Tribological properties of nanostructured Al_2O_3-40%TiO_2 multiphase ceramic particles reinforced Ni-based alloy composite coatings

The Ni-based alloy composite coatings reinforced by nanostructured Al2O3-40%TiO2 multiphase ceramic particles were prepared on the surface of 7005 aluminum alloy by plasma spray technology. The microstructure and tribological properties of the composite coatings were researched. The results show that the composite coatings mainly consist of γ-Ni, α-Al2O3, γ-Al2O3 and rutile-TiO2 etc, and exhibit lower friction coefficients and wear losses than the Ni-based alloy coatings at different loads and speeds. The composite coating bears low contact stress at 3 N and its wear mechanism is micro-cutting wear. As loads increase to 6-12 N, the contact stress is higher than the elastic limit stress of worn surface, and the wear mechanisms change into multi-plastic deformation wear, micro-brittle fracture wear and abrasive wear. With the increase of speeds, the contact temperature of worn surface increases. The composite coating experiences multi-plastic deformation wear, fatigue wear and adhesive wear.

Fabrication of in-situ synthesized ceramic reinforced Ni-based alloy composite coatings by reactive braze coating processing

In-situ synthesized ceramic such as TiC,Cr7C3 and Cr5B3 reinforced Ni-based alloy composite coating was fabricated on the surface of mild steel substrate by reactive braze coating processing with colloidal graphite,Cr,Ni,ferro-boron,Si and titanium powders as the raw materials at low temperature of 1000℃,and a new kind of coating materials was developed.By means of SEM,EDS,XRD and surface hardness tester,the microstructures,phases,hardness and wear-resistance of the coating were analyzed,respectively.The results revealed that the coating was mainly composed of the ceramic in-situ synthesized reinforcement phases of TiC,Cr7C3 and Cr5B3 and the binder phases in-situ synthesized of Ni31Si12 and(Ni,Fe)solid solution;The ceramic reinforcement phases of TiC,Cr7C3 and Cr5B3 were randomly distributed in the binder phases of Ni31Si12 and(Ni,Fe)solid solution;The coating had about 15vol%pores and can possibly be applied as a self-lubrication coating;The coating and the substrate were integrated together by metallurgical bonding;The coating had a hardness up to 91-94HR15N.

Microstructure and oxidation resistance of reactive plasma clad Cr_7C_3/γ-Fe ceramic composite coating

A new type oxidation resistance in situ Cr7 C3/γ-Fe ceramic composite coating was fabricated on hardened and tempered grade C steel by reactive plasma clad with Fe-Cr-C alloy powders. The oxidation resistance of the ceramic composite coating was investigated under the test condition of 900 ℃ and 50 hours. The results indicate that the coating has a rapidly solidified microstructure consisting of blocky primary Cr7 C3 and the inter-blocky Cr7 C3/γ-Fe eutectics and is metallurgically bonded to the hardened and tempered grade C steel substrate. The high temperature oxidation resistance of the coating is up to 1.9 times higher than that of grade C steel. The oxidation kinetics curve of the coating is conforming to the parabolic-rate law equation. The excellent oxidation resistance of the coating is mainly attributed to the continuous oxide films which consist of Cr203 and Fe203. The continuous oxide films can prevent the inner part of the coating from being further oxidized.

Ceramic-Metal Composite Coating by Laser Cladding

Four kinds of ceramics (silicon carbide, boron carbide, aluminum oxide and tungsten carbide) were added into Ni base self-fluxing alloy as reinforcing materials in order to obtain metalceramic composite coating by means of laser cladding. A lot of experiments have been carried out to test the processability of the four kinds of ceramics with different sizes and contents. The microstructures of sintered tungsten carbide (S-WC) and cast tungsten carbide (C-WC) reinforced Ni base alloy coatings were analysed, the distortion regulation of laser clad specimens was revealed. The wear resistance of the composite coating has been tested.

Residual Thermal Stresses of Laser Cladding of Intermetallic-Ceramic Composite Coatings

The stresses in laser cladding of Ni3Al-WC composite coating co and in heat affect zone (HAZ) σh have been induced based on considering the influences of laser processing parameters power P and beam traverse speed v.According to the calculated results, certain limits of P and v are necessary in order to obtain crack free coatings. It agrees well with the experimental results.

