Hardness and Elastic Properties of Superhard and Ultrahard Materials

非技术性描述：社会长期以来一直着迷于钻石作为已知的最坚硬的物质。比钻石还硬的材料能被创造出来吗？这个问题并不简单，因为硬度的定义使用金刚石作为参考，当测试材料接近或可能超过金刚石压头的硬度时，结果很难解释。基于金刚石和相关化合物的纳米多晶或纳米孪晶结构，正在开发一类新的超硬材料，所述相关化合物含有与金刚石相同结构配置的碳、硼和氮。这些材料是在高压和高温下在大容量压力机中合成的。使用新开发的超声波系统，在GHz频率下测量声波的速度，新型超硬材料的物理性能进行了研究。这些结果精确地确定了与硬度密切相关的剪切模量等物理特性。在硬度和热稳定性方面与天然金刚石相媲美或有可能超过天然金刚石的新材料可以制造在应力下不会燃烧或磨损的超硬机械零件。技术参数：高压高温合成的单晶体中间组成之间的立方氮化硼（c-BN）和金刚石证明了固体-解决方案，其中硬度和热稳定性针对一定范围的组合物进行了优化。确定理想的成分需要改进测量和对硬度-弹性关系的理论理解。鉴于传统的硬度测量材料比c-BN硬是难以解释的，因为塑性变形的压头，一种新型的GHz超声波干涉仪的开发，以非常高的精度测量超硬和超硬类材料的弹性常数。在该方向下，含有碳、氮和硼并且具有纳米多晶或纳米孪晶结构的类金刚石化合物被瞄准以生产没有解理、具有高热稳定性并且具有与天然金刚石相媲美并且可能超过天然金刚石的硬度的材料。该研究提高了对硬度和弹性之间关系的基本理解，从而提高了设计和预测超硬材料性能的能力。该提案是及时利用新开发的合成技术和表征方法。研究生培训的重点是在工业，学术界和国家实验室的相关领域的就业安置技能。外联活动的特点是参加Excite项目，这是一个向当地小学的少数民族学生提供课后科学和数学丰富经验的方案。

NON-TECHNICAL DESCRIPTION: Society has long been fascinated by diamond as the hardest known substance. Can a material harder than diamond be created? Answering this question is not so straightforward because the very definition of hardness employs diamond as the reference, and when materials under test approach or potentially exceed the hardness of the diamond-based indenter, results are difficult to interpret. A new class of superhard materials is being developed based upon nano-polycrystalline or nano-twinned structures of diamond and related compounds containing carbon, boron and nitrogen together in the same structural configuration as diamond. These materials are synthesized at high pressures and high temperatures in large-volume presses. Physical properties of novel superhard materials are investigated using a newly-developed ultrasonic system that measures the speed of sound waves at GHz frequencies. The results precisely determine physical properties such as the shear modulus, which are fundamentally correlated to hardness. New materials rivaling or potentially exceeding natural diamond in hardness and thermal stability can make possible the fabrication of ultrahard machine parts that do not burn or wear down under stress.TECHNICAL DETAILS: High-pressure high-temperature synthesis of single-crystals intermediate in composition between cubic-boron nitride (c-BN) and diamond demonstrate a solid-solution wherein hardness and thermal stability are optimized for a certain range of compositions. Identifying the ideal composition requires improved measurement and theoretical understanding of hardness-elasticity relationships. Whereas conventional hardness measurements on materials harder than c-BN are difficult to interpret because of plastic deformation of the indenter, a novel GHz-ultrasonic interferometer is developed to measure the elastic constants of materials in the superhard and ultrahard classes with very-high precision. Under that direction, diamond-like compounds containing carbon, nitrogen, and boron and having nano-polycrystalline or nano-twinned structure are targeted to produce materials without cleavage, with high thermal stability, and with hardness rivaling and potentially exceeding natural diamond. The research improves the fundamental understanding of the relationship between hardness and elasticity thus advancing the ability to design and predict the properties of ultrahard materials. The proposal is timed to take advantage of newly developed synthesis techniques and characterization methods. Graduate student training focuses on skills for job placement in related fields in industry, academia, and at the National laboratories. Outreach activities feature participation in Project Excite, a program providing after-school enrichment experiences in science and mathematics to minority students from local elementary schools.