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Editor's Choice : High-Temperature Protective Coatings Produced by EB-PVD
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Abstract: The paper presents some new technological sequences of electron beam evaporation and deposition of high-temperature metal-ceramic coatings. The main attention is given to two-layer Me-Cr-Al-Y/ZrO2-Y2O3 coatings with transition layers of the total thickness of up to 0.2 mm. Chemical composition and structures of the main layers (metal, ceramics) and substrate/metal and metal/ceramics transition layers, as well as the respective physico-mechanical properties are considered. A method of deposition of these coatings in one technological cycle of evaporation and condensation with application of evaporation composite ingot is proposed. Examples of coating “design” and respective equipment for practical application in gas turbine construction are given. Keywords: Electron-beam evaporation and deposition (EB-PVD), high-temperature coating, multilayered thermal-barrier coating, crucible-evaporator, gas turbine blades. |
Editor's Choice : Sliding Wear Study of Flame Sprayed Co-Base Powder Coatings
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Abstract: Commercially available Co-base powder was modified with the addition of 10 wt. percentage WC which was further modified with 5 and 10 wt. percentage CrC addition in order to obtain three coatings namely Co+10 wt. percentage WC, Co+10 wt. percentage WC+5 wt. percentage CrC and Co+10 wt. percentage WC+10 wt. percentage CrC. The coatings were deposited by flame spraying process. The microstructure of these coatings mainly showed eutectic containing Co with almost same amount in three coatings. Other phases such as W dominated and Cr dominated carbides were also observed. The 10 wt. percentage CrC coating showed the highest Vickers hardness and lowest wear rate. The coefficient of friction was also observed low in the 10 wt. percentage CrC coating as compared with other coatings. Keywords: Atomic force microscopy, time of flight secondary ion mass spectrometry, Auger electron spectroscopy, coil coating, Cr-free pretreatment, topography. |
Editor’s Choice : Bacterial Anti-Adhesion of Coated and Uncoated Thin-Film-Composite (TFC) Polyamide (PA) Membranes
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Abstract: This study investigates the bacterial anti-adhesion performance of uncoated and coated reverse osmosis (RO) membranes. All the membranes were commercially available fully-aromatic thin-film-composite (TFC) polyamide (PA) membranes. Two of the TFC PA membranes (SW30 and BW30) were coated using polyvinyl alcohol (PVA) coating, while the other three membranes (LE, XLE and NF90) were uncoated. Among the characterised TFC PA membranes, the PVA coated were more hydrophilic and their surface energy was higher in comparison to uncoated. In addition, the PVA coated membranes had lower surface roughness. AFM interaction force measurement demonstrated higher repellence performance for the more polar surface. Bacteria attachment test showed differences between the coated and the uncoated membranes. Indeed, the increase in hydrophilicity and surface polarity showed decrease in the attachment of Pseudomonas aeruginosa cells. Moreover, the results demonstrated that the surface polarity showed better correlation with the attachment of the bacteria. In addition, the type of the surface roughness may somehow contribute to the bacteria repellence. Keywords: Thin film composite (TFC) polyamide (PA) membrane, polyvinyl alcohol (PVA), surface energy, topography, biofouling. |
Editor’s Choice : DLC Coatings in Oil and Gas Production
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Abstract: Diamond-like carbon (DLC) coatings are recognized in many sectors as a promising way of controlling wear and the corrosion performance of components. DLC coatings are well established in the automotive industry where they are applied to the moving parts of direct injection fuel systems operating under frictional conditions at high pressures and in the aggressive environment of the combustion chamber. Over the last few years, there have also been an increasing number of reports of DLC coating applications in oil and gas production contexts, including in pipes, shut-off gates and various types of valves. This paper reviews current efforts to use DLC coatings in the oil and gas sectors and analyses typical coating degradation mechanisms including wear and wear-accelerated corrosion regimes. DLC coating deposition techniques including Physical (PVD) and Chemical Vapor Deposition (CVD) techniques are elaborated and the unique coating properties obtained from those two methods are assessed. Surface functionalization is discussed including dopants (W and Si) and gradient interlayers. Finally, the outlook for future use of DLC coatings in oil and gas production is discussed.
Keywords: Diamond-like carbon, DLC, surface engineering, functional coatings, tribology, corrosion. |
