Search Results (194)

Investigations of the synthesis of multicomponent coatings and their subsequent application to metal substrates to increase the wear resistance of materials is relevant for industry. Nickel compounds obtained from oxidized magnesia-iron nickel ores with a desorption rate of more than 94% were used to create Ni-MoO₃-WO₃ electroplating. Such composite samples formed from an aqueous alcohol solution reduced the content of sodium and ammonium chlorides. The annealing and dehydration of samples at a temperature of 725 °C in an air atmosphere made it possible to achieve the highest level of crystallinity. In this case, an isomorphic substitution of W atoms by Mo occurs, which is confirmed by electron paramagnetic resonance (EPR) spectroscopy studies. The invariance of the shape of the EPR spectrum with a sequential increase in microwave radiation power revealed the stability of the bonds between the particles. The surface morphology of Ni-MoO₃-WO₃ films deposited on an Al substrate is smooth and has low roughness. In this case, an increased degree of wear resistance has been achieved. Thus, a recipe for the formation of an electroplating with stable bonds between the components and increased wear resistance was obtained. Full article

W-Mo-Cu composites show promise for advanced applications, but their properties require optimization. In this study, a novel approach utilizing Cu-coated graphene (Cu@Gr) reinforcement with skeleton relative density adjustment was employed to tailor the microstructure and properties of W-Mo-Cu composites fabricated via infiltration sintering (1300 °C, 1.5 h). The results revealed that Cu@Gr significantly promoted sintering densification, modified the phase composition, and enhanced the properties of the composite. Specifically, the addition of 0.4 wt.% Cu@Gr resulted in a relative density of 98% for the composite, representing an 8% increase compared to the material without Cu@Gr. Furthermore, when higher amounts of Cu@Gr were incorporated, the composite consistently exhibited a high degree of densification. In addition to the primary W, Mo, and Cu phases, molybdenum carbide, Mo₂C, was formed at 0.4 wt.% Cu@Gr, with its content rising proportionally to graphene dosage. Notably, the composite containing 0.6 wt.% Cu@Gr exhibits the highest thermal conductivity and electrical conductivity, showing 64% and 73% increases, respectively, versus Cu@Gr-free samples. Additionally, although W-Mo green compact density variations (73–85%) did not compromise graphene-induced densification, a higher green compact density reduced the thermal/electrical conductivities but increased the hardness. These findings demonstrate that controlled Cu@Gr incorporation and green compact optimization synergistically improve the properties of W-Mo-Cu composites, providing insights into high-performance material design. Full article

Orthopedic implants are essential for treating severe fractures and incomplete bone regeneration. However, metal-based implants often suffer from corrosion and biocompatibility issues. This study developed 3D-printed Polylactic Acid Plus (PLA+) bone screws coated with molybdenum and zirconia (ZrO₂) nanocomposites using the dip-coating method. The Taguchi method optimized five coating parameters: molybdenum weight, zirconia weight, ethanol volume, incubation time, and coating duration. The Taguchi method and Response Surface Methodology (RSM) were used for data analysis, while NSGA-II and TOPSIS determined the optimal parameters. Molybdenum weight significantly increased compressive strength (35.45%), while coating time had the greatest effect on density (25.88%). Optimization improved compressive strength/Ec (Modulus of elasticity) to 315.808 MPa and density to 1.141 g/cm³. Compressive strength was significantly improved through optimized coating parameters; however, the achieved value of 315.808 MPa requires validation due to its relatively high magnitude compared to typical PLA materials reported in the literature. The study concludes that combining the Taguchi and NSGA-II methods effectively enhances the mechanical performance and biocompatibility of biodegradable bone screws. The optimal dip-coating parameters were 0.101 g molybdenum, 0.100 g zirconia, 59.523 mL ethanol, 6.025 h of incubation, and 7.907 min of coating time. However, the study is limited to in vitro mechanical testing, and further in vivo evaluations are necessary to confirm long-term biocompatibility and performance. Full article

