Partial dissolution of precipitated-calcium carbonate (P-CaCO3) in electroless nickel-phosphorus (Ni-P) coating and its surface characterization

Abstract

Nickel-phosphorus/precipitated-calcium carbonate (Ni-P/P-CaCO3) composite coating was prepared on mild steel using alkaline electroless coating process. The partial dissolution of P-CaCO3 in the Ni-P matrix and its influence on the surface morphology, surface hardness, phase structure, crystal size, lattice parameters, surface roughness, and friction - wear behavior was studied. The weight dispersion of P-CaCO3 is varied as 1.0 g l−1, 2.0 g l−1, 3.0 g l−1 and 4.0 g l−1 in the electroless Ni-P bath by keeping the bath parameters constant. Reduction in the size of P-CaCO3 particle from 2 μm to 1 μm after the shake-flask method confirms the partial dissolution of P-CaCO3. Calcium rich Ni-P matrix along with the P-CaCO3 particle was observed in the morphology of Ni-P/P-CaCO3 composite coating, which is distinguished with the actual NiP matrix. Formation of Ni3P and Ni12P5 phases was affected after the weight dispersion of P-CaCO3 from 2.0 g l−1 to 3.0 g l−1 in the bath. Ni-P/P-CaCO3 composite coating presented a lower hardness of 394 HV0.05 compared to the 511 HV0.05 of Ni-P coating. Hardness decreases with the increase in the weight dispersion of P-CaCO3 in the bath. However, the friction-wear resistance of Ni-P/P-CaCO3 composite coatings was improved considerably after the reinforcement of P-CaCO3. Restriction in the formation of Ni3P and Ni12P5 phases had caused a high material removal for the Ni-P/P-CaCO3 (3.0 g l−1) composite coatings. Various wear features in the wear track such as grooves, craters, and de-lamination were characterized and elaborated in this study.