from the conferences organized by TANGER Ltd. provisional website
Alloys based of the Ni-Ti binary system have important position in a branch of shape memory alloys. Zirconium is an important alloying element giving these alloys needed stability at high-temperature applications. The aims of this paper were a preparation of the Ni-35Ti-15Zr and Ni-45Ti-5Zr (at.%) alloys, description of their microstructures and monitoring of their purity. The alloys were melted by plasma metallurgy processes. Metallographic samples were prepared from a central part of the ingot. The optical and scanning electron microscopes were used for documentation of microstructure. In both cases, the microstructure was polycrystalline with random orientation of grains. Individual grains consisted of dendrites formed by the NiTi-phase. On the contrary, interdendritic space was rich with Zr, eventually it contained undesirable inclusions of TiC and ZrO2. They form in consequences of chosen technology of preparation in combination with high melting temperature. Because titanium is significant picker, contents of oxygen and carbon were monitored in the ingot samples of both alloys. The Ni-45Ti-5Zr alloy contained of 0.115 wt.% O2 and of 0.013 wt.% C. For the Ni-35Ti-15Zr alloy, the content of O2 was 0.103 wt.% and content of C was 0.012 wt. %. Compared to industrially manufactured NiTi-based memory alloys, contents of both elements should not exceed C < 0.07 wt.% and O2 < 0.05 wt.%. We can submit that chosen method of preparation – plasma metallurgy – did not prevent the oxidation of both alloys, even though the melts were in a protective atmosphere of Ar with a purity of 4N6. By contrast, the carbon content remained in the standard.Keywords: NiTiZr alloys, microstructure, plasma metallurgy, purity
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