Microhardness Of Composite Coatings Research Articles

Effects of Cu-Ni-Ti Interlayer on Microstructure and Wear Resistance around Gas Tungsten Arc Cladding Copper Matrix Composite Coatings on Steel

Due to the huge difference in thermophysical properties, it is difficult to obtain a defect-free bonding interface between copper and steel. A Cu-Ni-Ti interlayer was added between a TiC-reinforced copper matrix composite coating and Q235 steel in this study to improve its interfacial bond. The influence of the interlayer on its microstructure and properties was studied by characterizing microstructure, phase composition, and wear resistance of the composite coatings. Both coatings were found to consist of α-Cu matrix, in situ-generated TiC, and Fe-rich phases. With the addition of the Cu-Ni-Ti interlayer, the high-hardness unmixed zone at the interface was successfully eliminated due to the sufficient mixing of the molten pool. Even more importantly, liquid metal embrittlement cracks were also restrained, resulting from the Fe-rich solid solution band that reduced the contact probability around liquid copper atoms with the steel grain boundaries formed. In addition, the results showed that the microhardness of composite coatings was improved and the wear loss reduced by 4.2% after adding that interlayer, which was related to the combined action of solid solution strengthening, second-phase strengthening and grain-refinement strengthening mechanisms.

Dry Sliding Tribological Behaviors of Electrodeposited Ni-GO/SiC Composite Coating on the 2218 Aluminum Alloy.

Electrodeposition has attracted tremendous interest in functional coatings due to its advantages of high efficiency, inexpensiveness and ease of implementation. In this work, nickel graphene oxide (Ni-GO), nickel silicon carbide (Ni-SiC) and nickel graphene oxide/silicon carbide (Ni-GO/SiC) composite coatings were electrodeposited on the 2218 aluminum alloy (2218AlA) substrate. The microstructure, microhardness, bonding strength and tribological behaviors of the composite coatings were carried out. According to the results obtained, the composite coatings were dense and compact, with no visible defects and microcracks, and well bonded to 2218AlA substrate. The microhardness of composite coatings was significantly increased compared to that of the 2218AlA substrate. The microhardness of Ni-SiC composite coating was the highest, reaching 3.14 times that of the 2218AlA substrate. The friction response time, friction coefficient and wear rate of the composite coatings were obviously lower. For the Ni-GO composite coating, the average friction coefficient is the smallest at 45.35% of the 2218AlA substrate, while the wear rate is the smallest at 46.97% of the 2218AlA substrate. However, the comprehensive tribological performances of the Ni-GO/SiC composite coating were superior. The abrasive and adhesive wear were the main wear mechanisms of composite coatings, but the degree of damage was different.

Effect of CeO2 on high-temperature wear resistance of WC/Fe-based coatings

ABSTRACT In this study, the WC reinforced Fe-based composite coatings with various CeO2 contents were fabricated on the H13 hot-working die steel by laser cladding. The high-temperature wear resistance of composite coatings was analysed by friction-abrasion testing machine, white light interferometer, and scanning electron microscope (SEM). The microstructure and microhardness were investigated by SEM and Vickers hardness tester. The influence mechanism of CeO2 on microstructure and wear resistance was explained. The results showed that appropriate CeO2 could effectively refine the microstructure of coatings, and affect the crystal morphology. The microhardness of composite coatings was about 4–5 times that of the die steel substrate. Affected by microstructure and microhardness, the Fe-based composite coatings with CeO2 exhibited a higher high-temperature wear resistance than the substrate.

Microstructure and fretting wear of laser cladding self-lubricating anti-wear composite coatings on TA2 alloy after aging treatment

Fretting wear, as an unique form of material degradation, was researched relatively scarce compared with sliding wear in recent study, especially on influence of aging treatment on the fretting wear property of laser cladded composite coatings. In order to investigate the effect of aging treatment on microstructure and fretting wear of laser cladding self-lubricating anti-wear composite coatings on TA2 alloy, the composite coatings were prepared on TA2 alloy by laser cladding with precursor mixed WS2-TiC-Ti (mole ratio of 1:3:6) powders, and the fabricated coatings were heated at 300 °C, 500 °C and 700 °C in vacuum for 1 h, respectively. The microstructure, micro-hardness, fretting wear properties of as-laser cladded and heat-treated composite coatings were studied systematically. The results show that the composite coatings mainly contain three types of phases: the carbides (Ti,W)C1−x and TiC, α-Ti, sulfides TiS and Ti2SC. The micro-hardness of composite coatings after aging treatment is higher than the coating without aging treatment. The main wear mechanisms of composite coatings after aging treatment at 700 °C are abrasive wear and adhesive wear, and the composite coating exhibits good fretting wear property.