Non-hydrogenated diamond-like carbon (DLC) films and molybdenum-doped diamond-like carbon (Mo-DLC) films were deposited by direct current magnetron sputtering. The formation was carried out on Si (100) wafers. The influence of molybdenum concentration and deposition temperature on the surface morphology, chemical composition, type of chemical bonds, friction force at nanoscale, and nanohardness of the DLC coatings were investigated by atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and nanoindenter, respectively. The concentration of molybdenum in the films varies from 1.2 at.% to 10.3 at.%. The increase in molybdenum content promotes the graphitization of DLC films, lowering the sp³ site fraction and increasing the oxygen content, which contributes to the reduction in nanohardness (by 21%) of the DLC films. The decrease in the synthesis temperature from 235 °C to 180 °C enhanced the oxygen amount up to 20.4 at.%. The sp³ site fraction and nanohardness of the Mo-DLC films were enhanced with the reduction in the deposition temperature. The film deposited at a substrate temperature of 235 °C exhibited the lowest friction coefficient (CoF) of 0.03, where its molybdenum concentration was 1.2 at.%. The decline in the synthesis temperature increased the CoF of the Mo-DLC films up to seven times. Full article

The tribological behavior of molybdenum disulfide (MoS₂) coatings was systematically investigated under various controlled gas environments in a vacuum chamber. A hemispherical steel pin was slid cyclically over a MoS₂-coated steel disk, prepared via high-speed powder spraying. The study measured both dynamic and static friction coefficients under different gaseous atmospheres, including high vacuum, helium, argon, dry air, and water vapor. In high vacuum (10⁻⁵ Pa), an ultra-low dynamic friction coefficient (µ ≈ 0.01) was observed, while increasing values were recorded with helium (µ ≈ 0.03), argon (µ ≈ 0.04), dry air (µ ≈ 0.17), and water vapor (µ ≈ 0.30). Static friction coefficients followed a similar trend, decreasing significantly upon evacuation of water vapor or injection of inert gases. Surface analyses revealed that friction in vacuum or inert gases promoted smooth wear tracks and basal plane alignment of MoS₂ crystallites, while exposure to water vapor led to rougher, more disordered wear surfaces. Mass spectrometry and energetic modeling of physisorption interactions provided further insights into gas–solid interfacial mechanisms. These results demonstrate that the tribological performance of MoS₂ coatings is highly sensitive to the surrounding gas environment, with inert and vacuum conditions favoring low friction through enhanced basal plane orientation and minimal gas–surface interactions. In contrast, water vapor disrupts this structure, increasing friction and surface degradation. Understanding these interactions is crucial for optimizing MoS₂-based lubrication systems in varying atmospheric or sealed environments. Full article

Precursor-derived silicon carbide (SiC) ceramics have been widely used as absorbing materials, but the residual carbon sink produced by ceramicization limits their application under high-temperature and oxygen-containing conditions, such as the nozzle or jet vane of high-speed aircraft. In this paper, a novel molybdenum carbide/silicon carbide (Mo₂C/SiC) microwave-absorbing ceramic with a two-dimensional sheet structure was obtained through the pyrolysis of polycarbosilane-coated molybdenum sulfide (PCS@MoS₂). The results indicate that addition of an appropriate amount of MoS₂ can react with the free carbon generated during the pyrolysis of PCS, thereby reducing the material’s carbon content and forming Mo₂C. Concurrently, the layered structural characteristics of MoS₂ are utilized to create a two-dimensional composite structure within the material, which enhances the material’s absorption vastly. The as-prepared Mo₂C/SiC ceramics sintered at 1300 °C exhibit a minimum reflection loss (RL_min) of −46.49 dB at 8.96 GHz with a thickness of 2.6 mm. Additionally, the effective absorption bandwidth (EAB) of Mo₂C/SiC spans the entire X-band (8–12 GHz) due to the combined effect of multiple loss mechanisms. Full article

