Dr. Xin Wang, Posdoctoral Scholar from Department of Materials and Engineering, University of California, Irvine, will give a seminar titled "Transforming Mechanical Properties of Structural Materials through Defect Control" to the interested students and faculty at Discovery Park.

Abstract

Lattice defects of various dimensionalities, such as vacancies, dislocations, grain boundaries and twin boundaries, define the lifetime and safety of systems, from micro-devices to automobiles to nuclear reactors. These lattice defects can also induce mechanically or functionally intriguing properties. The capabilities to characterize and engineer lattice defects and their evolution hold potential for innovations in the design and synthesis of next-generation metals, ceramics and composites for critical structural applications.

In this presentation, I will discuss how advanced (in-situ) characterization approaches, especially electron microscopy, at multiple length scales, in combination with small scale mechanical testing can enable a comprehensive understanding of the defect structure, chemistry, dynamics, and defect-property relationships. In combination, these provide guidelines for new design principles and processing approaches to engineer materials with enhanced mechanical properties. The first part of the talk will focus on uncovering the nucleation and early-stage growth of deformation twins in Mg with in-situ TEM characterization and strategically designed nanopillar geometries, highlighting direct experimental evidence of a pure-shuffle twin nucleation mechanism. Next, I will show the use of alloying and external stimuli, particularly mechanical deformation, to tailor the structure and chemistry of critical defects in a Mg-Y alloy down to the atomic scale and to thereby transform the defect stability and mechanical behavior. Finally, I will discuss the role of solidification cell boundaries, a unique type of sub-grain boundary often observed in additively manufactured alloys, in determining the mechanical behavior of a 316L stainless steel fabricated by directed energy deposition. Using site-specific in-situ SEM micromechanical testing, I find that cell boundaries exhibit a weak dislocation barrier effect and a marginal effect on plastic anisotropy. The findings and methodologies can benefit materials design in a broad range of defect-sensitive and defect-controlled applications.
 

Biography

Dr. Xin Wang is a postdoctoral scholar at the University of California, Irvine. She earned her B.S. from Xi'an Jiaotong University (2011) and M.S. from Shanghai Jiaotong University (2014), followed by her Ph.D. in Materials Science and Engineering from the University of California, Irvine (2018). Dr. Wang has authored and coauthored over 30 peer-reviewed publications and has given multiple invited talks at conferences, including MRS and TMS. Her research interests lie at the intersection of microstructural characterization, mechanical properties, and advanced manufacturing of novel structural materials.