Porous Ni–Ti–Nb Shape Memory Alloys with Tunable Damping Performance Controlled by Martensitic Transformation

Porous Ni–Ti–Nb shape memory alloys (SMAs) with designed porosities and compositions were prepared by the powder metallurgy technique. The phase-transformation-controlled damping behavior of the porous alloys was investigated by dynamic mechanical analysis (DMA). Systematic microstructural study indicates that both the pore configuration and Nb distribution in the matrix of porous Ni–Ti–Nb alloys have significant influence on the damping performance of the alloys. Increase in both pore size and porosity in micro-scale leads to obvious decrease of the internal friction, while addition of Nb brings dramatic increase in the damping capacity of the porous alloys. The damping capacity can be optimized by adjusting the Nb/NiTi ratio, which balances the competitive contribution of Nb/matrix and B2/B19′ interfaces to the internal friction during martensitic transformation. Moreover, β-Nb phase of lamellar structure in the matrix plays a greater role in the internal friction than that of granular shape by offering a large amount of interfaces.