Microhardness Of Coatings Research Articles

Fabrication and tribological behavior of laser cladding Cu/Ti3SiC2 reinforced CoCrW matrix composite coatings on Inconel718 surface

To satisfy the need for high wear resistance of Inconel718 alloy under harsh working conditions, laser cladding technique was adopted to fabricate the Cu/Ti3SiC2-CoCrW metal matrix composite coatings on that surface. The phase composition, microstructure, microhardness, surface energy, and tribological properties of the composite coatings were systematically analyzed by characterization methods such as XRD/ SEM/ EDS/ XPS and performance test methods such as high-temperature friction and wear test, and the wear mechanism at different temperatures was deeply discussed. The research results indicate that the microhardness of coatings is increased by 2.2–2.9 times compared to the substrate, which is mainly owing to the solid solution strengthening effect and the diffusely distributed hard reinforcing phases such as Cr7C3, WCx, and TiC. Regarding the wear resistance, the wear rate of coatings is significantly reduced by 1–2 orders of magnitude over the substrate. Among them, the Co-based coating adding 10 wt% Cu - 10 wt% Ti3SiC2 exhibited the lowest wear rates at room and high temperatures, which were 0.22 and 3.23 × 10−5 mm3/ N·m, respectively, with 98.22 % and 88.19 % reductions in comparison with the substrate. The low surface energy (27.94 mN/m) was one of the main reasons for the good tribological properties. When the friction environment changes from room temperature to 600 °C, the primary wear mechanism of coatings changes from abrasive and adhesive wear to oxidative wear.

Effect of A and B-site ion doping on the structure and properties of KNN-based ceramic coatings

K0.5Na0.5NbO3 (KNN) ceramics have been widely studied for high Curie temperature (Tc) and good electrical properties. The structural and electrical properties of KNN ceramics were significantly improved by A-site and B-site doping modifications. In this paper, KNN-based ceramic coatings doped with Mn, and Sb were prepared by supersonic plasma spraying. The effects of doping ions at A-site and B-site on the microstructure, phase structure, mechanical properties, and electrical properties of KNN-based ceramic coatings were mainly analyzed. The results show that the surface of the three coatings KNN, K0.5Na0.5Nb0.94Sb0.06O3 (KNNS), and K0.49Na0.49Mn0.02NbO3 (KNMN) is relatively flat, uniform distribution of the elements. The surface roughness (Sa) is 3.85 μm, 3.88 μm, and 3.66 μm, respectively. Pores and cracks are present within the coatings, but the KNNS ceramic coatings have significantly fewer pores and cracks compared to the KNN and KNMN ceramic coatings. XRD results show that KNN-based ceramic coatings exhibit single perovskite structure, and both Mn and Sb are successfully introduced into the KNN ceramics without the generation of a second phase. XPS results showed that the valence states of the elements in the KNN ceramic coatings did not change. In KNMN and KNNS ceramic coatings, the valence state of the doped elements did not change. The addition of Mn2+ and Sb3+ reduced the oxygen vacancy in KNN ceramic coatings. Among them, the KNMN ceramic coatings microhardness increased by 45.3 HV0.2, remnant polarization (Pr) increased by 8.1 μC/cm2, the dielectric constant (εr) increased by 107, and dielectric loss greatly reduced, reaching 0.005. The KNMN ceramic coatings microhardness increased by 90.8 HV0.2, dielectric constant increased by 195, Pr increased by 16.7 μC/cm2, dielectric loss is 0.007. These findings demonstrate that doping with Mn2+ and Sb3+ has a positive impact on the performance of KNN ceramic coatings, with Sb3+ having a greater effect.