A method for preparing composite diffusion coating alloy on ceramic surface

Metallization of the ceramic surfaces of Si3N4 and Al2O3 was carried out in a composite diffusion coating vacuum furnace using a Ti-Cu composite target. The experimental process and influencing factors were discussed. Optical microscope （OM） , energy dispersive spectroscopy （EDS） , scanning electron microscopy （SEM） , X-ray diffusion （XRD） and sound emissive scratch test （SEST） were applied to evaluate the alloy layer formed on the ceramic surface. It was indicated that the diffusion coating alloy layer contained Cu, Ti, Fe, Al and Si etc. XRD result indicated that the diffusion coating alloy layer was composed of CuTi2, Cu, Si2 Ti and CuTi, Al2 TiO5 , Ti3O5. It was found that the diffusion coating alloy layer got bonded with ceramic well, and no spaUation occurred under the maximum load of 100 N. Deposited Si3N4 ceramic was welded with Q235 and the joining quality was examined. Robust joint was formed between Si3N4 ceramic/Q235. This present method has advantages in high efficiency and low cost and provides a new approach for producing ceramic and metal bond.

Coarse WC Particles Ceramic-Metal Composite Coating by Laser Cladding

The coarse WC particles ceramic-metal com- posite coatings with WC density of 67 wt-% and thickness of 1.0-1.2 mm have been cladded on 20Ni4Mo steel surface by a 2 kW CO_2 laser.The sintered WC particles with the size of 600-1000 μm are chosen as the main strengthening phase, Ni-base self-flux alloy as the binder in the compo- site coatings.The microstructure and microhardness of both WC particles and binder are analysed.The rigid ball indention with acoustic emission technique is used to evaluate the brittleness of the coating.Finally,the abrasive wear resistance of the coating is tested.Besides,the coatings with the same ratio and size of WC parti- cles in low carbon steel tube rod were cladded on 20Ni4Mo steel by atomic hydrogen welding tech- nique and analysed by the same way,their results are compared.

MICROSTRUCTURE OF ELECTRODEPOSITED Ni-W-P-SiC COMPOSITE COATINGS

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Corrosion resistance of electrodeposited RE-Ni-W-P-SiC composite coating

Immersion experiment results show that corrosion rate of the as deposited RE Ni W P SiC composite coating in HCl solutions increases with the rise of HCl concentration. On the contrary, the corrosion rate of the composite coating after heat treatment decreases with increasing HCl concentration. The corrosion rates of the composite coatings in as deposited state and after heat treatment in H 2SO 4 and H 3PO 4 solutions respectively decrease with the rise of H 2SO 4 and H 3PO 4 concentrations. The corrosion rate of the composite coating as deposited in FeCl 3 solutions decreases with increasing FeCl 3 concentration, while the rate of the composite coating after heat treatment increases with the rise of FeCl 3 concentration. The corrosion rate of 316L stainless steel in the corrosion media of H 2SO 4, HCl, H 3PO 4 and FeCl 3 solutions at different concentrations increases with rising concentration. In addition, the corrosion rate of 316L stainless steel in the corrosion media of H 2SO 4, HCl, H 3PO 4 and FeCl 3 solutions respectively is much greater than that of the RE Ni W P SiC composite coating as deposited and after heat treatment in the same corrosion media. [

Effects of addition of rare earth on properties and structures of Ni-W-B-SiC composite coatings

The effects of rare earth (RE) on the composition, phase structures, surface morphologies and hardness of electrodeposited RE Ni W B SiC composite coatings were discussed. The results show that W and SiC contents in the coatings increase with the increase of RE in the bath. When RE is added in the coatings, the grains are refined and the trend of formation of amorphous coatings is increased. Moreover, the thermal stability of the RE Ni W B SiC composite coatings is enhanced. The hardness of the coatings is increased with the increase of heat treatment temperature, and it reaches the peak value when heated at 400 ℃. Besides, the hardness of the RE Ni W B SiC coatings is higher than that of the Ni W B SiC coatings.

