Micro-abrasion of filled and unfilled polyamide 11 coatings

In this study, five polyamide (PA11) based coatings have been investigated; two filled with different types of solid fillers (TiO2) and in different proportions, and two unfilled coatings, deposited onto carbon steel substrates. Tests were conducted using a Phoenix Tribology TE99 micro-abrasion tester. A 25 mm diameter hardened and pitted carbon steel ball was loaded against the sample and rotated in the presence of 5 μm silicon carbide (SiC) abrasive slurry with a solids concentration of 0.375 g/cm3. Tests were conducted under optimum conditions for grooving (two-body) abrasion. The wear rates are presented as a function of load, total sliding distance and mechanical properties of the coating. The influence on coating performance of air-cooling and water-cooling the coating after deposition is explored. The unfilled coatings exhibited a specific wear rate (k) about 1.3 times lower than the filled coatings. The results, contrary to expectations, show that the fillers do not act as load-bearing elements within the coating matrix. The value of k decreased with increasing load for all the coatings but an irregular trend in k was observed as a function of sliding distance. Detailed scanning electron microscopy was performed on the wear scars to identify the wear mechanisms and the role of the fillers.