Abstract
The influence of the microstructure of WO 3 thin films upon friction and wear during sliding contact was studied using two different tribometers. The tungsten trioxide (WO 3) thin films of controlled microstructure were grown on R-plane sapphire substrates using electron cyclotron resonance (ECR) oxygen-plasma-assisted electron beam evaporation of WO 3 pellets. The WO 3 films were fabricated to consist of amorphous, polycrystalline or epitaxial microstructure, depending on the deposition temperature, as indicated by in situ RHEED analysis. Pin-on-disk testing of the WO 3 films was performed using 10 mm diameter sapphire and 440C stainless steel sliders and 1 N normal force. Epitaxial crystalline WO 3 films showed lowest friction ( μ∼0.3 for both sapphire and steel spheres) and greatest production of debris, while amorphous WO 3 films exhibited higher friction coefficients (up to μ∼0.6 for sapphire spheres and μ∼1.1 for steel spheres), less debris production, and more slider wear. Epitaxial WO 3 films exhibited low friction ( μ∼0.16) in single pass tests with sapphire and steel sliders (1 mm stroke, 0.1 mm/s, 0.1 N load,), whereas amorphous and polycrystalline WO 3 films showed transitions to much higher friction (up to μ∼0.7). Lower friction and wear of WO 3 films with epitaxial structure compared to amorphous structure appears to be due to a lubricious WO 3 layer transferred to the slider from the epitaxial film.
Published Version
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