Different materials are studied for environmental gas sensors as well as photodetection prototypes. A ZnO/MoS₂ p-n junction was synthetized to act as a multifunctional sensor prototype. After the ZnO was prepared on a silicon substrate by using DC sputtering at room temperature, molybdenum disulfide layers were spin-coated on a nanostructured zinc oxide flake-shaped surface to form an active layer. The heterostructure’s composite surface was examined using scanning electron microscopy, energy-dispersed X-ray, and Raman spectroscopy. Responses to light frequencies, light intensities, and gas chemical tracing were characterized, revealing an enhanced multifunctional performance of the prototype. Characterizations of light-induced photocurrents indicted that the obtained response strength (photocurrent/illumination light power) was up to 0.01 A/W, and the response time was less than 5 ms. In contrast, the gas-sensing measurements showed that its response strength (variation in resistance/original resistance) was up to 3.7% and the response time was down to 150 s when the prototype was exposed to ammonia gas, with the concentration down to 168 ppm. The fabricated prototype appears to have high stability and reproducibility, quick response and recovery times, as well as a high signal-to-noise ratio. Full article

High-entropy alloys (HEAs) have garnered significant global interest due to their outstanding properties. This study investigates the structural stability and mechanical properties of FeCoCrNiMo_x (x = 0, 0.4, 0.5, 0.8, 1.3) HEAs using a first-principles approach coupled with the special quasi-random structure (SQS) method. Of the alloys examined, all except FeCoCrNiMo_1.3 were found to be thermodynamically and dynamically stable. Elasticity calculations revealed that molybdenum improves the ductility and anisotropy of the alloys, though with a slight decrease in strength and stiffness, as confirmed by electronic structure analysis. Defect-free FeCoCrNiMo_0.5 HEAs coatings were then prepared using laser cladding and characterized for their microstructure and hardness. The coating exhibited a transition from columnar crystals at the bottom to equiaxed crystals at the surface, forming a honeycomb-like structure. Inside the crystal cells, high-density dislocations and σ-phase were observed. Elasticity calculations of the σ-phase confirmed its high hardness, low ductility, and classification as a brittle, hard phase. Full article

Cemented carbide has a relatively high surface friction coefficient, which can result in increased wear and energy consumption during friction, ultimately impacting service life and efficiency. In order to improve the tribological properties of the traditionally cemented carbide, the MoS₂ and PTFE (25 wt.%) mixed powders, which were blended with Polyamide-imide (PAI) as the adhesive, were sprayed on the carbide surface at 70 °C. Tests were used to measure the performance of MoS₂/PTFE-coated carbide, such as surface micrographs and cross-section micrographs, surface roughness, adhesion strength between coatings and substrate, and surface microhardness. Sliding friction tests were performed to investigate the friction performance. The test results showed that the adhesion strength between the coatings and substrate was up to 36 N, the hardness was about 0.42 GPa, and the friction coefficient was reduced by about 70%. The lower shear strength of MoS₂/PTFE coatings led to the reduction of friction and wear. The main wear mechanisms of MoS₂/PTFE coatings were surface abrasion and coating flaking. The MoS₂/PTFE coatings present a promising approach to enhance the friction performance of traditional cemented carbide. Full article

To enhance the high-temperature oxidation resistance of molybdenum-based materials, Y₂O₃-CeO₂ co-modified silicide coatings were produced on molybdenum substrates using two-step pack cementation. The microstructure and phase composition of Y₂O₃-CeO₂ co-modified composite coatings were examined both before and after oxidation. A detailed analysis of the antioxidant properties of the co-modified coatings and the mechanisms behind the modifications was also conducted. The incorporation of 1.0 wt.% CeO₂ and 1.5 wt.% Y₂O₃ into the composite coatings resulted in a dense, non-porous, maximum-thickness microstructure. This microstructure is characterized by the uniform distribution of parallel MoSi₂ and MoB layers on the substrate. In particular, the coating containing 1.5 wt.% Y₂O₃ exhibited superior oxidation resistance, with a weight gain of 0.29 mg/cm² and an oxidation rate constant of 6.68 × 10⁻⁴ mg²/(cm⁴·h) after oxidation at 1150 °C for 255 h. During oxidation, a dense SiO₂ oxide film is formed through the cooperation of Y₂O₃ and CeO₂, inhibiting further Si diffusion into the substrate and reducing the formation of the Mo₅Si₃ layer. Full article

