Subgrains and Dynamic Grain Growth in BCC Metals

非技术概述金属及其合金提供支撑我们现代社会的精密机器所需的承重结构。有用的应用范围从飞机到汽车再到桥梁。这些结构材料由被称为颗粒的微观晶体组成。颗粒的大小、形状和取向控制着材料的机械性能，如强度和延展性。这些微观特征是材料微观结构的一部分，由生产材料并将其塑造成有用的机械部件的制造过程决定。制造经常需要在高温下变形，以控制材料的微观结构和最终的部件形状。高温相当于古代铁匠的热锻造。在热变形过程中，颗粒的大小和形状会发生变化，这是我们还无法预测或完全解释的。该项目研究了热变形过程中颗粒形状、大小和取向变化背后的基础科学。该项目的目标是了解导致这些变化的机制。通过这种科学的理解，寻找机会：1.改善材料性能和2.确定制造方法，以创造改进的材料微结构。研究生和本科生都是通过实验研究进行教育和培训的。为小学教师提供暑期研究经验、培训和资源，以便带到课堂上。技术摘要动态颗粒生长涉及高温变形过程中颗粒形状、尺寸和取向的变化。它对许多技术上有用的金属和合金的加工至关重要。然而，导致这种情况的机制目前还不清楚。这项实验研究评估了几种控制动态颗粒生长的机制中的主要假说。研究了体心立方金属高温(力学)稳态塑性变形中亚晶驱动大角度晶界迁移的假想机制。本研究的目的是描述和定量测量动态正常生长和动态异常生长过程中亚晶与高角度晶界相互作用的影响。利用电子背散射衍射数据的高分辨率分析的最新进展，提供了亚晶与晶界相互作用的定量表征。对动态晶粒长大的深入理解将为预测和控制材料在热变形过程中的微观组织提供能力。这将有利于制造业和国内竞争力。与拟议的研究相结合的是针对研究生和本科生的培训和教育活动。外展活动包括小学教师参加一个暑期研究体验和课程开发计划，以积极影响他们自己的学生。这一推广活动的重点是通过实践项目和利用微结构的美学之美的例子来传授对材料的可获得性理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical SummaryMetals and their alloys provide the load-bearing structures needed in sophisticated machines that support our modern society. Useful applications range from aircraft to automobiles to bridges. These structural materials are composed of microscopic crystals called grains. The sizes, shapes, and orientations of grains control a material's mechanical properties, such as strength and ductility. These microscopic features, part of the material microstructure, are determined by the manufacturing processes that produce and shape materials into useful machine components. Manufacturing frequently requires deformation at elevated temperatures, the modern equivalent of hot forging by the ancient blacksmith, to control the material microstructure and final component shape. During hot deformation, grains change size and shape in ways that we cannot yet predict or fully explain. This project addresses the fundamental science behind the changes in grain shape, size, and orientation during hot deformation. The goal of this project is to understand the mechanisms responsible for these changes. Through this scientific understanding, opportunities are sought to: 1. improve material performance and 2. identify manufacturing methods that create improved material microstructures. Both graduate and undergraduate students are educated and trained through experimental research. Primary-school teachers are provided summer research experience, training, and resources to bring to their classrooms.Technical SummaryDynamic grain growth involves changes in grain shape, size, and orientation during deformation at elevated temperatures. It is critically important to the processing of many technologically useful metals and alloys. However, the mechanisms that cause it are not yet understood. This experimental study assesses the leading hypothesis among several proposed for mechanisms that control dynamic grain growth. The hypothesized mechanism of subgrains driving high-angle grain boundary migration is investigated for (mechanically) steady-state plastic deformation of body-centered-cubic metals at elevated temperatures. The goal of this study is to characterize and quantitatively measure the effects of subgrain interactions with high-angle boundaries during both dynamic normal grain growth and dynamic abnormal grain growth. Recent advances in high-resolution analysis of electron back-scattered diffraction data are leveraged to provide quantitative characterization of subgrain interactions with grain boundaries. An improved understanding of dynamic grain growth will provide capabilities for predicting and controlling material microstructures during hot deformation processing. This will benefit manufacturing and domestic competitiveness. Integrated with the proposed research are training and educational activities for both graduate and undergraduate students. Outreach involves primary-school teachers participating in a summer program of research experience and curriculum development to positively impact their own students. This outreach focuses on imparting an accessible understanding of materials through hands-on projects and examples that utilize the aesthetic beauty of microstructure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.