Editorial

Prof. Dr. Duk Yong Yoon

Duk Yong Yoon was born in 1940 and spent his early childhood in Pyongyang, North Korea. When he was 8 years old, he came to South Korea with his family, crossing the closed border between the divided South and North Koreas. During his final year at Kyunggy High School in Seoul, Korea, he went to the USA and entered M. I. T. in 1958 to major in physics. He studied French literature as a minor in humanities. Upon graduating from M. I. T. in 1962, he continued his graduate studies at Harvard University in the Division of Applied Physics and Engineering. His doctoral thesis work was on the effect of high pressure on order-disorder transformation in β-CuZn and was supervised by Professor A. Bienenstock, who is now at Stanford University. He thoroughly enjoyed the academic atmosphere of Harvard and studying under professors like H. Brooks, D. Turnbull, and W. Paul. In 1967 he went to the University of Illinois as a post-doctoral research associate to work with Professor D. Lazarus in the department of physics. He worked on ionic conductivity in alkali-halides under high pressure, and the exposure to ionic crystals at that time led him later to work on ceramic materials. In early 1970 he joined the faculty of the Wayne State University in Michigan.

In 1971 the Korean government was establishing the Korea Advanced Institute of Science (which later became the Korea Advanced Institute of Science and Technology) as a new leading graduate school. Duk Yong Yoon proposed to establish a department of materials science at this university and returned to Korea in January, 1972 as the first faculty in the department. He enjoyed the challenging task of establishing a new educational and research organization in Korea, which was at an early stage of industrialization. Although his education and experience in the U. S. A. were mainly in solid state physics, he decided to start a program in powder metallurgy because of the industrial demand in Korea. Although it was necessary to pay attention to practical problems, he realized that there were many fundamental questions yet to be resolved. His students performed critical experiments to observe the filling of artificially produced spherical pores during liquid phase sintering and analyzed the capillary driving force for such a process. They also studied the coarsening of spherical grains during liquid phase sintering.

In 1978, he went to the Max-Planck-Institut fuer Metallforschung in Stuttgart to work with Professor Petzow and Dr. Huppmann as a Humboldt fellow. His work in Stuttgart showed that the migration of Ni liquid films between W particles was related to the composition change and was therefore similar to diffusion-induced grain boundary migration (DIGM), which was drawing considerable interest. Various theories were proposed for the driving force of such interface migration, and Professor M. Hillert suggested that particularly for intergranular liquid film migration the coherency strain energy produced by solute diffusion in front of the migrating interface was the driving force. Yoon and his students at KAIST performed the critical test of this theory by using several combinations of solute atom pairs to vary the coherency strain from negative to positive values through 0. The solute atom concentrations were varied by using the equilibria between the solid and liquid phases in liquid phase sintered systems. Further experiments in ceramics showed that the migration directions were also consistent with the coherency strain theory. Duk Yong Yoon always searched for simple experiments for critical tests of theories and demonstration of new ideas, and these series of experiments were the prime examples. He now believes that the coherency strain theory has been fully verified experimentally for liquid film and grain boundary migration as well as for discontinuous precipitation and that some recent results against the theory are due to misunderstanding.

Since 1995, Yoon’s group has been mainly working on understanding the mechanism of abnormal grain growth. They showed that the grain shapes in liquid phase sintered systems often changed from polyhedral to nearly spherical shapes with either temperature or composition change as described for the surface roughening of pure materials, and that the normal or abnormal grain growth was related to such a grain shape change. Extending the experiments to pure or single-phase polycrystalline materials, they showed that the grain boundary roughening transition was also related to normal or abnormal grain growth. One important example of this experimental series was the observation that MgO addition to alumina doped with SiO₂ and CaO caused the grain boundary roughening transition and hence the change from abnormal to normal grain growth. Yoon believes that the puzzle of the MgO effect in alumina has now been resolved and generally the grain boundary roughening transition is important for understanding the grain boundary structure and properties.

Yoon also delved briefly into various other subjects such as diamond deposition, y’ precipitation in Ni-base superalloy, W heavy alloy, and oxide superconductors, but he found it difficult to do significant research in these areas. He often felt academically isolated in Korea and sought to maintain ties to the international community. He spent sabbatical years at the National Institute of Standards and Technology and the General Electric Corporate Research Center in the U. S. A. and the University of Tokyo in Japan, and maintained close working relationships with these institutions as well as the Max-Planck-Institut für Metallforschung in Germany.

Duk Yong Yoon also played a significant role in the science administration in Korea. He served as the general secretary of the Korea Science and Engineering Foundation in its early days, establishing the research support and evaluation system and increasing the budget through a World Bank loan program. While he was the president of the Korea Advanced Institute of Science and Technology for three years from 1995, he sought to enhance its education and research levels and contributed to establishing the Korea Institute of Advanced Study for theoretical physics and mathematics and the Graduate School of Techno-Management. He also was the second president of the Korea Powder Metallurgy Institute. But even after administrative duties, he always returned to research and teaching. He shared the view of most scientists that research was enjoyable and worthwhile even when the outcome was not successful. He received the Hoam Prize in 1995 and the Outstanding Scientist Award in 2004 in Korea. Forty-one students received doctoral degrees under his supervision.

He likes classical music and literature. He did judo, rock climbing, and ice hockey in his student days, and likes to play tennis, ski, and swim in his later years. He loves his charming wife and three daughters, who are happily married and active professionally. Although he left North Korea when he was a child, he hopes to return there someday to help the people and in particular the scientists.