Search Results (17)

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

The use of 3D-printed highly porous titanium acetabular cups in total hip arthroplasty (THA) is increasing. The porosity and mechanical properties of such highly porous titanium structures mimic those of natural cancellous bone, possibly allowing biological implant fixation to be improved. Recently, a 3D-printed highly porous Dual Mobility (DM) monobloc construct fully manufactured using Ti6Al4V alloy, with a titanium–niobium nitride (TiNbN) ceramic coating on the articular side to allow articulation against the mobile liner by improving the titanium vs. polyethylene tribological behavior, was introduced in THA. To the best of our knowledge, this is the first highly porous titanium monobloc DM implant on the market. The reasons for using a Ti alloy highly porous DM are multifarious: to prevent any possible adverse reactions due to the corrosion of Cobalt–Chromium–Molybdenum Alloy (CoCrMo) and Stainless Steel (SS) implants and to improve implant primary and secondary stability, particularly in cases of poor bone quality. Finally, with the introduction of an inner TiNbN ceramic coating surface, it was possible to overcome the poor tribological quality of titanium. Another interesting characteristic is this material’s higher implant radiolucency, which might facilitate the radiographic assessment of cup orientation, which can, in turn, facilitate the detection of any intraprosthetic dislocation (IPD) and the measurement of polyethylene wear, which is very important in the study of the durability of THA. Full article

Molybdenum carbide (Mo₂C) with a Pt-like d-band electron structure exhibits certain activities for oxygen reduction and evolution reactions (ORR/OER) in alkaline solutions, but it is questioned due to its poor OER stability. Combining Mo₂C with transition metals alloy is a feasible way to stabilize its electrochemical activity. Herein, CoFe-Prussian blue analogues are used as a precursor to compound with graphitic carbon nitride and Mo⁶⁺ to synthesize FeCo alloy and Mo₂C co-encapsulated N-doped carbon (NG-CoFe/Mo₂C). The morphology of NG-CoFe/Mo₂C (800 °C) shows that CoFe/Mo₂C heterojunctions are well wrapped by N-doped graphitic carbon. Carbon coating not only inhibits growth and agglomeration of Mo₂C/CoFe, but also enhances corrosion resistance of NG-CoFe/Mo₂C. NG-CoFe/Mo₂C (800 °C) exhibits an excellent half-wave potential (E_1/2 = 0.880 V) for ORR. It also obtains a lower OER overpotential (325 mV) than RuO₂ due to the formation of active species (CoOOH/β-FeOOH, as indicated by in-situ X-ray diffraction tests). E_1/2 shifts only 6 mV after 5000 ORR cycles, while overpotential for OER increases only 19 mV after 1000 cycles. ORR/OER performances of NG-CoFe/Mo₂C (800 °C) are close to or better than those of many recently reported catalysts. It provides an interfacial engineering strategy to enhance the intrinsic activity and stability of carbides modified by transition-metals alloy for oxygen electrocatalysis. Full article

Mechanical components frequently come into contact against one another causing friction that produces heat at the contact area and wear of the components that shortens part life and increases energy consumption. In the current study, an attempt was made to optimize the parameters for the pin-on-disc wear tester. The experiments were carried out in ambient thermal conditions with varying sliding speeds (0.5 m/s, 0.75 m/s, and 1.0 m/s) and applied loads (5 N, 10 N, and 15 N) for pure molybdenum disulfide with 9% and 20% weight percentage of graphitic carbon nitride (g-C₃N₄) in molybdenum-disulfide (MoS₂)-nanocomposite-coated steel substrate. Analysis of variance (ANOVA) was used to determine the outcome of interaction between various constraints. To identify the minimum wearing conditions, the objective was defined as the criterion ‘smaller is better’. The maximum impact of the applied load on the coefficient of friction and wear depth was estimated to be 59.6% and 41.4%, respectively, followed by sliding speed. The optimal condition for the minimum coefficient of friction and wear was determined to be 15 N for applied load, 0.75 m/s for sliding speed, and weight percentage of 9 for g-C₃N₄ in MoS₂ nanocomposite. At the 95% confidence level, applied load was assessed to have the most significant effect on the coefficient of friction, followed by sliding speed and material composition, whereas material composition considerably impacts wear, followed by loading and sliding speed. These parameters show the effect of mutual interactions. Results from the Taguchi method and response surface methodology are in good agreement with the experimental results. Full article

