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

高强度和韧性的材料一直受到工业界的青睐和高度要求。然而，强度和延展性通常在材料中是反相关的，并且难以同时实现。虽然单块纳米晶金属和非晶金属玻璃都表现出比常规金属和合金更高的强度，但它们的脆性性质严重限制了它们作为工程材料的应用。* 一些先前的研究表明，在纳米晶材料中引入一小部分非晶相或反之亦然，可以显著提高这些材料的延展性，而不会牺牲强度。例如，与常规纳米晶Cu中的< 2%相比，在结晶Cu/CuZr玻璃纳米层压材料中已经报道了高达~13.8%伸长率的优异拉伸延展性。还已经观察到，引入~7%体积分数的纳米晶体可以将非晶CuZr块体金属玻璃的压缩延展性从几乎为零增加到> 5%。虽然这些研究是基于试错和变形机制的深刻理解仍然缺乏，它打开了大门，设计材料和新的结构，同时具有所需的强度和延展性。* 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强度和塑性及其对结晶/非晶复合材料的微观结构的依赖性。该研究将大大推进当前对非晶金属玻璃和受限体积中晶体/非晶复合材料的微塑性的理解。最终，该研究将有助于设计新型结构和材料，这些结构和材料具有优化的强度和延展性组合，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.**