Microstructural evolution and tribological behavior of Mo–Cu–N coatings as a function of Cu content

Ternary Mo–Cu–N coatings with various Cu contents were deposited on Si wafers and AISI 304 substrates by magnetron co-sputtering from two elemental targets of Mo and Cu in Ar–N₂ gas mixtures. The influence of copper content was investigated with regard to the microstructure, morphology, and tribological properties of these coatings. The results indicated that the Mo–Cu–N coatings exhibited face-centered-cubic B1-MoN phase structure. No diffraction peaks of Cu phase appeared in the coatings with Cu content below 11 at.%. The copper segregated in the amorphous inter-granular phase in the coatings. Incorporation of Cu into the growing Mo–N coating led to grain refinement. The average friction coefficient of the Mo–Cu–N coatings decreased from 0.40 to 0.21 with increasing Cu content up to 11 at.% due to formation of lubricious oxides of CuMoO₄.     

Formation of composite Cu–graphite and Cu–PTFE coatings and their tribological characterization

The Dynamic Chemical Plating (DCP) technique allows production of 2-μm copper films containing particles of graphite or PTFE in 18 and 15 min, respectively, at ambient temperature. DCP yields composites with particle-incorporation fractions of 12% for graphite micro-particles and 22% for PTFE nano-particles. The composite films show excellent tribological properties, acting as self-lubricating coatings with friction coefficients as low as 0.18.     

Properties of electrodeposited Ni–B–Al2O3 composite coatings

Ni–B coatings have gained a great deal of attraction due to their promising mechanical properties. Owing to tempting properties, Ni–B coatings have succeeded to find their applications in automotive, aerospace, petrochemical, plastic, optics, nuclear, electronics, computer, textile, paper, food and printing industries. Despite having promising properties, further improvement in their properties is essential so that more challenging requirements and new developments can be successfully addressed. In the present study, novel Ni–B–Al₂O₃ composite coatings have been synthesized through electrodeposition process by reinforcing Ni–B matrix with Al₂O₃ particles. A comparison of properties of Ni–B and Ni–B–Al₂O₃ coatings in their as deposited states is presented to elucidate the beneficial role of Al₂O₃ addition. The structural analyses indicate that Ni–B coatings exhibit a single broad peak indicative of an amorphous structure. However, the addition of Al₂O₃ into Ni–B matrix considerably improves the crystallinity of the deposit. The surface morphology study reveals the formation of uniform, dense and fine-grained deposit in both Ni–B and Ni–B–Al₂O₃ composite coatings. However, addition of Al₂O₃ particles into Ni–B coatings results in high surface roughness. The nanoindentation results demonstrates that the addition of Al₂O₃ into Ni–B matrix results in significant improvement in mechanical properties (hardness and modulus of elasticity) which may be attributed to dispersion hardening of Ni–B matrix by hard Al₂O₃ particles. The linear polarization tests confirm that the addition of Al₂O₃ improves the corrosion resistance of Ni–B coatings. This improvement in corrosion behavior may be attributed to the reduction in active area of Ni–B matrix by the presence of inactive Al₂O₃ particles.     

Corrosion resistance of electrodeposited Ni–Al composite coatings on the aluminum substrate

Ni matrix–Al particle composite coating was adopted via sediment co-deposition (SCD) method on the zincate coated aluminum substrate. Surface morphology was investigated by scanning electron microscopy (SEM). The electrochemical behavior of the coatings was studied by polarization potentiodynamic test in 3.5 wt.% sodium chloride using a three electrode open cell. The effect of the electroplating parameters on the Al co-deposition was studied. Maximum of 22 wt.% Al particles were deposited in the coating. It was found that the zincate coating plays an important role in improving the nickel layer adherent. Furthermore, incorporation of aluminum particles in Ni matrix refined the Ni crystal coatings. However, polarization curves shifted to negative potentials and corrosion rate is decreased.     