Microstructure of electrodeposited RE-Ni-W-P-SiC composite coating

The components and microstructure of the RE Ni W P SiC composite coating were analyzed by means of EPXDS, SEM and XRD. The results showed that the composite coating containing 5%～14%RE, 4%～7%SiC, 12%～15%P and 5%～6%W was obtained by use of appropriate bath composition and plating conditions. The as deposited composite coating is amorphous and it becomes mixture when the temperature is raised from 200 ℃ to 400 ℃. However, the composite coating is crystal when the temperature is over 400 ℃. Scanning electron microscopy indicates that the heat treatment temperature has no effect on the surface morphologies of the RE Ni W P SiC composite coating. This is to say that the composite coating has a better heat stability of microstructure and high temperature oxidation.

Wetting of molten Sn-3.5Ag-0.5Cu on Ni-P(-SiC) coatings deposited on high volume faction SiC/Al composite

The wetting of molten Sn-3.5Ag-0.5Cu alloy on the Ni-P(-SiC)coated SiCp/Al substrates was investigated by electroless Ni plating process,and the microstructures of the coating and the interfacial behavior of wetting systems were analyzed.The SiC particles are evenly distributed in the coating and enveloped with Ni.No reaction layer is observed at the coating/SiCp/Al composite interfaces.The contact angle increases from^19°with the Ni-P coating to 29°,43°and 113°with the corresponding Ni-P-3SiC,Ni-P-6SiC and Ni-P-9SiC coatings,respectively.An interaction layer containing Cu,Ni,Sn and P forms at the Sn-Ag-Cu/Ni-P-(0,3,6)SiC coated SiCp/Al interfaces,and the Cu-Ni-Sn and Ni-Sn-P phases are detected in the interaction layer.Moreover,the molten Sn-Ag-Cu can penetrate into the Ni-P(-SiC)coatings through the Ni-P/SiC interface and dissolve them to contact the SiCp/Al substrate.

Microstructure and Corrosion Resistance of Cr_7C_3/γ-Fe Ceramal Composite Coating Fabricated by Plasma Cladding

A new type in situ Cr7C3/γ-Fe ceramal composite coating was fabricated on substrate of hardened and tempered grade C steel by plasma cladding with Fe-Cr-C alloy powders. The ceramal composite coating has a rapidly solidified microstructure consisting of primary Cr7C3/γ- and the Cr7C3/γ-Fe eutectics, and is metallurgically bonded to the degree C steel substrate. The corrosion resistances of the coating in water solutions of 0.5 mol/L H2SO4 and 3.5% NaCl were evaluated utilizing the electrochemical polarization corrosion-test method. Because of the inherent excellent corrosion-resisting properties of the constituting phase and the rapidly solidified homogeneous microstructure, the plasma clad ceramal composite coating exhibits excellent corrosion resistance in the water solutions of 0.5 mol/L H2SO4 and 3.5% NaCl.

Thermodynamics of electrodeposited Ni-B-SiC composite coatings

The φ pH diagram of Ni B H 2O system was drawn, and the mechanism of electrodepositing Ni B SiC composite coatings was discussed. The results show that the deposition of Ni and B occurs prior to that of H 2 because of the over potential of H 2 evolution on the Fe substrate. Boron can not singly deposit in aqueous solution. Nickel and boron can co deposit in the form of Ni 4B 3 without evolution of hydrogen when the cathodical potential is kept to be -1.415 ～ -1.700?V.

PROPERTIES OF ELECTRODEPOSITED AMORPHOUS Ni-W-P-SiC COMPOSITE COATINGS

The Effects of heat treatment temperature on the hardness,wear resistance and structure of the amorphous Ni-W-P-SiC composite coatings have been investigated.The results show that Ni-W-P-SiC composite coatings are amorphous under 300℃, partially crystalline at 300-400℃,and crystalline when heat treatment temperature reaches 400℃,the crystals being fine Ni3P phase particles.The hardness,wear resistance and the crystallization temperature of the composite coatings increase when an additive is added into the bath.The hardness and wear resistance of the coatings increase with increasing heat treatment temperature,and they will reach their peak values when the heat treatment temperature reaches 400℃.Corrosion experiment indicates that the corrosion resistance of amorphous Ni-W-P-SiC composite coatings in various kinds of corrosive media except nitric acid is better than that of stainless steel 1Cr18Ni9Ti.Scanning electron microscopy observation shows that the additive has no effect on the surface appearance of the coatings,but the current density and the pH value have considerable effects on the surface appearance.

