Characterization of mechanical and surface finishing properties of metallic coating obtained by arc electric thermal spray / Caracterização das propriedades mecânicas e de superfície de revestimento de revestimento metálico obtido por pulverização térmica elétrica arc

Pamella Kesseler de Campos, Bruno Reis Cardoso, Heloísa Cunha Furtado, André Rocha Pimenta, Marília Garcia Diniz

Abstract


The Brazilian thermoelectric plants that use coal as a thermal source use pulverized combustion technology. The aim of this work was to characterize some properties of a metallic coating obtained by arc electric thermal spray in order to protect boiler’s surface against ash’s aggressive action from coal burning. The evaluated parameters considerably influence the characteristics of the coating’s lifes service. An iron chromium base alloy, reference herein as Alloy B, was used in this study. A chemical analysis of the coating, Alloy B, was performed in order to compare if there were any difference between the chemical composition of the wires used and what was incorporated into the coating by the thermal spray process. Therefore, Energy Dispersive Spectroscopy technique (EDS), Quantax software and PyMCA program were used.  The chemical analisys results of the coating was quite similar to the given composition of the wires. To verify the coating hardness, Vickers (HV) microhardness measurements were performed on the coating region, on the substrate and on the boundary region of the coating between substrasts. Vickers microhardness measurements were obtained by PANTEC MV-1000A microdurometer. As substrate an 8 mm thick steel sheet with a chemical composition and thickness similar to the steels used in the water wall pipes of Brazilian boilers were used. The coating hardness (730 HV) was on the order of four times greater than the substrate’s hardness (179 HV) to be protected. This property was homogeneous for the coated layer showing that hardness values indicates that good adhesion of coating’s cast particles occurred, and the spray distance proved to be effective.  The roughness was obtained through measurements made on images generated by Optical Microscopy (OM). Measurements of the variation in heights between peaks and coating depressions were obtained on the generated images. These measurements generated an average value Ra = 27.5 μm. Roughness measurements obtained by conventional technique (Digital Surface Profile Gauge) were performed too and showed that the method of measurements on the OM images was not effective to evaluate the high coating roughness generated by the arc electric thermal spray method, in this case, 248 µm.


Keywords


Arc electric thermal spray, Thermoelectric plants, metallic coating, boiler, ash erosion.

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References


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DOI: https://doi.org/10.34117/bjdv6n3-106

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