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1274 |
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Tuesday, June 03, 2008, Auditorium 2 9:50 AM Gasturbines 1 Coatings for mobile and stationary turbines, protection against wear, high temperature corrosion and thermal stresses, clearance control coatings for a better efficiency |
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Development of oxide dispersion strengthened MCrAlY coatings |
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Markus Brühl* / Surface Engineering Institute, RWTH Aachen University, Germany Kirsten Bobzin / RWTH Aachen University, Surface Engineering Institute, Germany Felix Ernst/ RWTH Aachen University, Surface Engineering Institute, Germany Katharina Richardt/ RWTH Aachen University, Surface Engineering Institute, Germany |
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MCrAlY-materials are widely used as bond coat for thermal barrier coatings on turbine blades. Scope of this work is to improve mechanical properties and resistance against corrosion and oxidation of thermal sprayed NiCoCrAlY-coatings by strengthening the coating with hard phase particles. The application of these coatings in high temperature regions of the gas turbine does not allow the use of carbides as hard phases, because of decomposition effects at elevated temperatures of more than 800 °C. In order to retain the effect of the dispersion reinforcement at high temperatures, the use of temperature-stable oxide hard phases such as ZrO2 is necessary. For realisation of this new material structure the high energy ball milling process is applied and analysed. With this process it is possible to achieve a homogeneous distribution of the oxide dispersoid in the NiCoCrAlY matrix. The mixture ratio between NiCoCrAlY and ZrO2 was varied between 2 wt-% and 10 wt-% ZrO2. The influences of the milling time of the high energy ball milling process on the distribution of the hard phases in the metal matrix were analysed. Special attention was given to the particle size distribution and the grain size of the hard phases after milling. The particle size of powders plays an important role during processing with thermal spray processes, because it significantly affects the microstructure of the coatings. After spraying the mechanical properties of the produced coatings are measured and compared with conventional NiCoCrAlY coatings. Other important properties of MCrAlY coatings are the oxidation characteris-tics under high temperature and thermal shock behaviour, which were also measured. |