DEPENDENCE OF MICROHARDNESS OF ASD-1 COATINGS ON COLD SPRAYING PROCESS PARAMETERS

Purpose. To investigate the effect of the main parameters of the cold spraying process, particularly the temperature and pressure of the gas at the nozzle inlet and stand-off distance, on the microhardness of the ASD-1 aluminum coating. Research methods. The planning and conducting of experimental research were carried out using the design of experiment methodology and regression analysis. The analysis of the obtained results of the experiments was carried out in the software package for statistical data Stat-Ease 360. The research of the microhardness of the sprayed coatings was carried out following GOST 9450-76 “Measurements microhardness by diamond instruments indentation@ using a LECO AMH5 micro-Vickers hardness tester on the prepared cross-section of samples with coatings. Results. Three-dimensional (response surfaces) and contour graphs of the dependence of the microhardness of coatings deposited by the cold spraying method from ASD-1 powder on the main process parameters - the temperature and pressure of the gas at the nozzle inlet and stand-off distance in a wide range of values - were constructed. According to the results, it was established that the gas temperature and the spraying distance have the most significant influence on the microhardness of the coatings. The relationship between the investigated parameters of spraying with the temperature and velocity characteristics of the powder particles and their effect on the microhardness is described. Scientific novelty. The complex effect of the main parameters of the cold spraying process, particularly the temperature and gas pressure at the nozzle inlet and the stand-off distance, on the microhardness of ASD-1 aluminum coatings in a wide range of values, was investigated. Practical value. The obtained dependences of coating microhardness on process parameters can be used in developing scientifically-based recommendations and technological processes of deposition of protective and restorative coatings by cold spraying, particularly on parts of aircraft engines.

Preparation of AlCoCrFeNi/W-TiC HEA composite coating by laser cladding

In this paper, AlCoCrFeNiW2-x(TiC)x high-entropy alloy coatings (HEA) (x: mass fraction, x = 0, 0.5, 1.0, 1.5, and 2) were prepared on 316 stainless steel (316 L SS) substrate by laser cladding technique. The microstructure, phase, microhardness, wear resistance and corrosion resistance of the HEA composite coatings were discussed by adding different mass fractions of W and TiC particles. The results show that the coatings are metallurgically bonded under the experimental parameters, and the grain size of the coating decreases from the interface to the surface, which is in accordance with the constitutional undercooling criterion. Meanwhile, the contents of W and TiC can adjust the mechanical properties of the coatings. The microhardness of the coatings increases and then decreases with the variation of x value, which can be explained by the large number of TiC particles leading to severe lattice distortions and high internal stresses, which results in the fluctuation of microhardness in the cross-section. The coating exhibits the best microhardness, with an average microhardness of 452 HV when x = 0.5. The wear resistance of the coating is better with an average coefficient of friction of 0.4474 when x = 0.5. However, due to the presence of phase-boundary defects in the composite coatings, which contain cationic and anionic vacancies, When the passivation film is damaged by Cl-, the electrolyte will penetrate along the phase boundary defects and generate corrosive microcells.

Effects of Nb content on the microstructure and properties of CoCrFeMnNiNbx high-entropy alloy coatings by laser cladding

CoCrFeMnNiNbx (x = 0, 0.25, 0.5, 0.75, and 1.0) high-entropy alloy coatings were prepared on the AISI 1045 steel substrate surface by laser cladding to explore the effects of different Nb content on the microstructure, microhardness, wear resistance, and corrosion resistance of high entropy alloy coatings. The microstructure of CoCrFeMnNi was composed of single face-centered cubic (FCC) solid-solution phases without Nb addition. The high-entropy alloy coating was mainly composed of a dual-phase structure of the FCC and Laves phases after Nb addition. Nb addition transformed the microstructure of coatings from hypoeutectic to eutectic and hypereutectic compositions. The microhardness of CoCrFeMnNiNbx high-entropy alloy coatings increased gradually with the increase of Nb content. When Nb content x was 1, the average microhardness of coatings was optimal (416.54 HV0.5), which was 2.21 times that of Nb0. The wear resistance of CoCrFeMnNiNbx high-entropy alloy coatings increased gradually with the increase of Nb content, and the wear volume decreased from 0.0739 to 0.0145 mm3. The primary mechanisms responsible for friction and wear were identified as adhesive wear and abrasive wear. The corrosion resistance of coatings first increased and then decreased with the increase of Nb content. When Nb content was 0.75, the passivation film on the coating surface was the stablest and densest, with the optimal corrosion resistance. The results in the work provide a theoretical reference for preparing high-entropy alloy coatings with Nb content.

