Investigation of anti-corrosion properties of Ti:C gradient layers manufactured in hybrid deposition system

Excellent properties of hard carbon layers and especially, the unique combination of tribological, chemical and physical properties make them a popular coating material for use on surgical prosthesis, biomedical implants, and machine tools. However, their well-known poor adhesion and high internal stress disqualifies them in many possibilities of industrial applications. These drawbacks were improved by deposition of Ti buffer layer. By a combination of Radio Frequency Plasma Assisted Chemical Vapor Deposition (RFPACVD) and DC magnetron sputtering methods, thick carbon films were manufactured on Rex 734 steel. Structure and chemical composition of deposited layers was determined by scanning electron microscope and energy dispersive spectrometer analysis. The main purpose of this work was to determine the corrosion properties of Rex 734 alloy in a typical 0.5 M NaCl solution and to find the influence of Ti:C gradient layers on these properties. Anti-corrosion behavior was measured by the detection of corrosion potential in open circuit and the registration of potentiodynamic characteristics according to Stern-Geary and Tafel methods. Five different types of samples were studied: for full analysis the investigation was conducted for every structural component of the layer: for pure Ti deposited on Rex 734 as well as for Ti containing carbon layer and carbon layer deposited subsequently, and finally the corrosion resistance of Rex 734 steel was measured for comparison. As a result of the investigation it was noticed that the Ti-C interlayer enables to maximize the thickness of DLC films and Ti:C gradient layers have the good influence on the corrosion features of Rex 734 alloy.