Research On Structural Features And Performance Of β-FeSi₂ Prepared Through Laser Sintering

Thermoelectric material is a semiconductor material that can realize the direct conversion between thermal energy and electric energy, so it can serve as a good solution to the environmental problems and energy problems currently faced by the world.β-FeSi₂ thermoelectric material has a good performance in thermoelectric conversion in the temperature range from 200℃to 900℃, and its source material has such advantages of being abundant, free of pollution to the environment and possessing high inoxidizability, therefore, it enjoys a good application prospect.However, sinceβ-FeSi₂ semiconductor material only has a narrow phase tranformation range, it can easily contain bothε-phase andα-phase at the same time, which will lead to an obvious decrease of its thermoelectric performance. In addition, grain refinement will increase its thermoelectric performance. Therefore, the excogitation of a processing technique that can realize the preparation of single-phaseβ-FeSi₂ with refined grains is of great importance to its application. This thesis will study the processing technique of preparingβ-FeSi₂ by laser sintering, and the specific procedures are as follows:(1) First, the mixed powder will be ball milled and then the power that has been intensely and thoroughly mixed can be got, after which the power will be cold pressed into lumps for the convenience of sintering experiment. Then the lumps of power will be presintered in a tube vacuum furnace, in which process the sintering time and temperature's influence on the phase transformation of the alloy will be studied.(2) Laser sintering is applied to prepare specimen according to its advantages of rapid heating rate and high cooling rate. In this thesis, laser sintering is applied for the first time for the preparation ofβ-FeSi₂ material, and the sintering temperature field is simulated with the application of ANSYS in order to determine relatively good sintering parameters.(3) The study on sintering will be launched by two kinds of techniques: in the first technique, the presintered lumps will be laser sintered and the presintered alloy will be remelted to get micro crystalline grains through rapid solidification and moreβ-FeSi₂ phase through annealing; in the other technique, the powder lumps will be laser sintered directly, and then the specimen will be sintered for ninety seconds at the laser power of 500 watts, with the light spot radius of six millimeters after which single-phased and tinyβ-phase crystalline grains can be get through annealing.(4) At last, each test parameter's influence on the formation ofβ-FeSi₂ will be studied with the application of the analytical methods of XRD and SEM.In this thesis, the single-phasedβ-FeSi₂ material is got with the application of direct laser sintering, which provides a new method for the rapid preparation ofβ-FeSi₂ thermoelectric material with high performance.