Wear and Corrosion Resistant Coatings

We report the synthesis and characterization of two different types of Ni-based laminated composites (Types I and II). In Type-I composites, layers of Ni and Ti₃SiC₂ (Ni–Ti₃SiC₂) were interleaved with Ni, whereas in Type-II composites, Ni–Ti₃SiC₂ layers were interleaved with Al and Ni. The laminate thickness and Ti₃SiC₂ content in the individual Ni–Ti₃SiC₂ layers were systematically varied in both the composites. Detailed SEM studies showed that Ti₃SiC₂ particulates are well distributed in the Ni-matrix with little or no interfacial reactions with interparticle porosity. However, there were interfacial reactions between Ni and Al in Type II composites. In general, Type I multilayered composites had higher ultimate compressive strength (UCS) in parallel orientation as compared to perpendicular orientation (layers are aligned parallel or perpendicular to the wear surface then it will be referred to as parallel or perpendicular orientation). Comparatively, in Type II composites, the UCS was greater in perpendicular orientation as compared to parallel due to the presence of Al layers as bonding layers. Both the composite designs showed triboactive behavior against alumina disks and sensitivity to laminate thickness and orientation. In Type-I composites, the decrease in µ and wear rate (WR) with laminate thickness was more pronounced in the perpendicular orientation as compared to the parallel orientation. Comparatively, Ni–Ti₃SiC₂/Al/Ni composites showed that the parallel orientation was more effective in enhancing the triboactive performance. SEM analysis of tribosurfaces showed signs of triboxidation and abrasion, which led to the formation of O-rich tribofilms. Full article

Composite electrochemical coatings (CECs) are some of the most widely investigated coatings due to its versatility in tailoring physio-mechanical and tribological properties. The effectiveness of the CECs for tribological applications is dependent on the solid–liquid interfaces. The active and passive nature of the contact boundaries for a CEC with a solid/liquid interface is defined by the surface energy of these boundaries. Unless the effect of surface energy on the tribological properties of the CEC are understood, it is not possible to get a holistic picture on properties, such as corrosion and tribocorrosion. The present study investigates the surface energy of optimized nickel (Ni) and Ni–graphene (Ni–Gr) coatings and their effect on the dynamic friction and wear behavior. It was found that the addition of Gr to the Ni coating in small quantities could decrease the polar component of surface energy significantly than the dispersive component. The presence of Gr in the coating was able to reduce the wear while providing low friction. The Ni–Gr coating exhibited low surface energy that includes weak adhesive forces, which can prevent embedding of the wear particles during sliding. Full article