Effect of Current Density on the Microstructure and Adhesion of Ni-Co/Al 2 O 3 Composite Coatings

Abstract

Ni-Co/Al 2 O 3 composites with alumina particles below 0.53 µm in size were electrochemically deposited on carbon steel AISI-O1 substrates. The influence of current density (2, 3, 4 and 5 mA/cm 2 ) on the microstructure and adhesion behavior was investigated. It was found that the micro-hardness of the surface increased in 90% with respect to the plain substrate. SEM examination revealed an increased thickness from 3.7 to 10.7 µm at current density of 2 and 5 mA/cm 2 , respectively. The Co/Ni weight ratio in the coatings was determined by atomic absorption spectroscopy (AAS); the content of Co and Ni at 2 mA/cm 2 were 42.4 %Co and 57.6 %Ni, while at 5 mA/cm 2 were 44.5%Co and 55.5%Ni. The adhesion of the coatings was evaluated qualitatively according to the VDI 3198 norm; in all the cases, the adhesion was more than acceptable since no cracks or detachments were observed in the periphery of the marks. Details on the synthesis and properties of the Ni-Co/Al 2 O 3 composite coatings are presented together with the excellent properties they show despite of their thin thickness.