Property and Preparation of Porous NiTi Shape Memory Alloy

Porous NiTi shape memory alloy(NiTi SMA) was fabricated by powder metallurgy technology using ball milled NiTi powder as raw material and adding urea as a pore-forming agent.The effects of sintering temperature,holding time and pre-forming pressure on the microstructure and mechanical properties of the prepared porous NiTi SMA was studied.The results show that: compared with conventional sintering of mixture powder of Ni and Ti,the phase constituents of the porous NiTi alloy made by this method is more pure.And with the increasing of the sintering temperature,the pore size of porous NiTi alloy gradually increases,the pore distribution tends to be uniform,and compression strength is increased.With the extended holding time,pore size is decreased,the phenomenon of liquefaction is obvious and the strength is increased.There is an optimal value of the pre-forming pressure,and the porous NiTi alloy products can be well produced by the optimal pre-forming pressure.And the process of adding 70% pore-forming agent,pre-forming under the pressure of 150MPa,and holding at 1050℃ for 5h were ultimately determined,the porous NiTi alloy fabricated under the conditions has excellent property.