Revealing Ductility in Transition-Metal Carbides through Small Scale Experiments and Modeling

该奖项支持对过渡金属碳化物断裂和塑性变形微观机制的研究。过渡金属碳化物是一类具有重要技术价值的材料，具有极高的硬度、耐高温性能以及优异的耐磨、耐烧蚀和耐腐蚀性能。因此，这些材料在建造高超声速飞行器、宇宙飞船、刀具等方面很有吸引力。然而，人们普遍认为，它们在室温下很容易破裂。从这些研究中获得的新知识可以帮助开发性能优越、耐用、可持续的结构材料，用于更广泛的应用。因此，这项研究的成果和对下一代科学家和工程师的教育培训将造福美国经济和社会。由于离子键、共价键和金属键的混合，过渡金属碳化物被认为具有本质的延展性，尽管它们通常被认为在室温下是脆性的。受最近纳米机械测试揭示这些化合物单晶中的延展性的推动，该项目旨在促进对这些材料中导致塑性与断裂的因素的基本理解。为此，将在0.1至3微米的长度尺度上进行基于原位电子显微镜的机械表征和多尺度建模的组合。将开发一种新的模型框架，称为离散位错和裂纹动力学，并有可能预测这些材料中同时发生的塑性变形和裂纹扩展。这项研究计划揭示晶体取向、样品大小、过渡金属(IV组与V组)和加载方式(拉伸、压缩和压痕)在决定位错微结构、断裂起始和破坏中的作用。这些研究将提高对过渡金属碳化物塑性变形物理的基本理解，并可能提高用于航空航天和汽车工业、刀具和硬质涂层等先进结构部件的使用寿命，并可能导致更坚韧的微型结构部件的设计，如微电子机械系统和纳米机电系统。

This award supports an investigation of the microscopic mechanisms governing fracture and plastic deformation in transition-metal carbides. Transition-metal carbides are a technologically important class of materials that are extremely hard, can withstand high-temperatures, and exhibit excellent resistance to wear, ablation, and corrosion. As a result, these materials are attractive for building hypersonic vehicles, spacecrafts, cutting tools, etc. However, they are generally believed to break easily at room temperature. The new knowledge gained from these studies can help develop superior performance, long-lasting, sustainable structural materials for use in a wider variety of applications. Therefore, the results of this research and the educational training of next-generation scientists and engineers will benefit the U.S. economy and society. Transition-metal carbides, owing to a mixture of ionic, covalent, and metallic bonding, are expected to be intrinsically ductile even though they are generally considered to be brittle at room temperature. Motivated by the recent nanomechanical tests revealing ductility in single-crystals of these compounds, this project aims to develop fundamental understanding of the factors contributing to plasticity vs. fracture in these materials. To this purpose, a combination of in-situ electron microscopy based mechanical characterization and multi-scale modeling will be conducted at length scales between 0.1 and 3 micrometers. A new modeling framework, called the Discrete Dislocation & Crack Dynamics will be developed and has the potential for predicting concurrent plastic deformation and crack propagation in these materials. The research plans to reveal the role of crystal orientation, specimen size, transition-metal (group IV vs. V), and loading mode (tension, compression, and indentation) in determining dislocation microstructures, onset of fracture, and failure. These studies will improve the fundamental understanding of the physics of plastic deformation in transition-metal carbides and can likely enhance the life-time operation of advanced structural components used, for example, in aerospace and automotive industries, cutting tools, and hard coatings and may potentially lead to the design of tougher miniature structural components, such as micro- and nano-electromechanical systems.