In-situ transmission electron microscopy of microstructure formation during laser irradiation induced irreversible transformations in metals and alloys

激光照射引起金属和合金不可逆转变过程中微观结构形成的原位透射电子显微镜

• 批准号: 1607922
• 负责人: Jorg Wiezorek
• 金额: $ 50.34万
• 依托单位: University of Pittsburgh
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1607922&HistoricalAwards=false
• 关键词: situ; transmission; electron; microscopy; microstructure

Non-Technical AbstractThis activity develops scientific understanding of the formation of microstructures in multi-component metallic materials during solidification under far-from-equilibrium conditions. Binary and ternary model alloys will be studied using unique electron microscopy in conjunction with characterization of the microstructures. Direct correlation of local features in the solidification microstructure with the conditions of their formation will deliver experimental data sets unobtainable with other approaches that are suitable for validation of predictions from competing theoretical models of alloy rapid solidification. The research enhances scientific understanding of microstructure formation during solidification in complex alloys and contributes to the development of techniques for nano-scale resolved studies of materials. Understanding of microstructure formation during processing of engineering materials is a fundamental challenge of the field of materials science and engineering (MSE). It enables identification of strategies for property tailoring for optimal material performance in a technological application. Solidification is ubiquitous in fabrication of metallic materials, which are particularly critical to energy generation and transmission, advanced transportation, biomedical and information technologies. Research results will be emanated by journal publication and presentations at conferences. Integration with instructional resources and outreach module development will enhance the MSE undergraduate curriculum. Modules for targeted outreach will be developed collaboratively with student teams and sustain improved MSE outreach efforts at the University of Pittsburgh. Future members of the US science, technology, engineering and mathematics workforce will receive research training, advanced science and engineering education, leadership and mentoring opportunity. Collaboration with the Lawrence Livermore National Laboratory team provides synergy for project resources and multi-faceted professional preparation outside of academia. The activity will positively impact engineering education, promote lifelong learning, broaden participation of underrepresented groups in research and advance the scientific knowledge of transformations in metallic alloys under technologically relevant non-equilibrium conditions.Technical Abstract Solidification is a ubiquitous and fundamental process in materials fabrication. Under extreme conditions arising in rapid solidification processing the migration of solid/liquid interfaces is driven far-away from equilibrium and kinetic factors can become dominant over thermodynamic factors in determining the final microstructure. We use the movie-mode dynamic transmission electron microscope (MM-DTEM) for nano-scale spatio-temporal resolution in situ imaging observations and diffraction measurements of rapid solidification transformations in alloy thin films. Complementing the in situ studies with quantitative post-mortem micro-characterization delivers direct correlation of local features in the solidification microstructure with the conditions of their formation during the irreversible transformation under-far-from-equilibrium rapid solidification. Focusing on concentrated binary Al-Cu and Al-Ag alloys, and for ternary Al-Cu-Ag alloys the research will deliver accurate global and locally resolved information on the transformation interface, including average and local velocity, changes in these velocities, and the morphology associated with changes in crystal growth modes. Post-mortem analyses of solidification microstructures provide compositional gradients, crystal structures, as well as the local arrangements, size, shape and composition of the constituent phases, which may differ from those that would form at or near equilibrium conditions. The use of thin film alloy specimens enables study of rapid solidification transformation microstructure formation for unexplored regimes of composition (e.g. hypereutectics in Al-Cu) and very large transformation rate, suitable to elucidate details of transitions to banded morphology and partitionless alloy crystal growth for instance. Effects of atomic size misfit, faceting tendencies, chemical ordering and interfacial coherency, as well as Ag addition effects on two-phase solidification microstructure formation will be determined using Al-Cu and Al-Ag alloys Al-Cu-Ag ternaries. The proposed research will deliver unique experimental data sets and insights suitable to evaluate current rapid solidification models and will enhance scientific understanding of microstructure formation in solidification of multi-phase alloy systems.

这项活动发展了对多组分金属材料在远离平衡状态下凝固过程中微观结构形成的科学理解。二元和三元模型合金将研究使用独特的电子显微镜结合表征的微观结构。凝固微观结构的局部特征与其形成条件的直接关联将提供其他方法无法获得的实验数据集，这些数据集适用于验证来自竞争性合金快速凝固理论模型的预测。该研究提高了对复杂合金凝固过程中微观结构形成的科学认识，并有助于材料纳米级分解研究技术的发展。了解工程材料加工过程中的微观结构形成是材料科学与工程（MSE）领域的一个基本挑战。它能够在技术应用中识别属性定制策略以获得最佳材料性能。凝固在金属材料的制造中无处不在，这对能源的产生和传输、先进的运输、生物医学和信息技术尤为重要。研究成果将通过期刊出版和会议报告的形式发表。整合教学资源和拓展模块开发将提高MSE本科课程。有针对性的外展模块将与学生团队合作开发，并在匹兹堡大学维持改进的MSE外展工作。未来的美国科学、技术、工程和数学工作者将获得研究培训、先进的科学和工程教育、领导和指导机会。与劳伦斯利弗莫尔国家实验室团队的合作为项目资源和学术界以外的多方面专业准备提供了协同作用。这项活动将对工程教育产生积极影响，促进终身学习，扩大代表性不足的群体参与研究，并促进在技术有关的非平衡条件下金属合金转变的科学知识。凝固是材料制造中普遍存在的基本过程。在快速凝固过程中产生的极端条件下，固/液界面的迁移远离平衡，动力学因素在决定最终微观组织方面可能比热力学因素更重要。利用薄膜模式动态透射电子显微镜（MM-DTEM）对合金薄膜的快速凝固转变进行了纳米尺度的时空分辨率原位成像观察和衍射测量。用定量的死后微观表征来补充原位研究，可以将凝固微观结构的局部特征与其在非平衡快速凝固不可逆转变过程中形成条件直接联系起来。聚焦于浓缩二元Al-Cu和Al-Ag合金，以及三元Al-Cu- ag合金，该研究将提供准确的全局和局部转化界面信息，包括平均和局部速度，这些速度的变化，以及与晶体生长模式变化相关的形态。凝固显微组织的事后分析提供了成分梯度、晶体结构，以及组成相的局部排列、大小、形状和组成，这些可能与在平衡或接近平衡条件下形成的相不同。使用薄膜合金试样可以研究未开发的成分（例如Al-Cu中的过共晶）和非常大的转变速率的快速凝固转变微观结构形成，适合阐明向带状形态转变的细节和无分区合金晶体生长。采用Al-Cu合金和Al-Ag合金，研究了原子尺寸失配、饰面倾向、化学有序度和界面相干性以及Ag的加入对两相凝固组织形成的影响。所提出的研究将提供独特的实验数据集和见解，适用于评估当前的快速凝固模型，并将加强对多相合金系统凝固过程中微观结构形成的科学理解。