Composition, characteristics and tribological behavior of Cr, Co–Cr and Co–Cr/TiO2 nano-composite coatings electrodeposited from trivalent chromium based baths

Abstract

Cr, Co–Cr and Co–Cr/TiO2 nano-composite coatings were electrodeposited from Cr(III) based electrolytes onto 316L SS substrates. The effects of TiO2 nano-particles concentration on co-deposition of these particles along with Cr content and microhardness of the coatings were investigated. Morphology and structure of the Cr, Co–Cr and Co–Cr/TiO2 coatings besides their tribological behavior were studied, and the results were compared to the substrate. The results showed that co-deposition of TiO2 nano-particles and chromium content of the coatings increased with enhancing particles concentration in the bath. Microhardness of Co–Cr and Co–Cr/TiO2 coatings were improved by increasing their Cr and TiO2 content, respectively. However, the presence of more than 3wt.% TiO2 in the composite films had a negligible effect on microhardness of these samples. All the coatings had nodular morphology and contained microcracks. Nodules sizes and the number of microcracks in the alloy and composite coatings were lower than the Cr film. The structure of the Co–Cr and Co–Cr/TiO2 coatings were crystalline, while it was amorphous for Cr film. Wear results revealed that the Co–29.1Cr/3.0TiO2 coating had the lowest wear loss and coefficient of friction between all the samples. The wear resistance of the Co–29.3Cr coating was better than the substrate, while Cr film had the worst wear resistance. According to SEM micrographs from the worn surface of the samples, abrasion was the main wear mechanism in 316L SS substrate, as well as in the Co–29.3Cr and Co–29.1Cr/3.0TiO2 coatings. However, limited adhesion also occurred on the worn surface of the substrate. Detachment of Cr from the wearing surface during the sliding resulted in higher volume losses in this sample.