Superhard Metals

超硬金属

• 批准号: 1106364
• 负责人: Richard Kaner
• 金额: $ 69.2万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-11-15 至 2015-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1106364&HistoricalAwards=false
• 关键词: Superhard; Metals

TECHNICAL SUMMARYTransition metal borides have attracted increasing interest due to their physical properties that combine high hardness and electrical conductivity with straightforward ambient pressure synthesis. If designed properly, superhard metallic borides could lead to improved cutting tools and wear-resistant coatings. Rhenium diboride (ReB2) is a good example of this new and growing class of superhard, metallic borides. With support from the Solid State and Materials Chemistry Program, the possibility of improving on the properties of ReB2 by making solid solutions of ReB2 with other transition metals to activate dislocation-pinning mechanisms that could create harder materials will be explored. Less expensive transition metal borides will be synthesized by replacing rhenium with the relatively inexpensive transition metal tungsten. By completely replacing Re with W and increasing the boron concentration, another interesting boride, tungsten tetraboride (WB4), can be made which appears to have comparable hardness to ReB2. After characterizing its physical properties including micro- and nano-indentation, ambient and high pressure X-ray diffraction and resonant ultrasound spectroscopy of both polycrystalline and single crystalline WB4, its structure will be reexamined using neutron diffraction. This powerful tool should enable the determination of the exact positions of the boron atoms in the unit cell, something that is currently not known. This should provide better insight into the bulk modulus, high hardness and other properties of WB4. Making solid solutions of WB4 with other transition metal elements such as Ta, Mo, Cr and Mn, will be carried out in order to potentially increase hardness and impart improved corrosion protection, thermal stability and fracture toughness. A long-term goal of this project is to explore the feasibility of using these superhard, metallic borides for cutting tools. By taking advantage of their electrical conductivity, desired shapes will be cut using electric discharge machining (EDM). Cutting tool inserts will be made by EDM, and properties such as wear resistance will be tested. Coatings will be developed and friction tests carried out. Broader impact of this project will be achieved by engaging undergraduates in the research and providing high school students and teachers with lectures and demonstrations of materials and their applications.NON-TECHNICAL SUMMARYThe search for new superhard metals holds both great scientific and practical interest. Scientifically, an understanding of how and why materials known for their malleability can be turned into ultra-incompressible, superhard compounds will be gained. Practically, these metallic materials, no matter how hard, can be cut into precise shapes using a readily available process known as electric discharge machining. This will enable the exploration of their possible use for milling, sawing and drilling. Electric discharge machining will be used to turn these new materials into tools that will be tested for their ability to cut ferrous metals. Scratch resistant coatings with low friction surfaces will also be developed and tested. Broader impact of these projects will be achieved by engaging undergraduates in the research and providing high school students and teachers with lectures and demonstrations of materials and their applications.

技术概要过渡金属硼化物因其将高硬度和导电性与直接环境压力合成相结合的物理特性而引起了越来越多的兴趣。如果设计得当，超硬金属硼化物可以改进切削工具和耐磨涂层。二硼化铼 (ReB2) 是这一不断发展的新型超硬金属硼化物的一个很好的例子。在固态和材料化学项目的支持下，将探索通过将 ReB2 与其他过渡金属制成固溶体来激活位错钉扎机制，从而产生更硬的材料，从而改善 ReB2 性能的可能性。通过用相对便宜的过渡金属钨代替铼，可以合成较便宜的过渡金属硼化物。通过用 W 完全取代 Re 并增加硼浓度，可以制备另一种有趣的硼化物，四硼化钨 (WB4)，其硬度与 ReB2 相当。在表征其物理性质（包括多晶和单晶 WB4 的微米和纳米压痕、常压和高压 X 射线衍射以及共振超声光谱）后，将使用中子衍射重新检查其结构。这个强大的工具应该能够确定晶胞中硼原子的确切位置，而目前尚不清楚这一点。这应该可以更好地了解 WB4 的体积模量、高硬度和其他特性。将 WB4 与其他过渡金属元素（如 Ta、Mo、Cr 和 Mn）制成固溶体，以潜在地提高硬度并改善腐蚀防护、热稳定性和断裂韧性。该项目的长期目标是探索使用这些超硬金属硼化物作为切削工具的可行性。通过利用它们的导电性，可以使用放电加工 (EDM) 切割出所需的形状。切削刀具刀片将通过电火花加工制造，并测试耐磨性等性能。将开发涂层并进行摩擦测试。该项目将通过让本科生参与研究并向高中生和教师提供材料及其应用的讲座和演示来实现更广泛的影响。非技术摘要寻找新的超硬金属具有巨大的科学和实际意义。从科学角度讲，我们将了解以延展性着称的材料如何以及为何能够转变为超不可压缩、超硬的化合物。实际上，这些金属材料，无论有多硬，都可以使用一种现成的放电加工工艺切割成精确的形状。这将有助于探索它们在铣削、锯切和钻孔方面的可能用途。放电加工将用于将这些新材料转化为工具，并测试其切割黑色金属的能力。具有低摩擦表面的防刮涂层也将被开发和测试。这些项目将通过让本科生参与研究并向高中生和教师提供材料及其应用的讲座和演示来实现更广泛的影响。