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

技术：pi将研究用于航空、发电、化学、天然气和石油工业的浓镍基高温合金微观结构的时间演变。它们的微观结构由相干有序γ ？（g?）-在无序FCC γ (g)-矩阵中析出。关于相干g?的早期成核有许多重要的未解之谜。-相和相分离的g矩阵。此外，还研究了g？-沉淀物将在所有相关的长度尺度（微米到亚纳米尺度）上使用扫描电子、电子透射和高分辨率电子显微镜进行研究。在实验研究的同时，pi将基于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层析成像重建相同长度尺度下微观结构的时间演化，其中动力学参数是实验和/或从第一性原理密度泛函理论（DFT）计算得到的。pi将研究Ni-Al-Cr合金的成核动力学途径，这些合金的平均成分接近溶剂线，因此可以遵循经典成核理论（CNT）。此外，pi将研究两种具有相似体积分数的镍铝铬合金。-相，其平均组成远离溶剂线，因此不太可能服从碳纳米管。所有实验结果都与LKMC模拟和扩散理论进行了比较。为了分析这些数据，本文提出了一种新的多组分合金的成核理论，该理论充分利用了正态分析的优势，重新制定了包含固态扩散完整细节的相干相分离理论。此外，pi正在探索基于扩散方程重新表述碳纳米管的方法。最后，为了将ni基高温合金的显微组织与高温力学性能联系起来，pi将计算反相边界的亥姆霍兹自由能（sigma-APB）。提出了一种结合密度泛函计算和蒙特卡罗模拟的新方法——驻留权算法来计算APB的自由能。π吗?研究微观结构时间演化的原子尺度方法与现有方法有显著不同，pi结合了原子尺度实验、模拟和扩散理论。结合实验/计算方法将允许以前所未有的保真度跨越亚纳米到介观长度尺度的原子描述。非技术：通过西北大学原子探针断层扫描中心（NUCAPT）， pi正在为本科生提供工作学习，毕业论文，本科生研究经验（REU）和教师研究经验（RET），以使用LEAP层析成像仪进行原子探针断层扫描。这些项目已经并将涉及男性、女性和合法少数群体、西班牙裔和非裔美国人。NUCAPT还为其他大学、国家实验室和工业企业提供APT服务。此外，pi将开发一个关于？连接原子尺度的实验和计算，？将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、年轻教员和工业界参与者。pi计划约有50名参与者，并打算收取适度的注册费以弥补成本。

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.