Fabrication Of Porous NiTi And Effect Of C, O Impurities On The Properties

NiTi shape memory alloy has been widely used in the medical field for its unique shape memory properties, excellent biocompatibility and good corrosion resistance. Porous NiTi have favorable combined above properties, and have two more advantages:First, open porosity can enhance bone ingrowth and thus fixation at the interface between bone and implant. Second, porous decrease the mismatch in stiffness between bone and implant, thus reducing stress-shieding effects. Thus, porous NiTi is very promising as implant materials.Porous NiTi was produced by conventional powder metallurgy process with sodium chloride (NaCl) as spacer holder. The work investigated the effect of sintering temperature, particle size and amount of NaCl on structure factors including the porosity, pore size and distribution, and mechanical properties. Different C, O contents obtained through aging treatment, the effect of C, O impurities on the properties are systematic investigated. The results of this work are as follows:With the increasing of sintering temperature, the porosity increase at first and then decrease, reach the maximum when sintered at1050℃. the fracture strength and fracture strain of porous NiTi increase, and the optimum temperature is1050to1100℃.With the same addition NaCl of different particle size, the change in porosity is not significant, but the pore size decreases with the decreasing of particle size. The pore size of porous NiTi with NaCl60-100mesh as spacer holder is50-300μm, the compressive shape-memory recovery capability is similar to the pore-free NiTi.With increasing addition NaCl, the porosity increases, ranged from39.1%-72.3%, and percentage of pore bigger than50μm increase too. The samples with50,60and70(vol%) addition could fabricate NiTi with porosity of55.2%,64.5%and72.3%respectively. Up to45%of the pore size is bigger than50μm, which can form interconnected structure. Meanwhile, the elastic modulus can be adjusted at the range of1.5～10.8GPa, which is close to the elastic modulus of bone(01-27GPa).Aged at300℃for different time, C,O contents increase a little with aging time. With increasing the aging temperature, C,O content increase sharply, when aged at600℃, O content reached at4.30%. The presence of C,O impurities results in the formation TiC and Ti4Ni2Ox, with increasing O contents, the Ti4Ni2Ox increase, aggregation and grew up.With increasing O contents, phase transformation temperature decrease, mechanical properties change little at first, but then decrease sharply when O content increase from1.83%to4.30%, the high volume fraction of big Ti4Ni2Ox cause the brittle before load to8%strain。...