Microstructure control and thermoelectric properties improvement to n-type bismuth telluride based materials by hot extrusion

In this paper, hot extrusion process of Bi2Te3 based thermoelectric materials was simulated with FEM tools firstly, it is found that the friction condition between the extrusion die and the sample has large influence on the surface stress state of the sample, making the surface region under more tension stress, thus increases the possibility of surface crack. Extrusion ratio has significant influence on the degree of deformation. Extrusion angle also shows effect on the deformation, low extrusion angle die has longer or larger regions of deformation, which means lower deformation rate and will cause less micro-pores. Then n-type Bi2Te3 based materials were also hot extruded under different experiment conditions, and effect of extrusion parameters on microstructure and thermoelectric properties of the materials was studied, and a (0 0 l) preferred orientation microstructure was formed in the hot extruded samples. With increasing the extrusion ratio, the Lotgering orientation factor of the extruded sample increases, and the power factor also shows a magnificent increase. The experimental results are in consistence with the results of FEM analysis.