There is an increasing concern over simultaneous wear and corrosion (tribocorrosion) issues that cause the material failure of stainless steel in marine environments. The main objective of this study is to understand the effect of tribocorrosion conditions on pitting susceptibility and synergistic material loss for AISI 304 stainless steel. For this purpose, tribocorrosion tests were conducted in a natural seawater-filled corrosion cell integrated with a tribometer. An alumina ball of 6 mm radius slid against AISI 304 stainless steel plates under 5 N and 7.5 N loads in natural seawater. The cyclic polarization scans were carried out under corrosion and tribocorrosion conditions in the natural seawater by applying different loads. Also, tribocorrosion tests were conducted under anodic (0.3 V), cathodic (−0.5 V) and Open Circuit Potential (OCP) to determine the effect of electrochemical potential on pitting susceptibility and material loss rate. The study revealed that electrochemical potential significantly affects pitting corrosion and material loss, and the material losses increased significantly from the cathodic potential to the anodic potential. Furthermore, the material loss of AISI 304 alloy during tribocorrosion in natural seawater due to corrosion was significantly lower than wear. The wear-corrosion synergism played an essential role in total material loss, confirming that wear and corrosion affect accelerated material loss positively. The material loss of AISI 304 is mainly due to pure mechanical wear and corrosion-induced wear.
CrN, TiN and AlTiN coatings were applied by the Physical Vapour Deposition (PVD) method on AISI 4140 and plasma nitrided (PN) AISI 4140 steel. The study aimed to investigate the effect of plasma nitriding before PVD on the corrosion and tribocorrosion behaviour of AISI 4140 steel in seawater. The electrochemical corrosion behaviour of the samples was evaluated in natural seawater by the potentiodynamic polarisation method. Tribocorrosion tests were performed against alumina in natural seawater under 5 N load and open circuit potential (OCP) using a ball-on-disk tribometer coupled with an electrochemical cell. As a result of the study, plasma nitriding applied before the coating significantly improved corrosion and tribocorrosion resistance of PVD CrN, TiN and AlTiN coatings. Besides, it was concluded that duplex treated low alloy AISI 4140 steel could be a candidate instead of stainless steel in tribocorrosion conditions for the marine environment.
The safety of mooring systems and accessories is one of the most critical issues in the structural integrity of floating oil/gas and renewable offshore structures. Mooring chains and accessories operate under dynamic conditions in harsh marine environments. They are subject to severe wear and corrosion between their links due to relative movement from waves, wind, and ocean currents that disrupt structural integrity. To cope with this problem, the pack-aluminizing process was applied on the R4 grade offshore mooring chain steel for 2 h at 850 °C to improve corrosion and wear-corrosion (tribocorrosion) resistance in 3.5% NaCl. The tribocorrosion behaviour of untreated and aluminized samples was investigated by a tribo-electrochemical setup that simultaneously allows for collecting the wear and corrosion data. Potentiodynamic and potentiostatic corrosion and tribocorrosion tests were carried out to understand corrosion kinetics. Optical, SEM, XRD and EDS analyses were performed to characterize the aluminide layer and surface morphologies before and after tribocorrosion investigations. In polarization scans under corrosion and tribocorrosion conditions, the current showed a significant activation stretch of several orders of magnitude, with minor potential changes in the anodic region. Due to the galvanic effects of sliding under natural electrochemical conditions, the untreated R4 alloy exhibited cathodic properties in the wear track, while the aluminium coating was out of the wear track due to its oxide-forming ability. At the cathodic potential, two hard Al2O3 materials under pure mechanical effects and third bodies emerging from cracks on the coating surface increase the friction coefficient (COF), while the oxide product film, which has a lubricating ability and pits which reduces the contact area, caused a decrease in COF at the high anodic potential. The study revealed that while the aluminide layer improved the corrosion and tribological character of R4 alloy, material loss from wear track increased due to micro fractures and cracks in the coating layer during sliding tribocorrosion conditions.
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