Development of Ceramics and/or FGM Coatings Used in Slurry Erosion-Corrosion Environment

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In this study, the properties of slurry erosion of ceramics and/or functionally gradient materials coatings formed by low-pressure plasma spraying (LPPS) and laser thermal spraying (LTP) were assessed. Slurry erosion tests were carried out by the jet-in-slit type and the specimen-rotating type apparatus using silica sand slurry, gypsum slurry, fly ash slurry, and gypsum-fly-ash slurry respectively. The slurry concentrations were controlled at 30 wt% in the jet-in-slit type and 60 wt% in maximum in the specimen-rotating type apparatus respectively. Specimens were designed as disk type and the mock of impellers.The test results showed that the durability of coatings to erosion was strongly influenced by the conditions of spraying and other treatments. for instance, under-coating, sealing, heat treatment and pressure lowering conditions.Slurry erosion test revealed that the erosion-resistance characteristics differed depending on the erosion areas on the specimen surface. Such phenomena may be attributed to the influence of attack by individual slurry particles along the specimen surface, even though the slurry jet impacted at normal incidence. The impact angles, impact frequencies (concentration) of slurry particles were also calculated experimentally and theoretically in this study. As for the conditions of slurry environment, silica sand slurry is most adverse one, then fly ash is at the second, and gypsum one is at the last rank.Corrosion test showed that sealing treatment improved corrosion resistance it although has nothing to do with slurry erosion durabilities.