报告题目：Compatibility and scale law of plastic deformation and solute effect on GBM
报告人：Dr. Yan Huang
The presentation will share some challenging opinions about a few fundamental issues of physical metallurgy, including compatibility and scale law of deformation and the effect of solute elements on grain boundary migration (GBM).
Von Mises criterion that 5 independent slip systems are required to operate simultaneously in a grain for compatible deformation is unequivocally accepted since its publication in 1928. However, there is no single piece of experimental evidence to prove it and it can be shown that the criterion has critical flaws. It is proposed that 3 independent slip systems are essential and sufficient for compatible deformation. Accordingly, discussions will be made on the ductility of magnesium.
The mechanical response of crystalline materials depends on grain size. Hall-Petch relation holds for most engineering metals and alloys with a grain size from submicron to millimetres. At finer scales, however, inverse Hall-Petch relation takes place. The transition between these two scale laws is believed to occur when the grain size is down to 10nm or so. It is our opinion that deformation conditions (T, ), instead of absolute grain size, determine the transition. A general scale law of deformation is proposed based on the characterization of steady state deformation. The operation of grain boundary dislocations is key in explaining the inverse Hall-Petch relation.
GBM is substantially controlled by solute atoms and “solute drag theory”, which is based on the assumption of solute “lag behind” upon migration, has been widely accepted to account for the solute effect on GBM. However, it can be shown that in the linear range of irreversible thermos-dynamics, solute atoms segregated in a grain boundary will not “lag behind” when the boundary migrates. A novel “solute trap” model is proposed, in which the solute effect on GBM is attributed to the decrease in boundary energy as a result of boundary segregation. The predictions of the model are principally in agreement with experimental results.
Dr Yan Huang is a Senior Lecturer at BCAST (Brunel Centre for Advanced Solidification), Institute of Materials and Manufacturing, Brunel University London. He obtained his PhD degree in engineering from Northeastern University (NEU), China in 1990. Afterwards, he served at NEU as a lecture and associate professor until 1995. He then worked as a research fellow at the University of Manchester from 1995 to 2003 and as the Technical Director at CONFAE TECH Ltd (UK) from 2003 to 2010, before joining Brunel in 2010. He leads metallic biomaterials research at Brunel in the development of both permanent titanium implants and novel biodegradable magnesium medical devices for orthopaedic and cardiovascular applications. He is a founding member and co-investigator of the EPSRC Future Liquid Metal Engineering (LiME) HUB where he leads the activities on process development and light alloy processing involving both solidification and plastic deformation. He has extensive experience in process innovation for combined solidification and thermomechanical processing, solid state joining and severe plastic deformation, with particular interest in light alloys and light metal matrix composites. He has long-term interests in the characterization of microstructure and texture evolution during thermomechanical processing and fundamental issues of strengthening, plastic deformation and grain boundary migration. He has published over 100 peer reviewed journal papers and conference proceedings and filed 3 patents with an h-index of 19 and a total of 1731 citations. He is a fellow of UK Higher Education and EPSRC Peer Review College, a member of IOM3, MRS and TMS and TMS Shaping and Forming Committee, and editorial board member for MS J Biomed Eng, J Mater Sci & Res and J Aerospace Eng & Mech.
Yan Huang, BCAST, Institute of Materials and Manufacturing, Brunel University London
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