Electroless Ni-P/SiC Nanocomposite Coatings With Small Amounts of SiC Nanoparticles for Superior Corrosion Resistance and Hardness

Abstract

The addition of silicon carbide (SiC) nanoparticles into electroless nickel (Ni)-based coatings improves both corrosion resistance and mechanical properties of the resulting Ni-P/SiC nanocomposite coatings, making them potential candidate as protective coatings in aggressive environments. Ni-P/SiC nanocomposite coatings were produced from precursor bath with small SiC loading levels (0.25 or 1.0 g/L) and characterized for morphology, corrosion resistance, and hardness. Microstructural examination using FE-SEM and AFM revealed that incorporation of uniformly dispersed SiC nanoparticles leads to smaller nodule size with fine-grain structure and low surface roughness. Electrochemical impedance spectroscopy studies in 4 wt.% NaCl solution showed that the nanocomposite coatings exhibit excellent corrosion resistance, as indicated by high charge-transfer resistance and low double-layer capacitance values of ~137 kΩ cm2 and 19 µF cm−2, respectively. The coatings maintained their structural integrity even after 5 days of saline bath immersion, as there was no cracking in the deposit microstructure besides formation of shallow pits and submicron-sized pores. A two-fold increase in the average hardness value was noticed from 4.5 (pure Ni-P) to 8.5 GPa (Ni-P/SiC coating) which can be ascribed to modified deposit morphology and uniformly dispersed SiC nanoparticles that act as obstacles to plastic deformation.