An Atom-Probe Tomography and Lattice Kinetic Monte Carlo Study of Phase Separation in Ni-Al-Based Alloys from the Atomic Scale Up to Link with Continuum Theories

镍铝合金相分离的原子探针断层扫描和晶格动力学蒙特卡罗研究，从原子尺度到与连续体理论的联系

• 批准号: 1207539
• 负责人: David Seidman
• 金额: $ 58万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-15 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1207539&HistoricalAwards=false
• 关键词: Atom; Probe; Tomography; Lattice; Kinetic

TECHNICAL SUMMARY: The kinetic pathways in the early stages of phase separation of a concentrated multicomponent supersaturated solid-solution are critical to the development of the final microstructure, which is of significant technological importance for controlling the physical and mechanical properties of a material at the macroscopic scale. On the theoretical side, kinetic pathways are described in terms of nucleation, growth and coarsening, whose theory implies diffusion in the matrix, transfer of atoms across a matrix/precipitate interface together with the assumption of local equilibrium. The most recent achievements of high-yield atom-probe tomography (APT) and fast lattice kinetic Monte Carlo (LKMC) simulations make it possible to describe phase separation at the atomic scale. The necessary parameters for the thermodynamics and kinetics are deduced from first-principles calculations and experimental fits for the LKMC parameters. In the case of coherent precipitation, phase separation is simply the footprint left by the myriad of vacancy jumps in the inhomogeneous distribution of atomic species. Because the same vacancy jumps are at work in the equilibrium solid-solution, a link is established between features of kinetic pathways and diffusion in a solid-solution. Our APT experimental results demonstrate directly that correlation effects (flux-couplings) in solid-state diffusion control the early stage kinetic pathway for coherent-phase separation. Such effects are neglected by all extant variants of nucleation theory, which all rely on a simplified form of the diffusion matrix. We have developed a transformative approach that employs state-of-the-art APT coupled with LKMC simulations and diffusion theory for phase separation, which studies the kinetic pathways experimentally and models it via simulations and diffusion theory. And we have demonstrated the uniqueness of this approach for concentrated Ni-Al-Cr alloys. The combined use of APT and LKMC in model Ni-base superalloys provides a unique data-base (experimental and LKMC results) for developing a new theory of nucleation in binary (Ni-Al) and concentrated multi-component alloys (Ni-Al-Cr and Ni-Al-Mo). Classical nucleation theory assumes that the atomic fluxes are such that the decomposition path follows the steepest slope of the configurational free energy surface, whereas kinetic coupling of the fluxes is one reason why this isn't generally correct: also the disparate diffusivities involved is another reason. Our approach will take into account the coupled-flux effects that lead to nucleation of a second phase. In this new approach the interfacial width should be affected by the diffusion mechanism (unlike in the Cahn-Hilliard formalism). Additionally, we propose to implement a parallel LKMC simulation code for multi-component systems based on perfect time synchronicity, which is based on a code developed by Martinez et al. at LANL that will accelerate the LKMC simulations. The proposed research will lead to a completely different way of viewing kinetic pathways for phase separation of a solid-solution, and hence, nucleation, growth and coarsening.NON-TECHNICAL SUMMARY: Our unique approach to phase separation makes extensive use of a local-electrode atom-probe (LEAP) tomograph in the Northwestern University Center for Atom-Probe Tomography (NUCAPT). NUCAPT is unique university facility in the US, which has had and will have a significant impact on the research efforts of undergraduate work-study, senior thesis, research experiences for undergraduates (REU), M.S., Ph.D. and postdoctoral students: during the last four years many underrepresented groups of students have used NUCAPT. In the Department of Materials Science and Engineering at Northwestern six professors and their students make extensive use of NUCAPT. Additionally, NUCAPT has users from other US universities, and both national and industrial laboratories. Research results based on atom-probe tomography are published in the archival literature and our web site, http://nucapt.northwestern.edu , has a library from which reprints can downloaded as PDF files. Through NUCAPT we have educated a large number of people in the application of atom-probe tomography to a wide range of materials science and engineering problems, which is important for characterizing materials at the subnanoscale scale. Additionally, we are interacting with a materials scientist in France on the subject matter of this research and are supplying service to industrial companies in the US and abroad. There is no one else in the US doing this to the extent that we are accomplishing this objective.

