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New technique for the deposition of protective aluminide coatings on the internal surfaces of complex cooled industrial blades


BE95-1146 New Technique for the Deposition of Protective Aluminide Coatings on the Internal Surface ????

This research project concerns the study and the industrialisation of an aluminide coating process for the cooling cavities in critical components (rotor blades and nozzles) of gas turbines for industrial use operating at high temperature.

The blading and nozzle materials, particularly those used for the first stage, are subjected to particularly severe operating cycles which seriously affect durability. Presently established gas turbines are limited in their operation temperature due to oxidation and corrosion of the turbine blades. An improved corrosion and oxidation resistance is of great importance, since engine manufacturers demand longer component life at higher turbine inlet temperatures in order to achieve higher cycle efficiency and reduced waste gas emission. Internal cooling has been introduced to limit the temperature level on these components as the size of the components prohibits use of the materials and technologies developed for the aeronautic industry at present and in the near future. At the temperatures in question, over 850°C, the internal flow of cooling air gives rise to processes of oxidation of the superalloy material, which drastically reduce the life of blades and nozzles. This results in increased operating risks for the machine as well as higher maintenance costs due to the need for frequent replacement of critical components.

Processes such as slurry cementation, gas phase type out-of-pack and CVD, developed by the aeronautic industry for aluminide coating of cavities fail to achieve a comparable or acceptable quality standard when applied to larger components, either with straight-through ducts or cooling coils. The aim of this project is to investigate CVD deposition techniques with high throwing power that will deposit aluminide coatings in a consistent and uniform manner throughout the complex internal surfaces of large turbine blades. To this aim, two routes will be carried out:

- The first route involves modifying existing aluminide coating processes to adapt them to the shape of industrial turbine blades and nozzles. Basically, modification will concern the architecture of the coating equipment and the process parameters, such as: gas activity, gas pressure, deposition rate, temperature, gas flow rate and carrier gas.

- The second direction consists in adding other elements to aluminium (yttrium or platinum) to improve resistance to oxidation, corrosion and thermal cycles, applying the process developed in aluminide deposition.
The expected achievements are the following:

- that the required simple aluminide and modified aluminide coatings can be produced in a CVD demonstrator unit;
- that blades coated with the required internal coating will give an increased life in a gas turbine engine.

The consortium comprises a manufacturer of gas turbines, NUOVO PIGNONE (I) and a utility, ENEL (I), as users of the coated blades; a supplier of coated components for gas turbines, CUK Ltd (GB) and a supplier of CVD equipment, ARCHER TECHNICOAT Ltd (GB) as developers of the coating equipment; a university, Technische Universität Braunschweig (D) and a research center, JRC, as developers of the process.

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Nuovo Pignone
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Via Felice Matteucci 2
50127 Firenze

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Participants (5)