Chromium salt fillers commonly used in current anti-corrosion coatings are highly toxic. However, due to the unique high–low valence transformation and passivation mechanisms of chromium-based functional fillers and their wide applicability, chromium-free coatings find it challenging to achieve the same performance and industry acceptance. This study introduces an innovative approach that uses zinc to reduce molybdate (MoO₄²⁻) in an acidic solution, thereby forming a multivalent MoO₄²⁻ system (PMZ system), and applies it to chromium-free insulating coating for oriented silicon steel. The effects of reductant dosage on the valence composition of molybdenum in the PMZ system and the corrosion resistance of the coating were investigated. Additionally, the difference in the valence composition of molybdenum between the PMZ system and the multivalent phosphomolybdate system (PMNZ system) and its impact on corrosion resistance were studied. The results indicate that the PMZ system contains trivalent molybdenum and hexavalent molybdenum, while the PMNZ system contains pentavalent molybdenum and hexavalent molybdenum. The systems leverage the reactivity of lower-valence molybdenum to delay the corrosion by reacting with oxygen while maintaining the original mechanism of molybdenum salt fillers and forming sediment with iron ions to form a passivation layer. As the content of trivalent molybdenum in the PMZ system increases, the corrosion resistance of the insulating coating improves. When the amount of zinc added in the PMZ system is 0.006 g, the relative proportion of trivalent molybdenum reaches 20.52%, and the salt spray resistance of the coating developed with the PMZ system reaches 248 h with a corrosion area of less than 5%. When the contents of the main components and sodium molybdate in the PMZ coating and the PMNZ coating are the same, the corrosion resistance of the PMZ coating, which contains trivalent molybdenum, is better than that of the PMNZ coating, and the salt spray resistance exceeds 192 h. Full article

To improve the friction performance and service life of protective coatings in humidity-fluctuating environments, porous hard titanium nitride (TiN)–molybdenum disulfide (MoS₂) composite coatings were prepared by using direct current magnetron sputtering (DCMS) with the mode of oblique angle deposition (OAD) and chemical vapor deposition (CVD) technologies. The structure and chemical component were characterized by field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The tribological properties of these TiN–MoS₂ composite coatings were investigated. The results indicate that the porous TiN–MoS₂ composite coating exhibited outstanding friction performance and long service life under humidity-fluctuating environments. At the initial 20% relative humidity (RH) stage, the MoS₂ on the porous TiN–MoS₂ composite coating surface worked as an effective lubricant; thus, the coating demonstrated excellent lubrication performance, and the friction coefficient (COF) was about 0.05. As the humidity was alternated to 70% RH, the lubrication effect diminished due to the production of molybdenum oxide (MoO₃), and the COF was about 0.2, which was attributed to the degradation of MoS₂ on the wear track and the release of fresh MoS₂ from the porous TiN matrix. After the environmental conditions shifted from 70% to 20% RH, the MoO₃ was removed, and the lubrication effect was restored. In summary, TiN–MoS₂ porous composite coating offers a promising approach for lubrication in humidity-fluctuating environments. Full article

In recent years, there have been important developments in the refractory metal nitride coatings used for versatile applications, such as MoN, TaN, NbN, etc. Engineered approaches, including the deposition method, microstructure control, structural design, and the addition of functional elements, are put into practice for the promotion of coating characteristics. This study focuses on the microstructure and mechanical properties of ternary molybdenum tantalum nitride, MoTaN, coatings. MoTaN was deposited using a reactive radio frequency (r.f.) magnetron co-sputtering system with Mo/Ta target input power modulation control. The effects of composition and microstructure variations on its mechanical properties, including its hardness, elastic modulus, and wear behavior, were investigated. In general, the MoTaN coatings exhibited a columnar polycrystalline microstructure with MoN(111), Mo₂N(111), Mo₂N(200), TaN(200), and TaN(220) phases and orientations based on X-ray diffraction analysis. The addition of Ta triggered the transition of the primary orientation of Mo₂N(111) into Mo₂N(200). Transmission electron microscopy was utilized to analyze the transformation of the multiphase structure and changes in the grain size in terms of the Ta addition. According to nanoindentation and wear resistance analyses, superior hardness, elastic modulus, H/E, H³/E², and wear-resistance values were identified for the MoTaN coatings with 6.8 to 10.4 at.% Ta, and a maximum hardness of 18.0 GPa was found for the MoTaN coating deposited at an input power of Mo/Ta = 150/100 W/W. An optimized hardness of 18.0 GPa and an elastic modulus of 220.7 GPa were obtained. The adjustment of the input power during deposition played a critical role in determining the overall performance of the MoTaN co-sputtering coatings. The MoTaN coating with optimized mechanical properties is attributed to its multiphase microstructure and fine columnar grain size of less than 30 nm. Full article

