Role of Grain Boundary Character on Dynamic Recrystallization Megan Frary, Boise State University, DMR IMPORTANCE OF RESULTS: Developing an understanding of the role microstructure and especially grain boundary character play in DRX, we can develop processing routes that enhance materials’ properties in a range of applications. OVERVIEW: Dynamic recrystallization (DRX) occurs when low to medium stacking fault energy materials undergo deformation at high homologous temperatures (e.g., during hot working). The project objective is to elucidate the role of grain boundary character on DRX, both locally (e.g., through nucleation at individual triple junctions) and globally (e.g., when the fraction of special boundaries changes). HIGHLIGHTS FROM THE PROJECT YEAR: Monte Carlo simulations have been modified such that: (1) multiple cycles of DRX can occur, (2) the orientation of new grains can be defined with respect to existing grains, and (3) grain boundary character is considered during nucleation. These modifications, combined with our application of the Monte Carlo simulations to experimentally determined microstructures allows for realistic modeling of DRX. Our emphasis in analyzing the Monte Carlo data is understanding how grain boundary character affects the DRX behavior and which boundary triple junctions experience DRX at the lowest strain levels. Experimentally, test parameters are being identified that result in DRX in stainless steel specimens. Simulation and experimental results will be correlated with emphasis on grain boundary and triple junction character. Results from Monte Carlo simulations. The graph on the left shows the average stored energy in the system (in arbitrary units) as a function of time with different values of the incremental stored energy (or different “strain rates”). Higher strain rates do not permit multiple cycles of recrystallization. The images on the right show the initial microstructure and the resulting microstructure after the first cycle of recrystallization. When anisotropic boundary energies are used, nucleation occurs preferentially on high energy boundaries. Results from experimental work on stainless steel. The graph on the right shows the stress-strain curve for the sample tested at 1000°C and a strain rate of 0.01 s -1. The image on the left shows the microstructure of the gauge section after mechanical testing. DRX is evident along the grain boundaries.

Role of Grain Boundary Character on Dynamic Recrystallization Megan Frary, Boise State University, DMR Chris Stifter and Ben Albiston, undergraduates, won a Best Poster Award at the TMS 2010 Annual Meeting for their work on this project. Dr. Megan Frary, PI, presented a talk about the “Magic of Metals” to more than 50 visitors at NanoDays at the Discovery Center of Idaho in April She has also been involved in on-campus programs to recruit underrepresented students to MSE. The project supported two graduate and four undergraduate students this year. In the fall, two new students will join the project through a NSF STEP mentoring program. In collaboration with Dr. Yonnie Chyung, Professor, and Ayanne Levy, graduate student, from Boise State’s Instructional and Performance Technology Department, we have developed a web-based reusable learning object that summarizes both dynamic recrystallization in general and the specific work underway at Boise State. The web-based tool includes interactive guided images, results from this project, a timeline of DRX research, and a glossary. The resource has been submitted for inclusion in the NSDL.