CAREER: Role of Grain Boundary Character on Dynamic Recrystallization

TECHNICAL: The objective of the project is to better understand the role of grain boundary character on dynamic recrystallization, both locally and globally. This goal will be achieved through a combination of experiments and computer simulations. By using both approaches, the experimental work will provide input to the computer models, while the simulations will be used to better understand the experimentally observed behavior and to suggest future experimental designs. The experimental approach will rely on the use of high temperature mechanical testing and electron backscatter diffraction, which can map grain orientations and grain boundary misorientations over large areas of the sample. The first set of experiments will investigate how the nucleation of dynamically recrystallized grains at a triple junction depends on several factors including the stacking fault energy of the material, the character of the boundaries that comprise the triple junction, and the geometry of the triple junction. In the second set of experiments grain boundary engineering processing techniques will be used to create samples with varying fractions of low-energy twin boundaries. Dynamic recrystallization (DRX) experiments will then be performed to determine the effect of increasing the fraction of twin boundaries on DRX, especially with regard to the flow stress, peak strain and kinetics of recrystallization. The experimental work will focus on nickel, nickel-based superalloys, and stainless steel alloys, as components made from these materials often undergo hot working during processing during which the microstructural evolution is determined by DRX. The computer simulations will complement the experimental work and be used to better understand the experimental observations. An object-oriented finite element code called OOF will be used to study the stress concentration that arises at triple junctions as a function of crystallographic and geometric conditions and which plays a role in the nucleation of recrystallized grains at these points in the microstructure. Monte Carlo simulations will be used to study the effects of changing the fraction of twin boundaries on the kinetics and flow behavior in DRX. NON-TECHNICAL: The work is to be carried out at Boise State University, which is located in the Treasure Valley, nationally recognized as a high tech and entrepreneurial center. The PI is in the Department of Materials Science and Engineering (MSE) at Boise State University, which currently offers bachelors and masters degrees, with a Ph.D. program planned for 2008. The research program of the PI will play a critical role in the success of the MSE program, which offers a high quality education to students in Idaho, many of whom are first-generation college students. Education and outreach plans involve the development of web-based reusable learning objects as a novel approach to disseminating the results of the research to a broad audience. These stand-alone, electronic lessons will be available online and can be used independently by high school or college teachers or integrated into existing courses. In addition, the topic of dynamic recrystallization and the experimental capabilities developed here will be included in the PI's undergraduate course, Mechanical Behavior of Materials. Finally, the PI will continue to recruit and mentor a diverse group of students. In order to recruit women and under-represented minorities, the PI will continue to participate in programs such as the Women in Technical Careers lunch series at local high schools, e-Girls, a summer program for high school girls, and the Miranda Adelante Workshop for Hispanic high school students.