NiTiAl intermetallic alloys strengthened by Mo replacement

NiTiAl based alloys have attracted attention as potential high temperature structural materials. Alloying is an effective way to improve their mechanical properties. The microstructures and mechanical properties of Ni ₅₀Ti_44-xAl₆Mo_x (x = 0, 0.5, 1, 1.5, 3) alloys have been investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and compressive tests. It is found that Ni₅₀Ti_44-xAl₆Mo_x alloy is composed of NiTi (B2) and Ti₂Ni (FCC) phases when Mo content is no more than 1 at. The effect of Mo solid solution hardening at room temperature has been indicated by the rise of yield strength and the fall of plasticity with increasing Mo content. For Ni₅₀Ti _42.5Al₆Mo_1.5 and Ni₅₀Ti ₄₁Al₆Mo₃ alloys, a Mo solid solution appears and increases the yield strength by precipitation strengthening. The maximum yield strength at 600 °C and elevated temperatures is presented in Ni ₅₀Ti₄₃Al₆Mo₁ alloy not in alloys with a higher Mo content, which is possibly due to the softness of Mo-Ti-Ni solid solution phase.