STRUCTURE EVOLUTION OF AMORPHOUS TI-AL-SI DURING ANNEALING

Structure evolution of amorphous phase obtained by mechanical alloying for Ti-Al-Si during the annealing treatment was investigated. Microst ructure development was monitored by X-ray diffraction, differential t hermal analysis and transmission electron microscopy. The structure ev olution of the amorphous phase treatment can be classified into the fi rst stage partial crystallization of amorphous phase producing Ti5Si3 phase, the second stage crystallization of the remaining amorphous pha se producing the corresponding titanium aluminides, and last grain gro wth of all. Crystallization results in the formation of Ti3Al, TiAl an d Al3Ti according to the relative amount of elemental mixtures of Ti a nd Al. Ti5Si3 is the only titanium silicide produced by crystallizatio n. Annealing at less than 800 degrees C produced nanocrystalline compo sites of Al3Ti, TiAl, Ti3Al and Ti5Si3 with a grain size less than 20 nm. At high annealing temperature crystalline sizes of all phases incr ease. (C) 1997 Elsevier Science B.V.