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In order to increase the service life of critical products made of refractory metals, the most effective is the use of protective coatings based on oxidation-resistant ceramic materials. Using an electrode/target made of heterophase HfSi2–MoSi2–HfB2 ceramics by electrospark deposition (ESD), high-power impulse magnetron sputtering (HIPIMS) technologies, as well as the combined ESD + HIPIMS technology, coatings were deposited onto molybdenum substrate (MCh-1 brand). Electrode materials and coatings were studied by the X-ray diffraction, the glow discharge optical emission spectroscopy, the X-ray spectral microanalysis, and the scanning electron microscopy. Combined ESD + HIPIMS technology made it possible to create a hard layer of oxidation-resistant ceramics on the surface of the substrate, which does not produce through cracks inherent in ESD coatings. [ABSTRACT FROM AUTHOR]

Using plasma surfacing in a nitrogen environment with a PP-R18U non-current-carrying flux-cored wire, the layers up to 10 mm thick were formed on a 30HGSA steel, followed by an additional high-temperature tempering (at 580°C for 1 hour in 4 tempers). It is shown that the deposited layer has a frame-type structure formed by α-iron grains with extended layers of the Fe3W3C (M6C) carbide phase located along the boundaries. Nanosized particles of carbides of the V4C3, Cr7C3, Fe3C, Cr23C6 and WC1–x types are identified in the grain volume. It is found out that high tempering increases the microhardness of the deposited PP-R18U layer by 13% (up to 5.3 GPa) and decreases its wear resistance by 12.3% the friction coefficient by 7.7%. [ABSTRACT FROM AUTHOR]

The characteristics of multi-impurities and high-flow velocity in the marine environment can easily cause wear and tear of the surface coating of marine equipment, affecting the reliability and service life of the equipment. In this paper, silicon dioxide (SiO2) hybrid multi-walled carbon nanotubes (MWCNTs) composites were obtained by sol-gel method, and SiO2-MWCNTs acrylic silicone resin composite coatings were prepared. The results showed that SiO2-MWCNTs had good dispersion in acrylic silicone resin, and the lower surface energy could be found in the composite coating with 1.0wt.% hybrid material, with an average contact angle of 107.68°, the impact resistance reached 70 cm·2000 g and the interfacial bonding strength reached 3.29 MPa. The hardness and tribological properties of the composite coating with 2.0wt.% hybrid material were the highest, with the hardness reached 17.7 HV0.05, the wear volume and wear rate were 2.99 × 10− 3 mm3 and 0.12 mm3 N− 1 m− 1 respectively, which were 77.1% and 77.8% higher than those of pure acrylic silicone resin coating. This was mainly attributed to the effect of hybrid MWCNTs bridging to change the direction of crack, uniform distribution of reinforcement phase could formed a larger area of lubrication layer and reduced the friction coefficient and wear rate. In conclusion, the use of SiO2-MWCNTs could effectively improve the mechanical and tribological properties of silicone acrylate resin. [ABSTRACT FROM AUTHOR]

In this research work, fabrication of Al alloy metal matrix composites (MMCs) reinforced with electroless Ni-P-coated Al2O3 is carried out using the stir-squeeze casting method. Scrap Al alloy wheels as matrix materials and Al2O3 particles as reinforcements are used to develop the MMCs. The Ni-P coating on Al2O3 particles is carried out using an electroless process to improve mechanical and tribological properties by increasing the bonding strength between the ceramic particles and the matrix material. A pre-treatment process on Al2O3 particles is done before the electroless Ni-P coating. To analyse the properties, the composites are fabricated in three different variations, i.e. as-cast scrap Al alloy, scrap Al alloy with uncoated Al2O3 (5 wt%), and scrap Al alloy with coated Al2O3 (5 wt%). Metallurgical properties are analysed using an optical microscope (OM), scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDAX), and X-ray diffraction (XRD). The test results show that the porosity is reduced by 15.45% in a composite reinforced with coated Al2O3 compared to the as-cast scrap Al alloy. Also, the mechanical properties such as hardness, tensile strength, and impact strength are improved significantly by 15.2, 23, and 31.25%, respectively. Reduction of 31.47% in specific wear rate and 7.34% in coefficient of friction are achieved in the composite reinforced with coated Al2O3 particles compared to the as-cast scrap Al alloy. The compressive strength is decreased significantly with the addition of uncoated Al2O3 particles. After the addition of coated Al2O3, the compressive strength of the composite is increased compared with the uncoated Al2O3-reinforced composite. [ABSTRACT FROM AUTHOR]