In the current world of coatings and nanomaterials, specifically bearings, zinc, chromium, nickel, diamond-like coatings, and molybdenum disulfide are being used, to name but a few. Boron nitride in various forms has been used to enhance the surface properties, such as hardness, wear resistance, and corrosion resistance of dies, tools, etc. In this paper, a significant focus is being given to the improvement of the surface properties of bearing-steel materials by the impregnation of cubic and hexagonal boron nitride nanoparticles. The vacuum heat treatment method is used for treating the sample pins of material equivalents to EN31. In the design of the experiments, the Taguchi method with L₂₇ orthogonal array is used for the optimization of various parameters, such as the weight % of c-BN and h-BN nanoparticles and the temperature of the vacuum treatment. With the help of preliminary experimentation, the three levels of three parameters are decided. The microhardness analysis shows an improvement from 321 HV0.1 to 766 HV0.1 for a 50 µm case depth of nanoparticle impregnation. The evaluation of the influence of selected factors is also performed using ANOVA and the S/N ratio, and it was revealed that hex boron nitride (h-BN) affects the microhardness value more than the other two factors. The friction and wear testing reveal that the wear properties are improved by approximately 1.6 times, and the frictional force also decreases by approx. 1.4 times. Scanning electron microscope (SEM) analysis shows that the nanoparticles are penetrated by 21.09% and 46.99% atomic weight. In addition, a reduction in the friction coefficient and better wear response were achieved as a result of the heat treatment with nanoparticle impregnation. Full article

This study explores the tribological performance of microwave-assisted synthesized g-C₃N₄/MoS₂ coatings. The two-dimensional transition metal dichalcogenide (TMD) nanosheet is getting prominence in the study of tribology due to its layered structure. The graphitic carbon nitride (g-C₃N₄) nanosheet was made using the calcination method and its nanocomposite with molybdenum disulfide (MoS₂) was produced using a microwave-assisted method. The structure and morphology of the samples were characterized by some well-known methods, and tribological properties were studied by a pin-on-disc (POD) apparatus. Morphological analysis revealed that graphitic carbon nitride and molybdenum disulfide coexisted, and the layer structured MoS₂ was well dispersed on graphitic carbon nitride nanosheets. BET analysis was used to determine the pore volume and specific surface area of the synthesized materials. The inclusion of MoS₂ nanoparticles caused the composite’s pore volume and specific surface area to decrease. The reduction in g-C₃N₄ pore volume and specific surface area confirmed that the pores of calcinated graphitic carbon nitride were filled with MoS₂ nanoparticles. The tribological property of g-C₃N₄/MoS₂ nanocomposite was systematically investigated under different factors such as applied loads (5N to 15N), sliding speed (500 to 1000 mm/s) and material composition (uncoated, MoS₂-coated, 9 wt.% of g-C₃N₄ and 20 wt.% of g-C₃N₄ in the composite). The optimal composite material ratio was taken 9%, by weight of g-C₃N₄ in the g-C₃N₄/MoS₂ composite for a variety of levels of loads and sliding speeds. The results indicates that the incorporation of g-C₃N₄ in nanocomposites could reduce friction and improve wear life, which were better than the results with single MoS₂. This study demonstrates a solution to broaden the possible uses of g-C₃N₄ and MoS₂-based materials in the field of tribology. Full article

This paper presents the results of a study on the preparation and characterization of a Cr-DND/MoN detonation chromium-nanodiamond coating deposited on cemented tungsten carbide (WC–3 wt.% Co) mill blades using Arc-PVD and electrodeposition methods. The physical and mechanical characteristics of the coatings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), XRD analysis, Raman spectroscopy, micro-identification, and scratch test (evaluation of the coating adhesion). It was shown that the Cr-DND/MoN coating consists of successive layers of Cr-DND (top), Cu (middle) and MoN (bottom) with separate phases of γ-Mo₂N, α-Mo, α-Cu, Cr-DND and nanodiamonds. The Cr-DND composite electrochemical coating (CEC) was deposited from the conventional chromium plating electrolyte with the addition of nanodiamonds. The copper interlayer was deposited by the Arc-PVD method on the surface of the MoN coating to improve the adhesion strength of the Cr-DND CEC. The coating showed an optimum microhardness of about 14 ± 1 GPa and good adhesion with a critical load L_c of about 93 N. In addition to the expected experimental results, the coating has high wear resistance, confirmed by scratch tests. Full article

