Abstract This paper describes and discusses aspects of the erosion-corrosion behaviour of a WC-Co-Cr, HVOF sprayed coating when subjected to an impinging jet of an aqueous solution of 3.5% NaCl containing solid particles at 18°C. Although pure mechanical erosion has been found to contribute to a large part of material degradation, a considerable amount of material loss can be attributed to the direct and indirect (synergy) effect of corrosion. Aspects of the influence of time, solids loading and impingement angle have been investigated and the mechanisms of erosion-corrosion are discussed.

Abstract The elevated temperature erosion resistance of experimental amorphous thermal spray coatings was determined in a laboratory elevated temperature erosion tester. Test conditions attempted to simulate the erosion conditions found at the combustor waterwall tubes in fossil fuel fired boilers. Erosion tests were conducted on four experimental amorphous thermal spray coatings, using the bed ash retrieved from an operating coal fired boiler. An experimental arcspray process was used to spray coatings. These results were compared with erosion test results of two common structural materials, two commercially available arc-sprayed coatings, and a proprietary HVOF coating. Test results indicated that the Duocor coating had the highest erosion resistance among the four experimental coatings, it showed equal resistance to the HVOF coating (DS-200). Compared to AISI 1018 steel, both Duocor and DS-200 coatings reduced material wastage by 26-fold. Other test results indicated that the XJ-16, 60T and Armacor M coatings had equal erosion resistance reducing material wastage approximately 7-fold, while Armacor CW reduced by 10-fold. Only slightly better than the unprotected 1018 steel, the X-20 coating performed poorly on erosion tests. The high erosion resistance of Duocor and DS-200 coatings was attributed to their high densities and fine splat structures.

Abstract Different WC-based coatings have been sprayed by the HVOF process and characterised by different methods. The influence of different powder characteristics on the wear and corrosion performance was investigated. Powder characteristics investigated include: i) average WC particle size, ii) matrix composition and iii) powder grain size distribution. The results show that the coating properties are affected by the different powder characteristics. Small WC particles were found to be beneficial as regards the erosion and erosion-corrosion resistance. An increase of the Cr and Mo content increased the corrosion and erosion-corrosion resistance. Powders with narrow grain size distributions gave coatings of higher quality than powders with wider grain size distributions.

Abstract In corrosive media the wear resistance of ceramic-metallic coatings is dependent on the corrosion resistance of the metal matrix. Other factors that will affect the coating deterioration are the corrosivity of the medium and any galvanic interaction from the surrounding material. This paper presents results from a study where different types of WC(Co/Cr/Mo/Ni) powders have been sprayed by HVOF, Diamond Jet 2600 Hybrid equipment. The properties of the sprayed coatings have been verified by metallographic studies and by erosion-corrosion testing both under corrosive and non-corrosive conditions. The results clearly demonstrate the importance of having a metal matrix at least as corrosion resistance as the surrounding materials. When wear exposed components in pipe systems, pumps or valves are coated with a WC type coating, the corrosion resistance of the metal matrix should be compatible to the material of the rest of the system. This is especially important when the surrounding materials are corrosion resistant alloys as stainless steels, where the coatings otherwise will act as an anode.

Abstract WC-Co-Cr powders with different WC particle size have been sprayed by the HVOF process. At constant spraying conditions the powders give coatings of different quality. The deposition efficiency during spraying of powders containing large WC particles was found to be low compared to powders with finer WC grains. In addition the amounts of porosity and cracks were different. The coatings have been characterised by different methods. Erosion and erosion-corrosion tests showed that the WC particle size also influence the wear resistance of the coatings. Small WC particle size was found to be beneficial. Chemical composition of the matrix was also found to be decisive for the coating properties. An increase of the chromium content improved the erosion-corrosion resistance.

Abstract This paper reviews some data regarding the combined effect of erosion and corrosion of thermal spray ceramicmetallic coatings and their potential application in sea water and production systems for the oil industry. The paper also presents recent research results from SINTEF Corrosion and Surface Technology with respect to development of new and better ceramic-metallic coatings from the Norwegian coating industry. It has been shown that taking new high velocity spraying technology into use in combination with recent developed powders, the result is a more corrosion and erosion resistant coating than the traditional and most often specified type Praxair LW45.