Exploring the Impact of Spray Process Parameters on Graphite Coatings: Morphology, Thickness, and Tribological Properties

This study explores, through a full factorial experimental design, the effects of graphite concentration and spray flow rate on the morphology, thickness, and tribological performance of graphite coatings for potential tribological applications. Coatings were applied to rough substrates using varying concentrations and flow rates, followed by analysis of their morphological characteristics, roughness, thickness, coefficient of friction (COF), and wear behavior. The results revealed distinct differences in the coating morphology based on flow rate, with low-flow-rate coatings exhibiting a porous structure and higher roughness, while high-flow-rate coatings displayed denser structures with lower roughness. A COF as low as 0.09 was achieved, which represented an 86% reduction compared to uncoated steel. COF and wear track measurements showed that thickness was influential in determining friction and the extent of wear. Flow rate dictated the coating structure, quantity of transfer film on the ball, and the extent of graphite compaction in the wear track to provide a protective layer. SEM and elemental analysis further revealed that graphite coatings provided effective protection against wear, with graphite remaining embedded in the innermost crevices of the wear track. Low flow rates may be preferable for applications requiring higher roughness and porosity, while high flow rates offer advantages in achieving denser coatings and better wear resistance. Overall, this study highlights the importance of optimizing graphite concentration and spray flow rate to tailor coating morphology, thickness, and tribological performance for practical applications.