Characterization of Cr–ZrO2 composite coatings electrodeposited from Cr(III) bath

Abstract

The aim of this work was to incorporate ZrO 2 particles into a Cr matrix within the research work aimed at obtaining metal matrix composite coatings (CrZrO 2 ) under direct current and to evaluate their protective properties. A CrZrO 2 composite coating was deposited from an electrolyte based on trivalent chromium sulphate with formate-urea as a complexing agent containing various concentrations of ZrO 2 . Cross-section investigations have revealed that ZrO 2 particles incorporated into the Cr coating are uniformly distributed. The results indicate that ZrO 2 particles influence the microhardness, morphology and corrosion behaviour of Cr-ZrO 2 composite coatings obtained from the Cr(III) bath. Keywords: zirconium, electrodeposited films, SEM, XPS, EIS, interfaces INTRODUCTIONHard chromium electrodeposition is extensively used in modern industry as it provides good corrosion and wear resistances of the coatings obtained. Commonly, chromium coatings are deposited from hazardous hexavalent chromium baths. In view of a very high toxicity of Cr(VI) compounds, the development of an alternative hexavalent chromium plating process is urgently needed. According to the EU Regulation (EC) No. 1907/2006 the use of chromium trioxide baths for functional and decorative chromium plating will be forbidden or severely limited after 1 September 2017.Among many potential alternatives, trivalent chromium (Cr(III)) plating is considered as a very promising technology to replace conventional hexavalent Cr plating. Inasmuch as Cr coatings deposited in Cr(III) baths do not feature such good properties as Cr coatings deposited in Cr(VI) baths, efforts have been made to improve them by various methods.Electrochemical codeposition of inert particles in a metal matrix is a suitable technique to produce composite materials with new exploitation properties. Different hard dispersion phases distinguish themselves for different electrical conductivity and surface charge, therefore, to incorporate one or another hard disperse phase into a metallic matrix, specific deposition conditions are required [1].One of popular ceramic particles is ZrO 2 . It is known [2,3] that ZrO 2 has many superior properties, such as high G. Bikulčius, A. Češūnienė, A. Selskienė, A. Grigucevičienė, V. Jasulaitienė The aim of this work was to form a Cr(III)-ZrO 2 composite in an environment-friendly Cr(III) bath under the conditions of constant current and to study the incorporation of ZrO 2 disperse particles into the Cr matrix, the elemental composition of the Cr-ZrO 2 composite, surface microhardness (HV), surface morphology (SEM, XPS) and corrosion resistance (OCP, Tafel and EIS). EXPERIMENTALCr-ZrO 2 composite coatings were deposited from the Cr(III) bath containing Cr 2 (SO 4 ) 3 6H 2 O (150 g l -1 ), H 3 BO 3 (30 g l -1 ), Na 2 SO 4 (60 g l -1 ), Al 2 (SO4) 3 18H 2 O (120 g l -1 ), NaF (20 g l -1 ), HCOONa (27 g l -1 ), NH 2 COONH 2 (g l -1 ) under a 30 l h -1 agitation flow of compressed air with a direct current density of 0.2 A cm -2 and pH 2.0 at 20°C. This...