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Preparation and Properties of Functional Composite Coatings Embedded ZrO2 Ceramic Particles

Author: TanMingFeng
Tutor: SunWanChang
School: Xi'an University of Science and Technology
Course: Materials Processing Engineering
Keywords: Composite Coatings Micrometer-or Nanometer-sized ZrO2 Microhardness Wear Resistance High Temperature Oxidation Resistance
CLC: TG174.4
Type: Master's thesis
Year: 2011
Downloads: 53
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Abstract


Composite coating is a new kind of composite materials with special function, which has excellent characteristics of the metal matrix as well as special features scattered particles. In this paper, Ni-P-ZrO2 microcomposite coatings and Ni-ZrO2 nanocomposite coatings were prepared on low carbon steel （Q235） substrates by electrolessdeposition and electroplating. The effects of ZrO2 concentration in bath and stirring rate on properties of composite coatings were studied. And the optimal ZrO2 concentration in solution was fixed. The surface and cross-sectional micrographs of the composite coatings were observed with optical microscope and scanning electron microscopy （SEM）. And the chemical composition and phase transformation of composite coatings were analyzed with energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. It was shown that a relatively uniform concentration of ZrO2 particles along the cross section of electroless Ni-P-ZrO2 composite coatings, and the continuous and uniform composite coatings with about 55μm of thickness showed good adhere to substrate. The structure of Ni-P-ZrO2 composite coatings as deposited was amorphous. When the ZrO2 concentration in solution ascend to 9g/L, particles content in coating and deposition rate reached the maximum, 14.3wt.% and 21.2μm/h, respectively. The presence of ZrO2 particles can enhance significantly microhardness、corrosion resistance and wear resistance performances of Ni-P alloy. After heat-treated, the matrix of composite coatings crystallized into nickel crystal and nickel phosphide（Ni3P）, which result in an increase in the coating hardness, with a maximum hardness and excellent tribological behavior being achieved after annealed at 400°C.The effects of different kinds of dispersants on nano-ZrO2 composite electroplating bath as well as effects of stirring means in plating process on dispersion of nano-ZrO2 in composite coatings were studied. It was shown that the ZrO2 suspension which was added to the dispersant 752W with complex structure had better dispersion and stability. The mechanical stirring+intermittent ultrasonic had obvious stirring scatteredrole,strengthen and promoting role and refining the nickel grains. The oxidation resistance of the coatings was discussed by their weight gains in a muffle furnace. It was shown that the products of nanocomposite coatings consist of NiO with trait of small plane after high temperature oxidation over 800°C. These NiO which linked to each other to form a dense oxide film played a very good protection to the substrate. The reason why the Ni-ZrO2 nano-composite coatings can improve the high temperature oxidation resistance maybe that the rate-controlling Ni2+ diffusion along short-circuit paths is blocked by embedded nano-ZrO2 particles that originally existed in the Ni-ZrO2 nanocomposite coatings, which exerted a reactive-element effect on the growth of NiO scales on the composite coatings. What is more, the disperation of ZrO2 particles in the Ni-P matrix reduces the effective area of Ni alloy contacting with ambient oxygen, thus significantly decreasing weight grains of the composite coating. In addition, oxide layer grain size of nanocomposite coatings was smaller as compared with pure nickel coating, which can greatly enhance the deformation rate. During the circulating oxidation process, oxide layer of nanocomposite coatings can be released by the diffusion creep thermal stress. The growth of NiO layer was formed through the O2- inner diffusion （oxidation initially may be caused by some O2-） from the surface to the internal nanocomposite coatings.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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