Toward the overthrow of half of a major paradigm for interfacial structure deduction, with special attention to the massive transformation in Ti-46.5 A/O Al alloy

Abstract

In parallel with the successful development of the theory of dislocations within a given phase, the theory and also the experimental knowledge of interphase boundaries made partially coherent by the presence of misfit dislocations and/or other linear misfit compensating defects have greatly advanced. The central idea to be offered on the connections, or lack thereof, among orientation relationship (OR), habit plane and electron microscopically observed interphase boundary structure in this paper, though yet to be proved fully, suggest the unfolding of yet another level of complexity--and perhaps also of clarity--in evaluating the structure of interphase boundaries. The massive transformation is a special case in point. Studies of interphase boundary structure with TEM are notoriously difficult to perform on this reaction because its usually swift growth kinetics often transform largely or completely the matrix phase even during relatively rapid cooling. Even if a sufficient proportion of the matrix phase is not consumed by the massive transformation, a martensitic transformation taking place subsequently during quenching to room temperature will destroy all of the remaining matrix phase. These problems can either seriously inhibit or altogether prevent direct TEM study of the interphase boundary structure. The preliminary report on the structure of (hcp) {alpha}:(L1{submore » 0}) {gamma}{sub m} interfaces formed during the {alpha} {yields} {gamma}{sub m} massive transformation in a Ti-46.5 A/O Al alloy included in this paper is thus only the second on massive:matrix interfacial structure based on TEM yet to appear in the literature.« less