Microstructure Size Control through Cooling Rate in Thermoelectric PbTe-Sb_2Te_3 Composites

Microstructures of alloys with three compositions in the pseudobinary PbTe-Sb_2Te_3 system cast in copper molds using the injection molding technique were examined by scanning electron microscopy (SEM), energy-dispersive spectrometry, and X-ray diffraction (XRD). The microstructural length scales such as interlamellar spacing (ILS) and secondary dendrite arm spacing vary over two orders of magnitude, e.g., from 0.2 to 20 μm for SDAS in the hypereutectic alloy, depending on injection pressure, distance from surface, or thickness. The decrease in the microstructural length scale with the decrease in distance from the surface, thickness, and increase in injection pressure is attributed to an increase in the cooling rates estimated using the heat-transfer theory in solids. The difference in the injection pressures is represented as the difference in the heat-transfer coefficients.