FEATURES OF A EUTECTOID REACTION IN A TI-40 AT-PERCENT AL-ALLOY - EVIDENCE FOR AN AMORPHOUS-STATE FORMATION FROM A CRYSTAL

In an initial stage of a eutectoid reaction of a Ti-40 at. % Al alloy, hcp-->D0(19)+L1(0), an amorphous state was found to form around an in termediate precipitate with the B-19 structure, together with a change in crystal structure of the matrix from the hcp structure to the D0(1 9) one. Characteristic features of the amorphous state are that the de struction of the crystal lattice mainly takes place in the (001) plane of the D0(19) structure but is very slightly extended along the [001] direction. The shape of the amorphous region is just like a thin film . On the basis of the present data, the origin of the two-dimensional- like character of the lattice destruction is simply discussed.