Phase Transitions in the Formation of Ti sub 5Si sub 3/TiAl In Situ COmposites and Their Multiplex Structures

摘要

A mixture of elemental Ti, Al, and Si powders with a stoichiometry of Ti-14Al-21Si has been mechanicallyalloyed for producing metastable phases. Differential thermal analysis and x-ray diffraction have been used to identify the phase reactions and transitions that occurred in th metastable phases during heating. It has bee nfoundthat Ti su 5Si sub 3 is in situ formed through a phase trasnition chian, i.e., TiSi sub 2-Ti sub 5Si sub4-Ti sub 5Si sub 3. THe metastable phases that serve as reinforcemetn-precursors wre incorporated into Ti-Al powder matrix, and a final Ti sub 5Si sub 3/Tial composite was obtained when the constituent powders underwent a reactive sintering process followed byhot isostatic pressing. Scanning electron microscop observations revealed a hierarchical sructure including phases alfa sub 2, gamma and titanium silicides, and, more interestingly, an evident peripheral zone around the in situ silicide was foundto have fored during the composite formation. It is expected that this zone may take a differnet role in improving the ocmposite properties than the interfacial zone comonly formed in composite preparation using other methods. In addition, elemental Si powders of two different starting sizes were tried to evaluate the effect of the size of Si on the composite formation in this manner.