Synthesis Behavior of Ti-50.0∼66.7at%Si Powders by In situ Thermal Analysis during Mechanical Alloying

Abstract

Mechanical alloying (MA) of Ti-50.0～66.7at%Si powders was carried out in a high-energy ball mill, and in situ thermal analysis was also made during MA. In order to classify the synthesis behavior of the powders with respect to at%Si, the synthesis behavior during MA was investigated by in situ thermal analysis and X-ray diffraction (XRD). In situ thermal analysis curves and XRD patterns of Ti-50.0～59.6at%Si powders showed that there were exothermic peaks during MA, indicating TiSi, <TEX>$TiS_2$</TEX>, and <TEX>$Ti_{5}$</TEX> <TEX>$Si_4$</TEX> phase formation by a rapid exothermic reaction of self-propagating high-temperature synthesis (SHS). Those of Ti-59.8～66.7 at%Si powders, however, showed that there were no peaks during MA, indicating any Ti silicide was not synthesised until MA 240 min. For Ti-50.0～59.6at%Si powders, the critical milling times for SHS increased from 34.5 min to 89.5 min and the temperature rise, <TEX>$\Delta$</TEX>T (=peak temperature-onset temperature) decreased form <TEX>$26.2^{\circ}C$</TEX> to <TEX>$17.1^{\circ}C$</TEX> as at%Si increased. The critical composition of Si for SHS reaction was found to be 59.6at% and the critical value of the negative heat of formation of Ti-59.6at%Si to be -1.48 kJ/g.