Synthesis of TiAl-based Nano-and Submicro-grained Precursors by Mechanical Alloying

摘要

Supersaturated solid solution of Ti and small-grained intermetallic compounds were produced by mechanical alloying (MA) from elemental powders of Ti, Al, Si and C. These compounds are of immense use in the synthesis of high performance alloys through in situ pressure sintering. Blended compositions of Ti-30Al-6Si-6C (at%) and Ti-15Al-20 Si-15C(at%) were milled for a maximum period of 40 hours using a planetary ball-mill. The transformations that were occurring during MA process were studied using the samples withdrawn at several intermittent periods. The structural and compositional evolutions have been investigated by X-ray diffraction method (XRD) and scanning electron microscopy (SEM). XRD results showed that supersaturated solid solutions of Ti were formed for powder mixture of Ti-30Al-6Si-6C after 20h milling, while Ti_5 Si_3 and TiC compounds were produced in the powder mixture of Ti-15Al-20Si-15C just after 5h milling. With further milling to 40h the particle sizes obtained were in nano-and submicro-scales in both cases, but no major structural changes have been detected for both powder mixtures ; only the peaks broadened indicating decrease in grain size. This investigation indicated a promising way of producing several important intermetallic and ceramic compounds of ultra-fine grain sizes in the nanometer or sub-micro dimension that may subsequently be preserved while synthesizing TiAl-based composites.