In situ composite formation in Ti-Al-Si ternary system

Three stoichiometric TiAlSi-based metastable alloys (i.e. Ti-14Al-21Si, Ti- 11Al-21Si and Ti-9Al-27Si, at.%) have been synthesized by mechanical alloyi ng (MA). It has been found, by means of X-ray diffraction (XRD) and transmi ssion electron microscope (TEM), that these metastable phases (or precursor s) are mainly in nano-structures, with partially amorphous phases as for th e alloy Ti-14Al-21Si. Importantly, investigation of these metastable phases during heating (by using differential thermal analysis, DTA) shows a hiera rchical change in phase transition, and particularly Ti5Si3 is in situ form ed via a phase transition path TiSi2 --> TiSi --> Ti5Si4 --> Ti5Si3. This i s meaningful in materials design using a kinetics bias strategy. Microstruc tures of fully densified Ti5Si3/TiAl in situ composites have been observed by optical microscope. (C) 1999 Elsevier Science S.A. All rights reserved.