Mechanical Behavior of Novel Metal-Oxide Composites with Hierachical Microstructures: Effect of Scale and Interfacial Structure

Lehigh University, Bethlehem PA

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: Often, a material with nanometer-sized internal features has remarkable properties such as high strength (when compared to the same material with larger features). However, it can be difficult to create such materials with these nanometer-scale features at an affordable cost and in large quantities. This research project is focused on a new route for creating materials with nanometer-scale layers of ceramics and metals that have the potential to possess unusual and advantageous mechanical properties and to be processed at a reasonable cost. Electron microscopy techniques and specialized small-scale mechanical tests are revealing the role of the ceramics-metal interfaces, the orientation of the individual phases, and the size of the phases on mechanical properties. The results are providing a fundamental scientific understanding of these phenomena that can be applied to fields such as joining of ceramics and metals, creation of strong materials for load-bearing applications, and prevention of failure in microelectronic devices. In addition, the broad scientific concepts developed during this work are being incorporated into outreach activities that target K-12 children, thereby encouraging their participation in science and engineering fields. TECHNICAL DETAILS: This research project is focused on understanding the microstructure development and mechanical behavior of ceramic-metal composites derived from the partial reduction of mixed oxide ceramics that have a delafossite starting structure. Reducing this class of materials to partially remove oxygen yields a hierarchical structure with unique ceramic-metal composite morphologies that hitherto have not been studied and that promise to exhibit attractive mechanical properties. The microstructural scale of the ceramic/metal features range from tens of nanometers to tens of microns, and both layered and globular morphologies can be achieved. The discovery of a unique microstructure that can be created by reducing delafossite materials, combined with the relatively recent advent of aberration-corrected scanning transmission electron microscopes and in situ micro-mechanical testing instruments, make it possible for the first time to reveal the effects of ceramic-metal nanocomposite microstructure scale and lamellar orientation on stiffness, hardness, and toughness. The findings of the study are relevant to technological processes such as joining, and to understanding scaling effects in ceramic-metal systems. Additionally, university-level students are developing expertise in the emerging areas of aberration-corrected scanning transmission electron microscopy and in situ micro-mechanical testing.