Bond Strengthening and Grain Size Refinement in Superhard Metal Borides

Non-technical SummaryThe continuous creation and development of tools through the tuning of materials’ properties has been a cornerstone of much of the development seen in human societies. High mechanical hardness is a very desirable property for materials used in industrial settings for machining and cutting as it dramatically reduces wear and therefore turnover rate of machining tools. The industry standard superhard material is diamond, the hardest material currently known. The issue that arises with diamond, however, is that not only does it have an expensive high pressure, high temperate synthesis, but it is limited in its applications. This is because it is thermally unstable in air and when used to cut iron containing materials, diamond breaks down to form iron carbides. These both result in a high turnover rate for diamond tools, and an inability to be used with common iron containing materials, like steel. Cheaper alternatives such as tungsten carbide (WC) have an easier, low-cost synthesis, but lack the extremely high hardness values of diamond and therefore have high turnover rates and are less effective. With this project, supported by the Solid State and Materials Chemistry program and the Ceramics program, both in NSF’s Division of Materials Research, the principal investigators design and create superhard materials that approach the high hardness seen in diamond, while replicating the low cost, ambient pressure synthesis found in WC. These superhard materials made from boron not only lower the cost of synthesis, but they improve the lifetime of the tools that can be created and therefore, lower the amount of waste generated in industrial machining. Additionally, the metallic nature of these transition metal borides enables the use of high precision cutting and shaping instruments like plasma cutting, which is currently not usable with electrically insulating materials like diamond, which additionally reduces cost and waste in the formation of these tools. Beyond this research, the principal investigators undertake educational outreach in the greater Los Angeles area. This includes developing lessons and experiments for K-12 schools and presenting them to teachers, along with speaking to students in grade school about not just science, but higher education as a whole. Graduate students who work on this project also gain valuable skills through both the research they conduct as well as through the mentorship and outreach programs they participate in alongside their mentors. Technical SummaryHardness is a mechanical property that is defined by a material’s ability to resist irreversible shape change, known as plastic deformation. The hardness of a given material is dependent on several different materials’ properties, but they can overall be grouped into two categories: intrinsic bonding effects and grain boundary effects. These two contributors to hardness are not mutually exclusive and therefore can be optimized separately and combined to dramatically improve the hardness of a material. This project, with support from the Solid State and Materials Chemistry program and the Ceramics program, both in NSF’s Division of Materials Research, uses the described two-pronged approach towards superhard materials design and combines the synthesis of transition metal boride systems with high-pressure studies to obtain information about the internal deformation mechanisms of bulk and nanocrystalline materials. The research groups at UC Los Angeles study how small element doping into the boron sites of the metal borides affects the bonding. Using systems of di- and tetra- borides with varying amounts of carbon in them, the principal investigators investigate the different carbon bonding regimes, and their impact on hardness. Additionally, synthetic routes for the formation of nanostructured metal borides are explored. The principal investigators utilize new synthetic routes to create nanocrystalline forms of known superhard metal borides such as ReB2, WB2 and WB4 to further increase the hardness of these materials by maximizing the number of grain boundaries which can impede plastic deformation. These nanocrystalline materials also allow for new analytical techniques which are not possible for bulk materials such as Rietveld texture analysis. These two approaches to hardening metal borides can then be combined to create nanocrystalline solid solutions which benefit from both the improved bonding effects and grain boundary effects. The broader impacts of the project are multifaceted and include extensive outreach conducted by the principal investigators aimed at grade school children, the training of both graduate and undergraduate students in their Ph.D. studies and undergraduate research opportunities, respectively, and the development of novel superhard materials which have the potential to improve the quality of industrial manufacturing and machining tools.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术总结通过调整材料的特性的连续创建和开发工具一直是人类社会中许多发展的基石。高度机械硬度是用于机械和切割的工业环境中使用的材料的非常理想的特性，因为它大大降低了磨损，因此是加工工具的营业率。行业标准的超智材材料是钻石，是目前已知的最难的材料。但是，钻石引起的问题是，它不仅具有昂贵的高压，高温合成，而且在应用中受到限制。这是因为它在空气中是热不稳定的，并且当用来切割含铁的材料时，钻石会分解以形成碳化物。这两者都会导致钻石工具的更高周转率，并且无法与含有钢等普通铁的材料一起使用。便宜的替代品（例如碳化钨（WC））具有更容易的低成本合成，但缺乏极高的钻石硬度值，因此具有很高的周转率，并且效果较低。在NSF的材料研究部中，主要研究人员的设计和创建超级材料，这些项目在固态和材料化学计划和陶瓷计划的支持下，并创建了钻石中的高硬度，同时复制了WC中发现的低成本，环境压力合成。这些由硼制成的超智材料不仅降低了合成成本，而且可以改善可以创建的工具的寿命，因此降低了工业制造中产生的废物量。此外，这些过渡金属硼的金属性质使使用高精度切割和塑造仪器（如等离子体切割）的使用，目前无法使用钻石等电绝缘材料来使用，这些材料（如钻石）还降低了这些工具形成中的成本和浪费。除了这项研究之外，首席研究人员在大洛杉矶地区进行了教育外展。这包括为K-12学校开发课程和实验，并向教师介绍他们，以及与小学的学生交谈，不仅是科学，而且是整个高等教育。从事该项目的研究生也通过他们进行的研究以及通过他们的心态参与的心态和外展计划来获得宝贵的技能。技术摘要硬度是一种机械性能，它是由材料抵抗不可逆形状变化（称为塑性变形的）的能力来定义的。给定材料的硬度取决于几种不同材料的特性，但总体可以将它们分为两类：内在的粘结效应和晶界效应。这两个对硬度的贡献不是相互排斥的，因此可以分开优化并结合起来，以显着改善材料的硬度。在NSF的材料研究部中，在固态和材料化学计划和陶瓷计划的支持下，该项目都使用了描述的两种普通方法来实现超级材料设计，并结合了过渡金属硼化物系统与高压研究的合成，以获取有关散装内部变形机制的信息，以获取散装和纳米晶体材料的内部变形机制。加州大学洛杉矶分校的研究小组研究了小元素如何掺入金属硼化物的硼位置会影响粘结。主要研究人员使用二孔和四孔的系统，研究了不同的碳键合度及其对硬度的影响。此外，还探索了纳米结构金属硼的形成的合成途径。首席研究人员利用新的​​合成途径来创建已知的超级金属硼（例如Reb2，WB2和WB4）的纳米晶形式，通过最大化可能阻碍塑性变形的晶粒边界的数量来进一步增加这些材料的硬度。这些纳米晶体材料还允许新的分析技术，这些技术对于诸如Rietveld纹理分析等散装材料不可能。然后可以将这两种硬化金属硼化物的方法组合在一起，以创建纳米晶体固体溶液，从而受益于改善的键合效应和晶界效应。该项目的更广泛影响是多方面的，包括针对小学生的主要调查人员进行的广泛的外展活动，在博士学位上对研究生和本科生的培训。研究和本科研究机会分别是新型超级材料的开发，这些材料有可能提高工业制造和加工工具的质量。该奖项反映了NSF的法定任务，并被认为是通过基金会的智力优点和更广泛的影响来通过评估来获得的支持。