Cooperative Grain Boundary Sliding and Heterogeneities of Grain Boundary Character Distribution in Superplastic Materials

0109535 Garmastani本项目旨在利用最新的数字成像和原位显微镜技术，更好地了解不同铝合金结构超塑性变形的基本机制。研究表明，微晶超塑性过程中的晶界滑移是异质和协同作用的结果。协作晶界滑移的非均质性性质尚不清楚。对这一重要变形模式起源的基本认识，对于改进超塑性理论模型以及设计具有更高超塑性性能的先进材料具有重要意义。本研究的主要目的是：(1)确定三种细晶铝合金(AA7475、AA5083和D19)的晶界协同滑移与晶界错位(细观织构)的关系；(2)研究这三种细晶铝合金晶界滑移的拓扑模式；(3)探讨细晶铝合金晶界协同滑移的调节机制。为了达到这些目标，两种不同的微观表征技术被结合在一起：扫描电子显微镜中的定向成像显微镜(OIM)和扫描探针显微镜中的纳米刻划。这项工作基于原位微拉伸阶段能力，该能力将与实时OIM分析结合使用，以提供有关晶界滑动性质的重要信息。这项研究的资金为FAMU-FSU工程学院的少数民族学生提供了第一手接触科学技术前沿研究的机会。%这项研究对超塑性的机制有了新的理解，超出了目前的技术水平。研究结果可用于近净成形金属加工的成本节约。这项研究将对少数民族教育和研究做出重大贡献。*

0109535GarmastaniThis project is aimed at greater understanding of fundamental mechanisms of structural superplastic deformation in different aluminum alloys using the most current digital imaging and insitu microscopy techniques. It has been established that grain boundary sliding during micrograin superplasticity operates heterogeneously and in a cooperative manner. The nature of heterogeneity of cooperative grain boundary sliding remains unclear. Fundamental understanding of the origin of this important deformation mode can be fruitful for the improvement of theoretical models of superplasticity as well as for the design of advanced materials with improved superplastic properties. The main goals of this study are: (1) to determine the relationship between cooperative grain boundary sliding and grain boundary disorientation (mesotexture) in three fine-grained aluminum alloys (AA7475, AA5083 and D19) that manifest different micro-mechanical behavior; (2) to study topological modes of grain boundary sliding in these alloys; (3) to investigate accommodation mechanisms for cooperative grain boundary sliding. To reach these goals two different micro-characterization techniques are combined together: Orientation Imaging Microscopy (OIM) in Scanning Electron Microscope and Nanoscratching with Scanning Probe Microscope. The work is based on insitu micro-tensile stage capability that will be used in conjunction with real time OIM analysis to provide important information on the nature of the grain boundary sliding. The funding for this research provides a first hand exposure to research in forefront of science and technology to minority students at FAMU-FSU College of Engineering. %%%This research develops new understanding of the mechanisms involved with superplasticity beyond the present state of the art. The results are applicable for cost savings for metal fabrication through near net shaping. The research will make significant contributions to minority education and research.***