Synthesis and characterisation of Ni–B/Ni–P–CeO2 duplex composite coatings

Abstract

Binary (Ni–B, Ni–P) and duplex coatings (Ni–B/Ni–P, Ni–B/Ni–P–CeO2) with an inner Ni–B layer were electrodeposited on mild steel substrates. A comparison of the structural, surface, mechanical, and electrochemical properties of the coatings is presented to demonstrate the mechanical behaviour and corrosion protection performance. Scanning electron microscope and atomic force microscope images showed that Ni–B/Ni–P–CeO2 duplex coatings had a well-defined nodular structure compared to Ni–P coatings, and fewer surface defects compared to Ni–B and Ni–B/Ni–P duplex coatings. However, these coatings had high surface roughness owing to the presence of CeO2 ceramic particles. X-ray diffraction analysis revealed that Ni–B coatings were crystalline but Ni–P and Ni–B/Ni–P–CeO2 coatings exhibited an amorphous structure. Ni–B/Ni–P–CeO2 coatings exhibited superior hardness (15%) compared to Ni–P and Ni–B/Ni–P duplex coatings. Potentiodynamic polarisation results confirmed that Ni–B/Ni–P–CeO2 duplex coatings had superior corrosion protection efficiency (91%) compared to Ni–B (30%) and duplex Ni–B/Ni–P coatings (77%). The novel Ni–B/Ni–P–CeO2 duplex coatings demonstrated superior mechanical and promising anti-corrosion properties, which render them attractive for various applications.