The formation process of Mg₂Si based thermoelectric composite made by mechanical alloying was investigated.
The MA was performed in a planetary ball mill using three elemental powders. The powders were prepared by the mixing of Mg₂Si, Mg₂Si-xmass%SiC(x=4, 8) and Mg₂Si-xmass%FeSi₂ (x=20, 40, 60, 80, 100). The structural evolution during milling was detected by X-ray diffraction(XRD). The heat treatment was monitored by differential scanning calorimetry(DSC). Microstructural changes were mainly investigated by means of scanning electron microscopy(SEM) and optical microscopy(OM).
The formation of the Mg₂Si phase is observed after milling for 1080ks under At atmosphere. But the milling time to form Mg₂Si became shorter by milling with including another element such as Fe, Si, N and SiC. The structure of Mg₂Si milled under N₂ atmosphere became most fine. For Mg₂Si-xmass%FeSi₂ including less than 60mass%FeSi₂, the phase of Mg₂Si, FeSi, Fe and Si were observed in the powder milled after 360ks. On the other hand, for Mg₂Si-80mass%FeSi₂, the phase of Mg₂Si and FeSi was not observed but Fe and Si was only observed independent on milling time.