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1582 |
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Tuesday, June 03, 2008, Room 05 11:10 AM Case Studies and Further Applications 1 Showing the broad variety of thermal spraying in different examples, special processes and also specialized materials apart from standard coatings offer new possibilities and also new markets |
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Innovation of ultra-fine structured alloy coating having superior high temperature corrosion resistance |
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Xinqing Ma* / Inframat Corporation, USA Jeff Roth / Inframat Corporation, US David Gandy/ Electric Power Research Institute, US Frederick Frederick/ Electric Power Research Institute, US |
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High temperature protection requires full coating density, high adhesion, minor oxide inclusions, and preferably fine grains, which is not achievable in most thermal spray processes. High velocity oxygen-fuel (HVOF) thermal spray processes have been applied extensively for making such coatings with the highest density and adhesion strength, but the existence of not or partially melted particles are usually observed in HVOF-formed coatings because of relative low flame temperature and short particle resident time in the process. This work has investigated the development of an innovative HVOF process using fine powders typically less than 10 microns, which has no flowability in a conventional thermal spray process. The advantages of using small and even nano-sized particles in a HVOF process include uniform coating, less defective microstructure, higher cohesion and adhesion, full density, lower internal stress and higher deposition efficiency. Process investigations have proven the benefits for making alloy coatings with full density and high bond strength attributing to the better melting of the small particles and the very high kinetic energy of particles striking on the substrate. High temperature oxidation and hot corrosion tests at 800-850oC have demonstrated that the alloy coatings made by the novel process have superior properties to conventional counterpart coatings in terms of oxidation rates and corrosion penetration depths. One of the targeted applications is for the protection of fossil-fired ultrasupercritical (USC) boilers that operate in a high temperature and corrosive environment. |