GOALI: Deformation Microscopy of Retained Austenite Transformation in TRIP Steels

非技术总结：现代车辆的效率严重影响个人和国家的繁荣、国家能源独立、城市污染水平（及相关健康）和气候变化。决定这种效率的一个关键因素是车辆重量。虽然许多正在进行的努力旨在将轻质材料（如铝、镁和碳复合材料）引入汽车结构，但到目前为止，主要成分仍然是相对较重的钢。因此，该项目侧重于开发具有改进成形性的先进高强度钢的替代轻量化策略；这将允许更少的金属提供相同的结构和安全性能。新的和新兴的显微技术与模拟相结合，揭示了现代高强度钢的微观结构和性能之间的关系。由此产生的见解导致了对所谓的第三代钢材的诞生以及车辆重量和效率的逐步变化所需的更深层次的理解和改进模型。这个研究项目不仅为研究生和本科生提供了一个混合学术/工业环境的指导环境（通过与通用汽车公司的强有力合作），而且通过一个外展计划，高中教育正在得到改善。来自当地高中的教师在夏季的几个月里花时间在这个项目上，同时接受帮助，为他们的班级开发新的和相关的课程组成部分。技术概述：对TRIP（相变诱发塑性）钢进行了许多研究。然而，关于奥氏体化学和显微组织对最终转变为马氏体的影响，目前还没有系统的资料。这些知识对于设计残余奥氏体的织构、形貌和体积分数至关重要，从而使低合金TRIP钢获得更高的强度、成形性和抗断裂性，从而达到所需的汽车结构性能。提出的残余奥氏体和马氏体识别技术（基于新兴的电子背散射衍射技术），以及中尺度位错表征，与微数字图像相关（DIC）相结合，提供了一种新的“变形显微镜”能力。由此产生的框架允许评估位错和硬相边界之间的相互作用，同时也精确地捕获各种保留的奥氏体岛转变的应变。了解微观结构和成形性之间的基本联系，可以建立奥氏体向马氏体转变的中尺度模型，以及相关的变形现象。

NON-TECHNICAL SUMMARY:The efficiency of modern vehicles critically affects individual and national prosperity, national energy independence, city pollution levels (and related health) and climate change. A key element in deciding this efficiency is vehicle weight. While many ongoing efforts aim at introducing lightweight materials (such as aluminum, magnesium and carbon composites) into automotive structures, the dominant constituent, by far, is still relatively heavy steel. Hence this project focuses on the alternative light-weighting strategy of developing advanced high strength steels with improved formability; this will allow less metal to provide the same structural and safety performance. New and emerging microscopy techniques are combined with simulation to reveal the relationships between microstructure and properties of modern high-strength steels. The resulting insights lead to the deeper levels of understanding and improved models that are required for the nascence of so-called third-generation steels and a step-change in vehicle weight and efficiency. Not only does this research project provide an environment for mentoring graduate and undergraduate students in a mixed academic / industrial setting (via a strong collaboration with General Motors), but high school education is being improved via an outreach program. Teachers from local high schools spend time on the project during the summer months while receiving help in developing new and relevant curriculum components for their classes.TECHNICAL SUMMARY:Many studies have been carried out on TRIP (Transformation Induced Plasticity) steels. However, there is still no systematic information concerning the influence of austenite chemistry and microstructure on the resulting transformation to martensite. Such knowledge is critical to the design of texture, morphology and volume fraction of retained austenite in order to enable low-alloy TRIP steels to achieve enhanced strength, formability, and fracture resistance necessary to achieve the desired automotive structure performance. Proposed retained-austenite and martensite identification technologies (based upon emerging electron-backscatter diffraction techniques), along with meso-scale dislocation characterization, are combined with micro-digital image correlation (DIC) to provide a new 'Deformation Microscopy' capability. The resultant framework allows for the assessment of interactions between dislocations and hard phase boundaries, while also precisely capturing the strains at which the various retained austenite islands transform. Knowledge of the fundamental links between microstructure and formability enables the formulation of a meso-scale model for transformation of austenite to martensite, and related deformation phenomena.