Electroless NiP–TiO2 composite coatings: Their production and properties

Composite coatings of modified amorphous nickel were prepared by simultaneous electroless deposition of NiP and TiO2 on brass, from a solution in which TiO2 particles were kept in suspension by stirring. Following short-term heat treatment in a high vacuum, the plating acquires chromium equivalent hardness. The deposit surfaces were studied by SEM, profilometry and Vickers microhardness and its structure by X-ray diffraction. The fabricated composite materials were tested under corrosion conditions by linear polarization measurements. The results show that after the heat treatment in a high vacuum for a very short time (10 min) the deposits acquire a crystalline microstructure, with very good adhesion to the substrate. In addition, the microhardness of vacuum heat-treated particle-free NiP coatings attained values of 1200 HV, while the composite NiP–TiO2 coatings acquired an even higher microhardness, exceeding 1450 HV. The corrosion resistance of the fabricated composite layers after heat treatment remained almost unaffected.