Phase transitions in reactive formation of Ti5Si3/TiAl in situ composites

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Original languageEnglish
Pages (from-to)763-771
Journal / PublicationMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Issue number3
Publication statusPublished - 2000


A new method is developed for preparing Ti5Si3/TiAl in situ composites by incorporating metastable phases (called metastable precursors) into TiAl (a mixture of elemental Ti and Al) matrix powders. Metastable precursors with a starting composition of Ti-14Al-21Si are prepared by mechanical alloying (MA). They have been proven through X-ray diffraction (XRD) analysis and transmission electron microscope (TEM) observations to be mainly consisting of mixtures of nanostructured solid solutions and milling-formed TiAl compound. Particularly, phase reactions and transitions in the precursors and the composites during heating have been investigated in detail by using diffraction thermal analysis (DTA) in conjunction with XRD. It has been found that Ti5Si3 is in situ formed through a phase transition chain, TiSi2→Ti5Si4→Ti5Si3. When the composite powder (precursor, Ti and Al) is heated, a combustion reaction first occurs in the matrix, which results in the formation of TiAl3 and/or TiAl followed by the completion of the previously mentioned silicide transitions in a very short time. Scanning electron microscope (SEM) observations indicated the locations of reinforcements in the reaction-formed composite, and TEM observation provided some details of the structures for the reinforcements and their neighborhood. This method is intriguing because a designed phase hierarchy is possible.