Preparation of β-FeSi₂ Thermoelectric Coatings by Plasma Spraying of Mechanically-Alloyed Powders

Abstract

Much attention has recently been paid to thermoelectric conversion material (TEC) as one of the candidate technologies for energy saving. In many configurations of TEC, thick coating may be advantageous in laminating or joining. Thermal spraying, by which the thick coatings of hard-forming materials can be easily made, is worthy of remark among several processings. However, a conventional method, a spraying of blended elemental metals powder followed by post-heat treatment, is hard to apply because a strict control of elemental composition by delicate heat treatment is required to get the high performance TEC.
In this study, homogeneously mixed metal/metal composite powders, which were made by mechanical alloying (MA) process, were applied to plasma spraying in order to obtain the intermetallic TEC coatings, and the processing for getting the TEC coating was fundamentally investigated. The great merit of MA process is the possibility of controlling the additional dopant fraction and creating the fine and homogeneous structured composite powders.
Consequently, optimum conditions of mechanical alloying, plasma spraying and post heat treatment to get the appropriate thermoelectric phases for Fe-Si systems were empirically decided. Under the optimum conditions, the thermoelectric properties in the systems were estimated as a function of dopant molar fraction.