Abstract: Tungsten carbide based spray coatings are widely used in industry for application requiring abrasion, sliding, fretting and erosion corrosion resistance. High velocity oxy-fuel (HVOF) flame spraying was used for producing high quality carbide composite coatings. In this study, a WC-CoCr and WC-CoCrNi powders were thermal sprayed using a HVOF process. The spray parameters were varied in order to investigate their influence on microstructure and mechanical properties of coatings. It is possible to produce homogeneous coating by controlling the flame temperature, the velocity of the gun transverse, the powder feed rate and the nature of the powders. The mechanical properties and the porosity rate could be optimized in order to improve the functional properties.

This paper reports on the study of copper-nickel alloy (Cu70-Ni30) surface modifications during the corrosionerosion process taking place in flowing water containing marble particles. The surface modifications were evaluated at room temperature under agitation by potentiodynamic polarization curves and Electrochemical Impedance Spectroscopy (EIS). The electrochemical measurements showed that the corrosion current density decrease from 6,3mA/cm 2 to 4,8 mA/cm 2 whenthe marble powder concentration increases from 0 to 8 ppm. The morphology and the nature of corrosion products, formed on the copper alloy surface, were studied by optical microscopy and micro-Raman spectroscopy. At low concentration (from 0 to 4 ppm) the structural analysis showed the presence of Cu2O and CuO compounds while at 8 ppm the passive films are formed of Cu2O and NiO. White deposits of CaCO3 and a local abrasion are also evidenced for 8 ppm. The mechanism of Cu70-Ni30 corrosion-erosion as function of marble powder concentration are discussed. At low concentration (2 and 4 ppm) the presence of marble solid particles in flowing water leads to erosion and corrosion of the surface and for 8 ppm both erosion and abrasion are clearly observed.

Les revetements metalliques sont couramment utilises pour proteger l’acier. Dans ce cadre les revetements de cermet sont suggeres d’etre employe en milieu marin a cause de l’absence des elements nefastes dans leurs compositions chimiques. Nous avons consacre cette recherche a l’etude du comportement electrochimique du revetement de cermet applique sur un acier au carbone faiblement allie (35CD4) par la technique de projection thermique dans l’eau de mer synthetique, aux moyens des methodes electrochimiques stationnaires (E = f(T) ; log i = f(E) ; Rp) et non stationnaires (spectroscopie d’impedance electrochimique). Les resultats obtenus ont montre l’existence d’un couplage galvanique entre le substrat et le revetement et l’acier revetu se comporte mieux dans l’eau de mer synthetique que l’acier nu. Nous avons enregistre un taux de corrosion plus eleve de l’acier revetu dans le milieu agite devant celui non agite, et que, l’augmentation de l’agitation accelere le processus de corrosion de notre revetement. L’etude par spectroscopie d’impedance electrochimique au potentiel de corrosion conduite sur l’acier a l’etat revetu confirme les resultats obtenus par les methodes electrochimiques classiques.

The corrosion behavior in artificial seawater of different as-sprayed ceramic-metallic (cermet) coatings applied on low-alloy steel was studied. Five conditions, associated to modifications of the composition of the powder or deposition parameters were evaluated. The degradation mechanisms were studied during extended immersion tests using conventional electrochemical measurement and electrochemical impedance spectroscopy. The extended immersion tests reveal that these as-thermal-sprayed coatings present a cathodic behavior compared with steel. During the first hours of immersion, the electrolyte infiltrates the defects of the coatings, which then result to the local degradation of the substrate accelerated by the galvanic coupling with the cermet coating. Optical observations and Raman analyses reveal the formation of calcium carbonates like aragonite on the cermet surface, very close to the appearance of local anodic sites. The cross-sectioned views reveal the infiltration of the corrosive solution, and the depth penetration of the degradation of steel substrate probably due to the acidification of the anodic sites.