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Prove di deposizione epitassiale su superleghe monocristalline mediante laser

pubblicazioni - Articolo

Prove di deposizione epitassiale su superleghe monocristalline mediante laser

20-22 Aprile 2005 Nizza – France

Epitaxial laser cladding trials on single crystal superalloys

F. Cernuschi, P. Fraschini CESI SpA, Centro Elettrotecnico Sperimentale Italiano Via Rubattino, 54 20134 Milano Italy Introduction One of the major demands for industrial gas turbine manufactures is the improvement of the gas turbine efficiency. This objective goes through the increase of the turbine inlet temperature (TIT), but in order to make hot path components like vanes and blades able to face hot combustion gases, some developments are required. In particular, the design of a more efficient and complicated impingement cooling, coupled with a film cooling system is needed. Furthermore, the use of ceramic thermal barrier coatings (TBC) deposited onto the substrate allows to drop the metal temperature from 30°C up to 100°C depending on both the coating thickness and microstructure [1]. Notwithstanding these solutions contribute significantly to achieve the final objective, the development of new materials is an essential item. In the last years, the main breakthrough consisted in replacing the conventional equiaxed superalloys with directionally solidified and single crystal superalloys. In particular, the use of single crystals for manufacturing hot part components allows a higher service temperature since the removal from the alloy of the low melting point elements – typically used as carbides and borides for strengthening the grain boundaries – is possible. Moreover, in single crystal superalloys the content of the strengthening phase g’ can be increased from 45% and 60% for equiaxed and directionally solidified, respectively, up to 70% guaranteeing higher creep resistance and thermal fatigue performance [2,3]. Furthermore, the addition of Re improves the high temperature oxidation resistance of the material. Apart from the expenses for the alloy constituents, the final costs of single crystal components resulted significantly high because the production process, the machining and the heat treatments are time consuming. Thus, the availability of a repair technique that allows refurbishing single crystal components can be economically advantageous. This is especially true in the case of aero – engines when blade integrated disks (Blisks) are used for obtaining a weight reduction [4]. As far as the single crystal components are concerned, the tip of rotating blades is one of the most typical areas to be repaired. Unfortunately, the single crystal alloys are not easily weldable and achieving a repair with the same single crystal structure is not an easy task. In fact, most of the conventional repair processes can not be applied to advanced materials. PUBBLICATO A5011892 (PAD – 669321)

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