This paper evaluates an electrochemical mapping method for determining the corrosion resistance and structural integrity of thermally sprayed coatings. In the test setup, a potentiostat is suspended over the test sample, forming an electrochemical cell. The circuit is completed through an electrolyte-containing porous tip. Capillary forces keep the electrolyte on the surface of the tip, preventing transfer to the substrate surface. In the investigation, electrochemical, spatially resolved measurements are carried out on flame and vacuum plasma sprayed nickel-base coatings and compared with the results of salt spray testing. It is observed that the new method offers many advantages being faster, nondestructive, and quantitative in nature. Paper includes a German-language abstract.

Coatings have been prepared using the Diamond Jet hybrid and JP5000 high velocity oxyfuel (HVOF) systems with the objectives of improving corrosion resistance and reducing costs through increasing deposition efficiency. Models relating deposition efficiency, coating oxygen content and corrosion resistance to process parameters including fuel flow rate, oxygen flow rate and stand-off distance have been developed. A corrosion test cell has been designed and a procedure determined for studying the corrosion behaviour of large numbers of thermally sprayed coatings in an efficient manner. A significant improvement to the corrosion resistance of HVOF sprayed coatings has been achieved by spraying parameter optimisation and investigation of powder size and distribution. The project has also investigated the influence of spray angle on coating performance with a view to future onsite application. Coating materials tested and compared include nickel alloys Hastelloy C276 and 59, cobalt alloy Ultimet, duplex stainless steel S32750 and an experimental iron-based spray-fuse composition.

Stainless steel coatings were produced by supersonic air-gas plasma spraying method. Mixture of air and natural gas was used as a plasma forming gas. Powders of 304L and 316L stainless steels were used for plasma spraying. Thickness of coatings was up to 3 mm. Coating structure was studied. Dependence of oxygen content in coatings upon particle sizes and spraying conditions was established. Investigation of electrochemical properties of coatings was carried out by potentiostatic method. Corrosion potential and corrosion rate in sea water, hydrochloric and sulphuric acid solutions were determined.