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

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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.

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.

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.

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.

PROCESS AND PROPERTIES OF ELECTROLESS PLATING RE-Ni-B-SiC COMPOSITE COATINGS

Technology and properties of electroless composite RE-Ni-B-SiC coatings have been investigated.Results show that stabilizer plys a decisive role in electroless composite Ni-B-SiC,the addition of appropriate quantity of RE(rare earth) into the Ni-B-SiC bath not only increases SiC content in composite coatings,their hardness and wear resistance but also improves crystalline fineness,Wear resistance increases with the increase of SiC.Hardness and wear resistance of composite coatings reach peak values a fter heat treatment at 4OO and 500℃ for 1h respectively.

Erosion and Toughening Mechanisms of Electroless Ni-P-Nano-NiTi Composite Coatings on API X100 Steel under Single Particle Impact

The addition of superelastic NiTi to electroless Ni-P coating has been found to toughen the otherwise brittle coatings in static loading conditions, though its effect on erosion behaviour has not yet been explored. In the present study, spherical WC-Co erodent particles were used in single particle impact testing of Ni-P-nano-NiTi composite coatings on API X100 steel substrates at two average velocities—35 m/s and 52 m/s. Erosion tests were performed at impact angles of 30°, 45°, 60°, and 90°. The effect of NiTi concentration in the coating was also examined. Through examination of the impact craters and material response at various impact conditions, it was found that the presence of superelastic NiTi in the brittle Ni-P matrix hindered the propagation of cracks and provided a barrier to crack growth. The following toughening mechanisms were identified: crack bridging and deflection, micro-cracking, and transformation toughening.

Corrosion Behavior of Electrodepositing Ni/Al_2O_3 Composite Coatings under the Presence of NaCl Deposit

The morphology and corrosion behavior of Ni/Al2O3 composite coatings prepared using double-pulsed electrodepositing technique after oxidized under 800 ℃ NaCl deposit in air environment were analyzed by scanning electrical microscope (SEM), X-ray diffraction(XRD) and energy dispersive spectrum(EDS). The results showed that the corrosion of all composite coatings was accelerated under NaCl deposits, and the corrosion products were rather porous with poor adherence to the matrix. Al2O3 particles in the coatings can refine the grain size and improve the high temperature corrosion resistance of the coatings. Within the test scope, the more Al2O3 particles in the coatings, the lower corrosion rates could be obtained, and the corrosion mechanism was also discussed.

Effect of Attapulgite Added in Plating Bath on the Properties of Ni/TiC Nano-composite Coatings

Pure copper plates were coated by Ni-TiC dipulse current plating method. The effects of adding different concentration（ranging from 0.5 g/L to 3.0 g/L） of attapulgite nano particles to the plating bath on the surface morphology, wear resistance, and oxidation resistance of Ni/TiC/Attapulgite nano-composite coatings were investigated. The experimental results show that the composite coating is flat and compact with adding 3.0 g/L in the bath, and the coating preferred orientation is changed from the planes（111） to（200）. The coefficient of the composite coatings decreases from 0.68 to 0.18 with increasing content of attapulgite in the bath, a mixed mode of adhesive-abrasive wear occurs for all coatings, and the wear mechanism shows a transition from adhesive-abrasive to predominantly abrasive wear mechanism when the concentration of attapulgite is beyond 1.5 g/L in electrolyte. The oxidation resistance of composite coatings is the best prepared when adding attapulgite particles at 0.5 g/L in the bath, the oxide mainly consists of a NiO phase by X-ray analysis.

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. [

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.

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.

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.

Corrosion resistance of electrodeposited RE-Ni-W-P-SiC-PTFE composite coating in phosphoric and ferric chloride

Corrosion rate and anode polarization curves of electrodeposited RE-Ni-W-P-SiC-PTFE composite coating in various concentrations of phosphoric and ferric chloride were researched. The results show that corrosion rate of the composite coatings increases with the increasing concentrations of phosphoric and ferric chloride, and reaches the maximum value when phosphoric concentration is 40% and ferric chloride concentration is 20% (mass fraction, the same below if not mentioned). Anode polarization curves of the composite coatings show that anode polarization current density of the composite coatings heat-treated at 200 ℃ or 500 ℃ is lower than that of other coatings heat-treated at 300 ℃ or 400 ℃, which displays that the composite coatings heat-treated at 200 ℃ or 500 ℃ have better corrosion resistance. Besides, corrosion resistance of the composite coating heat-treated at 500 ℃ is better than that as deposited and RE-Ni-W-P-SiC composite coating heat-treated at 400 ℃, and is also better than that of 316L stainless steel.

Friction and Wear Characteristics of Brush Plating Ni/nano-Al2O3 Composite Coating under Sand-Containing Oil

Ni-matrix composite coating containing AI2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating under the lubrication of a diesel oil containing sand are investigated. The results show that the microstructure of the composite coating is finer than that of the pure nickel coating due to the codeposition of the nano-particles. When the nano-particle concentration in the electroplating bath reaches 20 g/L, the microhardness, and wear resistance of the composite coating is as much as 1.6 times and 1.3-2.5 times of those of the pure nickel coating respectively. The main hardening mechanism of the composite coating is superfine crystal grain strengthening and dispersion strengthening. The composite coating is characterized by scuffing as it slides against Si3N4 under the present test conditions.

Characteristics of electrodeposited RE-Ni-W-B-B_4C-MoS_2 composite coating

The high temperature oxidation resistance of RE Ni W B B 4C MoS 2 composite coating, the effects of electrodeposition conditions on the morphologies of the coating and the effect of heat treatment temperature on its hardness, abrasion resistance and phase structure were investigated by using scanning electron microscope(SEM), X ray diffractometer, microhardness tester and abrasion machine. The results show that the oxidation degree of RE Ni W B B 4C MoS 2 composite coating is small when the temperature is lower than 700 ℃, but it increases sharply when the temperature is higher than 700 ℃. The hardness of RE Ni W B B 4C MoS 2 composite coating increases with increasing heat treatment temperature, it comes up to the maximum value at 400 ℃,but it decreases gradually if the temperature rises continuously. The most favourable abrasion resistance was attained after RE Ni W B B 4C MoS 2 composite coating being heat treated at 400 ℃. Without heat treating, it is mainly amorphous and partially crystallized, but wholly crystallized after being heat treated at 500 ℃. RE in the composite coating is in the form of CeO 2 and additions of CeO 2 and B 4C can enhance the thermostability of RE Ni W B B 4C MoS 2 composite coating.

Structure and properties of electrodeposition RE-Ni-W-B-B_4C-PTFE composite coating

The components, surface and cross sectional morphologies, and the effects of heat treatment temperature on phase structure, hardness, abrasion resistance and oxidation resistance of pulse electrodeposition RE-Ni-W-B-B4C-PTFE composite coatings, were all investigated. The results show that W and B contents increase in the RE-Ni-W-B composite coating by using pulse electrodeposition. RE, PTFE and B4C particles can be co-deposited into the Ni-W-B composite coating, but the amount is very little. X-ray diffraction analysis displays that the RE-Ni-W-B-B4C-PTFE composite coating is mainly amorphous, partially crystallized as-deposited, but it turns into crystalline state and PTFE in the coatings will decompose after the heat treatment temperature is higher than 400℃. The hardness of the composite coating increases with increasing heat treatment temperature, it comes up to the highest value at 400℃. The oxidized film mass of the composite coating increases slowly when the oxidation temperature is lower than 500℃, but it increases linearly and sharply after the oxidation temperature is higher than 600℃.