The structure of a new ε-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 has been investigated by transmission electron microscopy (TEM). A novel phase 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 revealed that alpha and epsilon-phases have the approximate composition of Ti-48 at.% Al, suggesting an isoconcentrational formation process. The structure 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 close examination of the electron diffraction intensities and the high-resolution 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 icosahedrally close-packed manner. The epsilon-phase is attributed to a metastable phase which could appear at high temperatures in the Ti-Al system. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.