In this study, composite coatings of polyvinylidene fluoride (PVDF) and epoxy resin deposited with La 2 O 3 and MoS 2 nanoparticles on the surface of a Babbitt alloy have been studied in order to improve its tribological performance. A pin-on-disc tribometer was used to evaluate the tribological properties of the Babbitt alloys with and without the composite coatings. The results showed that compared with the polymer-La 2 O 3 composite coating, the polymer-MoS 2 composite coating was more effective in reducing the friction coefficient and the wear rate of the Babbitt substrate under both dry and boundary lubrication conditions compared with the polymer-La 2 O 3 composite coating. However, the wear rate of the Babbitt alloy with the polymer-La 2 O 3 composite coating was lower than that of the alloy with the polymer-MoS 2 composite coating. The wear scratches were analyzed using a scanning electron microscope (SEM). The worn surface of the polymer-La 2 O 3 coating was much smoother and more continuous than that of the polymer-MoS 2 coating, meanwhile transfer films were respectively detected on the pin surfaces. The addition of nanoparticles can reduce the wear rate and friction coefficient of polymer composite coating by forming a transfer film. Hence, the polymer composite coating can protect the Babbitt substrate.

Finite element analysis is conducted on an elastic-plastic full stick contact between a rigid flat and a deformable coated sphere with a soft coating. A combined normal and tangential load is applied to the rigid flat, and the sliding inception is assumed as a result of the decreasing tangential stiffness of the contact junction. As the coating becomes thicker, the static friction coefficient first decreases reaching a minimum and then increases. This demonstrates a friction reduction effect of soft coatings that is opposite to hard coatings. The static friction coefficient decreases with increasing normal load as the contact junction contains more plasticity and becomes more compliant.

Hydrophobic and self-cleaning photocatalytic ceramics and concrete with potential for the superhydrophobicity are promising novel materials for civil engineering applications including buildings, bridges, road pavements, and airport runways. Due to embedded liquid-repellent properties, such materials have low water and salt absorption and, therefore, enhanced durability. However, in applications requiring high traction (e.g., tire and pavement), there is a concern that reduced adhesion may compromise the friction. This paper reports on wetting, dry friction, and roughness properties of TiO 2 coated (hydrophilic) and polymethyl hydrogen siloxane (PMHS) coated (hydrophobic) self-cleaning ceramic tiles. The coefficient of friction values of the tile–rubber interface do not change significantly with the applications of the coatings up to 0.67 for hydrophilic TiO 2 based and up to 0.46 for hydrophobic TiO 2 + PMHS coatings versus 0.45 for uncoated reference. Friction has adhesion and roughness-related components and this response can be attributed to the roughness component of friction due to TiO 2 coating. The challenges related to hydrophobic coatings, including the durability and future research, are also discussed.

Among the alternatives for using low-carbon steel in parts with heavy wear, as gears and bearing surfaces, Ni-B electroless coatings deposited on these steels are considered due to their wear resistance. Wear maps, elaborated from friction or wear results found for different evaluated conditions, are a very useful tool for the selection of materials based on tribological properties. However, wear maps for electroless Ni-B coatings are very scarce. In this work, dry sliding wear tests with different loads and sliding velocities were performed on Ni-B electroless coatings applied on AISI/SAE 1018 steel, with and without heat treatment at 450 °C for 1 h, with the aim of determining the effect of the heat treatment on the friction coefficients and wear rates. Contour and profile maps, and finally friction and wear maps, were constructed for each of the coatings evaluated. The coating properties before and after the heat treatment were studied by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), scratch tests, nanoindentation, and differential scanning calorimetry (DSC). Sliding wear tracks were studied using SEM, energy-dispersive spectroscopy (EDS), and micro-Raman spectroscopy. Good agreement between experimental and predicted values was found in friction and wear maps. Wear mechanisms change from flattening in less severe conditions to abrasion in more severe conditions, besides spalling and adhesive wear in untreated coatings. Moreover, abrasive wear is lower in heat-treated coating than in untreated coating.

