Solid Particle Erosion of Coatings on Transparent Polycarbonate and Reinforced Composites

Abstract

Solid particle erosion of transparent hard coatings on polycarbonate and elastomeric and hard polyurethane and fluorocarbon coatings on glass-reinforced epoxy and quartz-reinforced polyimide laminates has been investigated at 35 to 42 m/s with 210 to 297 μm natural sand by using a sand blast nozzle apparatus. Erosion was determined as a function of impact angle, total weight of impacted sand, and velocity of impact. Characterization of eroded specimens included weight loss. Talysurf profilometry, scanning electron microscopy, and transmittance measurements (for the polycarbonate materials). The hard transparent coating (Du Pont's Abcite) on the polycarbonate exhibited maximum erosive weight loss at lower angles (30 deg) with brittle cracking and subsequent adhesion loss of the coating; the cracking was also observed in the substrate itself. The average surface roughness of the coated and uncoated polycarbonate increased with increasing weight of sand impacted, but was reduced at the higher (60, 75, and 90 deg) compared with the lower impact angles. Measurement of transmittance loss showed more reductions on coated and uncoated polycarbonate at 30 deg than 90 deg at low velocity and low sand weight impinged, but showed the opposite effect at higher velocity/sand weight conditions. Erosion of the reinforced composite materials was typically brittle in nature with a maximum weight loss at 75 deg. When they were coated with the elastomeric polyurethane or fluorocarbon, the maximum erosion occurred at 15 to 30 deg impact angles with minimum weight loss at 45 deg or above (in these exposure conditions). By contrast the hard MIL-C-83286 polyurethane paint on these composites exhibited continuously decreasing weight loss from 30 to 90 deg under these conditions. The primary mode of failure was tearing or chunking of the coating with microscopic cracking and adhesion loss; this was aggravated at the lower angles where the angularity of the impacting particles interacted with the surface to gouge out pieces of coating. Maximum surface roughness was measured at 30 deg, and surface roughness corresponded closely to erosive weight loss. This surface roughness did not change appreciably as a function of amount of sand impacted. The surface roughness of the hard polyurethane coatings was twice that of the elastomeric coatings.