Phase Formation, Microstructure and Mechanical Properties in Mixed Metal/Silicon Carbide Films

University Of New Hampshire, Durham NH

Investigators

Abstract

In this research program the structural and mechanical properties of mixed transition metal carbide/silicon carbide thin films will be studied. The strong chemical immiscibility between the metallic carbides and SiC, as well as the use of low-temperature deposition processes will promote the formation of heterophase nano-scale microstructures. Fundamental mechanisms of phase formation and microstructural evolution in these films, with particular emphasis on the structures formed near the percolation threshold of a-SiC on the grain boundaries of the metallic carbides, will be examined. Characterization methods will include high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. In addition, models of surface vs. bulk diffusion processes will be used to rationalize the observed microstructures, including observations of phase separation. The mechanical properties of these films, particularly the deformation mechanisms operating in these films by observing the microscopic deformation structure present after indentation, will also be investigated. %%% Recent research reports on the mechanical properties of mixed metal nitride/silicon nitride thin films with nano-scale heterophase structures have claimed dramatic property enhancements, including hardness levels exceeding that of diamond and high fracture toughness. The ability to create materials with hardness levels above that of diamond is a long-standing quest for materials scientists. If this objective can be achieved, it would allow significant advances in applications such as coatings for cutting tools and bearings. In this research program we will study transition metal carbide/silicon carbide coatings that are analogous to the nitride systems that have been the subject of much recent research interest. Using advanced characterization and testing methods, along with thermodynamic and kinetic modeling, we hope to achieve an improved understanding of strengthening mechanisms in these materials, along with new candidate ceramic materials for improved industrial coatings. ***