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

坚固和延展性好的材料总是受到工业的青睐和高度需求。然而，材料的强度和延性通常是反相关的，很难同时实现。虽然单片纳米晶金属和非晶金属玻璃都比传统金属和合金具有更高的强度，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，晶体Cu/CuZr玻璃纳米层合材料的拉伸延展性高达~13.8%，而传统纳米晶体Cu的拉伸延展性< 2%。研究还发现，引入~7%体积分数的纳米晶可以使CuZr非晶块体金属玻璃的压缩延展性从接近于零提高到>.5 %。尽管这样的研究是基于反复试验，对变形机制的深刻理解仍然缺乏，但它为同时具有所需强度和延展性的材料和新结构的设计打开了大门。****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结晶/非晶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金属玻璃和晶体/非晶复合材料在有限体积内微塑性的理解。最终，该研究将有助于设计具有优化强度和延展性组合的新型结构和材料，可用于各种工业应用，例如微机电系统和纳米机电系统

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.**