Novel superhard nanocomposite thin-film materials - from atomic-scale physics to macroscopic properties

PI和他的同事将开展研究，探索超硬材料的发展，即具有与钻石相当或更大硬度的材料。对这类材料的探索既是因为它们在广泛应用中的重要性，也是因为设计和合成它们的挑战。近年来，通过薄膜技术制备的一些纳米结构复合材料已经实现了超硬。虽然世界各地都在对超硬材料的合成和表征进行重要的研究，但由于缺乏对原子尺度机制的了解，进一步的发展(如优化、修饰和操纵)受到阻碍。这项研究将把实验合成和表征与量子理论和分子动力学模拟相结合，研究由纳米氮化钛或氮化钨微晶嵌入非晶氮化硅或氮化硼基质中的一系列纳米结构复合膜的力学、结构和电子性质。该项目的主要目标是研究这些材料的加工条件、残余应力、硬度、显微组织和成分之间的关系，并在原子尺度上阐明超硬的机理。复合结构的作用(界面类型、纳米颗粒的尺寸和体积分数等)在抑制位错方面，将阐明活性，并将为超硬纳米结构材料的优化设计提供指导方针。纳米结构超硬材料的成功制造将对工业产生重大影响，因为它们将比钻石便宜。新材料将用于防腐和耐磨保护涂层、刀具、承载部件以及微机械和微电子设备。特别是，将超硬纳米复合材料应用于高速切割和成形工具，以实现绿色加工操作，而不使用有毒冷却剂，将获得显著的社会经济效益，从而为减少废物的加工过程提供清洁的工作环境。这个项目还将发展一个由美国和香港的理论家和实验学家参与的国际合作。本科生和研究生都将参与这项研究。K-12教师将通过Vanderbilt的教师暑期研究体验计划参与该项目。新知识将被转化为可在K-12课堂上使用的模块和课程。因此，该项目将为各级教育做出贡献。

The PI and his associates will carry out research to explore the development of superhard materials, i.e., materials that have a degree of hardness comparable to or larger than that of diamond. The search for such materials is driven by both their importance in a wide range of applications and by the challenge to design and synthesize them. Superhardness has recently been achieved in a number of nanostructured composites prepared by means of thin-film technology methods. While significant research is being conducted worldwide on the synthesis and characterization of superhard materials, further developments (such as optimization, modification, and manipulation) are hampered by the lack of understanding of the atomic-scale mechanisms. The proposed research will combine experimental synthesis and characterization with quantum theory and molecular dynamics simulations to investigate the mechanical, structural, and electronic properties of a series of nanostructured composite films which are made up of nano-sized crystallites of a titanium nitride or tungsten nitride embedded in an amorphous silicon nitride or boron nitride matrix. The main objectives of the project are to investigate the relationships between the processing conditions, residual stress, hardness, microstructure and composition of these materials, and to elucidate the mechanisms underlying superhardness at the atomic scale. The role of the composite structure (type of interfaces, size and volume fraction of nano-particles, etc.) in inhibiting dislocation activity will be elucidated and guidelines will be extracted for the optimum design of superhard nanostructured materials. The successful fabrication of nanostructured superhard materials would have significant impact on industry because they would be less expensive than diamond. The new materials would be used as anti-corrosion and wear protective coatings, cutting tools, load-bearing components, and micro-mechanical and microelectronic devices. In particular, significant socio-economic benefits would be achieved by the applications of the superhard nanocomposite materials on high-speed cutting and forming tools for 'green' machining operations without the aid of toxic coolants, which offers a clean work environment for machining processes with reduced wastes. This project will also develop an international collaboration involving both theorists and experimentalists in the U.S. and Hong Kong. Both undergraduate and graduate students will be involved in the research. K-12 teachers will participate in the project through Vanderbilt's summer Research Experience for Teachers programs. New knowledge will be translated into modules and lessons that can be used in K-12 classrooms. Thus, the project will contribute to education at various levels.