Electrodeposition and thermal treatment of nickel layers containing titanium

Composite Ni+Ti layers were prepared by simultaneous electrodeposition of nickel and titanium on a steel substrate from a nickel bath in which 40 g dm(-3) of Ti powder was suspended by stirring. The presence of NaH2PO2 in the bath allows to obtain the Ni-P+Ti layers. The electrodeposition was carried out under galvanostatic conditions at a temperature of 343 K and at a current density of j(D)=0.1 A cm(-2) for 0.5 h. The phase composition of the layers was investigated by the X-ray diffraction method. Chemical and phase analysis of the layers confirm the composite character of amorphous or crystalline layers containing titanium. It means that in the process of nickel electrodeposition titanium powder grains have been built into crystalline or amorphous nickel matrix. The layer Ni+Ti contains up to 25% of Ti. The presence of NaH2PO2 in the bath reduces the content of embedded Ti in the Ni-P+Ti layer to about 17%. It was assumed that the mechanism of Ti embedding into the layer is based on the adsorption phenomena and migration of the charged solid particles towards the cathode. Thermal treatment of the layers in nitrogen atmosphere was done at temperature of 1093 K for 24 h. The surface morphology of the coatings was examined by means of a microscope with a morphometric computer system. On the basis of morphometric analysis the percentage volume fraction of selected TiN phase in Ni+Ti and Ni-P+Ti layers was determined. Additionally, the microhardness of the obtained coatings was determined. (C) 2002 Elsevier Science B.V. All rights reserved.