Metals and alloys are essential in modern society, and are used in our daily activities. However, they are prone to corrosion, with the conversion of the metal/alloy to its more thermodynamically-favored oxide/hydroxide phase. These undesirable corrosion reactions can lead to the failure of metallic components. Consequently, corrosion-protective technologies are now more important than ever, as it is essential to reduce the waste of valuable resources. In this review, we consider the role of emerging 2D materials and layered materials in the development of a corrosion protection strategy. In particular, we focus on the materials beyond graphene, and consider the role of transition metal dichalcogenides, such as MoS₂, MXenes, layered double hydroxides, hexagonal boron nitride and graphitic carbon nitride in the formulation of effective and protective films and coatings. Following a short introduction to the synthesis and exfoliation of the layered materials, their role in corrosion protection is described and discussed. Finally, we discuss the future applications of these 2D materials in corrosion protection. Full article

The coating system MoN-Ag is an interesting candidate for industrial applications as a low friction coating at elevated temperatures, due to the formation of lubricous molybdenum oxides and silver molybdates. Film deposition was performed by high-power impulse magnetron sputtering and direct current magnetron sputtering. To facilitate a future transfer to industry Mo-Ag composite targets have been sputtered in Ar/N₂ atmosphere. The chemical composition of the deposited MoN-Ag films has been investigated by wavelength dispersive X-ray spectroscopy. Morphology and crystallographic phases of the films were studied by scanning electron microscopy and X-ray diffraction. To obtain film hardness in relation to Ag content and bias voltage, the instrumented indentation test was applied. Pin-on-disc tribological tests have been performed at room temperature and at high temperature (HT, 450 °C). Samples from HT tests have been analyzed by Raman measurements to identify possible molybdenum oxide and/or silver molybdate phases. At low Ag contents (≤7 at.%), coatings with a hardness of 18–31 GPa could be deposited. Friction coefficients at HT decreased with increasing Ag content. After these tests, Raman measurements revealed the MoO₃ phase on all samples and the Ag₂Mo₄O₁₃ phase for the highest Ag contents (~23–26 at.%). Full article

In this study, a 3.5-GHz solidly mounted resonator (SMR) was developed by doping scandium in aluminum nitride to form AlScN as the piezoelectric thin film. Molybdenum (Mo) of 449 nm thickness and silicon dioxide (SiO₂) of 371 nm thickness were used as the high and low acoustic impedance films, respectively, which were alternately stacked on a silicon substrate to form a Bragg reflector. Then, an alloy target with atomic ratio of 15% Sc was adopted to deposit the piezoelectric AlScN thin film on the Bragg reflector, using a radio frequency magnetron sputtering system. The characteristics of the c-axis orientation of the AlScN thin films were optimized by adjusting sputtering parameters as sputtering power of 250 W, sputtering pressure of 20 mTorr, nitrogen gas ratio of 20%, and substrate temperature of 300 °C. Finally, a metal top electrode was coated to form a resonator. The X-ray diffraction (XRD) analysis showed that the diffraction peak angles of the AlScN film shifted towards lower angles in each crystal phase, compared to those of AlN film. The energy dispersive X-ray spectrometer (EDX) analysis showed that the percentage of scandium atom in the film is about 4.5%, regardless of the sputtering conditions. The fabricated resonator exhibited a resonance frequency of 3.46 GHz, which was a small deviation from the preset resonance frequency of 3.5 GHz. The insertion loss of −10.92 dB and the electromechanical coupling coefficient of 2.24% were obtained. As compared to the AlN-based device, the AlScN-based resonator exhibited an improved electromechanical coupling coefficient by about two times. Full article

Thermal spraying of aluminum nitride (AlN) is a challenging issue because it decomposes at a high temperature. In this work, the use of suspension plasma spray (SPS) technology is proposed for the in situ synthesis and deposition of cubic-structured AlN coatings on metallic substrates. The effects of the nitriding agent, the suspension liquid carrier, the substrate materials and the standoff distance during deposition by SPS were investigated. The plasma-synthesized coatings were analyzed by X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM). The results show higher AlN content in the coatings deposited on a carbon steel substrate (~82%) when compared to titanium substrate (~30%) or molybdenum (~15%). Melamine mixed with pure aluminum powder produced AlN-richer coatings of up to 82% when compared to urea mixed with the Al (~25% AlN). Hexadecane was a relatively better liquid carrier than the oxygen-rich liquid carriers such as ethanol or ethylene glycol. When the materials were exposed to a molten aluminum–magnesium alloy at 850 °C for 2 h, the corrosion resistance of the AlN-coated carbon steel substrate showed improved performance in comparison to the uncoated substrate. Full article