Synthesis and properties of electrodeposited Ni–B–CeO2 composite coatings

Ni–B coatings are extremely hard and wear resistant with decent anticorrosion properties which make them suitable for automotive, aerospace, petrochemical, plastic, optics, nuclear, electronics, computer, textile, paper, food and printing industries. However, further improvement in properties is essential to address more challenging requirements and new developments. In the present study, Ni–B and novel Ni–B–CeO₂ composite coatings were electrodeposited (ED) on mild steel substrates using dimethylamine borane (DMAB) as a reducing agent. A comparison of properties of Ni–B and Ni–B–CeO₂ coatings is presented to elucidate the useful role of CeO₂ addition. The structural analyses indicate that Ni–B coatings are amorphous in their as deposited state. However, addition of CeO₂ into Ni–B matrix considerably improves the crystallinity of the deposit. The surface morphology study reveals the formation of uniform, dense and fine-grained deposit in both Ni–B and Ni–B–CeO₂ composite coatings. However, Ni–B–CeO₂ composite coatings exhibit high surface roughness. The nano mechanical properties show that the addition of CeO₂ particles into Ni–B matrix results in remarkable improvement in mechanical properties (hardness and modulus of elasticity) which may be attributed to dispersion hardening of Ni–B matrix by CeO₂ particles. The electrochemical polarization tests confirm that the addition of CeO₂ improves the corrosion resistance of Ni–B coatings. This improvement in corrosion behavior may be ascribed to the reduction in active area of Ni–B coatings by the presence of inactive CeO₂ particles into Ni–B matrix.     

Morphological and electrochemical characterization of electrodeposited Zn–Ag nanoparticle composite coatings

Silver nanoparticles with an average size of 23 nm were chemically synthesized and used to fabricate Zn–Ag composite coatings. The Zn–Ag composite coatings were generated by electrodeposition method using a simple sulfate plating bath dispersed with 0.5, 1 and 1.5 g/l of Ag nanoparticles. Scanning electron microscopy, X-ray diffraction and texture co-efficient calculations revealed that Ag nanoparticles appreciably influenced the morphology, micro-structure and texture of the deposit. It was also noticed that agglomerates of Ag nanoparticles, in the case of high bath load conditions, produced defects and dislocations on the deposit surface. Ag nanoparticles altered the corrosion resistance property of Zn–Ag composite coatings as observed from Tafel polarization, electrochemical impedance analysis and an immersion test. Reduction in corrosion rate with increased charge transfer resistance was observed for Zn–Ag composite coatings when compared to a pure Zn coating. However, the particle concentration in the plating bath and their agglomeration state directly influenced the surface morphology and the subsequent corrosion behavior of the deposits.     

Pulse electrodeposition and corrosion properties of Ni–Si3N4 nanocomposite coatings

The development of modern technology requires metallic materials with better surface properties. In the present investigation; Si₃N₄-reinforced nickel nanocomposite coatings were deposited on a mild steel substrate using pulse current electrodeposition process employing a nickel acetate bath. Surface morphology, composition, microstructure and crystal orientation of Ni and Ni–Si₃N₄ nanocomposite coatings were investigated by scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction analysis, respectively. The effect of incorporation of Si₃N₄ particles in the Ni nanocomposite coating on the micro hardness, corrosion behaviour has been evaluated. Smooth composite deposits containing well-distributed silicon nitride particles were obtained and the crystal grains on the surface of Ni–Si₃N₄ composite coating are compact. The crystallite structure was face centred cubic (fcc) for electrodeposited nickel and Ni–Si₃N₄ nanocomposite coatings. The micro hardness of the composite coatings (720 HV) was higher than that of pure nickel (310 HV) due to dispersion-strengthening and matrix grain refining and increased with the increase of incorporated Si₃N₄ particle content. The corrosion potential (E _corr) in the case of Ni–Si₃N₄ nanocomposite had shown a negative shift, confirming the cathodic protective nature of the coating.     

Effects of SiC coating on ablation resistance of carbon fibre reinforced BN–Si3N4 matrix composite

Abstract

A SiC coating was prepared on the surface of a carbon fibre reinforced BN–Si₃N₄ composite by chemical vapour deposition. The coating was characterised by SEM and XRD, and the ablation behaviours of the coated and uncoated composites were investigated and compared. The coating is mainly amorphous SiC and quite compact; the ablated area of the composite is reduced considerably by the coating and the coated composite presents a lower linear ablation rate of 21˙4% and a lower mass ablation rate of 51˙6%. The SiC coating covers over the pores on the surface of the ablative composite, which prevents the flame from spreading to other regions and from penetrating the inside of the composite. As a result, both the chemical erosion and the mechanical denudation are restrained and the ablation resistance of the composite is improved.     

Effect of plasma nitriding on electrodeposited Ni–Al composite coating

In this study plasma nitriding is applied on nickel–aluminum composite coating, deposited on steel substrate. Ni–Al composite layers were fabricated by electro-deposition process in Watt’s bath containing Al particles. Electrodeposited specimens were subjected to plasma atmosphere comprising of N₂–20% H₂, at 500 °C, for 5 h. The surface morphology investigated, using a scanning electron microscope (SEM) and the surface roughness was measured by use of contact method. Chemical composition was analyzed by X-ray fluorescence spectroscopy and formation of AlN phase was confirmed by X-ray diffraction. The corrosion resistance of composite coatings was measured by potentiodynamic polarization in 3.5% NaCl solution. The obtained results show that plasma nitriding process leads to an increase in microhardness and corrosion resistance, simultaneously.     

