EXPERIMENTAL RESULTS:

1. Role of Grain Boundary Character on Dynamic RecrystallizationMegan E. Frary, Boise State University, DMR 0642363 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. SIMULATIONS: The final analysis that we performed from the Monte Carlo simulations involved determining where nucleation occurs (on grain boundaries of a certain character and/or at boundary triple junctions). The figures to the right show the results from simulations on a sample with low and high special boundary fraction. The plots on the left show where nuclei form (e.g., triple junctions or non-triple junctions) during the first cycle of DRX as compared to the population of the site type. The plots on the right show which triple junction sites, as characterized by the number of special boundaries at the junction (0 to 3), are most likely sites for nucleation. For both special fraction values, we find that triple junction sites are preferred and that, among those sites, junctions with fewer special boundaries are more likely to have nucleation occur. EXPERIMENTAL WORK: In the past year, we have been able to compare experimental results for nucleation location with those from simulations. Samples tested in tension at 900°C, with a strain rate of 10-2 s-1, and to strains ranging from 5 – 35% are analyzed. After the test, microstructural analysis focuses on the nuclei which form (see figure at the bottom right for 10% strain). Semi-automated analysis routines let us determine the type and number of nuclei that form and the character of the grain boundaries involved. These results are compared to those from simulations. The figure at the bottom left shows that more nuclei are found on grain boundaries (labeled total L) than at the triple junctions (labeled total J). Nevertheless, we find, as the simulations showed, that (1) general boundaries are preferred to special boundaries for nucleation, and (2) triple junctions with fewer special boundaries are more likely to be nucleation sites. This analysis work is still underway and we continue to collect data to make the analysis more statistically robust. SIMULATIONS OF LOW SPECIAL FRACTION SAMPLE: SIMULATIONS OF HIGH SPECIAL FRACTION SAMPLE: n A B C EXPERIMENTAL RESULTS: A

2. Role of Grain Boundary Character on Dynamic Recrystallization Megan E. Frary, Boise State University, DMR 0642363 Graduate Students Student Training The students who have worked on this project, and the undergraduates in particular, have developed levels of technical expertise that have uniquely positioned them within and outside of the university. The students still at Boise State are the most expert users on campus of the mechanical testing and electron backscatter diffraction systems. They are routinely asked to collaborate with other research groups where these tools are required. Students working on the project have also been able to build upon the skills they developed here as they move forward to positions in industry or graduate school. Here are highlights of where some of these students are now. In most cases, the positions are a direct result of the technical skills developed as part of this NSF sponsored project: Michael Morse (left) graduated with a M.S. in December 2011 and is now working as a TEM Engineer at Micron Technology. Callum Poole is still working toward a Master’s degree at Boise State. Undergraduate Students Caleb Corolewski(left) graduated in May 2012 and is now pursuing a Ph.D. in MSE from Washington State University. Chris Stifter(right) will graduate this fall. Sharla Hopkins is working as a research engineer for Black Diamond Equipment, testing the mechanical properties of carabineers. Megan Beck (left) and Koyuki Fritchman (right) will both be juniors in MSE this fall. Both work on the project throughout the school year. Koyuki spent the summer at an REU program at Clemson. Ben Albistonis pursuing a M.S. from Boise State, studying recrystallization during fatigue crack growth. Tram Bui received a graduate fellowship from the Nuclear Regulatory Commission and is about to complete her M.S. from Boise State University.