Print Email Facebook Twitter Promoting a-Al2O3 layer growth upon high temperature oxidation of NiCoCrAlY alloys Title Promoting a-Al2O3 layer growth upon high temperature oxidation of NiCoCrAlY alloys Author Nijdam, T.J. Contributor Thijsse, B.J. (promotor) Faculty Applied Sciences Date 2005-11-14 Abstract The turbine blades in gas turbine engines need to be protected against high temperature oxidation and corrosion with a coating system. This coating system comprises of a Ni-based superalloy substrate, a NiCoCrAlY bond coating (BC) and an insulating ceramic thermal barrier coating (TBC). Good protection is offered when during service of the turbine a continuous alumina (a-Al2O3) layer is formed in between the BC and the TBC. However, generally, the initial stages of oxidation of NiCoCrAlY coatings proceed by the simultaneous formation of a-Al2O3 and one or more less protective oxide phases. These less protective oxides promote the failure of the coating system and are considered detrimental for the life span of the turbine blade. It is therefore crucial to control the composition and microstructure of the oxide layer already during the production process of the coating system. In this thesis, the fundamental aspects and the processing windows for promoting the exclusive growth of an a-Al2O3 layer on a NiCoCrAlY coating by thermal oxidation were studied in detail. Using a mathematical oxidation model and a range of analytical techniques it was investigated which less protective oxides develop as a function of the oxidation conditions and the BC composition and microstructure. Besides that, it was established how the composition of the oxide influenced the failure mechanisms and the life span of the coating system. Based on the results, a combined pre-annealing and pre-oxidation treatment was developed for the formation of an exclusive a-Al2O3 layer on a NiCoCrAlY bond coating. This treatment can be applied as a separate processing step in the production of a coating system to enhance the life span of turbine blades during service. Subject thermal barrier coatingcorrosionbond coatingalumina To reference this document use: http://resolver.tudelft.nl/uuid:ca478dc5-9dea-4aa0-9997-802bacebb6f3 ISBN 90-901-9910-1 Part of collection Institutional Repository Document type doctoral thesis Rights (c) 2005 T.J. Nijdam Files PDF as_nijdam_20051114.pdf 65.54 MB Close viewer /islandora/object/uuid:ca478dc5-9dea-4aa0-9997-802bacebb6f3/datastream/OBJ/view