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.