Processing and damping capacity of NiTi foams with laminated pore architecture

Abstract

N_50.5Ti_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_50.5Ti_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 Ni₄Ti₃ precipitates. By contrast, the aged Ni_50.5Ti_49.5 foam showed two-step B2→R→B19' MT with homogeneous nano-sized Ni₄Ti₃ 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.

Keywords: Damping capacity; Foam; Martensite transformation; Powder metallurgy; Shape memory alloys (SMAs).