Microstructure and tribology of cold spray additively manufactured multimodal Ni-WC metal matrix composites

Cold spray produces thick and dense deposits that can be applied in additive manufacturing or as a repair to recover damaged components. One potential materials system is WC-reinforced Ni composites, which are known for a combination of high hardness and toughness. WC particle size and distribution are some of the most important variables that impact the mechanical properties and wear resistance. In this study, thick multimodal Ni-24 vol%WC composite coatings were additively manufactured using the cold spray technique. Spherical Ni powder and two types of WC particles, i.e., cast and agglomerated, were used as feedstock materials. The microstructure, porosity, WC distribution, and microhardness of coatings were investigated in comparison with cold-sprayed Ni and Ni-agglomerated WC coatings with similar WC fill ratios. Dry sliding wear of multimodal Ni-WC coatings was studied with a sliding speed of 3 mm/s under normal loads of 5 and 12 N and was then compared to Ni and composite coatings made with only agglomerated WC. Multimodal Ni-WC coatings with an altered distribution of WC particles offered an improvement in friction and wear as compared to Ni-agglomerated WC coatings. Characterization of worn surfaces revealed the formation of tribofilms following compaction of wear debris. A more stable tribofilm that developed to a higher coverage was identified for coatings with multimodal WC particles at both tested loads. However, the protective role of tribofilms was reduced at a higher load, caused by subsurface crack propagation. Subsurface microstructure of worn surfaces that are induced by sliding wear was studied, and a correlation between the mechanical properties and microstructure and wear mechanism of coatings was made. Overall, our findings highlight the potential of cold spray additive manufacturing in producing multimodal Ni-WC composite coatings with enhanced wear resistance.

Enhancing the Microhardness of Coatings Produced by Cold Gas Dynamic Spraying through Multi-Reinforcement with Aluminum Powders Containing Fullerenes and Aluminum Nitride

Coatings with high hardness were successfully obtained using low-pressure cold spray (LPCS) technology from nanocrystalline powders based on the aluminum alloy AlMg6, which were multi-reinforced with 0.3 wt.% fullerenes and 10–50 wt.% AlN. The powders were synthesized through a two-stage high-energy ball milling process, resulting in a complex mechanical mixture consisting of agglomerates and micro-sized ceramic particles of AlN. The agglomerates comprise particles of the nanocomposite material AlMg6/C60 with embedded and surface-located, micro-sized ceramic particles of AlN. Scanning electron microscopy and EDS analyses demonstrated a uniform distribution of reinforcing particles throughout the coating volume. An X-ray diffraction (XRD) analysis of the coatings revealed a change in the predominant orientation of matrix alloy grains to a more chaotic state during deformation over the course of cold gas dynamic spraying. A quantitative determination of AlN content in the coating was achieved through the processing of XRD data using the reference intensity ratio (RIR) method. It was found that the proportion of transferred ceramic particles from the multi-reinforced powder to the coating did not exceed ~65%. Experimental evidence indicated that LPCS processing of mono-reinforced nanocrystalline powder composite AlMg6/C60 practically did not lead to the formation of a coating on the substrate and was limited to a monolayer with a thickness of ~10 µm. The microhardness of the monolayer coating obtained from the deposition of AlMg6/C60 powder was 181 ± 12 HV. Additionally, the introduction of 10 to 50 wt.% AlN into the powder mixture contributed to the enhancement of growth efficiency and an increase in coating microhardness by ~1.4–1.7 times. The obtained results demonstrate that the utilization of agglomerated multi-reinforced powders for cold gas dynamic spraying can be an effective strategy for producing coatings and bulk materials based on aluminum and its alloys with high microhardness.

Effect of WC content on microstructure and properties of laser-cladded in-situ reactive ZrC/ZrB2 composite coatings on zirconium alloy

ZrC/ZrB2 in-situ reinforced composite coatings were prepared by laser cladding on zirconium alloy. The effect of WC content on microstructure and properties of in-situ reactive ZrC/ZrB2 composite coatings were investigated experimentally. The dilution rate and the inhomogeneity of reinforcements distribution were increased by increasing WC content. The increment of WC content contributed to the refinement of the fishbone dendrites. The microhardness and corrosion resistance of the composite coatings decreased with increasing WC content. When the WC content was 15 wt%, the average microhardness of the coating was the highest as 529 HV0.5. Meanwhile, the corrosion potential was the highest and the corrosion current density was the lowest, which were − 0.660 V and 1.627 × 10−8 A cm−2, respectively.

