'COATINGS FOR STEAM POWER PLANTS UNDER ADVANCED CONDITIONS'

摘要

To achieve higher power generation efficiency in steam turbines, operating temperatures are expected to rise from 550°C to 650°C. Two approaches are being followed in COST 522 in order to accomplish this goal: 1) the development of new materials and 2) for the first time in Europe, the use of oxidation resistant coatings on currently available materials with higher creep strength but inferior steam oxidation resistance, which is the object of this work. This presentation covers the efforts carried out while exploring the suitability of coatings for steam turbine components. In the initial stages of this work, commercially available materials, known to have good high temperature oxidation resistance, were applied by different deposition techniques. These techniques were chosen on the basis of being potentially appropriate for coating very large components: the application of aluminium slurries, the deposition of Al, Cr, Co, Fe and Ni alloyed materials by thermal spray and the application of electroless nickel. The aluminium slurry coating was deposited by brushing, and a series of post-heat treatments were evaluated in order to generate a uniform and stable diffusion coating. Thermal spray coatings were deposited by High Velocity Oxygen Flame (HVOF) spraying and optimisation to minimise porosity and maximise adhesion was carried out. Electroless nickel coatings were applied using commercial procedures. The coatings were characterised by metallography, SEM-EDS and XRD and steam oxidation laboratory testing was carried out at 650°C. The preliminary findings showed that some of the studied coatings are very promising. Results of the initial preliminary testing carried out for 10,000h. will be presented. Finally, mechanisms of protection as well as degradation for the different coatings will also be discussed.