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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.

The current study presents research into the effect of graphene oxide (GO) with a carbon to oxygen ratio of 4:1 on the fluidity, hydration, microstructure, mechanical and physical properties of Portland cement pastes and mortars. The amounts of GO investigated were 0.02%, 0.04%, and 0.06% by weight of cement, while for mortars, an extra composition with 0.1% was also prepared. According to the results, the fluidity of cement paste and mortar increased and the hydration process was slightly retarded with the addition of GO. Despite this, improvements in compressive and flexural strength were established in the mortars containing GO. The maximum effects (~22% and ~6%, respectively) were obtained with the addition of 0.06% GO. The calculation of estimated strength proportional to samples of equal density showed that for mortars cured for 7 days the gain in strength was directly related to the gain in density. For mortar samples cured for 28 days, the estimated strength was found to be significantly higher than that of the reference sample, indicating that besides density there are other factors determining the improvement in strength of mortars modified with GO. The possible structure strengthening mechanisms are discussed.

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