Hume-rothery symposium on structure and diffusional growth mechanisms of irrational interphase boundaries foreword
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Prof. Hubert I. Aaronson This symposium was organized in honor of the 2004 Hume-Rothery Award, which was presented to Professor Hubert Aaronson in conjunction with the celebration of his 80 th birthday. Although Professor Aaronson performed the organizational work on this symposium and its proceedings, it is quite sad that he did not live to see the final symposium proceedings in print, having succumbed to a long illness on December 13, 2005. “Hub,” as he was known to most of his students, colleagues, and friends, will be remembered for his reputation as one of the world’s foremost scientists in the area of classical physical metallurgy and solid state phase transformations, for his legendary work ethic, and for the lavish meals and festivities that he often bestowed on his friends and students over the years. He will mostly, however, be remembered for his unwavering and unselfish compassion for his friends, particularly for his many graduate students around the world, whom he often referred to as his “family.” The remainder of this foreword was reconstructed from the proposal that Professor Aaronson submitted to Metallurgical and Materials Transactions for the publication of this symposium. When atom patterns and spacings at an interphase boundary match poorly, the structure of this boundary has long been considered to be incoherent. A generally accepted crystallographic basis for incoherency is the presence of an irrational orientation relationship and irrational (and ill-matched) conjugate habit planes. The presence of planar interphase boundaries so characterized has been urged by some, however, as an indication that an interfacial structure with a sufficiently low interfacial energy is present to inhibit the migration of these boundaries significantly and to ensure their planarity. During a symposium on “The Mechanisms of the Massive Transformation,” the proceedings of which were published in the August 2002 issue of Metallurgical and Materials Transactions A, this debate dominated many of the articles and the General Discussion held at the end of the symposium. Although most of the articles favored the view that planar irrational interphase boundaries are incoherent, two articles suggested that low-energy boundaries can be formed by matching of atom patterns and spacings at the edges of planes of low indices (termed edge-to-edge matching) instead of at the faces of planes. The detailed nature of interphase boundaries at such irrational interfaces thus became the major topic of the current symposium. The first two articles published in this symposium (by Aaronson et al. and Massalski et al.) are thought-provoking overviews on the nature of interphase boundaries at irrational interfaces. Of the remaining articles, more than half are theoretically based. Articles centered about experimental studies of interphase boundary structure in a number of transformations, including the massive transformation, are included as well. Finally, a General Discussion concludes these proceedings. This discussion was recorded, tra
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