Lecture No.159

Title: A Multiscale Perspective on Nucleation, Propagation, and Growth of Deformation Twins in Hexagonal Materials
Speaker: Dr. Jian Wang, Los Alamos National Laboratory
Date/Time: 2015-01-23,9:30
Venue: Room.500, Material Building A
Inviter: Dr. Yao Shen
Dr. Jian Wang, Technical Staff Member, Los Alamos National Laboratory, received his Ph.D from Rensselaer Polytechnic Institute, Troy, NY, USA, in 2006. Dr. Wang’s research interests are focused on more quantitative exploring the structure-properties relationships of structural and nanostructured materials. He was awarded the LANL Distinguished Postdoctoral Performance Award in 2009, the LDRD/Early Career Award (2011), two LDRD-ER Awards (2013), Los Alamos National Laboratory, TMS MPMD Young Leader Award (2013), and International Journal of Plasticity Young Research Award (2015). He is leading a DoE BES Core Program ($1000 K/Yr) with the focus on Deformation Physics in Ultra-fine Composites. He served as Editorial Board of Research and Application of Physics (RAP) (2012~), Journal of Materials (2012~), and Science Advisor (2011~) of JOM, from Nanomechanical Material Behavior technical committee, Materials Processing and Manufacturing Division (MPMD), TMS. He has ~170 peer-reviewed publications (~ 3000 citations and H-index = 32, 20 papers selected as 25 Hottest Articles in Materials Science, and 4 papers were featured as Journal cover), one book chapter in Dislocations in Solids and 50+ invited/keynote presentations.
 Deformation twinning is a major mode of plastic deformation in hexagonal-close-packed crystals and exhibits more complex nucleation and propagation mechanisms than those in cubic structure. In this lecture, I highlighted several twinning-associated boundaries that play crucial roles in nucleation, growth, and interactions of deformation twins in hcp metals. According to microscopic characterizations and atomistic simulations, four types of boundaries are reviewed including (1) symmetrical tile grain boundaries (SCTGs) that favor twin nucleation or migrate based on twin dislocations, (2) prismatic-basal boundaries (PBs or BPs) associated with twin nucleation via pure-shuffle mechanism, (3) serrated coherent twin boundaries (SCTBs) associated with migration of twin boundaries via glide and climb of twinning dislocations, and (4) prismatic-prismatic (PPs) and basal-basal (BBs) boundaries associated with co-zone twin-twin interactions. More importantly, these boundaries affect twinning and detwinning processes that may correspond to twinning-induced hardening and seem universal associated with twins in hexagonal-close-packed metals. These findings provide theoretical base for researchers to revisit experimental data, rebuild the frame of twinning mechanisms including nucleation and propagation of twins, and advance the development of materials modeling tools at meso- and macro- scales as well as alloy design. 

Location:Room.500, Material Building A