New frontiers in synthesis of high-entropy transition metal borides enabled by microwave-induced plasma

该项目的意义在于，它解决了先进陶瓷作为航空航天、国防、发电和加工工业中许多应用的关键使能技术的需求，对国家具有重大影响。研究能够在恶劣条件下运行的材料对于应对一系列挑战至关重要——从创造更好的涡轮机、反应堆和电池到开发未来的能源系统。该项目的实验和计算组件有助于支持国家材料基因组计划（MGI）的目标，即以比以往更快的速度和更低的成本发现、制造和部署先进材料。在这个项目中开发的一类被称为高熵陶瓷的材料扩展了高温和耐锈蚀的范围，这是高超音速飞行器等先进材料系统所需要的。调查包括了解这些新材料是如何形成的，以及它们的机械和防锈性。这些材料是用一种高效的技术处理的，这种技术基于一种被称为等离子体的物质状态；在这一领域尚未探索的处理方法。实验和计算方法都被用来提供关于这些材料如何合成、表征和建模的新知识。社区通过与当地科学中心的合作，参与到等离子技术的奇迹中来，目的是吸引包括普通公众和K-12学生在内的广大观众。本项目研究了一种利用微波诱导等离子体合成高熵过渡金属硼化物的新方法。与主要依靠对流的传统工艺相比，这种方法的优点包括：增强扩散，减少能耗，加热速度非常快，大大缩短了加工时间，降低了烧结温度，改善了物理和机械性能。等离子体放电通过电子、离子和自由基等高活性物质促进微波加热和化学反应的效率很高。这种高熵陶瓷的合成路线尚未被探索，并为研究这种相对较新的材料类型的形成机制提供了机会。通过这种独特的方法研究了导致完全相变的动力学和反应途径，以及结构，硬度和抗氧化性的表征。计算量通过部分占位法计算熵形成能力来指导部件的选择，利用CalPhad将热力学与相图耦合预测抗氧化性，并用特殊的准随机结构来模拟力学性能。该项目的成果包括：对微波诱导等离子体如何影响和增强高熵硼化物形成的反应途径/动力学的新理解，以及机械和抗氧化性能的新模型的开发以及实验验证。该项目的社区外展重点是向广大观众（包括普通公众和K-12学生）展示等离子技术的奇迹。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYThe significance of this project is that it addresses the need for advanced ceramics as a key enabling technology for many applications in aerospace, defense, power generation, and processing industries having significant national impact. The study of materials designed for operation under harsh conditions is essential to meet a range of challenges—from creating better turbines, reactors, and batteries to developing future energy systems. The experimental and computation components of this project help support the goals of the National Materials Genome Initiative (MGI) in the effort to discover, manufacture, and deploy advanced materials faster and with less cost than ever before. The class of materials known as high-entropy ceramics developed in this project extends the range of high temperatures and resistance to rusting as needed for advanced material systems, such as hypersonic vehicles. The investigations involve understanding how these new materials form, along with their mechanical and rust resistance. The materials are processed using a highly efficient technique based on a state of matter known as plasma; a processing approach not yet explored in this field. Both experimental and computational methodologies are employed to provide new knowledge about how these materials can be synthesized, characterized, and modeled. The community are engaged about the wonders of plasma technology through involvement with a local science center, with aim for a broad viewing audience including the general public and K-12 students.TECHNICAL SUMMARYThis project investigates a novel approach for synthesis of high-entropy transition metal borides enabled by microwave-induced plasma. Compared to conventional processes that rely primarily on convection, the advantages of this approach include: enhanced diffusion, reduced energy consumption, very rapid heating rates and considerably reduced processing times, decreased sintering temperatures, and improved physical and mechanical properties. The plasma discharge is highly efficient in promoting microwave heating and chemical reactions via highly active species such as electrons, ions and radicals. This synthesis route is yet unexplored for high-entropy ceramics and presents opportunity to study the mechanisms contributing to formation of this relatively new class of materials. The kinetics and reaction pathway leading to complete phase transformation via this unique approach is investigated, along with characterization of structure, hardness and oxidation resistance. The computational effort guide component selection by computing entropy forming ability with partial occupation method, predict oxidation resistance using CalPhad to couple thermodynamics with phase diagrams, and model mechanical properties with special quasi-random structures. Outcomes from this project include: new understanding of how microwave-induced plasmas affect and enhance reaction pathways/kinetics toward high-entropy boride formation and development of new models for mechanical and oxidation resistance properties along with validation from experiment. Community outreach in this project focuses on the wonders of plasma technology for a broad viewing audience including the general public and K-12 students.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.