Cyclic Oxidation Behavior of HVOF Thermally Sprayed WC Cermet Based on AISI 1045 Steel

Thermal spray coating technology High-Velocity Oxygen Fuel (HVOF) has become one of solution for metal protect and parts recondition that work in critical environments such as oxidative, erosive, and corrosive. One of the thermal spray coatings (TSC) application has been carried out to improve the oxidation resistance of the Induce Draft Fan (IDF) as a part on coal fired steam power plant unit. Cermet WC10Co4Cr and WC17Co are intended to sustain the AISI 1045 steel substrate against the oxidative environment. In this works, the cyclic oxidation at a temperature 500oC were conducted to reveal the oxidation resistance behavior of the coatings. Several mechanical tests are also presented including surface roughness of the coatings, coatings microhardness, and coatings adhesion. The coatings morphology was also characterized using SEM microscope, as well as X-ray diffraction (XRD) for phase analysis after the oxidation test.

Estimation of microhardness and crystal grain size values of electrodeposited Ni-B/TiC nanocomposite coatings by artificial neural networks (ANN) method

In this study, composite coatings with Ni-B alloy main structure reinforced with TiC nanoparticles were coated on a stainless steel substrate by electrodeposition method. The microhardness and crystal structures of the produced nanocomposite films were examined and the relations between the obtained results and the production parameters were discussed in detail. In addition, the surface and section morphologies of the coatings were analyzed by SEM and EDS. Furthermore the complex relationship between the experimentally obtained microhardness, crystal grain size values and the production parameters was modeled by artificial neural networks (ANN) method. According to the hardness results, nanocomposite coatings microhardness values varied between about 470 HV and 820 HV. In XRD examinations, the crystal grain size values of nanocomposite coatings were found ranging from 6.6 nm to 17.4 nm. From the morphology results, it is understood that the surface structure and coating thicknesses are remarkably affected by the production parameters. Considering the EDS results, it was observed that the alloying with boron and the TiC reinforcement were successfully applied in nanocomposite coatings. With respect to the results obtained with ANN, the best results were obtained in the model with 10 neurons in the hidden layer and the highest error value of 2.02% was achieved for microhardness values. For the crystal grain size, the most successful results were acquired in the model with 12 neurons and the highest error value was obtained as 3.397%.

The Influence of CEO2 Content on the Microstructure and Hardness of Ni-WC Coating Formed by Vacuum Fusion Sintering

Made Ni-WC-CEO2 composite coatings of different CEO2 content on 45 steel matrixes by vacuum fusion sintering. The coatings microstructure and the morphology of WC were observed by SEM, the elements diffusion between WC and Ni-base alloy by EDS；The Rockwell hardness of coatings’ surface and micro-hardness of coatings’ longitudinal section were measured by Rockwell hardometer and microhardness instrument. The results showed that: The defects in the coatings become less, WC in the coating is further refined, and its distribution changes uniform with adding content CEO2. When the content of CEO2 is 0.5%, the surface’s hardness and section’s microhardness are the highest, In this paper, the optimum content is 0.5%.

Anodic Dissolution of Surface Layers as a Method of Increasing the Microhardness of Coatings by Alloys of the Iron Group Metals with Tungsten Obtained by Induced Co-Deposition

It is shown that the macroscopic dimensional effect of the composition and properties (microhardness and corrosion resistance) of coatings obtained by induced co-deposition of the iron group metals with tungsten (the effect of the surface area of electrodeposition on the composition and properties) due to the presence of oxide-hydroxide layers in the surface layer, as well as hydrogenation, is a special case of effects of this kind; this, in turn, requires a constant volumetric current density (mA/L) during electrodeposition. It has been established, using examples of electrodeposition of Fe-W and Co-W alloys from a citrate bath, that a change in the volumetric current density at a fixed electrodeposition current density leads to a change in the potential, the current output, and in the composition of the alloy in the coating. Anodic dissolution of the modified surface layer increases the microhardness, but does not eliminate the effect of dependence of the composition and properties of coatings on the electrodeposition surface area.