This research aims to evaluate the tribological performance of chromium molybdenum (CrMo) coatings under point and line-contact mixed elastohydrodynamic lubrication. This article studies the coatings made from two different methods and treated in an electrifying process of different durations, which produced microchannels and micropockets in the surfaces. The resulting surface topographies had varying impacts on lubricant film thickness, friction, and wear. Root-mean-square roughness (S q ) and porosity are used to characterize the surfaces and their performances in terms of film thickness, friction, and wear. The results suggest that the coated surfaces with a lower S q and porosity density tended to yield higher film thickness. However, their influence on friction is complicated; lower roughness and porosity are preferred for lower wear, but certain levels of small roughness and surface pores may help to reduce boundary lubrication friction when compared with the frictional behaviors of porosity-free surfaces and those with higher roughness and higher porosity.

Chromium (Cr)-based coatings have been widely used to strengthen the friction reduction and wear resistance on various kinds of surface. Here, the stable aqueous dispersion of oxidized multi-walled carbon nanotube (MWCNT) and graphene oxide nanosheets (GOS) was obtained by ultrasonic oxidation treatment. Then, MWCNT-Cr and GOS-Cr composite coatings were prepared using the direct current electrochemical co-deposition process on 420 stainless steel in the electrolyte with the addition of MWCNT and GOS under different current density and temperature. The morphology, structure, hardness and tribological properties of MWCNT-Cr and GOS-Cr composite coating are comparatively studied using pure Cr coating as a baseline. The friction reduction performance of MWCNT-Cr and GOS-Cr composite coatings was improved at optimum current density and temperature. The anti-wear properties of MWCNT-Cr and GOS-Cr composite coatings were enhanced by uniform embedment of MWCNT and GOS in coatings increasing the hardness and lubricity. This study suggests that the introduction of oxidized MWCNT and GOS with good dispersion could enhance the wear resistance and friction reduction of pure Cr coating due to their excellent dispersion, mechanical, and lubricant properties.

Titanium is a highly interesting material in engineering because of its unique combination of high strength to weight ratio, excellent resistance to corrosion, and biocompatibility. However, the material’s low wear resistance, which is its inherent nature, limits its application in highly erosive conditions. In order to enhance the wear resistance of biomedical grade titanium with the help of a WC-Co coating, an electrospark deposition method was used in this work. The goal of this work is to investigate the effect of frequency and current upper limit in the electrospark deposition process on substrate properties. Hardness of the layers was measured by a microhardness tester. In order to study the morphology and microstructure of surface layers, scanning electron microscope was used. Tribological tests were conducted under technically dry friction conditions at a load of 12.5 N by a pin-on-disk tribometer. Titanium was observed in coating and metallurgical bonding between the coating and the substrate. The optimized sample's hardness was about 930 HV 0.1. Results showed that the presence of a carbide layer on the surface of titanium leads to a great enhancement of wear resistance of about 68% in the pin-on-disk test.

The main objective of this investigation is the evaluation of the performance of hard diamond-like-carbon (DLC) or tungsten carbide (WC) and soft (epoxy composite) dual-coatings on the internal combustion (IC) engine piston rings as a protective coating to reduce their wear. The rings were coated with DLC or WC by physical vapor deposition (PVD) method and then soft polymeric composite coating (epoxy/graphene/base oil SN150) was applied on the hard coating. The tribological tests of the dual-coated piston rings were conducted for 3.6 × 10 5 cycles at 1500 rpm engine speed and 50% rated load of a diesel engine in order to evaluate the wear performance of the piston rings. Scuffing of cylinder liner and piston rings interface was prevented by the application of polymer composites over the hard-coated rings. DLC hard and soft polymer composite dual coating over the top piston ring was found to have the lowest wear rate 1.69 × 10 −12 mm 3 /N·m compared with the wear rate of dual coatings on the middle and lower rings.

Ti/MoS 2 coating was deposited by pulse laser deposition technology on Al-Si substrate. The microstructure, elemental analysis, nanotribological behavior of coating was investigated. The coating was composed of Ti, Mo, S, and O with typical diffraction peak around 2 θ range from 30 deg to 70 deg. Nanoscratch with ramp loading was performed at low loads. The scratch test with ramp normal loading was analyzed for failure of coating in three ranges, viz., range A, range B, and range C. Scratch test result shows that the peeling of coating occurred at the normal load of 1327.75 μ N and the lateral load of 75.96 μ N. Nanowear with 2, 4, 6, 8, 10 number of cycles was performed at low load 100 μ N. Nanowear results shows that wear rate decreases with increase in wear cycles, which attributed the self-lubricating property of Ti/MoS 2 coating. Also, Ti/MoS 2 coating display smooth wear path with no debris and cracks, which attributed plastic flow of coating around impression. Thus, mode of wear mechanism is mainly ductile and abrasive.

