Studies on the Precision Casting of NiTi Shape Memory Alloy

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Ni-Ti alloys which consist of nickel and titanium in nearly equal atomic proportions possess unique mechanical properties, such as shape memory effect and super-elasticity. They are expected a lot of application not only for industrial use but also medical and dental use. As the fabrication of these alloys is so difficult, the precision casting processes are useful where intricate shapes or high dimensional accuracy are required. However, there are a lot of problems in the casting of titanium alloys, because the molten titanium alloys are so reactive, both with the atmosphere and the refractory mold. In this study, the precision casting of NiTi alloys were studied.In the casting machine which we developed, as gas in the mold was removed by heating the mold in the high vacuum, oxidation of metal was less and reaction between alloy and mold was much decreased. NiTi alloys could be cast without losing their important properties, even with commercial dental phosphate bonded silica investme … More nt. The mechanical properties and castability of these alloys are practical and useful in the dental field.The corrosion resistance was much improved by the addition of Au, and the levels of Ni ion concentration released from the alloys decreased considerably compared with those of the original Ni-Ti alloys. The application of NiTi alloy to artificial joints was examined in wear and corrosion tests. The better fitness between NiTi alloy head ball and the hdp socket was obtained than that of commercial femoral head and socket. NiTi alloy is expected to be a promising candidate for artificial joint materials. Ni-Ti alloys showed higher breake down potential in anodic polarization curves than those of commercial Ni-Cr and Co-Cr alloys. The amount of Ni cations dissolved from Ni-Ti alloys in 0.9% NaCl solution is by far lower than those from commercial dental alloys. The properties NiTi alloys were much influenced by the heat treatment condition.The results obtained in this study seem to be useful for industrial, medical and dental field. Less