The purpose of the present work is to assess the effectiveness of a low-cost and environmentally friendly chemical modification of sisal fibers based on the usage of sodium citrate (SC) and stearic acid (SA) on the thermal, mechanical, tribological and morphological characteristics of sisal fiber reinforced epoxy composites (SREC). Scanning electron microscopy (SEM) was used to investigate the morphological properties of the sisal fibers, which demonstrated that the chemical treatment eliminated the contaminants from the fibers' surface. The reduction of hemicellulose and lignin contents of the fiber was confirmed by Fourier transform infrared (FTIR) analysis following both chemical treatments. Thermal stability of the treated fibers showed a slight reduction as revealed by Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC). Mechanical properties like tensile, flexural and inter-laminar shear strength showed appreciable improvement for the SA treated SREC (8.05%, 8.50% and 29.42%) and SC treated SREC (23.27%, 13.13% and 51.02%) when compared to untreated SREC. Furthermore, the tribological behaviour of the composites reinforced with treated fibers showed improved wear resistance and frictional properties in comparison to untreated composites. To better understand the fiber/matrix adhesion, morphological examinations of fracture and worn surfaces of composite samples were done using SEM. The test results suggest that the sodium citrate treatment is superior to the stearic acid treatment in improving the composites' mechanical and tribological properties. [ABSTRACT FROM AUTHOR]

Few-layered-graphene (FLG)-reinforced Al-4 wt.% Cu matrix composites were produced via the powder metallurgy (PM). FLG was incorporated into the matrix via a mechanical alloying (MA) process conducted for 5, 7 and 9 h in a planetary ball mill. The mechanically alloyed (MA'ed) powders were consolidated by uniaxial pressing and pressureless sintering. Properties of the Al-4Cu-xFLG composites were examined via Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), Archimedes method, microhardness, compressive and wear tests. According to the mechanical characterization, FLG addition relatively improved the hardness, whereas it caused the decline of compressive strength. However, the specific wear ratio of the same sample increased by two times compared to the Al-4Cu. [ABSTRACT FROM AUTHOR]

In this work, two copper metal matrix composites (MMCs) reinforced with 20 wt.% of Ti(C,N) or Ti2AlN particles were studied. The reinforcement particles were synthesized by flash sintering under 2 bar nitrogen atmosphere causing an SHS reaction ignited by electrical current. This reaction led to produce TiC0.7N0.3 solid solution for the MMC1 reinforcement and Ti2AlN, TiN, and Ti3Al titanium aluminide for the MMC2 reinforcement. Both MMCs were densified by liquid phase sintering. The structural characterization was performed by XRD analysis while the morphology and chemical element distribution of both MMCs were analyzed by SEM and EDS. The structure of the two MMCs was relatively dense and showed good wettability. The mechanical and tribological behavior of MMCs evaluated by nanoindentation and wear testing reveals that the addition of 20 wt.% of reinforcement considerably improves the properties of copper matrix. Indeed, the MMC1 proved to be 3 times harder and 10 times more wear-resistant than the MMC2 composite. [ABSTRACT FROM AUTHOR]

