Processing of Bi90Sb10 by Equal Channel Angle Extrusion - Texas A&M University (TAMU) Scholar

Cast billets of Bi90Sb10 have been processed by Equal Channel Angle Extrusion (ECAE) in an effort to make the alloy in a highly textured, polycrystalline form for use as a low-temperature n-type thermoelectric material. In this initial stage, we have focused on studying the evolution of the microstructure. The cast material has a random, mm-scale grain structure. As the material is deformed, there is a strong tendency toward a bimodal grain size distribution. Much of the sample readily refines to a fine grain size of 10 microns, while the remainder maintains a coarse grain size of 300 microns even after a large amount of plastic strain is imparted. We have found that the coarse grains are Bi-rich, while the fine grains are Sb-rich. An intermediate heat treatment that improved chemical homogeneity also improved microstructure uniformity achieved in subsequent multi-pass ECAE processing. We consider possible mechanisms by which chemical inhomogeneity leads to non-uniform grain refinement in Bi1-xSbx. In addition to homogeneity, texture is required to make good quality Bi 1-xSbx alloys. Pole figure analyses of our samples show that the ECAE process can be effective in creating crystallographic texture. 2008 IEEE.

Processing of Bi90Sb10 by Equal Channel Angle Extrusion Conference Paper