Tribo-Corrosion Wear Mechanisms of NiTiNOL60 Alloy in Aqueous Sodium Hydroxide

The vast applications of NiTi-based alloys in engineering and biomedicals follow their good mechanical and excellent corrosion properties. In most applications, these materials are exposed to aggressive conditions, leading to surface deterioration due to the combined actions of mechanical and chemical activities. This synergistic interaction under sliding wear contact and applied electrochemical potential informed the choice for this study. The experimental investigation involved coupling a linear reciprocating ball-on-plate tribometer to an electrochemical potentiostat cell of 3-electrode configuration. This allowed the reciprocating sliding of a counter material (alumina ball – Al 2 O 3 ) against the exposed surface area, 2 cm 2 of NiTiNOL60 alloy fully submerged in a 0.05 M NaOH medium. The unexposed surfaces were coated with a plasti-Dip adhesive to create an additional layer that ensures the isolation/ non-interference of the surfaces during electrochemical measurements while protecting the underlying material from corrosion attacks. The tribo-electrochemical actions at room temperature created a wear groove and deformations along the stroke length. Surface characterization techniques such as optical microscope, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and stylus profilometry were used to examine the resulting wear tracks. Our findings revealed surface and microstructural deformations alongside the various wear mechanisms, including abrasion, adhesion, localized corrosion, and plastic deformation. While the mechanical action due to the sliding contact resulted in grain elongation perpendicular to the sliding direction, the electrochemical activity at the anodic and cathodic polarizations showed that passive film dissolution is dependent on the corrosion potential. The continuous reciprocating sliding promoted accelerated corrosion and the material wear rate at higher loading conditions. This increased the depassivation rate and the oxidation concentration within the wear track, thereby promoting localized corrosion (pits, cracks and crevices) at the sliding interface. The findings from our analysis depict that both mechanical and electrochemical interactions strongly influence the tribocorrosion wear mechanisms of NiTiNOL60 alloy in a corrosive medium.