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

非技术性摘要本活动发展了对多组分金属材料在远离平衡条件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使用独特的电子显微镜结合微观结构的表征进行研究。直接相关的局部特征的凝固微观结构与它们的形成条件将提供实验数据集无法获得与其他方法，适合于验证的预测从竞争理论模型的合金快速凝固。该研究增强了对复杂合金凝固过程中微观结构形成的科学理解，并有助于材料纳米尺度分辨研究技术的发展。理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领域的一个基本挑战。 它能够识别属性定制策略，以在技术应用中实现最佳材料性能。凝固在金属材料的制造中无处不在，这对能源生产和传输，先进的交通运输，生物医学和信息技术特别重要。研究成果将通过期刊出版和会议演讲发布。与教学资源和推广模块开发的整合将加强MSE本科课程。将与学生团队合作开发有针对性的外展模块，并在匹兹堡大学持续改进MSE外展工作。美国科学，技术，工程和数学劳动力的未来成员将接受研究培训，先进的科学和工程教育，领导和指导的机会。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。该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在研究中的参与，并提高在技术相关的非平衡条件下金属合金转化的科学知识。技术摘要凝固是材料制造中普遍存在的基本过程。在快速凝固过程中出现的极端条件下，固/液界面的迁移被驱动远离平衡，并且动力学因素在确定最终微观结构时可以变得比热力学因素占主导地位。利用动态透射电子显微镜（MM-DTEM）对合金薄膜的快速凝固相变进行了纳米级时空分辨率的原位成像观察和衍射测量。补充原位研究与定量事后微观表征提供了直接相关的局部特征的凝固微观结构与它们的形成条件下的不可逆转变下远离平衡快速凝固。集中在二元Al-Cu和Al-Ag合金，三元Al-Cu-Ag合金的研究将提供准确的全球和局部解决的信息的转换界面，包括平均和局部速度，这些速度的变化，和形态与晶体生长模式的变化。凝固微观结构的事后分析提供了组成梯度、晶体结构以及组成相的局部排列、尺寸、形状和组成，这些组成相可能不同于在平衡条件下或接近平衡条件下形成的组成相。薄膜合金试样的使用使得能够研究快速凝固转变微观结构形成的未探索的制度的组成（例如，在Al-Cu中的过共晶）和非常大的转变速率，适合于阐明例如带状形态和无分区合金晶体生长的过渡的细节。采用Al-Cu和Al-Ag合金Al-Cu-Ag三元系研究了原子尺寸失配、小面倾向、化学有序性和界面相干性以及Ag添加对两相凝固组织形成的影响。拟议的研究将提供独特的实验数据集和见解，适合评估当前的快速凝固模型，并将提高对多相合金系统凝固中微观结构形成的科学理解。

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.