This work focuses on the tribochemistry of molybdenum dithiocarbamate (MoDTC) oil additive to improve friction behavior of diamond-like-carbon (DLC) coated systems lubricated in boundary regime. Raman microscopy has been used to investigate surface tribolayers formed on coated (hydrogenated a-C:H and non-hydrogenated ta-C) and steel surfaces when lubricated with model lubricants and commercial engine oils. The effect of the additive package and the type of DLC played a crucial role in the development and composition of the tribolayer and the friction performance. The additive package contained in the fully formulated (FF) oils limited the friction reduction capabilities of MoDTC additive for every material pair. Accelerated a-C:H coating wear related to MoDTC tribochemistry was found. For the first time, it has been shown that a distinctive MoS 2 -containing tribolayer can be formed on the ta-C surface, leading to a coefficient of friction lower than 0.04. The underlying mechanisms of MoDTC/surface interactions and their effect on friction and wear are discussed.

A finite element analysis was used to study the onset of plasticity of a coated sphere compressed by a rigid flat. This was done for soft coatings on a harder substrate. Generally, the results agree very well with the findings in the literature for the opposite case of an indentation of a rigid sphere into a coated flat, with a soft coating. In this case, a weakening prevails over the entire range of coating thicknesses, resulting in critical loads (at yield inception) lower than the critical load of the uncoated contact. However, a surprising strengthening effect was discovered, in this study, for very thin coating thicknesses resulting in a higher resistance to plasticity, compared to an uncoated sphere. This phenomenon resembles a mirror image of the opposite weakening effect which was reported for very thin hard coatings. These results may suggest that when very thin coatings are to be applied in a spherical contact, a softer, rather than harder, coating should be considered in order to increase the contact's resistance to plasticity inception.

A novel hybrid polymer nanocomposite coating of ultrahigh molecular weight polyethylene (UHMWPE) reinforced with nanoclay (C15A) and carbon nanotubes (CNTs) has been developed to protect metallic mating surfaces in tribological applications. The hybrid nanocomposite coatings were deposited on aluminum substrates using an electrostatic spraying technique. Ball-on-disk wear tests using a 440C stainless steel ball as the counterface were conducted on the coatings under dry conditions to determine the optimum amount of the loadings of the nanofillers and evaluate their tribological performance at different normal loads and linear velocities. Micro-indentation, raman spectroscopy, scanning electron microscopy (SEM), and optical profilometry techniques were used to characterize the coatings in terms of hardness, dispersion of the nanofillers, morphology, and wear mechanisms, respectively. Results showed that the UHMWPE hybrid nanocomposite coating reinforced with 1.5 wt % of C15A nanoclay and 1.5 wt % of CNTs did not fail even until 100,000 cycles at a normal load of 12 N and a linear speed of 0.1 m/s showing a significant improvement in wear resistance as compared to all other coatings evaluated in this study.

The graphite-MoS 2 coated on GCr15 bearing steel is prepared through air spraying and its tribological performances are investigated experimentally. Then its coefficient of friction (COF) and wear scar width (WSW) are investigated through the MFT-5000 multifunction tribometer and other test equipments. The experimental results show that the addition of the graphite can effectively decrease the COF and narrow the WSW of the MoS 2 . There exists a critical applied load for wearing out the surface with the graphite-MoS 2 coating. Moreover, there exists an optimal rotational speed of 500 rpm to decrease the COF and WSW of the GCr15 steel.

In this paper, the effect of compacted graphite iron (CGI) microstructure has been investigated in tribological strategy. From industrial context, two coatings have been chosen: a single layer coating (physical vapor deposition (PVD)) and a multilayer coating (chemical vapor deposition (CVD)). Pin-on-disk tests have been done to analyze wear mechanisms and to directly obtain the coefficient of friction. Rotation speed of the disk has been adjusted to get the same linear velocity on different disk radii to get up to 150 m min −1 similar to machining condition. Three-dimensional (3D) profilometer, scanning electron microscopy, and nano-indentation were used to observe the track profiles, the pin, and the disk wears and to measure the hardness of microstructure components, respectively. Results showed that PVD coating was more abrasive and had more volume of sticking materials. Chemical vapor deposition coating, which could be the most appropriate for machining CGI, has a real antisticking property and has less friction coefficient than PVD coating. But the presence of small TiCN precipitates in CGI material has a proven negative effect in CVD coating lifetime.

