Deformation by moving interfaces
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Deformation by Moving Interfaces
J.W. CHRISTIAN R. E Mehl Medalist
Quite large strains may be produced by the migration of glissile interfaces in processes such as deformation twinning, martensitic transformation, and variant conversion in a martensitic product. In the absence of appreciable dislocation glide, the atomic displacements associated with moving boundaries constitute highly ordered and reversible modes of either plastic or nonlinear pseudo-elastic deformation. Pure interface deformation is most readily obtained in specimens in which preexisting interfaces move under relatively small applied stresses and there are then well-defined limiting strains associated with a given distribution of interfaces, but in some alloys it is also possible both to nucleate and to grow reorientated or transformed regions at stresses lower than those at which dislocation deformation begins. Reversibility of interface-produced deformation leads to such phenomena as elastic twinning, thermoelastic martensite, superelasticity, shape memory and two-way (or reversible) shape memory effects, and rubber-like (or ferro-elastic) behavior. It now seems possible to provide a unified description of these effects and to include discussions of the strains which may be obtained from various interface configurations, the competition between dislocation and interface-produced deformation, the importance of elastic accommodation, geometrical and atomic models of coherent and semicoherent interfaces and of twinning and transformation dislocations, and the mechanisms of nucleation and growth.
The Institute of Metals Lecture was established in 1921, at which time the Institute of Metals Division was the only professional Division within the American Institute of Mining and Metallurgical Engineers. It has been given annually since 1922 by distinguished men from this country and abroad. Beginning in 1973 and thereafter, the person selected to deliver the lecture will be known as the "Institute of Metals Division Lecturer and R. F. Mehl Medalist" for that year. Dr. Christian graduated in Physics from Oxford University in 1945 and obtained a D. Phil. in Metallurgy in 1949. At Oxford he was successively Pressed Steel Research Fellow (1951-55), Lecturer in Metallurgy (1955-58), and George Kelley Reader in Metallurgy (1958-67) before being appointed to his present position of Professor of Physical Metallurgy in 1967. He has been a Fellow of St. Edmund Hall, Oxford, since 1963. He was Republic Steel Distinguished Visiting Professor of Metallurgy at Case Institute of Technology in 1962-63 and has also held visiting professorships at Massachusetts Institute of Technology (1971) and at the universities of Illinois, Urbana (1959 and 1963), Pennsylvania (1970), Virginia (1972), and Stanford (1972), and visiting appointments at N. R. C., Ottawa (1956) and N. B. S., Washington, DC (1979). Professor Christian was elected a Fellow of the Royal Society in 1975 and is also a Fellow of the Institute of Physics and the Institution of Metallurgists. He received th
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