OVERVIEW

1. 50 GPa MCS=3k, DRX=0.5% MCS=10k, DRX=28% MCS=13k, DRX=56% MCS=15k, DRX=76% 0 GPa ROLE OF GRAIN BOUNDARY CHARACTER ON DYNAMIC RECRYSTALLIZATIONMegan Frary, Boise State University, DMR 0642363 OVERVIEW Dynamic recrystallization (DRX) occurs when low to medium OOF2 SIMULATIONS are used to predict which triple junctions are most likely to act as nucleation sites for DRX. Different grain boundary characters are accounted for by assigning the GBs different stiffnesses relative to the bulk (i.e., making them more susceptible to GB sliding). OOF2 simulations show the resulting stress concentrations that would act as a driving force for nucleation. Results below are for a single triple junction and a small section of an experimental microstructure. MONTE CARLO SIMULATIONS on experimental microstructures consider anisotropic GB energy and preferential nucleation at triple junctions. 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). APPROACH EXPERIMENTAL: High temperature mechanical testing is being done on nickel, Nil-based superalloys and stainless steel. Grain boundary engineering creates microstructures with different grain boundary character distributions and EBSD is used to map grain orientations and boundary misorientations. COMPUTATIONAL: Monte Carlo simulations are being developed to study the effects of changing the fraction of twin boundaries on the kinetics and flow behavior in DRX. Experimentally-determined microstructures are used as the initial structures for the model. Orange line is stored energy vs. time and blue line is special boundary fraction. States a, b, c, d shown below. (left): No grain boundary layer. (right): Easily sheared GB layer. RESULTS MECHANICAL TESTING of grain boundary engineered stainless steel with different initial special boundary fractions is underway. The stress-strain curve below is for stainless steel tested at 1050°C and 10-5 s-1 with a special boundary fraction of 0.42. EBSD after testing shows dynamic recrystallization has occurred along some boundaries. (left) Experimental microstructure for OOF2. (right) GBs have same stiffness as bulk. 200 mm GBs 10% (left) and 1% (right) bulk stiffness

2. ROLE OF GRAIN BOUNDARY CHARACTER ON DYNAMIC RECRYSTALLIZATIONMegan Frary, Boise State University, DMR 0642363 To date, one graduate student and six undergraduate students have been involved in the project. The PI, advisor to the MSE Club, worked with club members to develop series of podcasts on processing of materials, available through the ASM webpage. In October 2008, the PI received the Bradley Stoughton Award for Young Teachers from ASM International. Undergraduate students Master of Science students JARED STEIN is a third year graduate student in Materials Science and Engineering working toward a M.S. degree. Jared is developing Monte Carlo simulations to study dynamic recrystallization and the role that grain boundary character plays during deformation. BEN ALBISTON: senior, processing and mechanical testing of stainless steel CHRIS STIFTER: sophomore, processing and characterization of Ni SHARLA HOPKINS: processing of Ni, now a high school teacher in Salt Lake City, UT WADE LANNING: models of triple junctions, now a PhD student at Penn State MICHAEL CARROLL: summer student from WSU TRAM BUI: senior, testing and characterization of Ni Podcasts: available soon http://www.materialsradio.org Outreach Activities by PI Dr. Frary has participated in the Women in Technical Careers Lunch series in Boise-area high schools for the last four years. These lunches are intended to recruit female students into science and engineering disciplines in college.