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2221 |
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Tuesday, May 04, 2010, Olivia Room 12:00 PM Hard Chrome Replacement |
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The interaction of process and particle size in HVOF spraying of WC-CoCr sub-micron carbide powders |
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Tommi Varis* / VTT Technical Research Centre of Finland, Finland Tomi Suhonen/ Technical research center of Finland, Finland Arash Ghabchi/ Technical research center of Finland, Finland Ulla Kanerva/ Technical research center of Finland, Finland Xuwen Liu/ TKK Department of Materials Science and Engineering, Finland Jussi Oksanen/ TKK Department of Materials Science and Engineering, Finland Outi Söderberg/ TKK Department of Materials Science and Engineering, Finland Simo-Pekka Hannula/ TKK Department of Materials Science and Engineering, Finland |
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The fine carbide size of the WC-CoCr thermally sprayed coatings has been shown to improve the wear resistance in the fine particle slurry abrasion conditions. Furthermore, in order to achieve fully dense structures with smooth surface roughness there has been a trend in thermal spraying to apply finer powder particle size. As the coatings thus can be manufactured thinner this facilitates that the WC-CoCr coatings become economically comparable to the hard chromium. However, the finer carbide and powder particle sizes require better temperature control of the coating process due to problems connected to the carbide dissolution and carbon loss of the powder in the high-temperature spraying. Therefore, the traditional HVOF systems have not been suitable for spraying the nanocarbide powders, while such processes as HVAF, CJS HVOF, Warm Spraying, etc. have recently been developed to produce coatings with nanocarbides from powders with very fine powder particle size distribution and limited solubility. In this study the WC-CoCr powders, having sub-micron carbide size, with different particle size distribution, were sprayed with the CJS HVOF and for comparison with the DJ Hybrid processes. Size distributions selected were -35+15, -25+10 and -10+2 µm. Manufacturing parameters for each powder were carefully optimised. During the spraying the particle temperature and velocity values were recorded. The linkage between the particle temperature and velocity on the coating characteristics such as hardness, Young?s Modulus, W2C, carbon loss and porosity via so called Process Mapping ?method was determined. |