Role of Grain Boundary Character on Dynamic Recrystallization Megan E. Frary, Boise State University, DMR Dynamic recrystallization occurs when materials are deformed at elevated temperatures and significantly impacts the final microstructure. Using both experiments and simulations, we are investigating what role the initial fraction of so-called “special” (generally low energy) grain boundaries has on the deformation and microstructural evolution in stainless steel 316. EXPERIMENTAL WORK: The parameter space where DRX will be observed in our materials of interest has been identified for both tensile and compressive loading (see top picture to the right). This means that samples with different initial special fractions can be produced by grain boundary engineering with varying geometries and tested using either method. We have also determined the appropriate characterization techniques that allow for resolution of very fine new grains and quantification of deformation, and therefore DRX, in these samples. SIMULATIONS: Using Monte Carlo simulations, the evolution of experimentally-determined microstructures are simulated. This year, we’ve been focused on the where nucleation occurs (on grain boundaries of a certain character and/or at boundary triple junctions). The lower figure on the right shows that triple junctions with no special boundaries are more likely sites for nucleation than their population in the microstructure would suggest. In contrast, junctions with three special boundaries are mostly inactive as nucleation sites. In addition to these activities, we’ve also begun to adapt a mass-spring-damper model to the phenomenon of DRX. Although many of the parameters that affect DRX behavior are understood (e.g., temperature, initial grain size), the role of special boundary fraction is still unknown. We expect that a higher special boundary fraction will lead to a higher “effective” grain size. Understanding this effect will allow for better prediction of the final microstructure when DRX is used in industrial applications. Of the available triple junction sites, the percentage of different triple junction types can be tracked along with the percentage of nucleations that form at each type. Only the fraction of nuclei that form at J0 types surpass the peak of the available sites, implying forming at J0 triple junctions occurs at a higher than random frequency. EBSD orientation maps of stainless steel 316 after (left) tensile testing at 900 C, and a strain rate of s -1 to a strain of 50% and (right) compression testing at 900 C, and a strain rate of s -1 to a strain of 70%. Both sets of test conditions show DRX along grain boundaries. Current work is analyzing the boundary character where DRX is initiated and the role of the fraction of special grain boundaries.

Role of Grain Boundary Character on Dynamic Recrystallization Megan E. Frary, Boise State University, DMR In the past year, four undergraduate and two graduate students contributed to this project. Two of these students, Koyuki Fritchman (left) and Megan Beck (right), are freshmen majoring in Materials Science and Engineering. Koyuki was supported through an NSF STEP grant at Boise State and both students participated in a seminar series related to the conduct of STEM research. Two more undergraduates, Caleb Corolewski (left) and Chris Stifter (right), both juniors in Materials Science and Engineering, continued their work on the project. Chris and Caleb now possess the skills such that they are routinely training other students in the MSE department how to use the tools involved in their research. Finally, two graduate students, Michael Morse (left) and Callum Poole (right), both of whom are working toward M.S. degrees have been involved in the research. All of the undergraduates and Michael traveled to the 2011 TMS Annual Meeting in San Diego, CA where they presented two different posters on the experimental and simulation aspects of the project. Especially for the undergraduate students, attending an international conference provided a great opportunity to broaden their perspectives in the field.