Plasma sprayed cast iron coatings containing solid lubricant graphite and h-BN structure

Water-atomized cast iron powder of Fe-2.17at.%C-9.93at.%Si-3.75at.%Al were deposited onto an aluminum alloy substrate by atmospheric direct current plasma spraying to improve its tribological properties. Preannealing of the cast iron powder allows the precipitation of considerable amounts of graphite structure in the powder. However, significant reduction in graphitized carbon in cast iron coatings is inevitable after plasma spraying in air atmosphere due to the in-flight burning and dissolution into molten iron droplets. Hexagonal boron nitride (h-BN) powders, which have excellent lubricating properties like graphite, were incorporated into the cast iron powder as a solid lubricant by the sintering process (1300 degrees C) to obtain protective coatings with a low friction coefficient. The performance of each coating was evaluated using a ring-on-disk-type wear tester under a paraffin-based oil condition in an air atmosphere. A conventional cast iron liner, which had a flaky graphite embedded in the pearlitic matrix, was also tested under similar conditions for comparison. Sections of worn surfaces and debris were characterized, and the wear behavior of plasma-sprayed coatings was discussed