The structure of a new epsilon-phase formed during the early stage of crystallization of Ti-48 AT.% Al amorphous film

The early stage of crystallization of a Ti-48 at.% Al amorphous thin film h as been investigated by transmission electron microscopy (TEM). A novel pha se denoted as an epsilon-phase with a cubic lattice of a=0.69 nm was found to precipitate in the amorphous matrix, together with the high-temperature alpha-Ti phase. Chemical analysis by energy-dispersive X-ray spectroscopy r evealed that alpha and epsilon-phases have the approximate composition of T i-48 at.% Al, suggesting an isoconcentrational formation process. The struc ture of the new epsilon-phase has been determined to be a beta-Mn type (P4( 1)32) with atomic sites occupied randomly by Ti and Al atoms, based on clos e examination of the electron diffraction intensities and the high-resoluti on TEM image contrasts with the aid of computer simulations. The Ti and Al atoms in this structure are shown to be packed densely according to an icos ahedrally close-packed manner. The epsilon-phase is attributed to a metasta ble phase which could appear at high temperatures in the Ti-Al system. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights r eserved.