CORROSION BEHAVIOR OF STEEL COATED WITH AN NI-P/PVD HYBRID LAYER

The corrosion behaviour of steel samples coated with a hybrid layer consisting of an ion-plated TiN coating and an electrolessly deposited Ni-P interlayer was investigated by electrochemical corrosion measurements and the salt spray test. Various deposition temperatures were used during the PVD process to maintain the amorphous structure of the Ni-P interlayer. The protection of the samples against pitting corrosion could be improved by the Ni-P interlayer. A heat treatment of the Ni-P-plated substrate is recommended before low temperature PVD coating to remove remnants of the plating solution which might lead to outgassing and spalling of the coating. Only slight differences in the corrosion behaviour were found between substrates coated at different deposition temperatures. Thus it was concluded that the improved corrosion protection of the hybrid layer is mainly due to the increased layer thickness and hence the reduced coating porosity.