Electrochemical Characterisation Study of Coatings Obtained by High Velocity Oxy-Fuel Spraying (HVOF)

 

P.H. Suegama, C.S. Fugivara, A.V. Benedetti*, J. Delgado^a), J.M. Guilemany^a)

 

Dep. Físico-Química, Instituto de Química, Universidade Estadual Paulista, UNESP. CP 355, 14801-970 Araraquara, SP, Brazil. E-mail:benedeti@iq.unesp.br.

^a) CPT Thermal Spray Center. Materials Engineering. Dept. Enginyeria Química i Metallúrgia. Universitat de Barcelona, C/Martí i Franquès 1. E-08028 Barcelona, Spain. E-mail:cpt@material.qui.ub.es

 

Received 10 September 2002; accepted in revised form 5 February 2003

 

Abstract

The electrochemical behaviour of coated Cr₃C₂-NiCr steel in aerated 0.5 M H₂SO₄ solution was studied by means of electrochemical ac and dc measurements. The structural characterisation of the coated steel, before and after electrochemical tests, was also performed in order to identify the mechanism of the electrolyte penetration through the coating up to the steel substrate, causing its corrosion. This characterisation may also help to explain electrochemical results.

Three types of Cr₃C₂-NiCr coatings performed by a High Velocity Oxy-Fuel Spraying system (HVOF) were analysed. The facility for the electrolyte penetration through the coating and the corresponding electrochemical behaviour of the samples were strongly influenced by the spray parameters used and heat treatment applied. It was observed that heat-treated coatings (Q1 and Q3) showed better corrosion resistance than the as-sprayed coating (A). For coatings Q1 and Q3, the electrolyte did not reach the steel substrate during the measurement, leading to a better protection of the steel substrate against corrosion.

Keywords: corrosion, Cr₃C₂-NiCr coating, electrochemical techniques, HVOF, thermal spraying.

 

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* Corresponding author. E-mail address: benedeti@iq.unesp.br. Communication presented at XV Ibero-American Meeting of Electrochemistry.