Research on plastic deformation and machinability of zone-melted N-type bismuth telluride thermoelectric materials

Abstract

Bismuth telluride, a leading thermoelectric material in the medium-to-low temperature range, is widely used in thermoelectric cooling and power generation. However, its brittleness limits plastic deformation and machinability, restricting miniaturization of thermoelectric devices. This paper introduces a stress-temperature plasticizing process that enables bismuth telluride to achieve over 50 % plastic deformation. Finite element simulations indicate the material remains under compressive stress, preventing cleavage along its layered structure. SEM analysis reveals that post-deformation, the internal structure shifts to a wrinkled form. After 40 % plastic deformation, the hardness of the sample on the plane parallel to the pressure direction increased by nearly 60 %, with greater stress leading to a larger increase in hardness. Following 30 % plastic deformation, the minimum machining size of bismuth telluride bulk samples during chip cutting was reduced to 0.26 mm, significantly improving the machinability, while the ZT value remained comparable to that of the matrix, ensuring excellent thermoelectric performance.