Comparison in erosion behavior of iron-base coatings sprayed by three different arc-spray processes

The elevated temperature erosion behavior of three iron-base coatings sprayed by high velocity continuous combustion (HVCC) process was determined in a laboratory elevated temperature erosion tester and compared with the behavior of coatings sprayed using combustion arc-spray and standard arc-spray processes. Test conditions attempted to simulate erosion conditions found at the heat exchanger tubes in the coal-fired boilers. Two bed ashes A (highly erosive) and B (medium erosive bed ash) retrieved from two operating boilers were used as erodent materials. In addition, some other properties, such as microhardness, porosity, and oxidation rate, of coatings were also measured and compared. Erosion test results indicated that the three iron-base coatings sprayed with HVCC process demonstrated higher erosion resistance than the ones sprayed with the other two arc-spray processes, when eroded by bed ash B. When eroded by high erosive ash (bed ash A), the three arc-sprayed iron-base coatings exhibited similar levels of erosion resistance, the ones sprayed with HVCC process being slightly better than those sprayed with the other two processes. The difference of erosion behavior between sprayed coatings produced by different processes closely correlated with their microstructure and the characteristics of ash materials rather than the microhardness of coatings. The erosion mechanism of coatings was also discussed and compared.