Study On The Structure And Properties Of Electrical Brush Planting Ni-P/Al₂O₃ Coating Aftering Heat Treatment

The main forms of failure of materials are corrosion and wear. Nano-composite brushplated coatings can not only protect the surface of the substrate material, but also improve itswear and corrosion resistance. So nano-composite brush plating technique has far-reachingapplication. This paper is mainly concentrated upon fabricating Ni-P/Al₂O₃ compositecoatings on the Q235 steel substrate using brush plating method, determining the surfacemorphology of the composite coatings and investgating the effect of heat treatment to thestructure, wearing and corrosion resistance. The conclusions are summarized as follows:1. The surface morphology of Ni-P coatings is cell-like and uniform, but the surface ofNi-P/Al₂O₃ composite coatings shows uneven cauliflower-liked morphology. Obvious defectswere not found in the Ni-P/Al₂O₃ composite coatings which present a uniform thickness andtightly bonded to the substrate.2. Hardness, wearing and corrosion resistance of the Ni-P/Al₂O₃ composite coatings arebetter than those of Ni-P alloy coatings due to the addition of hard nanoparticles of Al₂O₃.3. The Ni₃P phase in a small size is precipitated from Ni-P/Al₂O₃ composite coatingsafter the heat treatment of 300℃. The grain boundary has gradually become blurred after 450℃heat treatment, while the size of Ni₃P grain becomes bigger, and the effect of dispersionstrengthening decreases after 500℃heat treatment.4. The Ni-P/Al₂O₃ composite coatings made in 30g/L Al₂O₃ solution are a mixture ofmicrocrystalline Ni-P solid solution and amorphous Ni-P. After 300℃ 450℃heat treatment,sharp peaks in the XRD pattern of the coatings confirm that in the coatings crystallization ofthe amorphous Ni-P has taken place. After 450℃⁶00℃heat treatment, the main phases ofthe coatings are composed of the crystalline Ni-P and Ni₃P, represented by their very sharpdiffraction.5. The hardness of the coatings is affected by the heat treatment. The coatings show a maximum hardness (HV1400) when the heat treatment temperature reached 450℃. All of thecoatings reached their highest hardness at 1h holding time for different heat temperature.6. The hardness, wearing resistance and binding strength of the Ni-P/Al₂O₃ compositecoatings are improved after heat treatment, while the corrosion resistance is reduced.