Sliding wear behaviors of electrodeposited Ni composite coatings containing micrometer and nanometer Cr particles

Micrometer and nanometer Cr particles were co-deposited with Ni by electroplating from a nickel sulfate bath containing a certain content of Cr particles. Cr microparticles are in a size range of 1-5 μm and Cr nanoparticles have an average size of 40 nm. The friction and the wear performance of the co-deposited Ni-Cr composite coatings were comparatively evaluated by sliding against Si3N4 ceramic balls under non-lubricated conditions. It is found that the incorporation of Cr particles enhances the microhardness and wear resistance of Ni coatings. The wear resistance of Ni composite coating containing Cr nanoparticles is higher than that of the Ni composite coating containing Cr microparticles with a comparable Cr particle content. The co-deposition of smaller nanometer Cr particles with Ni effectively reduces the size of Ni crystals and significantly increases the hardness of the composite coatings due to grain-refinement strengthening and dispersion-strengthening,resulting in a significant improvement of wear resistance of the Ni-Cr nanocomposite coatings.

CATHODIC PROCESS AND WEAR RESISTANCE OF ELECTRO-DEPOSITED RE-Ni-W-P-SiC COMPOSITE COATING

Cathodic deposition current density of the composite coatings increases when SiC par-ticles and rare earth (RE) were added in the bath, which is profitable for Ni- W-P alloy to deposit in the cathod, forming Ni-W-P-SiC and RE-Ni-W-P-SiC composite coatings. On the contrary, the addition of PTFE in the bath decreases cathodic deposition current density of the coatings. The current density increases a little when the amount of RE is 7-9g/l; however, the current density increases greatly when the amount of RE is increased to 11-13g/l. Bui ij the amount of RE is raised further, the current density decreases. Hardness and wear resistance of RE-Ni-W-P-SiC composite coating have been studied, and the results show that the hardness and wear resistance of RE-Ni-W-P-SiC composite coating increase with increasing heat treatment tempera-ture, which reach peak values at 400℃; while the hardness and wear resistance of the coating decrease with the rise of heat treated temperature continuously.

Structure and characteristics of electrodeposited RE-Ni-W-P-B_4C-PTFE composite coatings

Hardness, friction and wear characteristics of electrodeposited RE Ni W P B 4C PTFE composite coatings were studied, and the reason for these fine characteristics was explained in respect of structure. The results show that 1) the structure of RE Ni W P B 4C PTFE composite coatings experiences a transformation process from amorphous to mixture then to crystal as the heat treatment temperature rises; 2) incorporating of B 4C greatly increases the hardness of the coating; 3) the wear resistance of the coating is best with heat treatment for 1?h at 300?℃, which is greatly superior to that of the other traditional coatings.

STUDY ON PROPERTIES OF PULSE ELECTRODEPOSITED RE-Ni-W-P-SiC COMPOSITE COATINGS

The effects of pulse frequency f and duty cycle r on the deposition rate, composition, morphology, and hardness of pulse electrodeposited RE （rare earth）-Ni-W-P-SiC composite coatings have been studied. The results indicate that pulse current can improve the deposition rate of RE-Ni-W-P-SiC composite coatings; W, P, and SiC contents in the coating decrease with the increase of pulse frequency and reach the lowest value at f = 33Hz, whereas the RE content in the composite coatings increases with the increase of pulse frequency. SiC content decreases with the increase of duty cycle, W content reaches the lowest value, and P content reaches the highest value at r = 0.4; pulse current and RE can lead to smaller size of the crystalline grains; however, the effects of different pulse frequency and duty cycle on the morphologies of RE-Ni-W-P-SiC composite coatings are not obvious. The hardness of RE-Ni-W-P-SiC composite coatings is the highest when the duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz. At the same pulse frequency, the hardness of RE-Ni-W-P-SiC composite coatings at r= 0.8 is higher than that at r= 0.6.

Oxidation resistance of co-deposited Ni-SiC nanocomposite coating

Ni-6.0%SiC (mass fraction) nanocomposite coating was prepared from a nickel sulfate bath by co-electrodeposition of Ni and SiC nanoparticles in an average size of 30 nm. The oxidation at 1 000 ℃ shows that the Ni-6.0%SiC nanocomposite coating has a superior oxidation resistance compared with the pure Ni film due to the formation of SiO2 oxide particles along grain boundaries, blocking the outward diffusion of Ni and changing the oxidation growth mechanism. The effect of SiC nanoparticles on the oxidation progress was discussed in detail.