Wear Performance and Corrosion behavior Investigation of Cr-TiO2 nanocomposite coatings

In this paper, Cr-TiO2 nanocomposite coatings with various contents of TiO2 nanoparticles were prepared by electroplating method on low carbon steel substrate from St.37 plate substance. The nanocomposite coatings were obtained by codeposition of TiO2 nanoparticles with the average particle size of 21 nm, 99.5% purity degree and anatase crystal structure prepared from Evonik Company with Chromium during plating process. The coating thickness average was 30 μm on low carbon steel substrate from St.37 plate substance. The influences of the TiO2 nanoparticles concentration in the plating bath,the current density and the stirring rate on the chemical composition of Cr-TiO2 nanocomposite coatings were investigated. The surface morphology and composition of coatings was investigated by scanning electron microscope (SEM) with energy dispersive analyzer system (EDX). The wear behavior of the pure Chromium and Cr-TiO2 nanocomposite coatings were evaluated by a pin-on-disc tribometer and The worn surface of coatings was observed using a scanning electron microscope (SEM). The electrochemical behavior of the coatings in the corrosive solutions such as 0.5M NaCl, 1M NaOH and 1M HNO3 was investigated by potentiodynamic polarization method at 25±1 °C temperature. It was found that The Cr-TiO2 nanocomposite coating surface morphology is smoother, more uniform and compact surface in appearance compare to that of pure Chromium coating and The codeposited TiO2 nanoparticles were uniformly distributed in the Chromium matrix. The microhardness and wear resistance of the nanocomposite coatings increase with increasing of TiO2 nanoparticles content in the coating. The worn surface morphologies show that the Cr-TiO2 nanocomposite coatings exhibit less abrasive width and depth and less tendency for plastic deformation when compare to that of pure Chromium coating. It is obvious that with increasing of TiO2 nanoparticles content in coating, the corrosion current density decreased and the corrosion potential of the coatings shifted to more positive potential values in 0. M NaCl and 1M NaOH solutions. Also, The Polarization resistance (Rp) increased with increasing of TiO2 nanoparticles content in coating. As Cr-8.3wt.%TiO2 nanocomposite coating polarization resistance in 0.5M NaCl and 1M NaOH solutions reached to 3.954 and 5.631 MΩ.cm2 respectively. It can be concluded that the codeposited TiO nanoparticles in Chromium matrix of coating increase the corrosion resistance and decrease the corrosion rate in salty and alkaline solutions. In anodic region of polarization curves of pure Chromium coating and Cr-TiO2 nanocomposite coatings in 1M HNO3 solution, Passive layer formation is observed. Passive layer formation current density of Cr TiO2 nanocomposite coatings (about 0.02A/cm2) is less than that of pure Chromium coating (about 0.03A/c 2). On the other hand, passive layer formation potential of Cr-TiO2 nanocomposite coatings (about 288mv) is more negative compare to that of pure Chromium coating (about 478mv). It can be concluded that presence of Ti 2 nanoparticles in Chromium matrix of coating aids to formation of passive layer. The passive current density of Cr-TiO nanocomposite coatings (about 10-4A/cm2) is more than that of pure Chromium coating (about 10-5 A/cm2). It means that passive layer corrosion rate of Cr-TiO2 nanocomposite coatings is more than pure Chromium coating because of The presence of TiO2 nanoparticles in the coating surface disturbs the continuity of nanocomposite coating passive layer and accelerates the destruction of passive layer which causes to increasing of corrosion rate. It can be concluded that Cr-TiO2 nanocomposite coatings is not a proper coating in HNO3 solution.