Laser cladding remanufacturing of aircraft landing gear based on 30CrMnSiNi2A steel

Remanufacturing landing gear is of great importance due to its vital function for the aircraft. The 30CrMnSiNi2A steel surface is remanufactured through laser cladding based on the actual service environment of landing gear. Six Ni-based wolfram carbide (WC) composite coatings with different proportions are prepared during the experiment. The microstructure, phase composition, microhardness, wear and corrosive resistance of the coatings are analyzed considering actual working conditions. Results show that the remanufactured coating well bonds with the substrate metallurgically without cracks and pores on the surface, except for the coating with 25 wt% WC content. The wear and corrosive resistance of the repaired coating greatly improve compared with those of substrate. It suggests that corrosive resistance for coating and substrate is different especially in a salt spray environment. The coating that is well-bonded with the substrate and has a compact structure can be obtained when the WC content is 20 wt%. In this case, the coating is characterized by an optimal hardness, wear and corrosive resistance. The coating microhardness is 542HV0.2. The weight loss of coating only accounts for 25.92 % of that of the substrate under dry friction. The electrochemical corrosion rate is 0.0025 mm/a, accounting for 1.37 % of that of the substrate. The surface of coating exhibits a good performance under a salt spray environment for 1000 h. This experiment aims to realize the remanufacturing of landing gear and hence provide a reference in its practical application.

Research on the Microstructure of Laser Remelted As-sprayed TiB2-TiC0.3N0.7 based Composite Coating

Ceramic coatings with excellent properties of wear resistance, corrosion resistance, oxidation resistance, stability in acid and alkaline environments, and good bond strength with a metallic substrate, are widely used in different industries. Air plasma spraying has high energy and efficiency for depositing ceramic materials with a high melting point. Due to intrinsic porosity and mechanical bond strength between coating and substrate, laser remelting technology can be applied to the coating surface for improving coating properties. As-sprayed TiB2-TiC0.3N0.7-based composite coating was surface remelted by laser. The surface roughness of as-sprayed and laser-remelted coatings was measured. The phase composition and the microstructure as well as the Vickers microhardness of coatings were studied by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and Vickers indentation instrument. It is found that the phase composition does not change after laser remelting. However, the surface roughness of laser-remelted coating is smoother than that of as-sprayed coating. And the microhardness on the cross-section is increased after laser remelting. There is a micro-crack in the laser-remelted coating due to the fast heating and cooling of the laser. The microhardness of the laser-remelted coating is increased with bimodal Weibull distribution.

Experimental study on friction-assisted electroforming of Ni-Co alloys

Owing to the complexity of the electroforming mechanism, the structure of electroformed deposits is affected by many process parameters, and defects such as pinholes and nodules in electroformed deposits must be solved. In this study, the mechanism by which hard particles inhibit the formation of the above defects in the electroforming process of Ni-Co alloys was analyzed. Through the friction-assisted electroforming Ni-Co alloy tests, the effects of friction and current density on the hardness, texture and microstructure of the Ni-Co electroformed deposits were studied. The results show that the microhardness of the Ni-Co coatings obtained is between 651 HV and 669 HV with the increase of the cathode speed from 8 rpm to 512 rpm. When the cathode speed is 16rpm, the grain sizes of Ni-Co coatings increase with the increase of cathode current density from 2 A dm−2 to 8 A dm−2, and the microhardness of the coatings is between 672 HV and 590 HV.

