Manipulating defect structure and behavior through segregation-induced complexion transitions

Abstract:

Defect engineering is known to be useful for manipulating material properties, yet often treats the crystalline flaws as temporary or metastable features. Recent advances have led to the identification of stable defect states or complexions, where local structure and chemistry can be controlled with thermodynamic variables such as composition or temperature. In this talk, we discuss how both grain boundaries and dislocations can host these complexions, with an eye toward increasing microstructural stability and tuning material response. First, the incorporation of amorphous intergranular films into a nanoscale grain structure is shown to solve many of the major, longstanding limitations of nanocrystalline metals. Notably, the ductility, toughness, strength, thermal stability, and radiation tolerance can all be simultaneously increased with the incorporation of amorphous grain boundary complexions, with examples shown for multiple alloy systems. Moreover, these materials can be fabricated into bulk forms with simple processing routes, demonstrating a clear path to commercial use. Next, complexion formation along dislocation lines offers a new pathway to manipulate higher-level, time-dependent mechanical properties associated with the collective behavior of dislocation populations and their interconnected networks. Local stress fields can modify the bulk solubility limits in nearby regions, leading to patterning of chemical order with nanoscale dimensions. Alternatively, local restructuring can occur to delocalize the dislocation core, resulting in new secondary defect structures. As a whole, this work lays the foundation for the engineering of defect structure and chemistry to design better nanomaterials, creating a new “defects-by-design” toolkit.

 

Bio:

Tim Rupert is a Professor of Materials Science and Engineering at Johns Hopkins University and the Director of the Hopkins Extreme Materials Institute (HEMI). Professor Rupert received a B.S./M.S. in Mechanical Engineering from Johns Hopkins University in 2007 and a Ph.D. in Materials Science and Engineering from MIT in 2011. His research focuses on uncovering new structure-property relationships in nanomaterials for structural and energy applications, as well as increasing the reliability and lifetime of nanostructured materials. The lab uses a combination of complementary computational and experimental techniques to tackle these challenges. Prof. Rupert has received the NSF CAREER Award, the DOE Early Career Award, the ARO Young Investigator Program Award, the Hellman Fellowship, the ASM International Bradley Stoughton Award for Young Teachers, the AIME Rossiter W. Raymond Memorial Award, the TMS Brimacombe Medal, and was elected as a Fellow of ASM International. He serves as an Editor for Acta Materialia and Scripta Materialia.