Investigation of the surface properties of heat treated electroless Ni-P coating

Electroless nickel phosphorus (Ni-P) coatings were synthesised from an acid chloride electrolyte. The synthesised coatings were heat treated at different temperatures, and the surfaces of the heat treated coating were characterised using scanning electron microscopy and X-ray diffraction. Adhesion, wettability, hardness and corrosion behaviour of the coatings were measured. The surface morphology showed the formation of a nano crystalline nickel matrix under heat treated condition. X-ray diffraction analysis of the heat treated samples revealed the recrystallisation of nickel and formation of Ni3P phase in the coatings. The wettabilty study showed that the as-deposited Ni-P coating is hydrophobic and wettability increases to a maximum of 70.8 degrees contact angle for heat treated temperature of 400 degrees C due to nano crystalline formation. The Rockwell C adhesion test revealed the presence of micro cracks with increase in heat treatment temperature, however the failure is within the acceptability limit. The micro hardness of the Ni-P coating increased with increase in heat treatment temperature. Corrosion potential of the Ni-P coating shifted to a positive potential under heat treated conditions owing to oxidation and precipitation of Ni3P phase. Decreased corrosion rate and corrosion current density (7.37-0.21 mu A cm(-2)) is attributed to heat treatment at 400 degrees C.