[LA-SiGMA] LASiGMA Seminar - Jian Wang, April 16th, 3:30pm (Please see new broadcast information)

[shelley lee]

Dear All,

Dr. Jian Wang of Los Alamos National Laboratory will be giving a talk, April 16th at 3:30pm in room 1008B at The Digital Media Center, Louisiana State University. The title of his talk is "Deformation Twinning Mechanisms in FCC, BCC and HCP Metals."

Abstract:
Crystal twinning results in an intergrowth of two separate crystals in a variety of specific configurations (in a symmetrical manner). A twin boundary separates the two crystals. Deformation twinning is a typical plastic deformation mechanism, accomplished by the glide of twinning dislocations. It is difficult in single-phase fcc metals with medium to high stacking fault energies and single-phase bcc due to the availability of multiple slip systems that are much easier to activate.  Therefore twinning in these cases usually requires extreme conditions, such as shock and/or cryogenic temperatures, which generate the large stresses required to nucleate twins via pole mechanisms or dislocation dissociations. Nucleation and growth of twins in cubic crystals are accomplished via successive gliding of twinning dislocations, resulting in macroscale shear strain. Interestingly, we recently also characterized macro-scale zero-shear strain twinning mechanisms in association with a zonal twinning dislocation with net zero Burgers vector in a 3-layer unit. However, in hcp metals, deformation twinning is a very common and important deformation mechanism and is responsible for the hardening and texture evolution characteristics of hcp metals and alloys subjected to plastic deformation. Unlike cubic crystals, the nucleation of deformation twins in hcp metals is accomplished via pure-shuffle mechanism, the growth is via shear-shuffle and climb shuffle mechanisms. In this lecture, I will talk about twinning in fcc, bcc, and hcp crystals based on the in situ and ex situ TEM observations and molecular dynamics simulations. Four aspects are discussed (1) zero-strain twinning in fcc crystals, (2) deformation twinning in Ag-Cu composites, (3) twinning in bcc resulting from dislocation dipole interaction, and (4) deformation twinning in hcp metals.

Biography:
Dr. Jian Wang, Technical Staff Member, Los Alamos National Laboratory, received his Ph.D from Rensselaer Polytechnic Institute, Troy, NY, USA, in 2006. Currently, his research interests are focused on more quantitative exploring the structure-properties relationships of structural and nanostructured materials by combining microscopic characterization and modeling at multi-scale. 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, USA, and TMS MPMD Young Leader Professional Development Award (2013). He served as Editorial Boards of Research and Application of Physics (RAP) (2012~), Journal of Materials (2012~), and Science Advisor (2011~) of JOM, TMS. He has more than 130 peer-reviewed publications (> 2200 citations and H-index = 29, 20 papers selected as 25 Hottest Articles in Materials Science, and 4 work featured as Journal cover), one book chapter in Dislocations in Solids and 50+ invited/keynote presentations.

Also available on site at the locations below:
UNO – 234, Liberal Arts Building
LATech – 122, Nethken Hall
SUBR – 211 J.B. Moore Hall
Xavier – 226 Qatar Pavillion

Please note, this seminar will ONLY be accessible through HD videoconferencing. 

Regards,
Shelley Lee
Project Coordinator
225-578-0465




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