The effect of process temperature and powder composition on microstructure and mechanical characteristics of low-pressure cold spraying aluminum-based coatings

The effect of operating gas temperature and powder type on microstructure and mechanical characteristics of cold spraying coatings deposited on EZ33A-T5 magnesium alloy was studied. Three aluminum-based cold spraying powder mixtures Al + Zn, Al + Al2O3 and Al + Zn + Al2O3 were used for the investigation. Deposition was performed using D423 low-pressure cold spray system at operating gas pressure of 1.0 MPa and different temperatures –300 °C, 450 °C, and 600 °C. The coatings microstructure was investigated with optical and scanning electron microscopy. Mechanical properties of the coatings were characterized through standard test methods for adhesion and cohesion strength, and standard test methods for Vickers hardness of thermal spray coatings. The results demonstrate that with increasing initial gas temperature at spraying nozzle inlet from 300 °C to 600 °C, an increase in the porosity of the coatings of all investigated powder mixtures can be observed. Microstructure characterization showed an increase in porosity from 2.3% to 4.1% for Al + Zn powder mixture, from 2.1% to 3.5% for Al + Al2O3 powder mixture, and from 2.5% to 5.6% for Al + Zn + Al2O3 powder mixture. The minimum porosity was obtained at 450 °C for all investigated powder mixtures. Adhesion and cohesion strength and microhardness of coatings were reach their maximum value at 450 °C. The best performance was obtained for Al + Al2O3 powder mixture: coating adhesion—31.9 MPa (was limited by the bonding strength of the glue), cohesion—93.5 MPa, microhardness—81 HV0.15. The influence of Al2O3 particles in the powder mixture on the above-mentioned parameters was also established. The results show that the presence of ceramic particles in powder mixtures can positively effect porosity level and mechanical characteristics.

Залежність структури електродугових покриттів від параметрів напилення деталей транспортної техніки

The use of special flux-cored wires for electric arc spraying allows for coatings with high wear resistance. However, the insufficient adhesion and cohesion of the resulting coatings does not allow these coatings to be used under increased operating loads. To improve the mechanical characteristics of gas-thermal coatings, a supersonic gas jet is used to transport molten droplets to the sprayed surface, increasing their kinetic energy. It is proposed to apply a supersonic air jet using a Laval nozzle and increasing the air jet pressure from 0.6 to 1.0...1.2 MPa. The aim of the study is to determine the effect of air jet pressure on the structure of electric arc coatings. It has been determined that an increase in the air jet pressure from 0.6 to 1.2 MPa causes a 2-fold increase in the air flow velocity from 300 to 600 m/s. At the same time, the velocity of droplets dispersed by the air jet during the spraying of electrode cored wires increases from 60-90 m/s to 160-220 m/s, and their size decreases. Reducing the flight time of the dispersed droplets from the arc to the sprayed surface ensures their higher temperature when they hit the sprayed surface. Increasing the air jet pressure also reduces the expansion angle of the metal-air jet from 30° to 15°. The microhardness of iron oxide inclusions - magnetite, wustite and hematite - in the coating of unalloyed steel wire sputtered is in the range of 700-800 HV. This ensures a microhardness of the U8 coating of 350-400 HV at a pressure of 0.6 MPa. Sputtering the same coating at a pressure of 1.2 MPa reduces the size of the lamellae and oxides, and their volume content increases, which increases the microhardness to 450...500 HV. The microhardness of coatings made of 90X17R3GS increases from 800 to 910 HV. It was found that an increase in air jet pressure from 0.6 to 1.2 MPa provides an increase in air jet velocity from 300 to 600 m/s, and the velocity of dispersed droplets from 120 to 220 m/s.

Evaluation of the corrosion resistance of AlCoCrFeMnNi high entropy alloy hard coating applied by electro spark deposition

