FABRICATION,TRANSFORMATION AND SUPERELASTICITY BEHAVIOR OF NiTi MEMORY ALLOY WITH LARGE PORE-SIZE AND GRADIENT POROSITY

Porous NiTi shape memory alloys with gradient porosity,large pore-size and satis- factory mechanical property were fabricated by using pore-forming agent combining with hot isostatic pressing(HIP)and conventional sintering process(CS).The results showed that the porosity ratio and pore-size can be changed in the ranges of 30%—61% and 50—500μm respectively under the reason- able addition amount of pore-forming agent(NH_4HCO_3)and sintering process.XRD and DSC proved the prepared samples exhibit multi-stage martensitic transformations,the transition temperature de- creases with increasing porosity.The sample with radial gradient porosity shows good compression property and excellent linear superelasticity higher than 4%.