Abstract
Crevice corrosion of metal/metal contacts in piping assemblies is a key issue for the design and the manufacturing of marine components. In this work, ceramic coatings onto alloy 625 were obtained using multi-processing CAPS facilities (Controlled Atmosphere Plasma Spraying). These coatings were sprayed in the CAPS chamber using air plasma spraying (APS, air at 100 kPa) or using high-pressure plasma spraying (HPPS, argon at 250 kPa) to achieve different coating microstructures and porosity levels. This allowed to investigate the corrosion behaviour in natural sea water of metal/ceramic contacts with different coating systems. Pure alumina or alumina-titania coatings with or without thermally-sprayed alloy 625 bond-coat were tested. Post-treatments like sealing of pores using epoxy resin were also achieved to study the resulting corrosion protection enhancement. Immersion and potentiostatic tests at +300 mV vs. SCE (Standard Calomel Electrode) tests were carried out in natural sea water at different temperature up to 60°C to expose specimens to the most severe working parameters. A beneficial protective effect of ceramic-coated alloy 625 has been clearly evidenced. Further investigations were performed using light microscopy and scanning electron microscopy to assess the corrosion behaviour and mechanical soundness of ceramic coated specimens which resulted in the determining of relevant technological solutions to prevent the risk of corrosion.