The Structure and Main Characteristics of Diamond-Bearing Ni–P Coatings

The effect of detonation-synthesis nanodiamonds (extracted from detonation products by thermal treatment in air in the presence of boric anhydride) on the characteristics of chemical composite nickel–phosphorous coatings has been investigated. It has been established that the introduction of nanodiamonds results in formation of a finer structure of the obtained coatings, reduction in the size of the coherent-scattering region, and an increase in the size of the crystal-lattice parameter. The coatings’ microhardness increased by 30% on average. Application of nanodiamonds with a surface modified with nickel compounds has yielded an additional increment of the microhardness of composite coatings by 33%.

Production and characterization of electrodeposited Ni-B/hBN composite coatings

Ni-B/hBN composite coatings were fabricated through conventional electrodeposition method in Watt's type solution bath on st-37 low carbon steel. Electrodeposition was carried out in different hBN bath concentration and trimethylamine borane (TMAB) was used as source of boron. Also pure Ni and Ni-B alloy coatings was deposited in order to make comparisons. Electrochemical behaviors, crystal structures, surface morphologies, chemical composition, microhardness, surface roughness and corrosion behaviors of the coatings were analyzed. In this study, the results indicate that smooth, compact and fine grained composite deposits were produced and the microhardness of composite coatings was 325% higher than pure nickel coating and was 10% lower than Ni-B coating. Besides, it was found that corrosion rate of the composite coatings was 87.5%, 86% and 30% lower than that of mild steel substrate, Ni-B alloy and pure nickel coating, respectively.

Influence of stirring conditions on Ni/Al2O3 nanocomposite coatings

The influence of the stirring conditions in the electrolyte on the structure and properties of Ni/Al2O3 nanocomposite coatings was studied. The coatings were produced by electrochemical reduction on a copper substrate in a Watts bath modified by nickel grain inhibitor, cationic surfactant and low concentrated nanometric alumina. The process has been carried out with different types of agitation (mechanical, ultrasonic stirring and with a copper rotating disc electrode). The structures of the produced coatings were characterised by scanning and transmission electron microscopy as well as X-ray diffraction. The influence of Al2O3 particles on the microhardness of composite coatings was also analysed. The adhesion of the composite coatings to the substrate and coefficient of friction were determined by means of the scratch test. The studies have shown that the bath stirring method affects the content and distribution of the alumina, as well as the properties of the produced composite Ni/Al2O3 coatings.

Microstructure and microhardness studies of nickel-based diamond composite coatings by electrodepositing in supercritical CO2

Nickel-based diamond composites were produced by electrodepositing in supercritical fluids CO2, and the samples were investigated using scanning electron microscope and digital microscope hardness tester. The results show that the surface of the coatings is smooth with diamond particles dispersed uniformly, and its average microhardness increases 80% than that of ordinary electrodepositing coatings. The influences of current density and diamond addition to the microhardness of composites were discussed as well as working pressure. The results show that the microhardness of composite coatings increases at first and then decreases with the increase of current density and diamond addition. Its maximum can reach 910 HV when the current density is 9 A dm−2. Working pressure variations from 10 to 14 MPa have no significant effect on the microhardness of coatings, which is more or less 900 HV. But the microhardness decreases dramatically when the working pressure is more than 14 MPa.

