The high velocity oxy-Fuel (HVOF) combustion spraying of ball-milled Nylon 11/ceramic composite powders is an effective, economical and environmentally friendly method for producing semi-crystalline micron and nano-scale ceramic reinforced polymer coatings. Composite coatings reinforced with multiple scales of ceramic particulate reinforcements are expected to exhibit improved load transfer between the reinforcing phase and the matrix due to interactions between the large and small ceramic particles. An important step in developing multi-scale composite coatings and load transfer theory is understanding the effect of reinforcement size on the distribution of the reinforcement and the properties of the composite coatings.

Composite feedstock powders were produced by ball-milling Nylon-11 with fumed silica particles of 7, 20 and 40 nm, fumed alumina particles of 50 and 150 nm, and with calcined alumina of 350 nm, 1, 2, 5, 10, 20, 35 and 50 µm size at 10 vol. % overall nominal ceramic phase loadings. The microstructures of the as-sprayed coatings were characterized by optical microscopy, SEM and XRD. The reinforcement particles were concentrated at the splat boundaries in the sprayed coatings, yielding a good 3-dimensional distribution of the reinforcing phase. The coatings were evaluated as a function of reinforcement size and compared with HVOF sprayed pure Nylon-11 coatings. The effects of the HVOF spray process on the coating properties were isolated by annealing the as-sprayed coatings to achieve maximum crystallinity and by remelting and quenching to achieve a completely amorphous Nylon 11 matrix. The microstructure and properties of the annealed and quenched coatings were evaluated as a function of reinforcement size and compared to the as-sprayed coatings. The microstructure of selected HVOF sprayed coatings was compared to coatings of the same composition produced by controlled melting of composite powders.