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 atte ntion 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 line ar-aligned elongated pore structure, have been successfully prepared by sel f-propagating high-temperature synthesis (SHS) using elemental nickel and t itanium powders. The porous Ni-Ti SMAs thus obtained have an open porous st ructure with about 60 vol.% porosity, and the channel size is about 400 mu m. The corresponding microstructural characteristics and the effect of preh eating temperature on the microstructure have been investigated. It is foun d that the combustion temperature increases with increasing preheating temp erature and results in melting of the NiTi compound above 450 degrees C. Mo reover, the preheating temperature has been shown to have a significant eff ect 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.