Influence of Substrate Surface Texture Parameters on the Wear Behavior of Polyether Ether Ketone (PEEK) Coatings

The effectiveness of a coating system heavily depends on the surface texture characteristics of the underlying material, as these play a crucial role in determining how well the coating adheres. This adhesion is vital for maintaining the coating's integrity and ensuring reliable performance under demanding conditions. Key surface texture characteristics such as average roughness (R_a), root mean square roughness (R_q), maximum peak-to-valley height (R_z), peak density (N_p), and statistical properties like kurtosis (R_ku) and skewness (R_sk) of surface profiles directly influence the bonding strength between the coating and its substrate. This study is focused on investigating how different surface texture characteristics influence the adhesion strength and wear behavior of PEEK polymer coatings applied to mild steel through electrostatic spraying. To conduct this analysis, two substrates with distinct roughness profiles were coated with PEEK layers approximately 45 ± 5 μm thick, and their wear resistance was assessed using a ball-on-disk tribological test. Wear experiments were conducted over 10,000 cycles at room temperature under applied loads of 30, 40, and 50 N, with a constant sliding speed of 0.2 m/s. The findings revealed that coatings applied to rough surfaces withstood the full 10,000 cycles even at 50 N, whereas coatings on polished substrates failed after just 200 cycles under the same load. The superior performance of the rough surface is linked to its higher surface roughness, elevated R_z values, and positive skewness (R_sk), all of which contribute to more effective mechanical interlocking. In contrast, the smoother, polished surface, with its reduced roughness, lower R_z, and negative R_sk, provided fewer anchoring points, resulting in weaker adhesion of the coating.