Synthesis and characterization of functionally graded nickel‐nickel coated ZrO₂ composite coating

Abstract

Electroless‐nickel plated ZrO2 (NCZ) particles have been used to produce a functionally graded nickel‐electroless‐nickel plated ZrO2 composite coating. So, electroless‐nickel plated ZrO2 particles concentration was continuously increased from 0 to an optimum value in the electroplating bath (Watt's bath). The substrate was ST37 steel and the thickness of the coating was approximately 50 μm. Also a uniformly distributed nickel‐electroless‐nickel plated ZrO2 composite coating has been manufactured as comparison. The composite coatings were characterized by scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Structure and phase composition were identified by X‐ray diffraction analysis. Microhardness of the coatings was evaluated by employing a Vickers instrument. Three‐point bend test was carried out to compare the adhesion strength of the coatings. Dry sliding wear tests were performed using a pin‐on‐disk wear apparatus. The electrochemical behavior of the coatings was studied by electrochemical impedance spectroscopy. The microhardness measurements showed that, with increasing the co‐electrodeposited electroless‐nickel plated ZrO2 particle content in the nickel matrix, the microhardness increases from interface towards the surface of the functionally graded composite coating. Bend, wear and electrochemical test results confirmed that the functionally graded composite coating has higher adhesion, wear resistance and corrosion resistance as compared with the uniformly distributed coating. This has been attributed to lower mechanical mismatch between coating and substrate in functionally graded composite coating with respect to the uniformly distributed one.

Controlled adsorption of titanium(IV) oxide particles on electroplated zinc coatings to improve the corrosion resistance of chromium(VI)‐free conversion layers

“…The realized investigations and resulting observations show that * the freshly electrodeposited zinc coating is already partially passivated by a zinc-oxide-hydroxide (ZnÀOÀOH) surface layer, * the adsorption of titania particles on the electroplated zinc coating with a simple dip-coating technique is possible within an aqueous, acceptably stable titania suspension, * the aqueous titania suspension is acceptably stable at pH values smaller than 5 or greater than 9, * the adsorbed area-related titania mass is controlled by the pH value and solid concentration of the suspension, * a linear dependence of the area-related titania mass by changing the solid concentration of the suspension arises in the range between about 10 wt.% and 30 wt.%, * close to the isoelectric points of the titania particles (IEP TiO2 = 6.7) and of the zinc layer (IEP Zn = 9), the area-related titania mass is largest (about 6 mg/cm 2 ) and the electrodeposited zinc layer is compactly coated with titania particles, * the required porous structure of the adsorbed titania layer is obtained at < 20 wt.% and pH < 3 where the first zinc layer is still visible. This is an essential requirement for the anchoring and fixation of the titania particles on the first electroplated zinc layer by the application of a second electroplated thin zinc over-layer and their subsequent embedding during the passivation process [8]. Lowering the pH value and solid concentration of the suspension enables to control the particle content in the passivation layer and to adjust the corrosion resistance to specific requirements of different applications [8,9].…”

“…This is an essential requirement for the anchoring and fixation of the titania particles on the first electroplated zinc layer by the application of a second electroplated thin zinc over-layer and their subsequent embedding during the passivation process [8]. Lowering the pH value and solid concentration of the suspension enables to control the particle content in the passivation layer and to adjust the corrosion resistance to specific requirements of different applications [8,9].…”

“…An alternative procedure is to adsorb the hard particles directly onto the electroplated zinc layer by a simple dip-coating technique within an aqueous suspension, followed by an electroplated thin second zinc-layer embedding the hard particles with a sub-sequent top-coat and a final passivation [8,9]. This would eliminate the problem of strong agglomeration in highly ionic environments, facilitate a controlled entrapment of hard particles into hexavalent chromium free conversion layers of electrodeposited zinc coatings.…”

Impact of high‐velocity oxy‐fuel sprayed TiAlN surface coating on mechanical and slurry erosion performance of aluminium alloys

“…The most promising approach achieving wear resistant material is surface coating. In the last few decades, various surface coating techniques have been developed to improve the performance of materials [4][5][6][7][8][9]. In these techniques, high-velocity oxy fuel has received significant consideration worldwide due to its wide applications.…”