The molybdenum silicon nitride (Mo–Si–N) films were deposited by a radio frequency (RF) magnetron reactive dual-gun co-sputtering technique with process control on input power and gas ratio. Composition variation, microstructure evolution, and related mechanical and tribological behavior of the Mo–Si–N coatings were investigated. The N₂/(Ar + N₂) flow ratios were controlled at 10/20 and 5/20 levels with the tuning of input power on the Si target at 0, 100, and 150 W. As the silicon contents increased from 0 to 33.7 at.%, the film microstructure evolved from a crystalline structure with Mo₂N and MoN phases to an amorphous feature with the Si₃N₄ phase. The analysis of selected area electron diffraction patterns in TEM also indicated an amorphous feature of the Mo–Si–N films when Si content reached 20 at.% and beyond. The hardness and Young’s modulus changed from 16.5 to 26.9 and 208 to 273 GPa according to their microstructure features. The highest hardness and modulus were attributed to nanocrystalline Mo₂N and MoN with Si solid-solution. The crystalline Mo–Si–N films showed a smooth tribological track and less wear failure was found. In contrast, the wear track with severe failures were observed for Mo–N and amorphous Mo–Si–N coatings due to their lower hardness. The ratios of H/E and H³/E² were intensively discussed and correlated to the wear behavior of the Mo–Si–N coatings. Full article

In this paper, we report on the characterization of the sensitivity and the directionality of a novel ultrasonic hydrophone fabricated by micro-electro-mechanical systems (MEMS) process, using aluminum nitride (AlN) thin film as piezoelectric functional layer and exploiting a stress-driven design. Hydrophone structure and fabrication consist of four piezoelectric cantilevers in cross configuration, whose first resonant frequency mode in water is designed between 20 kHz and 200 kHz. The MEMS fabricated structures exploit 1 µm and 2 µm thick piezoelectric AlN thin film embedded between two molybdenum electrodes grown by DC magnetron sputtering on silicon (Si) wafer. The 200 nm thick molybdenum electrodes thin layers add a stress-gradient through cantilever thickness, leading to an out-of-plane cantilever bending. A water resistant parylene conformal coating of 1 µm was deposited on each cantilever for waterproof operation. AlN upward bent cantilevers show maximum sensitivity up to −163 dB. The cross configuration of four stress-driven piezoelectric cantilevers, combined with an opportune algorithm for processing all data sensors, permits a finer directionality response of this hydrophone. Full article

Surface roughness on orthopedic implant materials has been shown to be highly influential on the behavior of osteogenic cells. Mesenchymal stem and progenitor cells (MSPCs) migrate to the interface, adhere, proliferate, and differentiate into osteoblasts, which subsequently form bone matrix. Modifications of the implant surfaces should accelerate this process and improve biocompatibility. In this study, five surface topographies on cobalt chromium molybdenum (CoCrMo) were engineered to examine the influence on MSPCs. Scanning electron microscopy revealed significant differences in the morphology of untreated CoCrMo discs in comparison with CoCrMo with a titanium nitride (TiN) coating, polished and porous coated CoCrMo surfaces, and CoCrMo with a pure titanium (cpTi) coating. Elemental analysis was performed using energy-dispersive X-ray spectroscopy (EDX). Human primary MSPCs were expanded from tissue samples of spongiosa bone and characterized according to the criteria of the International Society for Cellular Therapy. The characteristic phenotype of MSPC was confirmed by flow cytometry and multilineage differentiation. Alcaline phosphatase and osteopontin expression increased significantly in all groups about 5-fold and 10-fold, respectively, in comparison to the undifferentiated controls. The porous coated surface showed a reduced expression of osteogenic markers. Due to the osteogenic differentiation, the expression of integrin α5β1, which is particularly important for cell-material contact, increased 4–7-fold. In the dynamic process of bone biology, MSPCs cultured and differentiated on cpTi, showed significant upregulation of IL6 and leptin. Full article