A New Experimental/Computational Approach for Predicting Phase Evolution and Defect Thermodynamics: Application to Concentrated Multicomponent Ni-Based Superalloys

技术支持：PI将研究浓缩镍基高温合金中微观结构的时间演变，这些合金用于航空，发电，化学，天然气和石油工业。它们的微观结构由相干有序的γ？（g？）─在无序的FCC γ（g）-基质中沉淀。有重要的未回答的问题有关的早期阶段成核的相干g？-从G-矩阵的相和相分离。此外，还讨论了该晶体的晶体学和形态学随时间的演化。将使用扫描电子、电子透射和高分辨率电子显微镜在所有相关的长度尺度（微米到亚纳米级）上研究沉淀物。在实验研究的同时，PI将根据空位扩散机制进行晶格动力学蒙特卡罗（LKMC）模拟，以模拟与LEAP断层重建相同长度尺度的微结构的时间演变，其中动力学参数是实验和/或从第一原理密度泛函理论（DFT）计算的。PI将研究Ni-Al-Cr合金中的形核动力学途径，其平均成分接近固溶线，因此它们可能遵循经典形核理论（CNT）。此外，PI将研究两种具有相似g？相的平均组成是远离固溶线，因此不太可能服从CNT。所有的实验结果进行了比较，LKMC模拟和扩散理论。要分析的数据，一个新的理论，在集中的多组分合金的成核开发，充分利用正常模式分析重新制定的相干相分离的理论，结合了固态扩散的完整细节。此外，PI正在探索基于扩散方程重新表述CNT的方法。最后，为了将镍基高温合金的微观组织与高温力学性能联系起来，PI将计算反相界的亥姆霍兹自由能σ-APB。PI提出了一种新的方法，驻留重量算法，它结合了密度泛函计算和蒙特卡罗模拟，计算APB自由能。派？的原子尺度的方法来研究微观结构的时间演化是显着不同的现有方法，在PI结合原子尺度的实验，模拟和扩散理论联合收割机。结合实验/计算的方法将允许一个原子的描述，跨越亚纳米到介观的长度尺度与前所未有的保真度。非技术性：通过西北大学原子探针断层扫描中心（NUCAPT），PI正在教育本科生工作学习，毕业论文，本科生研究经验（REU）和教师研究经验（RET）使用LEAP断层扫描仪进行原子探针断层扫描。这些方案已经并将涉及男子、妇女和法律的少数群体、西班牙裔和非洲裔美国人。NUCAPT还为其他大学、国家实验室和工业公司提供APT服务。此外，PI将开发一个夏季研讨会？连接原子尺度实验和计算，？在西北大学第二年的夏天举行。本课程将面向对原子尺度和多尺度计算，原子尺度实验感兴趣的研究生，以及年轻的教师和工业参与者。PI正在计划CA。50名与会者，并打算收取适度的注册费，以支付费用。

TECHNICAL: PIs will study temporal evolution of microstructures in concentrated Ni-based superalloys, which are used in the aviation, electric generation, chemical, and gas and oil industries. Their microstructures consist of coherent ordered gamma?(g?)-precipitates in a disordered FCC gamma(g)-matrix. There are significant unanswered questions concerning the early stage nucleation of the coherent g?-phase and phase separation from the g-matrix. Additionally, the temporal evolution of the crystallography and morphology of the g?-precipitates will be studied at all relevant length scales (micron to subnanoscale) using scanning electron, electron transmission, and high-resolution electron microscopies. In parallel with the experimental research, PIs will perform lattice kinetic Monte Carlo (LKMC) simulation, based on a vacancy diffusion mechanism, to simulate the temporal evolution of the microstructures at the same length scale as the LEAP tomograph reconstructions, where the kinetic parameters are experimental and/or calculated from first-principles density functional theory (DFT). PIs will study the kinetic pathways for nucleation in Ni-Al-Cr alloys whose mean compositions are close to the solvus line and therefore they may follow classical nucleation theory (CNT). Additionally, PIs will study two Ni-Al-Cr alloys with similar volume fractions of the g?-phase whose mean compositions are farther from the solvus line and hence less likely to obey CNT. All the experimental results are to be compared to LKMC simulation and diffusion theory. To analyze the data, a new theory of nucleation in concentrated multi-component alloys is developed that takes full advantage of a normal mode analysis to reformulate the theory of coherent phase separation that incorporates the complete details of solid-state diffusion. Additionally, PIs are exploring ways to rephrase CNT based on a diffusion equation. Finally, to make a link between the microstructure and the high-temperature mechanical properties of Ni-based superalloys PIs will calculate the Helmholtz free energy of anti-phase boundaries (APBs), sigma-APB. PIs present a new approach, the residence weight algorithm, which combines density functional calculations and Monte Carlo simulations, to calculate the APB free energy. PI?s atomic scale approach to studying the temporal evolution of microstructures is significantly different from existing methods in that PIs combine atomic-scale experimentation, simulation, and diffusion theory. The combined experimental/computational approach will allow an atomistic description that spans the subnanometer to mesoscopic length scales with unprecedented fidelity. NON-TECHNICAL: Through the Northwestern University Center for Atom-Probe Tomography (NUCAPT) PIs are educating undergraduate work-study, senior-thesis, research-experiences for undergraduate students (REU), and research experiences for teachers (RET) to perform atom-probe tomography using a LEAP tomograph. These programs have and will involve men, women and legal minority groups, Hispanic, and African-American. NUCAPT also provides APT services to other universities, national laboratories, and industrial firms. Additionally, PIs will develop a summer workshop on ?Linking Atomic-Scale Experiments and Computations,? to be held during the summer of the 2nd year of the grant at Northwestern. This course will be geared toward graduate students interested in atomic-scale and multiscale computation, and atomic-scale experimentation, as well as young faculty members and industrial participants. PIs are planning for ca. 50 participants and intend to charge a modest registration fee to cover costs.