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

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

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.