Electroless plating of Ni-P coatings on carbon steel in a stirred bed of glass balls

The electroless plating of Ni-P coatings was carried out in a stirred plating solution containing a bed of glass balls with a fixed stirring rate of 1,800 rpm. The diameters of the glass balls were 2 and 3 mm and the total weight of the balls was ~200 g; the weight ratio of the 2 mm to the 3 mm balls was 3:2. The as-deposited Ni-P coating was composed of fine polycrystalline Ni grains and had a smooth appearance. The hardness and corrosion resistance of the novel coatings were considerably improved compared with the conventional electroless (CE)-plated amorphous Ni-P coatings. After heat treatment at 400 °C for 1 h, cracks occurred in the CE-plated Ni-P coating, while no cracks appeared in the mechanically assisted electroless (MAE)-plated Ni-P coating. These improved properties of the MAE-plated Ni-P coatings demonstrate the advantages of this novel technique, which may find wide application in industry.