Effects of partial pressure of methane on deposition rate, hardness, bonding strength and friction coefficient of TiAlN/TiAlC 0.37 N 0.63 multilayer coating were investigated. The TiAlN coating was deposited at a N 2 flow rate of 70 sccm, and TiAlC 0.37 N 0.63 coating were deposited at a N 2 flow rate of 35 sccm and a CH 4 flow rate of 35 sccm. TiAlN/TiAlC 0.37 N 0.63 multilayer coatings with different modulation periods but the same total thickness of 3.56 μ m were deposited on high speed steel (HSS) substrates using multi-arc ion plating technology. Microhardness and tribological measurement show that the multilayer coating with a modulating ratio of 1:1 and a modulation period of 68 nm had a hardness of 2793.9 HV 0.10 , an excellent bonding strength of 52 N, and the minimum friction coefficient of 0.46 and a relatively low wear rate.

(Ti,Mo)C, TiB 2 , and Mo 2 B particles reinforced Fe-based composite coatings were fabricated by laser cladding process. The effects of Molybdenum (Mo) on the microstructure and wear properties of the coatings were investigated. The results show that block-like or cuboidal TiB 2 , Mo 2 B and flower-like (Ti, Mo)C ceramics reinforcements were formed in the coatings. The size of reinforcements reduced with the increasing of FeMo 70 . However, cracks were found in the coating, while the addition of FeMo 70 exceeded 9 wt %. The laser cladding coating presented a good wear resistance with a 9 wt % addition of FeMo 70 . With the increasing of FeMo 70 , the coatings enhanced the capability of resisting microcutting, microplowing, and surface plastic deformation.

To enhance the friction property of Al–Si alloy cylinder liner in running-in period, MoS 2 coatings were electrodeposited on the chemical-etched surface of cylinder liner. The friction coefficient decreased by 15% comparing with the original honed surface, indicating the better friction property. This is because the synergistic action between solid lubricant and etched surface. MoS 2 coatings prevent the direct contact between silicon particles and piston ring during friction. At top dead center, the oil film was thinnest and even was broken during the reciprocate friction. When oil film was invalidated, MoS 2 coatings undertook lubrication. Then, MoS 2 coatings were depleted, and advantage of etched surface became apparent.

TiAlN and TiSiN coatings were deposited on YT15 cemented carbide using a cathodic arc ion plating (CAIP). The surface-cross section morphologies, chemical elements, surface roughness, phases, and chemical valences of as-obtained coatings were analyzed using a scanning electron microscopy (SEM), energy dispersive spectroscopy, atomic force microscopy (AFM), X-ray diffractometer (XRD), and X-ray photoelectron spectroscopy (XPS), respectively, and the bonding strength, hardness and Young's modulus of TiAlN and TiSiN coatings were measured using a scratch tester and nano-indentation, respectively, and the wear mechanism at high temperatures was also discussed. The results show that the surface roughness of TiAlN and TiSiN coatings is 69.1 and 58.0 nm, respectively, and the corresponding average particle size is 998.8 and 817.2 nm, respectively. The TiAlN coating is composed of TiAlN and AlN, while the TiSiN coating is composed of TiN and Si 3 N 4 . The bonding strength of TiAlN and TiSiN coatings is 84.3 and 72.6 N, respectively, the hardness and Young's modulus of TiAlN coating is 23.67 and 415.80 GPa, respectively, while that of TiSiN coating is 20.46 and 350.40 GPa, respectively. The average coefficients of friction (COFs) of TiAlN and TiSiN coatings are 0.4516 and 0.4807, respectively; the corresponding wear rate is 589.7 × 10 −6 and 4142.2 × 10 −6 mm 3 N −1 s −1 , respectively; the wear mechanism of TiAlN and TiSiN coatings is oxidation wear and abrasive wear.

A chromium nitride (CrN) coating was deposited on YT14 cemented carbide using a cathodic arc ion plating (CAIP). The high temperature friction and wear of the obtained coating were investigated using a wear test. The results show that the Cr and N form the atom-rich zones in the coating. The average coefficient of friction (COF) of CrN coatings at 300 °C, 400 °C, and 500 °C is 0.50, 0.62, and 0.43, respectively. The wear mechanism of CrN coating at 300 °C and 400 °C is abrasive wear, and that at 500 °C is abrasive wear, accompanied by slight oxidation wear.