Investigation on cored-eutectic structure in Ni60/WC composite coatings fabricated by wide-band laser cladding

Ni60 composite coatings reinforced with WC particles were fabricated on the surface of Q550 steel using LDF4000-100 fiber laser device. The wide-band laser and circular beam laser used in laser cladding were obtained by optical lens. Microstructure, elemental distribution, phase constitution and wear properties of different composite coatings were investigated. The results showed that WC particles were partly dissolved under the effect of wide-band fiber laser irradiation. A special cored-eutectic structure was synthesized due to dissolution of WC particles. According to EDS and XRD results, the inside cores were confirmed as carbides of M23C6 enriched in Cr, W and Fe. These complex carbides were primarily separated out in the molten metal when solidification started. Eutectic structure composed of M23C6 carbides and γ-Ni(Fe) grew around carbides when cooling. Element content of Cr and W is lower at the bottom of cladding layer. In consequence, the eutectic structure formed in this region did not have inside carbides. The coatings made by circular laser beam were composed of dendritic matrix and interdendritic eutectic carbides, lacking of block carbides. Compared to coatings made by circular laser spot, the cored-eutectic structure formed in wide-band coatings had advantages of well-distribution and tight binding with matrix. The uniform power density and energy distribution and the weak liquid convection in molten pool lead to the unique microstructure evolution in composite coatings made by wide-band laser. Experiment results indicated the wear resistance and microhardness of composite coatings were both significantly improved.

High-Energy Electrospark Surface Strengthening of Steels with Composite Ceramics

The surface and cross-sectional structure, composition, and microhardness of composite coatings on ShKh15 and R6M5 steels have been studied under high-energy electrospark deposition with electrode materials based on zirconium boride and titanium (zirconium) nitride. It is shown that mass transfer of doping components into a metallic substrate is determined by wetting of the refractory component by iron. The strengthening/softening of the steel substrate is ascertained under high-energy electrospark deposition.

Effects of SiC Volume Fraction and Particle Size on the Deposition Behavior and Mechanical Properties of Cold-Sprayed AZ91D/SiCp Composite Coatings

AZ91D/SiCp composite coatings were fabricated on AZ31 magnesium alloy substrates using cold spraying. The effects of SiC volume fraction and particle size on the deposition behavior, microhardness, and bonding strength of coatings were studied. The mean sizes of SiC particles tested were 4, 14, and 27 μm. The results show that fine SiC particles (d 0.5 = 4 μm) are difficult to be deposited due to the bow shock effect. The volume fraction of SiC particles in composite coatings increases with the increasing SiC particle size. The microhardness and bonding strength of composite coatings also show increases compared with AZ91D coatings. The volume fractions of SiC particles in the original powder were set at 15, 30, 45, and 60 vol.%. The corresponding contents in composite coatings are increased to 19, 27, 37, and 51 vol.%, respectively. The microhardness of composite coatings also increases as the volume fraction of SiC particles increases.

Forming Mechanism of Composite Coating with Nano-Particles and its Wear Resistance

Ni-SiC nano composite coatings were prepared on pure copper substrate. The surface morphology and distribution of nanometer particles of the composite coatings were observed by scanning electron microscope (SEM), micro-hardness of coatings was tested by HXD-1000 microharder. The results showed that microstructure of Ni-SiC nano composite coating is different from that of electrodeposited nickel coatings. Its electrodepositing process abided by the principal of adsorption. By adding nanometer particles, the structure of composite coatings can be effectively fined, microhardness of composite coatings is improved apparently by comparing with that of electrodeposited nickel coatings. Abrasion resistance of Ni-SiC nano composite coatings is excellent.

Deposition Mechanism and Wear Resistance Nano Ni-Al<sub>2</sub>O<sub>3</sub> Composite Coatings

Nano Ni-Al2O3 composite coatings were prepared on pure copper substrate. The surface morphology and distribution of nano-particles of coatings were observed by SEM, the components of the coatings analyzed by X-ray diffractometer, and the microhardness of coatings tested by HXD-1000 microhardness tester. The microstructure of nano Ni-Al2O3 composite coating was different from that of the electrodeposited nickel coatings. The inserted Al2O3 particle can effectively hinder the growth of crystals. The microhardness of composite coatings around the inserted particles was much higher than that of electrodeposited nickel coatings. The more the size of Al2O3 decreased, the more the microhardness and wear resistance of the composite coatings increased.