技术摘要：浓缩多组分超饱和固定溶液的相分离早期的动力学途径对于最终微观结构的发展至关重要，这对于控制材料的物理和机械性能至关重要。在理论方面，动力学途径是用成核，生长和粗化来描述的，其理论意味着在基质中扩散，原子在基质/沉淀界面中的转移以及局部平衡​​的假设。高产原子探针断层扫描（APT）和快速晶格动力学蒙特卡洛（LKMC）模拟的最新成就使得可以在原子量表上描述相位分离成为可能。热力学和动力学的必要参数是从第一原理计算和LKMC参数的实验拟合中推导的。在相干降水的情况下，相位分离仅仅是原子种类不均匀分布中无数空位跳跃留下的足迹。由于相同的空缺跳跃在平衡固体溶液中起作用，因此在动力学途径的特征与固定溶液中扩散之间建立了联系。我们的恰当实验结果表明，固态扩散中的相关效应（通量耦合）控制着相干性分离的早期动力学途径。成核理论的所有现有变体都忽略了这种效果，该理论都依赖于扩散基质的简化形式。我们已经开发了一种变革性的方法，该方法采用了最先进的APT，以及LKMC模拟和相位分离的扩散理论，该方法通过实验研究动力学途径，并通过模拟和扩散理论对其进行建模。我们已经证明了这种浓缩的Ni-Al-Cr合金的独特性。在Ni碱模型超合金中，APT和LKMC的合并使用提供了独特的数据库（实验和LKMC结果），以开发新的二元（NI-AL）和浓缩多组分合金（NI-AL-AL-AL-AL-CR和NI-AL-MO）的新成核理论。经典的成核理论假设原子通量是使分解路径遵循构型自由能表面的最陡峭斜率，而通量的动力学耦合是另一个原因：同样涉及的不同扩散率是另一个原因。我们的方法将考虑导致第二阶段成核的耦合升级效应。在这种新方法中，界面宽度应受到扩散机制的影响（与Cahn-Hilliard形式主义不同）。此外，我们建议基于Martinez等人开发的代码，为多组件系统实施平行的LKMC仿真代码。在LANL，将加速LKMC模拟。拟议的研究将导致一种完全不同的方法来查看动力学途径，以进行固体的相位分离，因此，成核，生长和浓缩。Non-technical摘要：我们的相位分离的独特方法可以广泛使用局部电子原子 - 原子 - probe（LEAP）在西北大学中心的Atom-Probe probapt（Nuboppe）（Nuctopt）。 Nucapt是美国独特的大学设施，该设施对本科生工作，高级论文，本科生研究经验（REU），M.S.，Ph.D。的研究工作有重大影响。和博士后学生：在过去的四年中，许多代表性不足的学生使用了核心。在西北六位教授及其学生的材料科学与工程系中，广泛使用了核心。此外，Nutapt拥有来自美国其他大学以及国家和工业实验室的用户。基于Atom-Probe断层扫描的研究结果发表在档案文献中，我们的网站http://nucapt.northwestern.edu有一个库，可以从中转载以PDF文件下载。通过Nutapapt，我们已经教育了许多人在将原子螺旋桨断层扫描应用于广泛的材料科学和工程问题上，这对于在亚纳米级量表中表征材料很重要。此外，我们正在与法国的一位材料科学家进行有关这项研究的主题的互动，并为美国和国外的工业公司提供服务。在我们实现这一目标的范围内，美国没有其他人这样做。