Synthesis of porous Ni–Ti shape-memory alloys by self-propagating high-temperature synthesis: reaction mechanism and anisotropy in pore structure Original Research Article

Porous Ni–Ti shape-memory alloys (SMAs) have attracted a great deal of attention recently because they have a similar microstructure to human bone and have significant prospects in medical applications. In the present study, equiatomic porous Ni–Ti SMAs, especially those with an unusual kind of linear-aligned elongated pore structure, have been successfully prepared by self-propagating high-temperature synthesis (SHS) using elemental nickel and titanium powders. The porous Ni–Ti SMAs thus obtained have an open porous structure with about 60 vol.% porosity, and the channel size is about 400 μm. The corresponding microstructural characteristics and the effect of preheating temperature on the microstructure have been investigated. It is found that the combustion temperature increases with increasing preheating temperature and results in melting of the NiTi compound above 450°C. Moreover, the preheating temperature has been shown to have a significant effect on the microstructure of the SHS-synthesized porous Ni–Ti SMAs, and the mechanism of anisotropy in pore structure is attributed to the convective flows of liquid and argon during combustion.