Study On The Microstructure And Properties Of As-Cast Ti-Ni-Sn Materials

Thermoelectric materials are currently being investigated for their potential against the problems of energy and environment. They can be served as a substitution of traditional energy. TiNiSn materials were prepared in arc furnace under Ar atmosphere. Corrosion properties, morphology, physical properties, and some mechanical properties of TiNiSn material were investigated.XRD analysis of as-cast TiNiSn material showed that it was difficult to get single-phase TiNiSn. TiNi2Sn, Ni3Sn2, TiNi, Ti3Ni4, Ti6Sn5, and Sn were tested in the sample. Results of energy spectrum analysis of the as-cast sample showed that there were Ti6Sn5 and TiNi2Sn phases, and also there were some micro-cracks in the material. TEM image of as-cast TiNiSn material and diffraction pattern on appointed site showed that there were Ti6Sn5 and Ti3Ni4 in the as-cast TiNiSn material.Results showed that resistance ability of corrosion in 3wt.% NaCl solution can be improved by heat treatment. The as-cast sample corroded fast, there are pitting corrosion and surface tension corrosion. It was corroded thoroughly after 25 days. There are not pitting corrosion on the sample treated for 96 hour, and this sample was not corroded thoroughly until the 55th days. There were many casting flaws and processing stresses in the as-cast and heat treatment samples. And the corrosion started from those areas. Pitting flaws in the sample of 96 hours heat treatment in vacuum furnace were basically eliminated, but the processing stresses still existed. Corrosion of this sample was mainly surface tension corrosion. Results of XPS showed that Sn was oxidized on surface of the sample. Ti and Ni were corroded off the surface of the sample.There are significant passivation areas in samples treated for 48h and 96h, current density of sample treated for 96h is higher than sample treated for 48h. With increase of heat treatment time, corrosion resistance increases.Results of the physical property showed that with the increase of the temperature, electrical resisitivity of the as-cast TiNiSn material decreased. Seebeck coefficient, heat conductivity, and ZT value increased. The mechanical experiment indicated that TiNiSn material was brittle material. Heat treatment could improve hardness of the material.