Preparation And Properties Of Ni-W-ZrO₂Composite Coatings

Amorphous composite coatings, with excellent general physical and chemicalcharacteristics due to its special structure, have aroused great attention in recent years. Withthe development of modern industry, Functional Gradient Material has become one of thenew materials. The consistency of FGM’s internal structure and component can enhance thebonding strength between coating and substrate, therefore improve the corrosion resistanceand wear resistance. In the process of composite electrodeposition, Rare earth can improve theproperties of plating bath, purify the interface, enhance the quality of the coating due to itsfavorable physical, chemical, electrical, magnetic and optical properties. Re has beensuccessfully applied in electrodeposition, hot dip galvanizing, conversion coating andchemical heat treatment and surface treatment.In this paper, crystalline, amorphous and gradient Ni-W-ZrO2composite coatings wereprepared by electrodeposition, based on LY12duralumin alloy substrate. In the condition ofoptimal concentration of ZrO2particles and the Rear earth being fixed, by means of scanningelectron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction(XRD),microhardness, corrosion tests, the friction and wear test and oxidation weighing, themicrostructure, component, hardness, corrosion resistance, wear resistance andhigh-temperature oxidation resistance of the composite coatings were analyzed. The resultsshowed that Ni-W-ZrO2composite coatings reached the best hardness and wear resistancewhen the ZrO2concentration in solution ascended to40g/L. Meanwhile, the Ni-W-ZrO2composite coatings showed the best corrosion resistance when Rear earth, the concentrationof which was1.5g/L, was added into the solution.The structure and properties of Ni-W-ZrO2composite coatings is closely related to thecontent of W deposited in coatings. The amorphous and gradient Ni-W-ZrO2composite coatings were prepared when the temperature of the solution and the concentration ofNa2WO4in solution were adjusted appropriately. It was proved that the Ni-W-ZrO2compositecoatings have presented amorphous state when ωW＞44%in composite coatings from theresults of energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). AmorphousNi-W-ZrO2composite coating is the type of substitutional type solid solution which the nickelis solvent and the tungsten is solute. The content of W in gradient Ni-W-ZrO2compositecoating increases gradually along the growing direction, and the composite coatings graduallytransit from crystalline to amorphous structure which distribute as continuous gradient. Thestudies showed that the degree of crystallization of the composite coating had been enhanced,and the structure of the composite coating transited from crystalline state to amorphous statewith the crystallization of Ni4W after400℃heat-treatment. Subsequently, the hardness, thecorrosion resistance and the abrasive resistance of the composite coatings were improved.Thegradient Ni-W-ZrO2composite coatings can enhance the adhesion strength between thecoating and substrate, further improve the corrosion resistance and abrasive resistance due toits special structure.