Y. Tsunekawa, T. Ueno, T. Kozaki, M. Okumiya, Toyota Technological Institute, Nagoya, Japan; I. Ozdemir, Dokuz Eylul University, Izmir, Turkey
Cast iron coatings with solid lubricant of graphite carbon structure are an attractive surface hardening candidate to achieve wear-resistant aluminum alloy components. Plasma-sprayed coatings via as-atomized cast iron powder contain no graphite structure owing to the rapid solidification. A short period of pre-annealing at 1173 K allows the formation of graphite carbon instead of carbides in the cast iron powder. However, marked reduction in graphite carbon occurs to coatings sprayed with the pre-annealed powder because of the in-flight burning and dissolution into molten iron. In-process post-annealing at substrate temperature of 773 K for 60 s reveals the formation of graphite carbon structure resulted from the carbide decomposition in splats and also in coatings sprayed with the as-atomized powder. Chemical analysis exhibits that graphitization level of post-annealed cast iron coatings is higher than that of coatings sprayed with the pre-annealed powder. By contrast, precipitated intersplat graphite carbon structure appears in cast iron coatings when introducing methane as a powder feeding carrier gas which is liable to decompose in plasma flame. Lower droplet temperature arising from the endothermic reaction of methane also prevents graphite carbon from the in-flight burning and dissolution into molten iron. The resultant coatings with graphite carbon structure embedded in hard matrix are anticipated to offer superior wear resistance in comparison to centrifugally cast iron containing flaky graphite structure.
Summary: Cast iron coatings with solid lubricant of graphite carbon are an attractive surface hardening candidate to achieve wear-resistant aluminum alloy components. Through the controls in flying droplet temperature and velocity, the resultant cast iron coatings are anticipated to offer superior wear resistance like gray cast iron.