Molybdenum disulfide is a 2D material with excellent lubricant properties, resulting from weak van der Waals forces between lattice layers and shear-induced crystal orientation. The low forces needed to shear the MoS₂ crystal layers grant the tribological system low coefficients of friction (COF). However, film oxidation harms its efficacy in humid atmospheres, leading to an increased COF and poor surface adhesion, making its use preferable in dry or vacuum conditions. To overcome these challenges, doping MoS₂ with elements such as Nb, Ti, C, and N emerges as a promising solution. Nevertheless, the adhesion of these coatings to a steel substrate presents challenges and strategies involving the reduction in residual stresses and increased chemical affinity to the substrate by using niobium-based materials as interlayers. In this study, Nb-doped MoS₂ films were deposited on H13 steel and silicon wafers using the pulsed direct current balanced magnetron sputtering technique. Different niobium-based interlayers (pure Nb and NbN) were deposited to evaluate the adhesion properties of Nb-doped MoS₂ coatings. Unlubricated scratch tests, conducted at room temperature and relative humidity under a progressive load, were performed to analyze the COF and adhesion of the coating. Instrumented indentation tests were conducted to assess the hardness and elastic modulus of the coatings. The microstructure of the coatings was obtained by Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), and Transmission Electron Microscopy (TEM), with Energy-Dispersive X-Ray Spectroscopy (EDS). Results indicated that niobium doping on MoS₂ coatings changes the structure from crystalline to amorphous. Additionally, the Nb concentration of the Nb:MoS₂ coating changed the mechanical properties, leading to different cohesive failures by different loads during the scratch tests. Results have also indicated that an NbN interlayer optimally promoted the adhesion of the film. This result is justified by the increase in hardness led by higher Nb concentrations, enhancing the load-bearing capacity of the coating. It is concluded that niobium-based materials can be used to enhance the adhesion properties of Nb-doped MoS₂ films and improve their tribological performance. Full article

A study of the antifriction properties of suspension solid-lubricating coatings based on molybdenum disulfide (MoS₂) at high temperatures depending on the type of substrate, binder, additives, and load parameters was carried out. The solid lubricants were sprayed on two different substrates, high-temperature alloy (Inconel X-750) and stainless steel (AISI 430), tested under 10 N and 23 N loads at temperatures ranging from 25 °C to 800 °C. For comparison, different types of solid lubricants were used. In this work, it was established that the antifriction properties of solid lubricant suspension coatings at high temperatures significantly depend on the type of solid lubricant and the binder used. Moreover, it was shown that the use of Inconel X-750 as a substrate can lead to an increase in the critical operating temperature of coatings containing MoS₂, graphite, and titanate as solid lubricant, additive, and binder, respectively. For instance, at load 23 N, the operating temperature increased from 480 °C to 496 °C. On the other hand, the coating based on graphite, containing ceramic as an additive, and an inorganic binder showed the best performance in terms of a combination of properties (low coefficient of friction and longer operation with a coefficient of friction below 0.3 under increasing temperature) when it was applied on the Inconel X-750 substrate. In addition, it was established that the coefficient of friction of graphite-based coatings gradually increases as they lose their antifriction properties due to their failure, while the coatings based on molybdenum disulfide show the opposite behavior, where the coefficient of friction increases sharply when it loses its lubricating properties. Full article