Preparation and corrosion behavior of Ni and Ni–graphene composite coatings

The graphite oxide was synthesized using the Hummers method, and then it was reduced by hydrazine hydrate to obtain graphene. It was characterized with UV (ultra violet), IR (infra red), XRD (X-ray diffraction) spectra and SEM (scanning electron microscope) images. The composite coating of Ni–graphene on mild steel specimens was obtained by the electrodeposition technique. The composite coating was subjected to various electrochemical tests to know its corrosion behavior and compared with pure Ni coating. The EIS (electrochemical impedance spectroscopy) was performed to confirm the corrosion resistance property. The composite film was studied by recording its XRD and SEM. The crystallite size, texture coefficients and hardness of coating was measured.     

Structure and tribological properties of composite materials based on Al–Cu–Fe formed at high pressure

The use of high pressure (~8 GPa) in the formation of composite quasi-crystalline materials from powders made it possible to create practically poreless samples with a density close to the maximum known for this type of quasi-crystals. For samples with a nickel binder, sintered at a temperature of 550°C, a very low coefficient of friction was obtained, which retain its value during the testing.     

Microstructure and solidification behavior of Cu–Ni–Si alloys

The microstructure and solidification behavior of Cu–Ni–Si alloys with four different Cu contents was studied systematically under near-equilibrium solidification conditions. The microstructures of these Cu–Ni–Si alloys were characterized by SEM and the phase composition was identified by XRD analysis. The phase transition during the solidification process was studied by DTA under an Ar atmosphere. The results show that the microstructure and solidification behavior is closely related to the composition of Cu–Ni–Si alloys. The microstructure of Cu–Ni–Si alloys with higher than 40% Cu content consists of primary phase α-Cu(Ni, Si) and eutectic phase (β₁-Ni₃Si + α-Cu(Ni,Si).When the Cu content is about 40%, only the eutectic phase (β₁-Ni₃Si + α-Cu(Ni,Si)) is present. DTA analysis shows there are three phase transitions during every cooling cycle of alloys with higher than 40% Cu content, but only one for 40% Cu content. Cu–Ni–Si alloy with 40% Cu solidifies by a eutectic reaction, but Cu–Ni–Si alloys with higher than 40% Cu content solidify as a hypoeutectic reaction.     

Electrochemical Properties of Nitride Phases in the Si3N4–Ca3N2and Si3N4–AlN–Ca3N2Systems

The electrical conductivity of silicon nitride and its solid solutions with calcium nitride and aluminum nitride was measured in the ranges 400–900 and 1000–1300°C. The conduction mechanisms were found to be substantially different in these temperature ranges. The Si₃N₄–Ca₃N₂solid solutions exhibited high ionic conductivity between 400 and 900°C. The densest and most oxidation-resistant materials were obtained in the Si₃N₄–AlN–Ca₃N₂system (Al introduced as fine powder and then nitrided).     

Effects of Si and Cu contents on grain size of Al–Si–Cu alloys

The influence of the silicon and copper contents on the grain size of high-purity Al–Si, Al–Cu, and Al–Si–Cu alloys was investigated. In the Al–Si alloys, a poisoning effect was observed and a poor correlation between the grain size and growth restriction factor was obtained. A possible cause of the poisoning effect in these alloys is the formation of a TiSi₂ monolayer on the particles acting as nucleation sites or another poisoning mechanism not associated with TiSi₂ phase formation. In the Al–Cu alloys, a good correlation between the grain size and growth restriction factor was found, whereas in the Al–Si–Cu alloys, the correlation between these two parameters was inferior.     

Use of thermodynamic calculation to predict the effect of Si on the ageing behavior of Al–Mg–Si–Cu alloys

Thermodynamic calculation was employed to predict the influence of Si content on the ageing behavior of Al–Mg–Si–Cu alloys. In addition, experiments were carried out to verify the predictions. The results show that thermodynamic calculation can predict the effect of Si content on the ageing behavior of the studied alloys. This study further proposes that the hardness level of alloys during ageing is directly related to the Si content in the as-quenched supersaturated solution, while the precipitation strengthening effect is directly related to the Mg₂Si level of the alloys.     

