MSE Seminar - Dr. Roger Doherty - Drexel University
"Abnormal Grain Coarsening: Role of particles and low angle grain broundaries"
Abstract: The unsolved problem of abnormal grain coarsening (growth) AGC, also known as secondary recrystallization is reviewed. Though intensively studied for electrical steel this is complicated by the generation of a very sharp texture and so is not considered here until the simpler problem of AGC in the absence of texture is better understood. AGC only occurs when the competing problem of normal grain coarsening (NGC) is inhibited either by strong single component texture giving a high density of low angle grain boundaries (LAGB) or much more commonly by a low volume fraction of second phase particles that due to their finite solubility can themselves coarsen. New models on NGC and particle limited NGC are presented to update the classic Smith Zener model and this matches the extensive current experimental data in two phase metallic systems. However by itself it predicts that AGC in two phase systems is impossible! ! Two possible solutions to this conflict are offered (i) a model based on particle shape change plus coarsening and (ii) some experiments that reveal the role of a critical density (> 10%) of LAGBs.
Biography: Undergraduate and doctorate degrees from Balliol College and the Dept of Metallurgy (as it was then) at Oxford University. Two years 1963-65 as a research Scientist at Tube Investements Lab Cambridge UK investigating Ingot solidification and segregation. 17 years, 1965-1982, at the University of Sussex where I helped found one of the first Materials groups in Europe. In my last year there, as “Sunject Chairman”, I was required to close the Materials Science “Subject Group”. I spent one year (1975-76) at the Brazilian Governments Materials Lab in the Aerospace Center near Sao Paulo and one year (1978-79) as a Guest Professor at Delft Technical University substituting for Professor Kievits who was then Rector of the University. From 1982 till present I was a Professor of Materials at Drexel University, serving as Interim Department Head from 1998-2000. I spent 6 months sabbatical first at The Technical University of Trondheim, Norway in 1975, then at the Risoe National Research Lab in Roskilde Denmark in 2002-3 and finally at L’Ecole des Mines St.Etienne France in 2003. I retired as The Grosvenor Professor in 2008 and became an Emeritus Professor. I have consulted widely most notably at Alcoa Researcgh Center 1982-2005. Since retirement, I have continued to interact with other people’s research students most notably those of an Ex-Drexel Ph.D student Dr Indradev Samajdar who is now at Professor in IIT –Bombay in Mumbai, India. My research is on thermo-mechanical processing of metallic alloys and the resulting microstructure. This has covered: solidification, deformation, recrystallization and grain coarsening, precipitation and precipitate coarsening. From three universities I advised or co-advised over 40 doctoral students and a similar number of MS students. From my collaboration with students and with many colleagues, I have published two textbooks, over 200 journal articles and invited reviews and also 7 US patents.