Deformation Twinning in FCC and HCP Crystal Systems

Affiliation: McMaster University 

Title: Deformation Twinning in FCC and HCP Crystal Systems

Abstract: This talk is concerned with the mechanical twinning and its role in the plasticity of FCC and HCP single crystals of metals and alloys. The crystallographic models of twinning will be reviewed including the dislocation models for twin nucleation and growth. The formation of a macroscopic twin requires every layer of the parent lattice be swept by twinning dislocations which transform the existing microstructure to the new microstructure. Details will be given of the mechanisms by which the new defects originate during mechanical twinning. The effect of twinning on mechanical properties will be discussed in reference to FCC and HCP single crystals undergoing twinning during tensile and compressive deformation.

 Bio: Marek Niewczas is Professor in the Department of Materials Science and Engineering and Deputy Director in Canadian Centre for Electron Microscopy at McMaster University. He holds Master’s degrees in Science and Engineering and Ph.D. in Materials Physics from AGH University of Science and Technology in Cracow, Poland. He was the recipient of Science Fellowships, from Centro Sviluppo Materiali in Rome (1990) and Instituto Nazionale Phisica della Materia in Genova (1991). He joined McMaster University in 1993 as a post-doctoral fellow and has been at McMaster after that. In 2006-2007 he was the Los Alamos Director Research Fellow. In 2014 he received the Canadian Metal Physics Medal. He was Visiting Research Professor at the Centre for Advanced Structural Analysis, Norwegian University of Science and Technology in Trondheim and at Friedrich-Alexander-Universität Erlangen-Nürnberg in Erlangen. In 2015 he was Guest of Honour at the Opening of Magnesium Research Center at Kumamoto University in Japan. Dr. Niewczas’ research spans the areas of Materials Science and Solid State Physics, with a focus on mechanical, magnetic and electrical properties of materials. He uses electron microscopy to investigate the relationship between microstructure and properties in crystalline materials.