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.
