CAREER: Role of Grain Boundary Character on Dynamic Recrystallization

技术支持：该项目的目的是更好地了解动态再结晶的晶界特征的作用，在本地和全球。这一目标将通过实验和计算机模拟相结合来实现。通过使用这两种方法，实验工作将为计算机模型提供输入，而模拟将用于更好地理解实验观察到的行为，并建议未来的实验设计。实验方法将依赖于高温机械测试和电子背散射衍射的使用，这可以映射大面积的样品的晶粒取向和晶界取向差。第一组实验将研究动态再结晶晶粒在三重结处的成核如何取决于几个因素，包括材料的堆垛层错能、包括三重结的边界的特性以及三重结的几何形状。在第二组实验中，晶界工程处理技术将用于创建具有不同比例的低能孪晶界的样品。然后进行动态再结晶（DRX）实验，以确定增加孪晶界分数对DRX的影响，特别是关于流动应力，峰值应变和再结晶动力学。实验工作将集中在镍，镍基高温合金和不锈钢合金，因为由这些材料制成的部件通常在加工过程中进行热加工，在此过程中，显微组织演变由DRX决定。计算机模拟将补充实验工作，并用于更好地理解实验观察。一个面向对象的有限元代码称为OOF将被用来研究应力集中，出现在三重结作为晶体学和几何条件的函数，并在这些点的微观结构中的再结晶晶粒的成核中发挥作用。采用蒙特卡罗模拟方法研究了孪晶界比例的变化对动态再结晶动力学和流动行为的影响。非技术性：这项工作将在博伊西州立大学进行，该大学位于国家公认的高科技和创业中心金银谷。PI在博伊西州立大学的材料科学与工程系（MSE），该大学目前提供学士和硕士学位，计划于2008年。PI的研究计划将在MSE计划的成功中发挥关键作用，该计划为爱达荷州的学生提供高质量的教育，其中许多人是第一代大学生。教育和推广计划涉及开发基于网络的可重复使用的学习对象，作为向广大受众传播研究成果的一种新方法。这些独立的电子课程将在网上提供，高中或大学教师可以独立使用，也可以整合到现有的课程中。此外，动态再结晶的主题和实验能力的发展，这里将包括在PI的本科课程，材料的力学行为。最后，PI将继续招募和指导不同的学生群体。为了招募妇女和代表性不足的少数民族，PI将继续参加当地高中的技术职业妇女午餐系列、电子女孩、高中女生暑期项目和西班牙裔高中生米兰达阿得兰特讲习班等项目。

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.