The Influence of Thermal Sprayed Coats Chemical Composition on the Microstructure and Properties

In the present work, the microstructure, phase composition and microhardness of Cr3C2-NiCr, WCCo, and powdered composite NiCrSiBCr10%,Fe2.5%,Si3.1%,Bi2.1%C; NiCrSiBFe5; NiCrSiBCr5; NiCrSiBFe2.5Cr2.5; HVOF coatings applied on the Al-Si substrate have been compared. The coating cross-sections were examined by optical microscopy (OM), scanning electron microscopy (SEM) and electron transmission microscopy (TEM). For hard Cr3C2-NiCr and WC-Co coatings, a total microhardness level of about 860 and 1240 HV, respectively, was obtained. The microhardness of composite coatings was essentially lower and comprised in the range of values between 420 and 540 HV. The lowest level of microhardness showed the NiCrSiBFe2.5Cr2.5 coating. The most refined microstructure was found in Cr3C2 and WC coatings. The mean size of splat granules obtained in Cr3C2-NiCr had the value of about 2.7 m and of 0.5 m in WC-Co. For comparison, the granules obtained in composite coatings had the dimensions of about 30 μm. An Xray diffraction (XRD) revealed the presence of Cr3C2 and WC carbides in Cr3C2-CrNi and WC-Co coatings. In composite coatings, the phases of Cr3Ni5Si2, Ni3Si, FeSi, Fe2B, Cr3Si, BCr as well as other phases were found. The existence of the analyzed phases was additionally confirmed by the selective etching of coating microstructure. The annealing of coatings at 823K resulted in pore disappearance and increased the coating microhardness.

Mechanical and Tribological Properties of Pulse and Direct Current Electrodeposited Ni-TiO2Nano Composite Coatings

Ni-<TEX>$TiO_2$</TEX> nano composite coatings were fabricated using pulse current electrodeposition technique at 100 Hz pulse frequency with a constant 50% pulse duty cycles and reference was taken with respect to the direct current (dc) electrodeposition. The properties of the composite coatings were investigated by using SEM, XRD, Wear test and Vicker's microhardness test. Pulse electrodeposited composite has exhibited enhancement of (111), (220), and (311) diffraction lines with an attenuation of (200) line. The results demonstrated that the microhardness of composite coatings under pulse condition was significantly improved than that of pure nickel coating as well as dc electrodeposited Ni-<TEX>$TiO_2$</TEX> composite coatings. Wear tracks have shown the less plastic deformation in pulse plated composite. Coefficient of friction was also found to be lower in pulse plated composite coatings as compared to dc plated composite coatings.

Electrodeposition of Ni-SiC Nano Composite in Presence of Ultrasound

Ni-SiC nano composite coatings were fabricated using electrodeposition technique with the aid of ultrasound. The properties of the nano composite were investigated using SEM and Vicker’s microhardness tester. The results demonstrated that the microhardness of composite coatings under ultrasonic vibrations was improved significantly as compared to conventional electrodeposition techniques without ultrasound. The nano particles were found to be distributed homogeneously with reduced agglomeration due to the ultrasonic vibration.

Advanced composite coating by electrodeposition technique

This work aims to prepare Ni–RuAl composite coatings from Watts’ solution containing suspension of the single phase powder of the intermetallic compound RuAl. The chemical composition, phase structure and surface morphology of pure Ni and Ni–RuAl composite coatings are investigated using energy dispersive analyser system (EDX), X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The microhardness and oxidation resistance of Ni–RuAl composite coatings in comparison with pure Ni are evaluated. The corrosion behaviour for both of Ni and Ni–RuAl deposits is evaluated by polarisation curves in 3·5% NaCl solution. The results reveal that the content of RuAl in the Ni matrix is a function of applied current density and concentration of RuAl powder in the plating bath. Moreover, the presence of RuAl improves the oxidation and corrosion resistance of Ni coatings. The microhardness of composite coatings increases with the increasing content of the RuAl particles in the deposit.

Electrodeposition of Au/nanosized diamond composite coatings

Ultra-dispersed diamond UDD particles were codeposited in gold matrix coatings from a sulphite electrolyte, changing bath load and key operating parameters. The influence of electrolyte pH, current density and bath load on current efficiency, particle co-deposition, surface morphology and microhardness of composite coatings was investigated. UDD incorporation is mainly affected by bath load; however, particle embedding is specifically sensitive to electrolyte pH and deposition current density. The maximum mass fraction of carbon in the coating, about 0.55%, is obtained by depositing from ultrasonically pre-treated electrolytes with UDD concentration 20 g l−1, pH 9.5 and 3 mA cm−2 . Au/UDD composites are characterised by an increased microhardness and improved wear resistance. When compared to pure gold coatings which are notoriously weak, Au/UDD electrodeposits from sulphite electrolytes represent a significant improvement.