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The effect of applied load on the tribological behaviors of single DLC coating and DLC/Cr 3 C 2 –NiCr duplex coating was explored in the paper experimentally, and the role of cermet interlayer on the duplex coating tribological behavior was analyzed from the perspective of carbonaceous transfer film formation. Results proved that the duplex coating wear rate under 20 N was the lowest, about 1/6 of that of the single coating. The existence of Cr 3 C 2 –NiCr interlayer can prevent the top DLC film from being damaged in high load friction, reduce the fluctuation and vibration of the friction interface, and help the friction-induced graphitized carbonaceous transfer film to maintain on the friction counterpart, thus realizing the low-friction of the duplex coating. Furthermore, the critical conditions under which the friction-induced carbonaceous transfer film of a single coating maintains on the friction counterpart are explored by designed experiments. Results show that the carbonaceous transfer film derived from the single coating can only maintain on the friction counterpart under conditions of low load, low sliding frequency, and high humidity, which indirectly confirms the excellent tribological performance of the duplex coating. [ABSTRACT FROM AUTHOR]

Tribological behaviors of three typical kinds of diamond‐like carbon (DLC) films (a‐C, a‐C:Cr, and a‐C:H) in sulfuric acid and sodium hydroxide solutions were investigated. The a‐C film showed the lowest stable coefficients of friction (COF) in both sulfuric acid and sodium hydroxide solutions but the worst wear resistance in sulfuric acid solution. The a‐C:H film showed the highest COF in sulfuric acid solution and the best wear resistance in both sulfuric acid and sodium hydroxide solutions. The a‐C:Cr film exhibited superior comprehensive tribological performance in sulfuric acid solution, while in sodium hydroxide solution, high COF and very poor wear resistance was observed. What is more, friction and wear mechanism was revealed by investigating the friction‐induced material evolutions on the sliding surface. [ABSTRACT FROM AUTHOR]

Duplex coating consisting of a Cr 3 C 2 -NiCr interlayer and a top DLC film was prepared using the high-velocity oxyfuel (HVOF) spraying and a closed field unbalanced magnetron sputtering (CFUBMS). The electrochemical behaviors of the Cr 3 C 2 -NiCr/DLC duplex coatings in 3.5 wt% NaCl solution was investigated by comparing it with a single DLC film and a single Cr 3 C 2 -NiCr coating. Then the role of cermet interlayer on the anticorrosion mechanism of the duplex coatings was explored. Results showed that introducing the cermet interlayer increased the surface roughness of DLC films without changing its microstructure. In the dynamic potential polarization test, duplex coatings maintained high surface integrity even after corrosion, and corrosion only occurs in localized areas. The inclusion of an interlayer avoided substrate corrosion caused by penetrating cracks and therefore provided excellent corrosion resistance. • The top DLC film covers the pores of the Cr 3 C 2 -NiCr coating. • The corrosion occurs the island boundaries, but duplex coating remains dense surface. • Oxide of Cr and Ni protects the coating system from diffusion of corrosive ions. [ABSTRACT FROM AUTHOR]

Effects of carbide content on the mechanical and tribological properties of DLC/Cr 3 C 2 –NiCr duplex coatings were systematically investigated. Results revealed that cermet coating with high carbide content provided strong support for the top DLC film by bearing most of the contact stress, thus improving its hardness, load-bearing capacity, and adhesion strength. The increased carbide content increased the contact and shear stresses on duplex coating during the friction process, intensifying the graphitization of the top DLC film but inhibiting the formation of a graphitized transfer film on the counterpart, thus slightly increasing its friction coefficient. However, the predominant wear mechanism changed from high-efficiency abrasive wear to low-efficiency adhesive wear for low to high carbide content, superior wear resistance was thereby achieved. [Display omitted] • Effects of carbide content on mechanical and tribological properties of duplex coatings was systematically studied. • Contact stress distribution in duplex coatings during the load-bearing process was clarified by FEM analysis. • Tribological mechanisms were revealed from many aspects of energy description, phase transition and contact mechanics. [ABSTRACT FROM AUTHOR]

Super-thick diamond-like carbon (DLC) film is a potential protective coating in corrosive environments. In the present work, three kinds of DLC films whose thickness and modulation periods are 4 µm and 3, 21 µm and 17 and 21 µm and 7, respectively, were fabricated on stainless steel. The effect of different thickness and modulation periods on corrosion and tribocorrosion behaviour of the DLC-coating stainless steel was investigated in 3.5 wt% NaCl aqueous solution by a ball-on-flat tribometer equipped with a three-electrode electrochemical cell. The DLC-coating stainless steel served as a working electrode, and its OCP and potentiodynamic polarization were monitored before and during rubbing. The wear-corrosion mechanism of the DLC films was investigated by SEM. The results showed that the increasing thickness can prolong significantly lifetime of DLC films in NaCl aqueous solution. In particular, the modulation period has a significant impact on the tribocorrosion resistance of the DLC super-thick films. The study suggested that the increasing thickness of compressive stress layer could suppress film damage by reducing crack propagation rate. Thus, the super-thick DLC film with thickness of 21 µm and 7 periods presented the best tribocorrosion resistance among all studied films. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Titanium alloys are characterized by poor tribological performance, and their conventional use has been restricted to non-tribological applications. Surface films and surface texturing are effective methods to improve the tribological properties of sliding surfaces. In this study, the patterns of micro-dimples with different densities and diamond-like carbon (DLC) films were fabricated on the surface of titanium alloy by laser surface texturing and magnetron sputtering, respectively. The effects of dimple densities and DLC phase transformation on the tribological behavior of the titanium alloy under dry friction and liquid lubrication conditions were investigated. The results showed that DLC film with appropriate dimple area density (44%) are effective in enhancing reducing-friction property of titanium alloy substrate because of the entrapment of wear particles in the dimples and dimple-induced graphitization during sliding motions, while the 24% textured specimen exhibited outstanding wear resistance. [ABSTRACT FROM AUTHOR]

