CAREER: Fundamentals of dislocation ensemble evolution in polycrystalline metallic alloys during flow

NON-TECHNICAL SUMMARY Some of the most taxing applications for metallic alloys, such as rotary components, pressure vessels, and critical fasteners, place them at the limit of permanent deformation. During this process, defects in the material organize from influences at both the nanoscale and microscale, dictating important properties such as yield strength, fracture toughness, and fatigue life. In this project, next-generation synchrotron X-ray light sources, a critical recent US scientific investment, and machine learning techniques are being utilized to quantify the organization of defects across length scales with new fidelity. This research is answering long-standing questions regarding how defects organize across different alloy structures and, ultimately, the initiation of damage. Elucidating and slowing damage initiation is critical for applications such as aerospace propulsion, space travel, and power generation (including nuclear). To help translate synchrotron characterization to industry, a partnership with the Air Force Research Laboratory and the Dutton Institute at Penn State is being leveraged to develop and deploy measurement guidelines for mature synchrotron X-ray techniques. Furthermore, to train a world-wide X-ray characterization community of graduate students and professionals, instructional materials are being developed and placed online, along with workshops being hosted at synchrotron users' meetings. TECHNICAL SUMMARY This research examines how the activity and organization of dislocation ensembles in polycrystalline metallic alloys are influenced by long-range interactions (i.e., backstresses) generated by mesoscale microstructural features. Characterizing the nature of this structural evolution is an important component of improving the prediction of incipient damage in demanding service conditions. Here, bulk dislocation reconfiguration is being directly characterized through coherent diffraction from grains embedded deep within polycrystals (supported by existing 3D microstructure characterization) by taking advantage of new high-brilliance 4th generation synchrotron X-ray sources. Studies of dislocation ensemble kinetics in different macroscopic loading conditions and grain configurations are being performed on model face-centered cubic and hexagonal close-packed systems with substitutional strengthening. Unsupervised machine learning is also being leveraged to analyze these new experimental data. Findings are aiding the creation of new structure-property relationships between microstructure and deformation rate-sensitivity which, to date, has not been possible due to an inability to probe these processes at appropriate time and length scales. This program is also being used as a foundation for future research investigating more complex alloy systems and loading conditions, such as fracture, creep, and fatigue. In addition, research findings are being used to inform an education program that supports the broader metals profession, particularly translation of synchrotron characterization capabilities to industry. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2539617 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT,01002930DB NSF RESEARCH & RELATED ACTIVIT,01003031DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Darren Pagan | Institution: Pennsylvania State Univ University Park, UNIVERSITY PARK, PA | Award Amount: $388,868 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2539617 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2539617.html