Coatings formed on steel 40Kh by electrospark alloying (ESA) using TiC–NiCr and TiC–NiCr–Eu2O3 electrodes are investigated. The coatings are deposited using an Alier-Metal 303 installation in argon under a normal pressure in the direct and opposite polarity modes. The structure, elemental composition, and phase composition of electrodes and coatings are investigated using X-ray phase analysis, scanning electron microscopy, energy dispersion spectroscopy, glow discharge optical emission spectroscopy, and optical profilometry. Mechanical and tribological properties of coatings are determined by nanoindentation and testing according to the "pin–disc" scheme, including elevated temperature in a range of 20–500°C. The tests for abrasive wear are performed using a Calowear tester, the impact resistance is studied using a CemeCon impact tester, and gas and electrochemical corrosion resistance are studied. The results show that the electrodes contain titanium carbide, the solid solution of nickel in chromium, and europium oxide in the case of a doped sample. Coating also included these phases, but the solid solution is formed based on iron. Coatings with the Eu2O3 additive are not substantially different in regards to structural characteristics, hardness, and friction coefficient, but exceed base coatings by abrasive resistance, cyclic impact resistance, and heat and corrosion resistance. An increase in impact resistance by a factor of 1.2–2.0, a decrease in the corrosion current more than 20-fold, and an almost twofold decrease in the oxidation index are observed upon the passage to doped coatings. [ABSTRACT FROM AUTHOR]

Single-component coatings of Cu and C and coatings in the Cu–C system with different carbon contents have been obtained by the magnetron sputtering method. The structure of coatings was investigated by the following techniques: scanning electron microscopy, energy-dispersive and X-ray diffraction analysis, Raman spectroscopy, and radio-frequency glow-discharge spectroscopy. The mechanical and tribological properties have been determined using the nanoindentation and testing by the "rod–disk" scheme. It has been established that the introduction of carbon into the composition of copper-based coatings is accompanied by an increase in the density of the structure and by the reduction of the crystallite size from 35 to 21 nm. It has been revealed that the characteristics of the Cu–C coatings exceeded those of the Cu coatings. The Cu‒C coatings obtained using the best regimes had a hardness of more than 1.5 GPa and coefficient of friction ~0.19. [ABSTRACT FROM AUTHOR]

Some research directions of formulations and technology of development for polymeric antifrictional composites (solid lubrican Fts) with increased physicomechanical tribological properties are considered. These composites are based on polytetrafluoroethylene and semi-interpenetrating polymer network (SIPN) matrices and mixed organic-inorganic fillers. Comparative analysis of qualification of materials when tested in field conditions and express testing using laboratory equipment provide a reliable screening of the service life of the materials to evaluate the performance of machines and mechanisms operating under the climatic conditions of the Russian North and the Arctic. [ABSTRACT FROM AUTHOR]

Deformation and fracture of electroplated Au-Ni coatings subjected to tribological testing under dry conditions were studied. Wear of the coatings is shown to result from macroscopic contact interaction of the specimen with the counterbody, and from abrasive action of microasperities on the counterbody surface and wear particles. The formation mechanisms of wear particles and a transfer layer were investigated, and their contribution to wear of the electroplated Au-Ni coatings was demonstrated. The significance of shear stresses arising at the coating/sublayer interface in coating fracture was substantiated. [ABSTRACT FROM AUTHOR]

Different approaches to formation of hard multicomponent coatings with improved tribological characteristics in a wide temperature range are considered. It is shown that deposition of a thin surface layer or introduction of additional structural components into nanocomposite coatings, which play the role of a solid lubricant, lowers substantially the friction factor and increases the wear resistance [ABSTRACT FROM AUTHOR]

The mechanical and tribological properties of chemically modified UHMWPE are studied. X-ray diffraction analysis, IR spectroscopy, scanning differential calorimetry, and electron emission are used to study the permolecular structure and friction surface of polymers with different amounts of copolymers UHMWPE and LDPE grafted with maleic anhydride. Addition of grafted UHMWPE is shown to have no effect on the viscoelastic properties of the polymer-polymer composite, while the addition of grafted LDPE noticeably improves its performance (ductility, plasticity) while retaining its strength. Chemical modification of UHMWPE significantly improves its wear resistance (two to three times), which is due to the features of polymer crystallization and the formation of a permolecular structure. [ABSTRACT FROM AUTHOR]