External authors:

• Dennis Konopka ( Leibniz University Hannover )
• Ricardo Crespo Martins ( Leibniz University Hannover )
• Mareike Dukat ( Leibniz University Hannover )
• Florian Pape ( Leibniz University Hannover )
• Kai Mohwald ( Leibniz University Hannover )
• Gerhard Poll ( Leibniz University Hannover )

Abstract:

Solid lubricant coatings are essential for reducing friction and wear in tribo-mechanical systems, particularly in environments where traditional liquid lubricants can't be used or fail. It has been reported in literature that self-regenerating physical vapor deposition (PVD) coatings can be designed in such a way that they continuously release MoO3 as a solid lubricant through tribo-oxidation. However, a disadvantage of PVD coatings is the limited layer thickness of just a few micrometers and thus the limited solid lubricant reservoir. In contrast, atmospheric plasma spraying (APS) allows the deposition of thicker reservoir layers, potentially extending service life under tribological stressing. Therefore, the aims of this study are to determine whether APS coatings with regenerative properties can be deposited on bearing steel and to assess their tribological performance. The mechanical, tribological, and structural behavior were analyzed using microindentation, ball-on-plate tribometer testing under dry conditions, optical and laser scanning, scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDX). Despite the relatively low hardness of the APS coating, excellent wear resistance protection was demonstrated at various loads and sliding velocities. Additionally, EDX analyses revealed that abrasive wear was prevented and a protective film was formed through tribo-oxidation, effectively shielding the surfaces. The results thus indicate the effectiveness of the APS coating and underline its potential for large-scale machine elements, such as rolling bearings.