The effect of Mo additions to high damping Ti-Ni-Nb shape memory alloys

The effect of Mo addition on the microstructure, phase transformation, mechanical behavior and damping capacity has been investigated. It is found that the Mo addition depresses the solubility of Nb in the TiNi matrix and results in abundant dispersive Nb-rich precipitation. The R-phase transformation is induced in Ti-Ni-9.0 at.%Nb alloys by the substitution of Mo for Ni. The yield strength and rupture strength increase with increasing Mo content due to the precipitation strengthening of Nb-rich particles and the solution strengthening of the Mo, while the elongation remains at a high level. With the increment of Mo content, the damping in the martensitic state and the damping during the phase transformation are enhanced. The increment of the martensite volume fraction and the presence of abundant Nb-rich particles are responsible for the high damping in the martensitic state. The improvement of the damping properties during the phase transformation is related to the volume fraction of the transformed martensite phase per unit time and the contribution of the R-phase transformation.