Texture Evolution and Softening During Discontinuous Dynamic Recrystallization

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Metals are enablers of numerous advanced engineering designs that require high strength and toughness, and remain irreplaceable for key components in structural applications in aviation, transportation, power generation, etc. The mechanical properties of engineering metals are closely related to their internal microstructure, which is obtained and optimized through thermal and mechanical processing. However, the processing-microstructure relationship is still poorly understood, which severely limits the prospect of direct one-step microstructure engineering. This award supports an integrated computational and experimental study to establish a quantitative physics-based model that will be used to explore the fundamental mechanisms that control microstructure evolution during hot working. The model will have the ability to assist in the design and optimization of thermomechanical processes for many engineering alloys including nickel-based superalloys for high temperature applications and magnesium-alloys for light structural applications. The PIs are committed to support an undergraduate research program as well as an existing university program that engages undergraduate researchers as mentors who develop K-12 engineering outreach activities under the guidance of K-12 educators.Dynamic recrystallization (DRX) involves the nucleation and growth of new grains during straining at elevated temperatures and plays a critical role in controlling microstructure changes during thermomechanical processing (TMP). Nevertheless, many aspects of DRX remain poorly understood, with the lack of both fundamental knowledge and predictive physics-based models for the evolution of dislocation density, grain structure and texture and the corresponding effects on the macroscopic stress-strain response. This award supports an integrated computational and experimental study that will first establish a full-field DRX model by dynamically coupling a phase-field recrystallization model with a fast Fourier transform crystal plasticity model. Then the model will be used to investigate the following central hypothesis on DRX: The orientation of newly nucleated grains and the degree of subsequent softening are direct consequences of the long-range, inter-granular stress field resulting from plastic anisotropy and the dislocation structure evolution near grain boundaries. In addition to the traditional bulging mechanism, a new DRX nucleation mechanism that selects orientations for easy elastic or plastic deformation will be tested. The computational model established in this project will be directly applicable to many important engineering alloys such as nickel-base superalloys and magnesium-alloys during TMP. The processing-texture-property relationship established in this research will improve the fundamental understanding of the interplay between microstructural and micromechanical fields during DRX and may lead to better optimization of industrial processing.