Processing and damping capacity of NiTi foams with laminated pore architecture

N _50.5 Ti _49.5 foams with porosity 25.5% were prepared by transient liquid sintering process. Laminated pore architecture was created in the foam via pre-mixing Ni and Ti powders layer-by-layer. The foam consists of alternate less porous alloy layers with discontinuous closed pores and highly porous layers with continuous open pores. The sintered Ni _50.5 Ti _49.5 foams exhibited three-step martensite transformation (MT), i.e. B2→ (R + B19′), B2→B19′ and R→B19′, due to the presence of heterogeneously distributed micron-sized Ni ₄ Ti ₃ precipitates. By contrast, the aged Ni _50.5 Ti _49.5 foam showed two-step B2→R→B19′ MT with homogeneous nano-sized Ni ₄ Ti ₃ phase. Anisotropic compressive strength and modulus were found in the sintered foam. The sintered foam had a high damping capacity (tanδ = 0.047) in the martensite and low damping capacity (tanδ = 0.002) in the austenite. However, the aged foam exhibited improved damping capacity (tanδ = 0.01) in the austenite. The enhanced damping capacity of austenite was attributed to the localized plastic deformation in nodes/struts and stress-induced B2-R MT. Furthermore, a damping peak at a temperature of 130 °C related to the (R + B19′)→B2 transition during heating was confirmed. The laminated pore architecture foams with anisotropic mechanical properties may be promising candidate materials for bio- and mechanical applications.