• Textured DLC films were in-situ deposited by masking substrate with metallic meshes. • Covered region became concave part while exposed region became protruding part. • In-situ surface texturing improved film hardness, elastic modulus and lipophilicity. • DLC-T52% reached the lowest COF and wear rate under dry and lubricated conditions. Surface texturing is emerging as one of the viable means that can be applied to improve the tribological properties of diamond like carbon (DLC) films. In this study, textured DLC films were in-situ fabricated by masking the substrate with metallic meshes during the deposition process. The tribological behaviors of the textured DLC films with micro-dimples densities of 39%, 52% and 58% were studied and compared with that of the un-textured DLC films under dry friction and liquid lubrication conditions. The results showed that the textured DLC films with micro-dimples density of 52% exhibited the lowest average coefficient of friction (COF) and wear rate both under dry friction and liquid lubrication conditions. The improved tribological performance of the textured DLC films with optimum micro-dimples density (52%) under dry friction could be attributed to the friction-induced graphitization of the textured layer and entrapment of wear debris in the micro-dimples. Under liquid lubrication condition, the micro-dimples played the double role of wear debris and lubricating oil reservoirs, then the graphitized textured layer on the worn surface combined with the liquid lubrication film formed a solid-liquid duplex lubricating, thus achieving significantly lower friction and wear. [ABSTRACT FROM AUTHOR]

A top DLC film was deposited on the surface of Cr 3 C 2 -NiCr coated 38CrMoAl steel substrate, and the effect of Cr 3 C 2 -NiCr cermet interlayer thickness on the mechanical and tribological properties of the duplex coating was investigated by experimental analysis and finite element modeling (FEM). Results shown that, compared with single DLC film, the load-bearing capacity and tribological performance of DLC/Cr 3 C 2 -NiCr duplex coating were significantly improved, especially its anti-wear performance was nearly ten times higher than that of the single DLC film. Moreover, the duplex coating with an optimum cermet interlayer thickness of 100 μm showed the best comprehensive performance. FEM analysis also shown that the presence of Cr 3 C 2 -NiCr cermet interlayer limited the stress concentration area within the interlayer, which made the stress concentration area far away from the interface of DLC film and cermet interlayer, thus improved duplex coating durability. What's more, the cermet interlayer thickness increase resulted in the contact stress on DLC film increase, which contributed to the improvement of its tribological performance. • C100 duplex coating achieved superior mechanical and tribological properties. • C100 duplex coating anti-wear rate is ten times higher than single DLC film. • Stress concentration in C100 is the farthest against film/cermet interlayer interface. • Thickened interlayer increased contact stress and intensified DLC graphitization. [ABSTRACT FROM AUTHOR]

Boron carbide doped DLC coating can combine the property superiority of these two materials to create high-performance carbon-based coating, while the final property of the composite coating is strongly dependent on the proportion of coating components. The aim of this study was to investigate the effect of boron carbide content on the mechanical and tribological properties of the magnetron sputtered B 4 C/a-C coatings, as well as the relevant low friction mechanism. It was found that both the carbon matrix and introduced boron carbide were amorphous and the composite coating exhibited typical columnar structure. Appropriate doping of boron carbide significantly enhanced coating hardness, toughness as well as the adhesion strength and carrying ability, and all of them reached the optimal value when the B concentration was 2.92 at.%. It was also found that the B 4 C/a-C coating with B 2.92 at.% exhibited the lowest steady friction coefficient about 0.05 and highest wear resistance at 20% RH. None of boric acid was formed on the sliding interface under the tested humidity range. Thus, the improved tribological properties were mainly attributed to the enhanced mechanical properties and friction-induced formation of an intact graphitized carbon transfer layer on the counterpart under specific humidity condition. [ABSTRACT FROM AUTHOR]

Si-doped diamond-like carbon (Si/DLC) films appear very attractive due to their superior mechanical and tribological properties and chemical inertness. In the present work, Si/DLC films with silicon concentration from 1.64 to 15.32 at.% were fabricated on 304 stainless steel by adjusting Si target current using unbalanced magnetron sputtering system. The microstructure, surface morphology and mechanical properties of the films with different Si concentration, as well as the tribological and electrochemical properties of the films under HCl corrosive environment were systematically investigated. Results showed that Si doping increased the sp3 C C content, hardness, and elastic modulus of as-fabricated films, lowered the residual stress, but deteriorated the adhesion strength. At the same time, the appropriate Si concentration was conducive to low surface roughness and dense microstructure. The Si/DLC films presented good tribological performances in 1 M HCl solution, including low friction coefficient and wear rate. The degradation of tribological properties was attributed to the synergistic effect of less solid lubrication, declined adhesion strength, worse resistance to elastic and plastic deformation. The wear mechanism was mainly dominated by abrasive wear. Furthermore, the Si/DLC film with 15.32 at.% Si provided the best corrosion resistance, which benefited from its dense structure, higher thickness, and the highest sp3 C C content. [Display omitted] • The Si/DLC films with various Si concentrations were fabricated by UBMS technology. • The Si/DLC films showed favorable tribological behaviors in 1 M HCl solution. • The Si/DLC film with 15.32 at.% Si exhibited the best corrosion resistance. [ABSTRACT FROM AUTHOR]