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1171 |
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Monday, June 02, 2008, Auditorium 2 11:50 AM Automotive Coatings on cylinder liners and piston fire faces, testing of coatings and means of surface preparation for inner diameter coatings |
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Increase in graphite carbon in plasma sprayed cast iron coatings based on flying droplet diagnostic |
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Yoshiki Tsunekawa* / Toyota Technological Institute, JAPAN Tomoko Kozaki/ Toyota Technological Institute, Japan Kazuya Iwata/ Toyota Technological Institute, Japan Masahiro Okumiya/ Toyota Technological Institute, Japan |
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Cast iron coatings containing solid lubricant of graphite are an attractive candidate for wear resistant applications of an aluminum alloy substrate. It is difficult to generate a graphite structure in coatings sprayed with as-atomized cast iron powder which does not contain graphite owing to their high solidification rate. Although a graphite structure is remained in coatings sprayed with fully annealed cast iron powder, graphite carbon becomes lower than that in the annealed powder because of the in-flight oxidation and dissolution into molten iron. The present study is focused on an increase in graphite carbon through flying droplet diagnostic at a certain spray distance, that is, in-situ measurements of droplet temperature and velocity. Water-atomized cast iron powder which was annealed at 900oC for 3.6ks, was supplied as a spray material. The fully annealed powder was plasma-sprayed onto an aluminum alloy substrate, as well as flying droplet diagnostic. The graphite carbon can be estimated by flying droplet temperature and velocity, which are controlled by spray parameters such as plasma gas flow rate and plasma current. It is confirmed that droplet velocity exhibits stronger influence on graphite carbon compared with droplet temperature. High velocity causes an increase in graphite carbon, so that it is possible to fabricate graphite-graded cast iron coatings with high amount at the surface and low at the interface. Besides the spray parameters, the endothermic reaction of plasma flame with methane inserted from the powder port is also effective to remain a higher level of graphite carbon due to the low oxidation and dissolution. |