Rapid Homogenization of Bi0.85Sb0.15 Alloy by Equal Channel Angular Extrusion

Equal Channel Angular Extrusion (ECAE) was tested on as-cast Bi0.85 Sb0.15 alloys of different purity (4N and 5N), with the aim of eliminating microstructure inhomogeneities (Sb segregation on dendrite arms). The homogeneity degree promoted by hot plastic deformation was monitored by optical microscopy, SEM, X-ray diffraction, differential thermal analysis and electron microprobe analysis. After 6 ECAE passes at 523 K no trace of dendrites was observable at optical microscope; the micro-homogeneity, however, improved with further increasing the number of passes. High density material was obtained, with an average grain size of about 20 ?m. In the temperature range of 90 to 300 K, the variation of the Seebeck coefficient of the ECAE processed alloys, prepared from 5N purity starting elements, approaches the behaviour of single crystals of similar composition; at temperatures above 150 K, the figure of merit is higher than in single crystals.