recovery and tensile properties in the martensitic state at room temperature, determined using bending tests, are lower than those of cast TiNi counterparts. Through hot isostatic pressing and annealing above the peritectic temperature for sintered specimens, these properties are improved due to the increase in density and spheroidization of the Ti2Ni compound. The phase transformation temperature and enthalpy are also enhanced due to the continuing carbon absorption by the Ti4Ni2X (X = C, O) phase, which decreases the carbon content in the TiNi matrix.