John Wyrill ‘Jack’ Christian

John Wyrill "Jack" Christian collapsed and died suddenly on 27 February 2001 while doing what he loved best: working in his office at the department of materials, Oxford University, in England. Although he had been suffering from Parkinson's disease for more than 20 years, he was active both socially and academically—the evening before he died, he and his wife had gone to the cinema.Jack was born on 9 April 1926 in Scarborough on the east coast of Yorkshire, England. At age 17, he went to Oxford University's Queen's College to study physics. He completed the accelerated wartime course with honors two years later. Although a physics graduate, Jack joined William Hume-Rothery's science of metals group in the university's Inorganic Chemistry Laboratory for his doctorate. He worked on the chromium-manganese and cobalt-manganese phase diagrams and was awarded his DPhil in 1949.Jack found the determination of phase diagrams rather dull, so when "H. R." invited him to stay with the group, he started to look at problems in what was then called metal physics, which fascinated him. In 1951, he published his first important paper, in the Proceedings of the Royal Society, on phase transformations, explaining the solid-state transition in cobalt in terms of dislocation theory. International recognition soon followed, and Jack became a leading authority on martensite, an alloy of iron and carbon. A review paper (Institute of Metals Monograph and Report Series) with Bruce Bilby in 1956 on martensitic transformations is particularly noteworthy.Jack (known as "Chris" to his students) believed in describing research projects in broad terms, so students were obliged to work out their own inclinations. He was also kind to his students. On one occasion, in the days of mechanical typewriters and rigid submission dates, Jack, on hearing that one of his students was having difficulty finding a typist to do the thesis, offered his services with the words, "I'm two fingered, fast, not very accurate, but I don't charge."His first research student was the late Z. S. "Bas" Basinski, whose project was on the martensitic-type phase transitions that occurred in manganese-copper and indium-thallium alloys. The transformed structures are heavily twinned and the application of stress gives rise to a reversible deformation, which is now known as the shape memory effect. It was with Basinski, then in Ottawa, Canada, in 1956, that Jack started his work on the deformation of metals and alloys; their 1960 paper, published in the Australian Journal of Physics, on the deformation of iron at low temperatures was the first to show that pure iron had a large Peierls-Nabarro force and that thermal activation was the key process for dislocation glide. On returning to Oxford in 1956, Jack initiated the building of crystal-growing facilities and special mechanical testing machines. His research on the deformation of single crystals of iron and other body-centered cubic (BCC) alloys (especially pure niobium) established that a large Peierls-Nabarro force exists in all crystals with the BCC structure. It also became clear that there was an asymmetry of slip for glide on {211} planes (shear in the twinning sense being easier than the reverse) and at temperatures below ambient, there was a complete breakdown of Schmid's law with the occurrence of anomalous slip. He also established that the screw dislocation was important in the deformation of these materials.A great reader of the scientific literature, Jack was able to draw together seemingly unrelated theories and show that they were different facets of a common model. The earliest, and probably the best known, example concerns martensite; in 1955, he was able to prove (see Journal of the Institute of Metals) the equivalence of the two general phenomenological theories of the crystallography. Later, in 1976, he performed similar research on the structure of interfaces, and in the field of deformation married the rival Peierls-Nabarro and dislocation dissociation models.Jack was a modest and self-effacing man with a brilliant intellect. In scientific discussion, he listened carefully and courteously to what others had to say, be they visiting world authorities or undergraduates. However, he subjected their comments to a rigorous analysis, never failing to point out any weaknesses in the argument. He also was a lucid, inspiring teacher. One student claims that Jack never answered a question directly in eight years of undergraduate, postgraduate, and postdoctoral supervision. Instead came the dreaded words, "Well, what do you think?" The ensuing discussion not only solved the problem but developed intellectual powers far more than any direct answer could have done.Jack corresponded and collaborated with many scientists worldwide. He used his sabbaticals to take up visiting professorships across North America; he enjoyed visiting and lectured in India, China, Japan, Australia, and South America. He also was editor or assistant editor of several international scientific journals. Jack was elected a fellow of the Royal Society in 1975.Jack, with Hume-Rothery and Bill Pearson, wrote the book Metallurgical Equilibrium Diagrams (Institute of Physics, London, 1952). However, his passion was his masterwork, The Theory of Transformations in Metals and Alloys. A work of immense scholarship, the first edition (Pergamon Press, 1965) quickly became the definitive work in its field. The first volume of the enlarged second edition was published in 1975 (Pergamon Press). Partly because of Parkinson's disease, Jack took early retirement in 1988, which allowed him more time to concentrate on the next volume of the book. The manuscript was completed a couple of years before Jack died; it is sad that he did not live to see it in print.Outside the laboratory, Jack enjoyed the theater, cinema, literature, and hill-walking, particularly in his native Yorkshire.Jack had extraordinary courage in the face of a debilitating disease, yet he was modest, approachable, and inspiring to all who knew him, especially those of us who had the good fortune to have been his students. John Wyrill "Jack" Christian PPT|High resolution© 2001 American Institute of Physics.

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