Multiscale Computational and Experimental Analysis of Deformation Mechanisms in Amorphous-Crystalline Metallic Materials with Microstructure Complexity

提高材料的强度总是以牺牲其有意变形或成形的能力为代价，即延展性。最近，受生物材料（如珍珠和牙釉质）的启发，一种新型的金属复合材料将非晶合金（称为金属玻璃）与结晶金属（如铜或铝）结合在一起，在不牺牲其延展性的情况下，强度得到了明显的提高。然而，到目前为止，这种材料的发展仍处于“试错”阶段，因为：(1)金属玻璃与结晶金属的集成导致了复杂的材料微观结构，其长度范围从原子尺度的纳米到微米；（ii）许多现有的技术，要么将材料视为原子的集合，要么将其近似为可变形体，而不考虑其内部结构，无法全面解释这种材料如何响应诸如拉力，压缩或剪切等机械力。该项目支持通过对金属复合材料在一定长度范围内的变形进行计算和实验分析来解决这些问题的研究。本研究将把原子变形物理与其整体力学性能联系起来。要回答的两个基本问题是：(a)非晶相和晶相之间的界面如何促进它们的共变形？（二）如何设计金属复合材料的微观结构，以延缓其失效？这项研究将通过为研究人员提供一个平台来推动该领域的发展，该平台可用于合理设计高性能材料，用于各种工程应用，如生物医学植入物、飞机结构和能源基础设施。它将使下一代劳动力接触到与数学、物理、力学、超级计算、材料合成、加工和表征相关的广泛知识和技能。此外，将开发几个金属复合材料套件，以说明复合材料中每个相的体积量的微小变化如何显著改变其性能。这些工具包将赠送给爱荷华州吉尔伯特初中和高中的科学教师，以向K-12学生推广科学和工程。在寻找强韧性的金属材料时，一种策略是引入界面，如晶界和孪晶界，以抵抗位错运动。这种策略通常伴随着延展性的降低，尽管它确实会导致强度的提高。相比之下，非晶金属复合材料不是阻断位错，而是利用非晶相吸收位错，这可能从根本上改变“强度-塑性困境”。然而，到目前为止，由于在将其多层次微观结构与整体力学性能相关联方面的知识差距，开发这种复合材料的系统工程方法尚未实现。本项目支持填补这一空白的研究。具有复杂微观结构的非晶金属复合材料的力学行为将从原子尺度到微观尺度进行分析。并发原子连续体模型类似于能源部-艾姆斯实验室制造的非晶金属复合材料的微观结构。将对这种材料中的塑性流动进行多尺度模拟，以深入了解位错与剪切转变区之间的相互作用。磁控溅射正交各向异性纳米层压板和球磨多晶聚集体变形机制的内在差异将被识别。这项研究为设计金属复合材料的微观结构以获得所需的性能开辟了可能性。这项研究的许多方面将不仅限于金属，而且很容易扩展到其他类别的材料，如仿生陶瓷，机电设备的金属玻璃基复合材料，核电厂的耐腐蚀和抗辐射材料。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYEnhancing the strength of a material is always at the expense of its ability to be purposely deformed or shaped, referred as ductility. Recently, inspired by biological materials, like nacre and dental enamel, a novel metallic composite which combines amorphous alloys (called metallic glass) with crystalline metals, such as copper or aluminum, is shown to have an appreciable strength improvement without sacrificing its ductility. However, up to date, the development of such materials is still at a 'trial and error' stage because: (i) the integration of metallic glass with crystalline metals leads to a complex material microstructure spanning a wide range of length scales from nanometers at the atomic scale to microns; (ii) many existing techniques, which either resolve the material as a collection of atoms or approximate it as a deformable body without considering its internal structure, are incapable to provide a full-scale interpretation on how such material responds to a mechanical forces like tension, compression, or shear. This project supports research addressing these problems through a combined computational and experimental analysis of the deformation in metallic composites over a range of length scales. This research will link the atomistic deformation physics with its overall mechanical performance. Two fundamental questions to be answered are: (a) how does the interface between the amorphous and crystalline phases contribute to their co-deformation? (b) how to architect the metallic composite microstructure such that its failure can be delayed? This research will advance the field by providing researchers with a platform that can be used in a rational design of high-performance materials for a variety of engineering applications such as biomedical implants, aircraft structures, and energy infrastructures. It will expose the next-generation workforce to a broad range of knowledge and skills related to mathematics, physics, mechanics, supercomputing, materials synthesis, processing, and characterization. Moreover, several kits of metallic composites will be developed for illustrating how little changes of the volume amounts of each phase in composites can significantly change its properties. These kits will be presented to science teachers at Gilbert middle and high schools in Iowa for promoting science and engineering to K-12 students.TECHNICAL SUMMARYIn the search of strong and ductile metallic materials, one strategy is introducing interfaces, such as grain boundaries and twin boundaries, to resist dislocation motions. This strategy is usually accompanied by a decrease in ductility although it does lead to an enhancement in strength. By contrast, instead of blocking dislocations, the amorphous-crystalline metallic composites utilize the amorphous phases to absorb dislocations, and may fundamentally change 'the strength-ductility dilemma'. Nevertheless, a methodical engineering approach for developing such composites is not achieved so far due to a knowledge gap in correlating its multi-level microstructure with the overall mechanical performance. This project supports research to fill this gap. The mechanical behavior of amorphous-crystalline metallic composites with microstructure complexities will be analyzed from the atomistic to the microscale. Concurrent atomistic-continuum models that resemble the microstructure of the amorphous-crystalline metallic composite fabricated at the Department of Energy-Ames Laboratory will be developed. Multiscale simulations of plastic flow in such material will be conducted to gain the insight into the interplay between dislocations and shear transformation zones. The intrinsic difference in mechanisms for the deformation in magnetron sputtered orthotropic nano-laminates and ball-milled polycrystalline aggregates will be identified. This research opens up the possibility of architecting the metallic composites microstructure for a desired property. Many aspects of this research will not be limited to metals but are readily extendable to other classes of materials, such as biomimetic ceramics, metallic glass-based composites for electromechanical devices, corrosion-, and radiation-resistant materials for nuclear power plants.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.