Mechanical alloying characteristics and thermal stability of Ti-Al-Si and Ti-Al-Si-C powders

Several stoichiometric ternary Ti-Al-Si and quaternary Ti-Al-Si-C alloys have been prepared by mechanical alloying of elemental powder blends. The structural and morphological evolutions in these powders are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results have shown that the elemental powders Ti-Al-Si are progressively transformed into a nanocrystalline solid solution and amorphous phase during mechanical alloying. The results for the powder mixture of quaternary 58Ti-30Al-6Si-6C have shown that supersaturated solid solutions of Ti in nano- and submicro-scales are formed, while Ti₅Si₃ and TiC compounds are produced in the powder mixture of 50Ti-15Al-20Si-15C. These compositions may be used as distinct precursors for preparing in situ titanium aluminide composites. Investigations on thermal stability of 40 h-milled quaternary powders have indicated that Ti₅Si₃ is first formed at a lower temperature followed by Al₂Ti₄C₂ and TiC at an intermediate temperature (820 °C). In the case of ternary system a stable Ti₅Si₃ phase is formed through a series of transitions when heated to 1200 °C. All the above phases are stable at elevated temperatures.