Deposition and properties of electroless Ni–P–B4C composite coatings

The present article investigates and compares factors affecting the process of electroless deposition of Ni–P and Ni–P–B4C composite coatings. The process of autocatalytic–catalytic reduction of Ni in nickel sulfate and sodium hypophosphate solution with B4C suspended particles has been employed in the formation of the electroless Ni–P–B4C composite coatings. The concentrations of 1, 2, 4 and 8 g/l of B4C in bath were used and resulted in Ni–P–B4C electroless coatings with 12, 18, 25, 33 vol.% of B4C. Techniques such as SEM, EDAX, optical microscopy and micro-hardness testing were employed to investigate the effect of factors such as thickness, deposition rate and heat treatment cycles on coating properties. Experiments also showed that an increase in the percentage of the particles in the coating, increases hardness. Heat treatment of the electroless composite coatings with 33 vol.% of B4C at 400 °C for 1 h in an Argon environment, increased the hardness by 1400 HV.