Mechanical Properties of NiTi-Based Foam with High Porosity for Implant Applications

In order to better understand NiTi-based shape memory alloy foams for implant applications, Ni₄₀Ti₅₀Cu₁₀ foams were heat treated and then deformed under incremental and cyclic compression loading. After heat treatment, the microstructure consists of a (Ni,Cu)Ti matrix with small (Ni,Cu)₄Ti₃ precipitates and a large Ti₂(Ni,Cu) secondary phase. The heat-treated Ni₄₀Ti₅₀Cu₁₀ foam exhibits a two-step transformation, involving B19′ → B19 and B19 → B2 on heating and B2 → B19 and B19 → B19′ on cooling, respectively. One Ni₄₀Ti₅₀Cu₁₀ foam was compression loaded for 10 cycles at each subsequent strain level, i.e., 1, 2, 3, 4, 5, and 6 % strain. In each set of compressive stress–strain loops, the maximum stress level decreases due to plastic damage accumulation and/or retention of transformed martensite. Cross-sectional images from micro-computed tomography were collected during compression loading, which shows very uniform deformation without severe structural damage even up to 5 % strain. Localized deformation is visible at 6 % strain.