Study of Tribocorrosion Processes by Electrochemical Techniques

Résumé

Tribocorrosion is defined as the chemical-electrochemical-mechanical process leading to a degradation of materials in sliding, rolling or erosion contacts immersed in a corrosive environment. That degradation results from the combined action of corrosion and wear. The mechanism of tribocorrosion is not yet fully understood due to the complexity of the chemical, electrochemical, physical, and mechanical processes involved. Examples of the occurrence of tribocorrosion in service are the accelerated corrosion of steel conveyors exposed to ambient air of high relative humidity, the fall out of electrical connectors in the automotive industry, the degradation of hip prosthesis and dental fillers, the erosion wear of turbine blades, etc. The combined corrosion-wear degradation of materials in sliding contacts immersed in electrically conductive solutions is investigated in-situ by electrochemical techniques. Such techniques are the open circuit potential measurements, E_OC, the potentiodynamic polarization measurements, PD and the electrochemical impedance. Capabilities and present limitations of these techniques are discussed based on a tribocorrosion study of a cobalt chromium alloy hard coating (Stellite6) and stainless steel (304L) immersed in water-based electrolytes, namely aerated 0.5 M sulphuric acid, Ringer solution or cooling water reactor (12 ppm Li as LiOH+1000 ppm Boric Acid) and sliding against a corundum counterbody. Some novel insights into the tribocorrosion mechanism of active and passive materials are discussed. These in-situ electrochemical data provide insights into a possible synergism between corrosion and wear processes in sliding contacts. This paper concludes on the benefit of using different electrochemical analyzing techniques when investigating the behaviour of materials under corrosion-wear test conditions.