Abstract Samples of a TiNiSn half-Heusler thermoelectric alloy were prepared using arc melting and rapid solidification by planar flow casting. On the one hand, arc melted samples show multiple phases and need long annealing time to be homogenized into a single phase. On the other hand, rapidly solidified samples show an almost single phase, with a grain refined microstructure. This result is a consequence of the melt undercooling, that allows to bypass the primary solidification of TiNi2Sn full-Heusler and to hinder grain growth. Rapidly solidified samples were consolidated into dense bulk samples by means of open die pressing. The grain refined microstructure obtained by rapid solidification is maintained after sintering, leading to a reduced lattice thermal conductivity, due to a scattering of phonons at grain boundaries. The role of the residual secondary phases (Ni3Sn4, TiNi2Sn and Sn) on the electrical conductivity and thermopower is discussed in the framework of the effective medium theory and related models, explaining the dispersion of thermoelectric properties observed in the literature for nominally stoichiometric TiNiSn. Thermal cycling above 700 K causes surface oxidation, leading to altered thermoelectric properties.

中文翻译：

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二次相和热循环对不同加工工艺制备的TiNiSn半赫斯勒合金热电性能的影响

摘要 采用电弧熔化和平面流铸快速凝固方法制备了TiNiSn半赫斯勒热电合金样品。一方面，电弧熔化样品呈现多相，需要较长的退火时间才能均匀化为单相。另一方面，快速凝固的样品显示出几乎单相，具有晶粒细化的微观结构。这个结果是熔体过冷的结果，它允许绕过 TiNi2Sn 全赫斯勒的初级凝固并阻碍晶粒生长。快速凝固的样品通过开模压制被固结成致密的块状样品。由于声子在晶界处的散射，通过快速凝固获得的晶粒细化微观结构在烧结后得以保持，导致晶格热导率降低。在有效介质理论和相关模型的框架中讨论了残余第二相（Ni3Sn4、TiNi2Sn 和 Sn）对电导率和热电势的作用，解释了文献中观察到的名义化学计量 TiNiSn 热电性能的分散。高于 700 K 的热循环会导致表面氧化，从而导致热电特性发生改变。