Size-Dependent Strength and Plasticity in Metallic Nanocrystalline-Amorphous Composites

坚固而延展性强的材料总是受到工业界的青睐和高度要求。然而，材料的强度和延性通常是反相关的，很难同时达到。虽然单块纳米晶金属和非晶态金属玻璃都表现出比传统金属和合金更高的强度，但它们的脆性严重限制了它们作为工程材料的应用。先前的一些研究表明，在纳米晶材料中引入一小部分非晶相或反之亦然，可以在不牺牲强度的情况下显著提高这些材料的延展性。例如，据报道，晶态铜/铜锆层状玻璃的拉伸延伸率高达13.8%，而传统的纳米晶铜的延伸率只有2%。还观察到，引入~7%的纳米晶可以将非晶态CuZr大块金属玻璃的压缩延展性从几乎为零提高到&5%。虽然这些研究都是基于反复试验，对变形机制仍缺乏深入的了解，但它同时也为设计具有所需强度和延性的材料和新型结构打开了大门。*申请人建议主要使用原子模拟和随后的原位变形实验来研究晶体/非晶态复合材料的强度和塑性及其对微观结构的依赖。所提出的研究将极大地促进目前对非晶态金属玻璃和受限体积中的晶体/非晶态复合材料中微塑性的理解。最终，这项研究将有助于设计强度和韧性优化组合的新型结构和材料，这些结构和材料可用于各种工业应用，例如微电子机械系统和纳米电子机械系统。

Materials that are strong and ductile are always favored and highly demanded by industry. However strength and ductility are usually anti-correlated in materials and are difficult to achieve simultaneously. While monolithic nanocrystalline metals and amorphous metallic glasses both exhibit higher strength as compared to conventional metals and alloys, their brittle natures severely limit their application as engineering materials. ****Some prior studies suggest that introducing a small portion of amorphous phase in nanocrystalline materials or vice versa can significantly improve the ductility of these materials without sacrificing the strength. For instance, exceptional tensile ductility up to ~13.8% elongation has been reported in crystalline Cu/CuZr glass nanolaminates as compared to < 2% in conventional nanocrystalline Cu. It has also been observed that introduction of ~7% volume fraction of nanocrystals can increase the compressive ductility of amorphous CuZr bulk metallic glass to > 5% from nearly zero. Although such investigations were based on trial-and-error and a deep understanding of the deformation mechanisms is still lacking, it opens the door to design materials and novel structures with desired strength and ductility at the same time. ****The applicant proposes to use mainly atomistic simulation and subsequent in-situ deformation experiments to study the strength and plasticity and their dependence on microstructures of crystalline/amorphous composites. The proposed study will significantly advance current understanding of the microplasticity in amorphous metallic glass and crystalline/amorphous composites in confined volumes. Ultimately, the research will contribute to the design of novel structures and materials with optimized combination of strength and ductility that can be used for various industrial applications, for example in microelectromechanical systems and nanoelectro-mechanical systems.**