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1539 |
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Tuesday, June 03, 2008, Room 08 12:10 PM Nanomaterials 1 Most coating materials gain superior coating performance when applied as nanostructured coating, new designed materials and optimized processes show promising results for this |
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Improving the properties of HVOF sprayed Cr2O3 by nanocomposite powders |
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Tommi Varis* / VTT Technical Research Centre of Finland, Finland Jari Knuuttila / Millidyne Oy, Finland Tomi Suhonen/ VTT Technical research center of Finland, Finland Ulla Kanerva/ VTT Technical research center of Finland, Finland Jussi Silvonen/ Millidyne Oy, Finland Jarkko Leivo/ Millidyne Oy, Finland Erja Turunen/ VTT Technical research center of Finland, Finland |
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Superior wear performance combined with excellent friction properties against metals makes chromium oxide (Cr2O3) an interesting coating material for many industrial applications. Poor toughness and sintering properties limits the use of Cr2O3 in bulk form. Limited toughness hinders also when applied as a coating. According to recent studies, high velocity oxy-flue (HVOF) spraying is suitable method to produce high quality ceramic coatings. The challenges in HVOF spraying of chromia is in high material melting temperature (2604 °C) relative to the flame temperature and short remain time of particles at high velocity flame. That makes Cr2O3 challenging material for HVOF spraying in terms of deposition efficiency and interlamellar cohesion. Powder morphology, composition, and nanocrystallinity can be seen to offer different routes to coating formation mechanism in HVOF process related to improved melting behaviour as well as phase structure of the coating. Potential possibility to affect on the coating properties is to use ceramic-ceramic ?composite powders, which can form compounds or mixture structures with two different ceramic phases. The use of agglomerated nanopowders gives two advantages: a) formation of compounds may easily take place during spraying and b) non soluble nano-particles can be used as dispersed particles to increase toughness. Under these bases, Cr2O3-TiO2 and Cr2O3-ZrO2 ceramic powder systems were selected for studies, which are believed to behave differently in terms of solubility. The goal is to improve interlamellar cohesion and toughness of HVOF-Cr2O3 ?coatings. Agglomerated and sintered chromia powder structures with alloying elements of TiO2 and ZrO2 in different primary sizes were used. Mechanical properties of coatings such as hardness, wear resistance and fracture toughness are determined. Coating structures are studied by microstructure analysis including porosity measurements and XRD-analysis. |