Influence of Oxidation Treatments and Surface Finishing on the Electrochemical Behavior of Ni-20Cr HVOF Coatings
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JMEPEG DOI: 10.1007/s11665-017-3048-1
Influence of Oxidation Treatments and Surface Finishing on the Electrochemical Behavior of Ni-20Cr HVOF Coatings H. Ruiz-Luna, J. Porcayo-Calderon, J.M. Alvarado-Orozco, A.G. Mora-Garcı´a, L. Martinez-Gomez, L.G. Tra´paga-Martı´nez, and J. Mun˜oz-Saldan˜a (Submitted April 27, 2017; in revised form July 31, 2017) The low-temperature electrochemical behavior of HVOF Ni-20Cr coatings was assessed. The coatings were evaluated in different conditions including as-sprayed, as-ground, and heat-treated in air and argon atmospheres. A detailed analysis of the coatings was carried out by means of XRD, SEM, and EPMA, prior and after the corrosion test. The corrosion rate was analyzed in a NaCl solution saturated with CO2. Results demonstrate that the use of a low-oxygen partial pressure favors the formation of a Cr2O3 layer on the surface of the coatings. According to the electrochemical results, the lower corrosion rates were obtained for the heat-treated coatings irrespective of the surface finishing, being the ground and argon heat-treated condition that shows the best corrosion performance. This behavior is due to the synergistic effect of the low-pressure heat treatment and the grinding processes. The grinding promotes a more homogeneous reaction area without surface heterogeneities such as voids, and the pre-oxidation treatment decreases the porosity content of the coating and also allows the growing of a Cr-rich oxide scale which acts as a barrier against the ions of the aqueous solution. Keywords
Cr-oxide, electrochemical corrosion, ground surface, heat treatment, HVOF Ni-20Cr coatings
1. Introduction Corrosion is one of the main phenomenon causing significant economic losses in several industrial applications including boilers or incineration plants (Ref 1, 2), petroleum (Ref 3, 4), pipelines used in the oil, gas, and geothermal plants (Ref 5, 6). Particularly, one of the most important problems found in the steam-generating plants worldwide is the presence of high concentrations of Na, Cl, dissolved CO2, H2S, and traces of undesirable species including SO4, K, and Fe (Ref 6-8). The corrosive nature of these species contributes to the material deterioration resulting in its premature failure. For instance, H. Ruiz-Luna, Centro de Investigacio´n y de Estudios Avanzados del I.P.N., Libramiento Norponiente 2000, Fracc. Real de Juriquilla, 76230 Queree´taro, Mexico; and Conacyt – Universidad Auto´noma de Zacatecas, Av. Ramo´n Lo´pez Velarde 801, 98000 Zacatecas, Mexico; J. Porcayo-Calderon, Universidad Auto´noma del Estado de Morelos, CIICAp, Av. Universidad 1001, 62209 Cuernavaca, Mexico; J.M. Alvarado-Orozco, CIDESI Unidad Quere´taro, Desarrollo San Pablo, 76130 Quere´taro, Mexico; A.G. Mora-Garcı´a and J. Mun˜ozSaldan˜a, Centro de Investigacio´n y de Estudios Avanzados del I.P.N., Libramiento Norponiente 2000, Fracc. Real de Juriquilla, 76230 Quere´taro, Mexico; L. Martinez-Gomez, Instituto de Ciencias Fı´sicasUNAM, Av. Universidad s/n Col. Chamilpa, 62210 Cuernavaca, Mexico; and
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