Dr. Georges Ayoub
Assistant Professor, Industrial & Manufacturing Systems Engineering, University of Michigan– Dearborn
Held in the ETRL 101 Lecture Hall
Refreshments served in ETRL 119 at 10:30 am
Uncovering the deformation mechanisms in Ti/TiN multi layer under compressive, multi axial and nano-indention behavior with MD simulations
The promising mechanical, physical and chemical properties of nano-scale metal/ceramic multilayers (MCMs) are of high interest for extreme environment applications. Understanding the plastic deformation mechanisms and the variables affecting those properties is therefore essential. The interface characteristics and the plastic deformation mechanisms under compressive, multiaxial and nano-indentation loadings in a Ti/TiN multilayer with a semi-coherent interface are numerically investigated. The interface structure of the Ti/TiN interface and the interface misfit dislocation were characterized using molecular dynamic simulations combined with atomically informed Frank-Bilby method. Three possible atomic stacking interface structures are identified according to the crystallographic analysis of the interface. Upon relaxation, large interface areas are occupied with the energetically stable configuration. Furthermore, the higher energy stacking are transformed into misfit dislocations or dislocation nodes. The Ti/TiN multilayer structure shows high strength and ductility under uniform compression loading. However, low strength and ductility are observed under tensile loading favored by crack initiation and propagation. Unlike typical metal stress-strain curves, metal/ceramic multilayers show two main yield points. Furthermore, the Ti/TiN multilayer structure shows three distinctive peak points for compressive loading normal and parallel to the interface. Furthermore, the misfit dislocation network at the Ti-TiN interface is found to dissociate to partials under driving force on the indenter tip and play an important role in the strengthening of Ti/TiN multilayers. We have observed several deformation mechanisms such as dislocation pile-up on the interface, and movement of misfit dislocations.
Dr. Georges Ayoub completed his Ph.D at Lille University of science and technology in north France. Dr. Ayoub obtained his Master’s degree in 2007, also from Lille 1 University. Dr. Ayoub undergraduate work was completed at the Polytechnic Engineering School of the Lille 1 University (Polytech’Lille) in the field of mechanical engineering. Dr. Ayoub also obtained an Undergraduate Diploma in materials science at the University of Rennes 1 with highest distinction.
As a researcher, Dr. Ayoub started his career working in the capacity of a Post-doctoral Research Fellow at Texas A&M University at Qatar. He was promoted, in 2012 to Assistant Research Scientist and took leadership over 3 research projects in Qatar. Since then he has been able to establish his own independent research program and was awarded funding for 3 projects. Between August 2014 and August 2016 Dr. Ayoub worked as assistant professor at the American University of Beirut (AUB) and maintained an affiliation with Texas A&M University at Qatar as a Visiting Associate Research Scientist. Dr. Ayoub joined the University of Michigan Dearborn in September 2016, as assistant professor. His research projects involve experimental testing, characterizing and modeling the behavior of polymers and metal alloys. The research also entails developing algorithms and coupling them with finite element analysis to predict the material behavior under desired temperatures, deformation rates and loading conditions. Dr. Ayoub research has been published in more than 30 journal papers appearing in journals with high impact factors.