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Low friction MoS2(Ti, W) coatings deposited by magnetron sputtering

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Self-lubrication of graphite or of some metal dichalcogenides (such as MoS2 or WS2) is a very desired property in many technical applications. The phenomenon of self-lubrication in these materials is a result of a very big anisotropy of the crystallographic structure of these materials. In case of the MoS2-based material the basal planes of MoS2 elementary cells consist of hexagonal, strong covalent- -bonded planes of metal atoms between two planes of sulfur atoms. In a perpendicular direction exist weak Van der Waals interactions between the neighbouring planes built from sulfur atoms, what brings about a low shear strength [1, 2]. Limitation of use of grease and oils in friction couples becomes more and more important due to difficulties with smearing at high loads and to high costs of recycling of used oils. Nowadays, coatings’ engineering is able to tailor the most outward areas of mating machine elements to working conditions. Coatings based on MoS2 have been largely used in numerous applications, such as, for example, ceramic tools for dry machining of stainless steel [3÷6], inserts for dry high speed milling of steel and grey cast iron [7, 8], ejector pins used for plastic moulds [4], punches for piercing and fine blanking of stainless steel [6], in a variety of engine components such as fuel injection systems, tappets, pistons, piston rings and bearings [5] and recently also as coatings for gears [9, 10] or for elements of friction simulator working in real space environment in a lunar orbiter [11]. On the other hand, pure MoS2 coatings exhibit relatively high wear during sliding in humid atmospheres or temperatures higher than 400÷500°C due to heavy oxidation [2]. Many attempts have been made to extend the range of convenient working conditions. Firstly, by incorporating different metals atoms into MoS2 matrix, as, for example: Au, Ni, Pb, Ti, Ta, Cr, Ce, Re, Mo, Cr, Zr, W, Si [2, 12÷14]. Secondly, by using comp[...]

The effect of surface modification of LaNi4.5Co0.5 hydride alloy with SiC layer on its hydrogen storage and kinetic electrochemical properties DOI:10.15199/40.2018.3.3

  1. Introduction The conventional rare-earth based AB5-type alloys are considered as the most promising candidates for negative electrode materials of NiMH rechargeable batteries. However, the functional properties of the metal hydrides tend to worsen in repeated charge/discharge cycles which harmfully affects the performance of hydrogen storage systems. The requirements for NiMH rechargeable batteries with high discharge capacity and electrochemical hydrogen storage kinetics are still relevant and of crucial significance. Among AB5 type intermetallics, the LaNi5 compound belongs to the most known representative of hydrogen storage materials. Its physicochemical properties in view of hydrogen sorption ability have been widely investigated for over 30 years [9,10,14,20,32]. One of the most efficient methods for improving of the functional hydride electrode properties is partial substitution of the compound constituents by other elements [1,13,33]. In particular, the partial substitution of Ni by Co increases the hydride thermodynamic stability and inhibits corrosion degradation [1]. Therefore, Co-substituted alloy displays a longer cycle life (longer corrosion degradation half time, t1/2 degr) as compared to LaNi5 Artykuł naukowy Ochrona przed Korozją, ISSN 0473-7733, e-ISSN 2449-9501, vol. 61, nr 3/2018 67 [13]. Surface modification of hydride powder materials, e.g. by particles encapsulation, is considered to be very effective way to improve a comprehensive electrochemical performance of metal hydride electrodes [8,12,18,23]. As it has been shown in Ref. [8], for the 10 first charge/discharge cycles in 6M KOH, the LaNi4.5Co0.5 powdered material coated with Fe-Cr-Ni nanofilms (obtained by magnetron sputtering) reveals relatively high values of the discharge capacity [8]. After encapsulation with a Fe- Cr-Ni layer, the structural degradation of the powder-composite electrode is limited owing to inhibition of active surface expans[...]

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