Nanocrystalline Si3N4 with Si–C–N shell structure

Nanocrystalline Si₃N₄ with an amorphous Si–C–N shell structure was synthesized by mechanically activating Si₃N₄ and graphite powder in argon atmosphere at room temperature. Twenty hours of mechanical activation resulted in occurrence of CN bond, which can be identified using Fourier transform infrared spectrometry (FT-IR). When the mechanical activation period was extended to 67 h and then to 90 h, the CN bond was further established. The formation of CN bond under the mechanical activation for 90 h was further confirmed using X-ray photoelectron spectroscopy (XPS). The thickness of Si–C–N shell is 5–7 nm as observed using high-resolution transmission electron microscope.     

An investigation on electroless Cu–P composite coatings with micro and nano-SiC particles

Cu–P/micro-SiC and Cu–P/nano-SiC composite coatings were deposited by electroless plating and their composition and microstructure were observed by EDX (energy-dispersive analysis), SEM (scanning electron microscope) and XRD (X-ray diffraction). The corrosion resistance, microhardness and the wear resistance of the Cu–P/nano-SiC composite coatings were measured and the comparison with those of Cu coatings and Cu–P/micro-SiC coatings were given. The anti-corrosion properties of Cu coatings were investigated in 3.5% NaCl solution by the potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. Among three kinds of Cu–P based coatings, the corrosion resistance, hardness and wear resistance of Cu–P/nano-SiC coatings were the largest. This indicates that the precipitation of nano-SiC particles would improve the corrosion resistance, hardness and wear resistance of the Cu–P coatings significantly.     

Electro co-deposition of Ni–Al2O3 composite coatings

Nickel–Al₂O₃ composite coatings have been successfully deposited galvanostatically on to stainless steel substrates by electro co-deposition from a Watts bath containing between 50 and 150?g/l of sub-micron or nano- sized alumina particles applying current density of ?10, ?20 and ?32?mA?cm^?2. The alumina distribution in the composite films on the two sides of the substrate was remarkably different due to solution hydrodynamics and electric field effects. The effect of current density, particle concentration in the bath and particle size are studied systematically producing a comprehensive set of data for better understanding the effects of these variables on the amount of particles co-deposited. The amount of Al₂O₃ co-deposited in the films increases with the particle concentration in the bath and strongly depends on the current density and on particle size. The effect of the current density and of the alumina inclusions on the crystallinity of the Ni matrix and on the Ni crystallites grain size has also been studied. The inclusions of nano or sub-micron-Al₂O₃ particles are found to strongly influence the metallic nickel microstructure.     

Mechanical and tribological properties of V–C–N coatings as a function of applied bias voltage

The aim of this work is to determine the mechanical and tribological behavior of V–C–N coatings deposited on industrial steel substrates (AISI 8620) by using carbon–nitride coatings as a protective materials. The coatings were deposited on silicon (100) and steel substrates via magnetron sputtering and by varying the applied bias voltage. The V–C–N coatings were characterized by X-ray diffraction (XRD), exhibiting the crystallography orientations (111) fcc for V–C–N conjugated by VC (111) and VN (111) phases and (200) fcc for VCN conjugated by VC (200) and VN (200) phases. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical composition of metallic carbon–nitride materials. Atomic force microcopy (AFM) was used for determination of the change in grain size and roughness with deposition parameters. By using nanoindentation, pin-on-disk, and scratch test curves, it was possible to estimate the hardness, friction and critical load of V–C–N surface material. Scanning electron microscopy (SEM) was performed to analyze morphological surfaces changes. Mechanical and tribological behavior in VCN/steel_[8620] system, as a function of a bias voltage deposition, showed an increase of 58% in the hardness, and reduction of 39% in the friction coefficient, indicating thus that the V–C–N coatings may be a promising material for industrial applications.     

Microstructural characterization of electroconductive Si3N4–TiN composites

Electroconductive Si₃N₄–TiN composites from Si and TiN powders have been fabricated by in situ reaction-bonding and post-sintering under N₂ atomosphere. The values of fracture strength and electrical resistivity in the Si₃N₄–50 wt.% TiN composite were 531 MPa and 2.5×10⁻² Ω cm, respectively. The dispersion of TiN particles inhibited the abnormal growth of rod-like Si₃N₄ grains with large size in diameter. An amorphous phase observed in most grain boundaries and triple points is attributed to liquid phase sintering. Many dislocations formed by the difference of thermal expansion coefficients were observed in Si₃N₄ and TiN grains.