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MatSE Colloquium - "Order-disorder-property relationships in structural materials: Guided by randomness"

Event Type
Seminar/Symposium
Sponsor
Materials Science and Engineering Department
Date
Mar 1, 2021   4:00 pm  
Speaker
Dan Gianola, Materials Department, University of California - Santa Barbara
Views
52
Originating Calendar
MatSE Colloquium Calendar

"Order-disorder-property relationships in structural materials:  Guided by randomness"

Emerging classes of structural materials proposed to meet the demands of aggressive applications requiring structural integrity in extreme environments, such as those encountered in the aerospace and power generation sectors, share a common theme: complexity across a large range of length scales. A common denominator is the intentional design of randomness – or disorder – in  these new materials.  In load-bearing materials, this disorder can manifest as topological disorder (uncertainty in atomic positions) as found in interface-dominated or glassy materials, or chemical disorder (uncertainty in elemental occupancy) as found in compositionally-concentrated alloys. This begs a question that underpins new materials-by-design strategies: could the conventional wisdom of searching for structure-property relationships give way to those that focus on disorder-property ones?  This talk will show two examples that lend credence to the notion of embracing the role of disorder in materials.

The first will highlight the novel materials design paradigm of multi-principal element (MPE) alloying that has shown great success. Yet opportunities to advance the refractory-based body centered cubic (BCC) variants of these alloys for high temperature structural applications must confront fundamentally different avenues for the accommodation of plastic deformation. We show a unique combination of homogeneous plastic deformability and strength at low temperature in the BCC MPE alloy MoNbTi, enabled by the rugged atomic environment through which dislocations must navigate. In situ observations of dislocation motion and atomistic calculations unveil the unexpected dominance of non-screw character dislocations and numerous equiprobable slip planes for dislocation glide. This remarkable behavior reconciles theories explaining the exceptional high temperature strength of similar alloys.  Our results, when paired with a material density lower than that of state-of-the-art superalloys, provide sharp focus to alloy design strategies for materials capable of performance across the temperature spectrum.

The second example will demonstrate novel synthesis and processing routes for controlling disorder in nanocrystalline materials – and as a consequence, their mechanical properties.  We study relaxation processes at grain boundaries in nanocrystalline materials that facilitate atomic reconfigurations toward a lower energy state, but further present strategies for rejuvenation at grain boundaries with the goal of suppressing shear localization and endowing damage tolerance. We also demonstrate the intentional design of disorder at interfaces, a notion generally associated with thermal runaway in traditional materials, in a segregation-engineered ternary nanocrystalline Al-Ni-Ce alloy that exhibits exceptional thermal stability and elevated temperature strength.

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