All possible binary dislocation locks in FCC metals and alloys
Guest Speaker: Prof. Daolun Chen, professor of Toronto Metropolitan University，Canada
Date & Time: 9:30-11:00, 23. Oct., 2025
Location: Yiucheng Lecture Hall （500），Xu Zuyao Building
Inviter:.Assco.Prof.Jingya Wang
主讲嘉宾介绍/ Biography
Dr. Daolun Chen is a Professor in the Department of Mechanical, Industrial and Mechatronics Engineering, Toronto Metropolitan University, Canada. He received his BSc and MSc from Northeastern University in 1983 and 1986, respectively, PhD from the Institute of Metal Research, Chinese Academy of Sciences, 1989, and Dr.rer.nat. from the University of Vienna, Austria, 1993. Dr. Chen has published 544 peer-reviewed journal (452) and conference (92) papers in the area of advanced materials and key engineering materials, and their deformation, fatigue, welding and joining, plus 250+ non-refereed conference papers/research reports. His pioneering work on nanocomposites leads to a well-known method that bears his name. Since 2019 he has been annually featured in the World's Top 2% Scientists List in a study from Stanford University, USA. He is a recipient of many prestigious awards, including International Magnesium Award for Lifetime Achievement, Premier's Research Excellence Award, Canadian Metal Physics Award, G.H. Duggan Medal, MetSoc Award for Research Excellence, MetSoc Distinguished Materials Scientist Award, Sarwan Sahota Distinguished Scholar Award, Ontario Professional Engineers Awards (OPEA) Engineering Medal – R&D. Dr. Chen is an elected Fellow of three academies (The Academy of Science of the Royal Society of Canada; Canadian Academy of Engineering; and European Academy of Sciences and Arts) and five professional associations/societies (AAAS, IMMM, CIM, CSME, CWBA). He serves on editorial boards of 28 journals, including Journal of Magnesium and Alloys, Journal of Materials Science and Technology, Materials Science and Engineering A, etc. He has been invited by science reporters to give interviews and comments on some key scientific breakthroughs published in the journals of Nature and Science.
Dislocations and their mutual reactions play a pivotal role in the plastic deformation and strengthening mechanisms of crystalline materials. Although several dislocation locks in FCC materials have been identified through HRTEM and molecular dynamics simulations, the full picture about how many types of dislocation locks can exist has remained elusive—an open question that has puzzled researchers for seven decades. Recently, we introduced a novel discrete mathematics-based approach to systematically uncover all possible binary dislocation locks in FCC materials. This method evaluates all feasible reactions between mobile dislocations—specifically perfect and Shockley partial dislocations—under two distinct configurations: i) Non-coplanar dislocations situated on intersecting {111} slip planes at both obtuse (109.47°) and acute (70.53°) angles, and ii) coplanar dislocations confined to the same slip plane. Our key findings reveal that seven dislocation locks emerge from 50 possible non-coplanar dislocation reactions. These include four well-established dislocation locks named after pioneering scientists and three other stair-rod locks, plus the 8th collinear lock arising from the coplanar dislocation reactions. Among the seven non-coplanar locks, five—namely the Lomer lock, Cottrell lock, Frank lock, 1/3<110> stair-rod lock, and 1/6<310> stair-rod lock—form exclusively from dislocations on slip planes intersecting at obtuse angles. In contrast, the Hirth lock is the sole product of acute-angle interactions. The 1/6<411> stair-rod lock is unique because it appears in both non-coplanar scenarios, although its degree of immobility varies. Statistical analysis shows that 68% of the 25 binary dislocation reactions in the obtuse-angle scenario result in lock formation, compared to just 24% in the acute-angle scenario, underscoring a pronounced structural asymmetry in binary dislocation lock formation. Interestingly, all identified dislocation lock planes converge within a distinct fan-shaped sector. Also, a new definition for the degree of lock immobility is proposed based on the misorientation angle between non-close-packed lock planes and the close-packed slip planes. Further details and broader implications of these findings will be discussed during the upcoming seminar.