General discussion sessions of the pacific rim conference on the roles of shear and diffusion in the formation of plate-
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J.P. Hirth, Washington State University, U.S.A.; General Discussions Chairman: To begin the General Discussions, Hub Aaronson would like to take a few minutes to summarize the intent of the conference in order to set the stage for these discussions. Then, we can more or less follow the sequence of the conference organization and look at different aspects of phase transformations yielding plate-shaped products.
H.I. Aaronson, Geo-Centers/Naval Research Laboratory, U.S.A.: This conference arose from discussions among the four organizers and others concerning the increasingly contentious dichotomy that has developed amongst two quite different schools of thought as to the atomic mechanism through which plate-shaped transformation products form above the Ms (or Md) temperature. From the standpoint of the school espousing the shear or martensitic mechanism, if the shape change and the crystallography of the transformation product can be well explained by the phenomenological theory of martensite crystallography (PTMC), then the atomic mechanism of transformation is likely to be one in which the shear of parent into product phase is accomplished by the glide of transformation dislocations, supplemented, if necessary, by that of lattice-invariant deformation dislocations. The other school, advocating the ledgewise diffusional growth mechanism, views plates as the result of a strong anisotropy of the inter-growth ledge spacing, with the broad faces of plates forming at that boundary orientation at which this spacing (as normalized by the growth-ledge height) is a pronounced maximum. The migration of ledges, in this view, is controlled by the kinetics of (usually volume) diffusion in the matrix phase toward or away from kinks on the risers of growth ledges. Members of each school have recently H.I. AARONSON, Administrative Chairman for the Conference, is associated with Geo-Centers, Inc., Ft. Washington, MD and stationed in the Physical Metallurgy Branch of the Naval Research Laboratory, Code 6320, Washington, D.C. 20375. J.P. HIRTH, who chaired the General Discussion sessions and also served as Advisory Chairman to this Conference, is Professor, Department of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164. B.B. RATH, Conference Government Relations Chairman, is Associate Director for Materials Science and Component Technology of the Naval Research Laboratory, Washington, D.C. 20375. C.M. WAYMAN, Conference General Chairman, is Professor, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. This conference was held from Dec. 18 through Dec. 22, 1992 at the Kona Hilton Hotel, Kona, Hawaii, under the sponsorship of the Phase Transformations Committee of ASM INTERNATIONAL. The two General Discussions, which occupied most of the conference's time on Dec. 22, were tape-recorded, transcribed by Ms. Rene Wamsley, edited by the symposium organizers and then reviewed and modified by the contributors to the General Discussions prior to su
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