AVS 50th International Symposium
    Advanced Surface Engineering Monday Sessions
       Session SE-MoA

Paper SE-MoA1
High-resolution TEM Study the Microstructure of W-Si-C Films in the Vicinity of the Crystalline-Amorphous Transition

Monday, November 3, 2003, 2:00 pm, Room 323

Session: Hard Coatings: Preparation, Properties, Wear, and Nanotribology
Presenter: J.E. Krzanowski, University of New Hampshire
Authors: J.E. Krzanowski, University of New Hampshire
J. Wormwood, University of New Hampshire
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The addition of silicon to transition metal nitride and carbide thin films has generated considerable interest due to reports of greatly enhanced mechanical properties. It has been proposed that the effect of adding Si is to gradually reduce the crystallite size while introducing a thin amorphous interlayer between crystallites, ultimately resulting in an amorphous structure. In our work, we have examined a series of WC/SiC thin films over a composition range where the crystalline to amorphous transition occurs. By using high-resolution transmission electron microscopy, we have obtained a detailed picture of the mechanisms of this transformation in the W-Si-C system. These experiments have led to observations of novel microstructures not previously reported for Si-containing carbide/nitride thin films. A series of WC-SiC thin films has been deposited by RF magnetron co-sputtering, with compositions ranging from 15 to 38% SiC. X-ray diffraction analysis of these films confirmed the crystalline-to-amorphous transition in this compositional range. HRTEM observations revealed the following microstructural changes as the Si content increases: first, we observed fully crystalline nano-crystallites embedded in an amorphous matrix. Next, we observed the formation of larger (~50 nm) domains within which a novel droplet-like morphology of an amorphous phase is found. As Si is further increased, the droplets adopt a morphology where they appear to be strung together as the matrix phase becomes increasingly disordered. Finally, at yet higher Si contents, a spinodal-like two-phase structure is observed where one phase is amorphous and the second is best described as highly disordered. Despite the presence of these extensive microstructural changes, the hardness of the films within this compositional range was essentially constant.