Effect of Laser Processing Parameters on Microstructure, Hardness and Tribology of NiCrCoFeCBSi/WC Coatings

In the present study, pulsed laser post-processing was applied to improve the properties of the thermally sprayed NiCrCoFeCBSi/40 wt.% WC coatings. The powder mix was deposited onto a mild steel substrate by flame spray method and then the as-sprayed coatings were processed by Nd:YAG laser. The peak power density applied was between 4.00 × 106 and 5.71 × 106 W/cm2, and the laser operating speed ranged between 100 and 400 mm/min, providing processing in a melting mode. Scanning electron microscopy, energy dispersive spectroscopy, Knop hardness measurements, and “ball-on-disc” dry friction tests were applied to study the effect of the processing parameters on the geometry of laser pass and microstructure, hardness, and tribology of the processed layers. The results obtained revealed that pulsed laser processing provides a monolithic remelted coating layer with the microstructure of ultrafine, W-rich dendrites in Ni-based matrix, where size and distribution of W-rich dendrites periodically vary across remelted layer depth. The composition of W-rich dendrites can be attributed to a carbide of type (W, Cr, Ni, Fe)C. The cracks sensitivity of coatings was visibly reduced with the reduction of power density applied. The hardness of coatings was between ~1070 and ~1140 HK0.2 and correlated with microstructure size, being dependent on the processing parameters. The friction coefficient and wear rate of coatings during dry sliding were reduced by up to ~30% and up to ~2.4 times, respectively, after laser processing.

Пороговый эффект деградации супергидрофобных покрытий, вызванный воздействием озона

It is shown that the use of nanosecond pulsed laser processing of an aluminum alloy makes it possible to obtain a coating with a multimodal roughness. The coating consists mainly of micro- and nanoparticles of aluminum oxide. Subsequent vapor deposition of the hydrophobic agent provides a coating with superhydrophobic properties. Infrared (IR) reflectance spectroscopy has been used to study the effect of ozone on the properties of a superhydrophobic coating fabricated on the surface of an aluminum alloy. At times of exposure to ozone (with a concentration of 50 mg/m3) not exceeding 250 min, the effect of degradation of the coating was practically indetectable, which is associated with self-recovery of the coating performance during the ozonation process. At longer times, exposure to ozone leads to irreversible degradation of the superhydrophobic coating, which is mainly due to the desorption of the hydrophobic part of the fluorooxysilane molecule upon rupture of bonds of the Si-C type, as well as the adsorption of ozone on the textured surface.