Although hard coatings have good resistance to wear and scratching, their corrosion resistance has decreased, failing. Improving the corrosion resistance of the hard coating has lately become a difficult subject. This work produced a newly created AlCoCrFeNiMn alloy with a high entropy using mechanical alloying and spark plasma sintering. Aluminum was added as the sixth elemental component to the chemical composition of the CoCrFrNiMn high entropy alloy to achieve this objective. Subsequently, the AlCoCrFeNiMn layer was deposited via electro-spark deposition on a substrate (ESD). To achieve a uniform layer, parameter optimization was performed, and the effects of frequency (5, 8, and 11 kHz), duty cycle (50, 60, and 70 %), and applied current (15, 25, and 35 A) were studied. Using the Vickers technique, the acquired surface microhardness of coatings was measured. The most significant measurement of hardness was around 1426 HV0.05. Using potentiostat-polarization testing and electrochemical impedance spectroscopy at room temperature, the corrosion of the coatings was evaluated. The AlCoCrFeNiMn HEA coating considerably increased the corrosion resistance of the substrate, according to the results. Corrosion rates for uncoated and coated samples were 1.44 and 0.13, respectively. At the optimal frequency of 11 kHz, the duty cycle of 60 %, and the current of 35 A, the coating exhibited the highest corrosion resistance, which was 10 times greater than the corrosion rate of the substrate. All of the coated samples displayed a passivation behavior, ascribed to the production of chromium oxide and aluminum oxide on the surface of the HEA layers due to their lower free Gibbs energy formation values. In addition, the coating's roughness was assessed, and the correlation between surface roughness and corrosion resistance was determined.

Electrodeposition of Ni-zirconia or Ni-titania composite coatings from a methanesulfonic acid bath

The study addresses the patterns of formation of Ni-ZrO2 and Ni-TiO2 composite coatings from methanesulfonate and sulfate electrolytes at pH 3. It has been shown that the aggregative stability of the dispersed phase particles is better in the methanesulfonate electrolyte than in the sulfate electrolyte. As a result, at the same volume concentration of the non-metallic phase in both electrolytes, the concentration of particles is larger in the methanesulfonate electrolyte. This ensures the formation of composite coatings from methanesulfonate electrolyte with a content of non-metallic particles increased by 20–30 vol% compared to sulfate electrolyte. A mechanism for forming a composite coating has been proposed, which takes into account the different rates of the metal phase electrodeposition on the electrode surfaces that are free from the dispersed phase or conditionally occupied. A mathematical model of composite coating formation has been developed, which adequately describes the obtained experimental data. Incorporation of the non-metallic phase into the nickel matrix leads to a change in the coating structure and decrease in the sizes of metal grains. It has been found that the physicochemical properties of Ni-ZrO2 and Ni-TiO2 composite coatings depend on the content of non-metallic phase particles in them. It has been revealed that the microhardness of Ni-ZrO2 coatings obtained from methanesulfonate electrolyte is 10 % higher than the microhardness of coatings deposited from sulfate electrolyte, which is due to a higher content of the non-metallic phase. The photocatalytic activity of Ni-TiO2 composite coatings correlates with the content of the dispersed phase in them, which is due to the participation of TiO2 particle surfaces, accessible to irradiation, in the photocatalytic reaction. It has been found that an increased content of the dispersed phase in Ni-ZrO2 and Ni-TiO2 composite coatings obtained from methanesulfonate electrolyte leads to increased values of their microhardness and photocatalytic activity.

A study on the microhardness and corrosion behavior of the ZnO and SiC reinforced multi layer electroless nickel coating

ABSTRACT An attempt has been made to fabricate electroless duplex (Ni-P-ZnO/Ni-P-SiC) coatings on the mild steel materials. Present investigation focused on ZnO and SiC nanoparticles concentration on the corrosion resistance and microhardness of duplex coating. Coated substrates are characterised by using the X-ray diffraction analyses to know the structure of deposit. Surface morphology and element composition was evaluated by means of scanning electron microscope (SEM) attached with the energy dispersive spectrometer (EDX). Coating was heat treated for 1 hour at 400°C temperature. Microhardness of the coatings was examined by using Vickers microhardness tester. Corrosion parameters of the duplex coating were evaluated by performing the potentiodynamic polarisation studies in 3.5% NaCl solution. Experimental observations confirm that Ni-P-SiC outer layered coating offers maximum microhardness and duplex coating with Ni-P-ZnO as external layer provides maximum corrosion protection. Maximum load bearing ability of SiC nanoparticles offers superior microhardness to the Ni-P-SiC external layer coatings. Higher electrochemical resistive ZnO nanoparticles provide good corrosion protection to the Ni-P-ZnO external layer coatings. Formation of intermetallic compounds after heat treatment process enhances the both the coatings microhardness and resistance to corrosion.