Modeling and Design of Enhanced Strength and Ductility Through Grain Boundary Engineering--A Study of Boron Carbide Based Superhard Materials

强度是指材料承受失效或屈服的能力，而延展性是指材料永久变形而不断裂的能力。许多重要的工程应用需要高强度和韧性的材料，如切割工具，士兵的防弹衣和制造工艺。一个有希望的候选者是碳化硼，一种所谓的超硬陶瓷，因为它的强度而得名;然而，它的延展性很低。在多晶材料中，强度和延展性通常与较低长度尺度（微米及以下）的微观结构特征相关。关于显微结构对超硬陶瓷的强度和延展性的影响，存在显著的知识缺口。该项目旨在使用计算建模和模拟研究碳化硼基材料的微观结构与强度和延展性之间关系的物理机制。该项目还将根据所获得的知识建立设计原则，用于开发具有增强强度和延展性的新型碳化硼基材料。设计策略将可扩展到各种其他超硬材料，如硼化物，碳化物和金刚石。这项研究将被纳入本科和研究生教育，以及当地高中学生的推广活动。该研究项目还将针对妇女和代表性不足的少数民族学生在科学，技术，工程和数学学科的参与。 本计画的研究目标是阐明微结构如何决定碳化硼基材料的变形与机械过程。研究小组将采用多尺度方法耦合原子模拟和介观相场方法，以（1）研究晶界对碳化硼机械性能，变形和失效机制的影响;（2）建立设计原则，通过微合金化设计晶界性能来提高碳化硼的强度和延展性。该研究将为阐明多晶超硬陶瓷在实际条件下强度和塑性的成因做出开创性的贡献。材料设计原则将被应用于激发实验合成更强和更坚韧的碳化硼基材料的商业应用。

Strength refers to a material's ability to withstand failure or yield, while ductility is its ability to permanently deform without fracture. Many important engineering applications require high strength and yet ductile materials, such as in cutting tools, body armor for soldiers, and manufacturing process. One promising candidate is boron carbide, a so-called superhard ceramic names so because of its strength; however, it has low ductility. In poly-crystalline materials, the strength and ductility are commonly associated with microstructural features at the lower length scales (micrometers and below). There is a significant knowledge gap regarding the impact of microstructure on the strength and ductility of superhard ceramics. This project is directed towards the study of the physical mechanisms that underlie the relationships between microstructure, and strength and ductility of boron carbide based materials using computational modeling and simulations. The project will also establish design principles based on the knowledge gained for the development of new boron carbide based materials with enhanced strength and ductility. The design strategies will be extendable to a variety of other superhard materials, such as borides, carbides, and diamond. The research will be integrated into both undergraduate and graduate education, as well as outreach activities for local high school students. The research project will also target the participation of women and under-represented minority students in science, technology, engineering, and math disciplines. The research objective of this project is to illustrate how microstructure determines the deformation and mechanical processes in boron carbide based materials. The research team will apply a multiscale approach coupling atomistic modeling and the mesoscale phase field method to (1) investigate the impact of grain boundaries on mechanical properties, deformation, and failure mechanisms of boron carbide; and (2) establish the design principles to enhance the strength and ductility of boron carbide through engineering of grain boundary properties with microalloying. The research will make original contributions in elucidating the origins of the strength and ductility of polycrystalline superhard ceramics under realistic conditions. The materials design principles will be applied to inspire experimental synthesis of stronger and tougher boron carbide based materials for commercial applications.