Influence of Heat Treatment on Crystal Structure, Microhardness and Corrosion Resistance of Bilayer Electroless Ni-P-SiC/Ni-P-Al 2 O 3 Coatings

Purpose Improvements in physical and mechanical properties of structures are essential for industrial applications. Electroless coatings are among the most suitable choices for this purpose. To improve the surface properties of mild steel, such as microhardness and resistance to corrosion, Al 2 O 3 and SiC nanoparticle-reinforced multilayer Ni-P coatings were fabricated using an electroless surface coating technique. Methods Al 2 O 3 and SiC-added duplex Ni-P coatings were developed using dual electroless baths containing Al 2 O 3 and SiC nanoparticles individually. Scanning electron microscopy with energy-dispersive spectrometry and X-ray diffraction were used to examine the morphology, elemental composition, and coating structure. The microhardness of the deposits was examined using a Vickers hardness tester. The corrosion protection ability of the coatings was analyzed by performing potentiodynamic polarization studies in a 3.5% NaCl solution. Results The experimental results showed that among the samples analyzed in this study, a bilayer coating with Ni-P-SiC as the external layer provided the highest microhardness. The Ni-P-Al 2 O 3 outer layered duplex coating offers the maximum resistance to corrosion owing to the higher electrochemical resistivity of the Al 2 O 3 particles. The thermal process performed at the optimized temperature of 400 °C enhanced the coating properties owing to crystallization. Conclusions Duplex coatings with high hardness and good corrosion protection have a broad range of applications.