Nanotribological properties and scratch resistance of MoS_(2)bilayerona SiO_(2)/Si substrate

The tribological properties and scratch resistance of MoS_(2)bilayer deposited on SiO_(2)/Si substrates prepared via chemical vapor deposition are investigated.Friction force microscopy(FFM)is employed to investigate the friction and wear properties of the MoS_(2)bilayer at the nanoscale by applying a normal load ranging from 200 to 1,000 nN.Scratch resistance is measured using the scratch mode in FFM based on a linearly increasing load from 100 to 1,000 nN.Kelvin probe force microscopy(KPFM)is performed to locally measure the surface potential in the tested surface to qualitatively measure the wear/removal of Mos,layers and identify critical loads associated with the individual failures of the top and bottom layers.The analysis of the contact potential difference values as well as that of KPFM,friction,and height images show that the wear/removal of the top and bottom layers in the MoS_(2)bilayer system occurred consecutively.The FFM and KPFM results show that the top MoS_(2)layer begins to degrade at the end of the low friction stage,followed by the bottom layer,thereby resulting in a transitional friction stage owing to the direct contact between the diamond tip and SiO_(2)substrate.In the stable third stage,the transfer of lubricious MoS_(2)debris to the tip apex results in contact between the MoS_(2)-transferred tip and SiO_(2).Nanoscratch test results show two ranges of critical loads,which correspond to the sequential removal of the top and bottom layers.

Effect of Pulse and Direct Current Electrodeposition on Microstructure,Surface,and Scratch Resistance Properties of Ni-W Alloy and Ni-W-SiC Composite Coatings

The present work aims to study the influence of direct current and pulse current techniques as well as embedded SiC nanoparticles on the mechanical properties of the electrodeposited Ni-W coating.The electrodeposited coatings were studied for morphological,microstructural,mechanical,and scratch resistance properties using the surface roughness tester,scanning electron microscopy,energy-dispersive X-ray spectroscopy,X-ray diffraction,Vickers microhardness,and scratch tester.Application of pulse current exhibited relatively homogeneous and smooth surface of the coatings.A remarkable increment of microhardness was observed in both Ni-W and Ni-W-SiC coatings prepared under pulse current as compared to the direct current technique.Similarly,the scratch test revealed a considerable improvement in the scratch resistance behavior of the Ni-W alloy and the composite coatings from the pulsed current condition.Hence,the application of pulse current not only improved the surface-and microstructure-related properties but also enhanced the Vickers microhardness and scratch resistance properties of the coatings.In addition,the reduction in micro-cracks revealed the improvement in scratch resistance properties of the coatings due to the incorporated SiC nanoparticles into the Ni-W alloy matrix.

Comparative Study on Optical Properties and Scratch Resistance of Nanocomposite Coatings Incorporated with Flame Spray Pyrolyzed Silica Modified via in-situ Route and ex-situ Route

A new type of transparent scratch resistant coatings including in-situ modified SiO2 （g-SiO2） in flame spray pyrolysis （FSP） process was prepared. The maximum content of g-SiO2 in the coating was 15 wt%, which is higher than that of SiO2 modified by traditional wet chemical route （I-SiO2, only 10 wt%）. The results of transmission electron microscopy have demonstrated that in-situ surface modified g-SiO2 particles dispersed well with smaller agglomerates in the final coating, which was much better than the particles modified via wet chemical route. Visible light transmittance and haze tests were introduced to characterize the optical quality of the films. All coatings were highly transparent with the visible light transmittance of above 80%, especially for coatings containing g-SiO2, which exhibited slightly higher visible light transmittance than l-SiO2 embedded one. The haze value of coatings incorporated with 15 wt% g-SiO2 was 1.85%, even lower than the coating with 5 wt% I-SiO2 （haze value of 2.09%）, indicating much better clarity of g-SiO2. The excellent optical property of g-SiO2 filled coatings was attributed to the good dispersion and distribution of particles. Nano-indention and nano-scratch tests were con- ducted to investigate the scratch resistance of coatings on nano-scale. The surface hardness of the coatings rose by 18% and 14%, and the average friction coefficient decreased by 15% and 11%, respectively, compared to the neat coat due to the addition of 10 wt% g-SiO2 and I-SiO2. The pencil hardness of the coating with 15 wt% g-SiO2 increased from 2B for the neat coating to 2H. However, the pencil hardness of coating with 10 wt% I-SiO2 was only H. The results showed that the g-SiO2 embedded coatings exhibited higher scratch resistance and better optical properties.