Synthesis of porous Ni-Ti shape-memory alloys by self-propagating high-temperature synthesis: Reaction mechanism and anisotropy in pore structure

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 mu m. 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 degrees 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 pole structure is attributed to the convective flows of Liquid and argon during combustion. (C) 2000 Acm Metallurgica Inc. Published by Elsevier Science Ltd. Ali rights reserved.