A tribute to Terence E. Mitchell
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6/30/04
19:45
Page 2203
A Tribute to Terence E. Mitchell S.S. HECKER
THIS volume of Metallurgical and Materials Transactions, based on the symposium held in his honor, allows us to pay tribute to Terence E. (Terry) Mitchell for his many contributions to materials science. It is a pleasure and a special honor for me to present the opening remarks. I was one of Terry’s first students at Case Western Reserve University. My colleague, Robert Smialek, and I did an undergraduate senior research project with Terry and published our first scientific article based on that research. I will not attempt to give a detailed listing of Terry’s many contributions. Instead, I’ll focus on three areas that I consider especially remarkable about Terry: The breadth of his scientific impact, the depth of his collaborations, and his love of life, family, and the outdoors. Terry began his scientific career in the area of metals and alloys at Cambridge, where he received his Ph.D. degree with Professor Peter Hirsch. Sir Peter Hirsch[1] recently stated that, “His thesis was remarkable for the vast range of experiments carried out on copper and -brass single crystals, for the critical assessment of some of the relevant theory current at that time, and for the theoretical calculations of stress fields from pileups of primary dislocations and the amount of slip induced on secondary systems. These calculations . . . represented an important first step toward a self consistent theory of work hardening.” At Case Western Reserve University, he performed critical experiments on dislocation behavior in the body-centered-cubic (bcc) metals niobium and tantalum, demonstrating that intrinsic lattice friction is dominant in determining yielding and plasticity, and that impurity effects are additive. He and his colleagues also performed systematic internal friction experiments on the dislocation relaxation peaks in bcc metals to reveal the important role of impurities. At Case, Terry teamed with colleague, Professor Arthur Heuer, to begin a systematic study of the mechanical behavior and phase transformations in ceramics. Terry’s knowledge of dislocations and his expertise in transmission microscopy combined with Professor Heuer’s knowledge and expertise in ceramics brought a new, fundamental dimension to the understanding of these phenomena in ceramics. Together, they transformed the field. Notable achievements include the first observation of dislocation deformation substructures in ceramic oxides to explain quantitatively work hardening, solution hardening, and precipitation hardening behavior, as well as the first observation of the climb dissociation of a dislocation (in alumina) in any material. They also used electron microscopy to systematically study phase transformations in ceramics, for example, polytypism in silicon carbide, preS.S. HECKER, Senior Fellow, is with the Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545. Contact e-mail: [email protected] This article is based on a presentation in the s
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