POWRE: A Fundamental Study of Microstructual Evolution in Titanium Alloy Friction Stir Welds

本项目旨在更好地了解钛合金搅拌摩擦焊缝高温变形和显微组织演变的基本机制。选择了两种合金，纯（CP）钛和Ti-6Al-4V， a + b合金。CP钛因其良好的成形性而被广泛应用于化工行业，具有良好的耐腐蚀性。Ti-6Al-4V广泛应用于各种焊接和非焊接条件下的航空航天和船舶应用。除了“正常”焊缝外，在到达待连接的两块板的末端之前将工具收回的断续焊缝也将进行评估。通过这种方法，将热机械影响区和热影响区的微观组织与焊接前的材料进行比较。这些又将与搅拌区（实际的动态再结晶焊缝）和基材的显微组织进行比较。样品将在横向和纵向上进行金相检查，以揭示每个不同的微观结构区域，并作为TEM箔最终位置的地图。双束（电子束+离子束）聚焦离子束（FIB）将用于在焊缝内精确指定的位置去除TEM箔。这将大大提高获得具有所需显微结构信息的箔片的机会。衍射对比技术将用于飞利浦CM 200和CM 300场发射枪tem上，以确定变形过程的细节，即变形子结构（例如，亚晶粒和子带）的发展，动态恢复和再结晶的发生，退火效应和相变。扫描电子显微镜将在飞利浦XL-30 FEG仪器上使用定向成像显微镜进行，以显示可能来自基材残留的微纹理。这些微观结构研究的结果将用于补充工艺优化和力学性能数据。这是在研究和教育领域妇女专业机会（POWRE）计划下提供的一项研究加强补助金。在担任行政职务四年后，PI计划重新调整她的职业。在担任爱迪生焊接研究所航空航天团队负责人和俄亥俄州立大学材料加速成熟中心（CAMM）副主任之前，她领导了15年的积极技术职业生涯。该研究有望在与金属行为特别相关的基础水平上贡献基础材料科学知识。该项目由材料研究司和MPS OMA（多学科活动办公室）共同支持。＊＊＊

This project is aimed at greater understanding of fundamental mechanisms of high temperature deformation and microstructural evolution in titanium alloy friction stir welds. Two alloys have been selected, pure(CP) titanium and Ti-6Al-4V, a + b alloy. CP titanium, used for its corrosion resistance especially in the chemical process industry, was chosen for its good formability. Ti-6Al-4V is widely used in a variety of aerospace and marine applications in welded and unwelded conditions. In addition to "normal" welds, interrupted welds, where the tool is retracted before reaching the end of the two plates to be joined, will also be evaluated. In this way, the micro-structures of the thermomechanically-affected and heat-affected zones will be compared with material just ahead of the weld. These in turn will be compared with microstructures of the stir zone (the actual dynamically recrystallized weld) and the base material. Samples will be obtained for metallographic examination in both the transverse and longitudinal directions to reveal each distinct microstructural zone and serve as a map for the eventual location of TEM foils. A dual beam (electron beam + ion beam) Focused Ion Beam (FIB) will be used to remove TEM foils at precisely designated locations within the welds. This will greatly improve the chances of obtain-ing a foil with the desired microstructural information. Diffraction contrast techniques will be used on a Philips CM 200 and CM 300 Field Emission Gun TEMs to determine the details of the deformation processes, i.e., the development of deformation substructure (e.g., sub-grains and sub-bands), the occurrence of dynamic recovery and recrystallization, annealing effects, and phase transformations. Scanning electron microscopy will be performed on a Philips XL-30 FEG instrument using Orientation Imaging Microscopy to reveal possible microtexture that may be residual from the base material. The results of these microstructural studies will be used to complement process optimization and mechanical property data.%%% This is a research enhancement grant made under the Professional Opportunities for Women in Research and Education (POWRE) program. The PI plans to realign her career after a four-year hiatus in an administrative capacity. Prior to working as Aerospace Team Leader at Edison Welding Institute and Associate Director for the Center for the Accelerated Maturation of Mate-rials (CAMM) at the Ohio State University, she led an active technical career for 15 years. The research is expected to contribute basic materials science knowledge at a fundamental level of special relevance to the behavior of metals. The project is co-supported by the Division of Mate-rials Research, and the MPS OMA(Office of Multidisciplinary Activities). ***