38 research outputs found
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Influence of environmental parameters on the frictional behavior of DLC coatings
In a previous studies it was shown that diamond like carbon (DLC) films possess low friction coefficient (f) and excellent wear resistance. The reduction in f was found to be consistent with a ``wear induced graphitization`` mechanism of the DLC structure. A recent study showed that operational parameters (sliding velocity and loading level) influence the tribological behavior of DLC film through control of the kinetics of the graphitization process. The objective of the present study was to investigate the influence of environmental parameters (humidity and temperature) on the tribological behavior of DLC film and provide further support to the wear induced graphitization mechanism. Ion beam deposition was utilized to deposit DLC on a SiC substrate. Pin-on-disc experiments were conducted by varying humidity (0%, 40% and 100%) and temperature ({minus}10 C and 25 C). As-deposited DLC and wear debris was characterized by transmission electron microscopy. It was found that lower humidity increases the graphitization rate more than likely due to the reduction in the effect by the water molecules. A decreased graphitization rate was observed at lower temperature and higher humidity and can be attributed to suppression of temperature rise at hot spots. The present findings are consistent with and further verify the wear induced graphitization mechanism
Remarkable improvement in corrosion properties of Al substrates by means of alumina-zirconia nanostructured coating through PEO method
Effects of Y and Ho doping on microstructure evolution during oxidation of extraordinary stable Hf-B-Si-Y/Ho-C-N films up to 1500 °C
Hard, and optically transparent amorphous Hf6B12Si29Y2C2N45 and Hf5B13Si25Ho3C2N48 films were prepared by reactive pulsed dc magnetron co-sputtering and annealed up to 1500 °C in air. The evolved microstructures were studied by X-ray diffraction and transmission electron microscopy to understand the Y- and Ho– doping effects on thermal stability and oxidation behavior. A three-layered microstructure developed in both annealed films. A fully oxidized layer formed at the top surface consisting of cubic fluorite Hf(Y/Ho)O2 nanoparticles embedded in an amorphous SiOx-based matrix. The oxide layer is about 36 % thinner compared to undoped films with similar composition [1]. A recrystallized structure formed at the bottom of both films composed mainly of Hf(Y/Ho)N and α-/β-Si3N4. All Hf(Y/Ho)N in the middle layer was oxidized producing vertically oriented Hf(Y/Ho)O2 nanocolumns surrounded by Si3N4 nanocrystalline. The Y- and Ho– doping found to stabilize the cubic fluoride oxide structure and promoted its (1 1 1) columnar texture. The oxidation mechanism of Si3N4 nanodomains occurs via formation of β-SiO2 first followed by its transformation to amorphous SiOx. It is suggested that substitution of Hf4+ with Y3+ and Ho3+ ions within the Hf(Y/Ho)O2 formed an anion vacancy defect structure to preserve charge neutrality affecting the oxidation mechanism in the doped films