Over the past decades many advances were obtained in the aircraft industry in the area of gas turbines. Compared to the engines of the first generation made of heat resistant steel, newly designed turbine parts by using nickel base superalloys lead to a doubling of the gas inlet temperature and hence to an increase of turbine efficiency. The introduction of new vacuum casting technologies of directional solidification enables the development of hot gas path components without weakening large angle grain boundaries (single crystal alloys) as well as components without vertical, to the load axis running grain boundaries (directionally solidified alloys). However, as a consequence of mechanical, thermal and corrosive loads during operations, the engine parts are damaged. This leads to a loss of efficiency of the engines as well as a decrease of flight safety. Among maintenance and repair procedures, the high temperature brazing is established as an important method. In particular worn nozzle guide vanes and turbine blades can be repaired by means of special repair brazing processes. In case of the high temperature repair brazing process for polycrystalline nickel base superalloys, special powdery repair mixtures are used. Those usually consist of a nickel base brazing alloy containing small amounts of boron mixed with an additive alloy. For single crystal and directionally solidified turbine components made of nickel base superalloys, the combination of filler metal and additive material will need a different chemical composition. It may exhibit changed diffusion behaviour when compared to repair brazing of polycrystalline turbine blades due to the lack of grain boundaries. Nickel base repair mixtures containing hafnium as a melting point depressant to reduce the content of boron significantly were developed for the repair procedure of single crystal and directionally modified turbine components. Commercial products were used in order to allow and guarantee as practical as possible an assessment of the developed repair mixtures.
Advanced high temperature repair brazing for single crystal and directionally solidified turbine components
2008
9 Seiten, 4 Bilder, 3 Tabellen, 11 Quellen
Conference paper
English
British Library Conference Proceedings | 2008
|Directionally solidified materials for high temperature service
TIBKAT | 1983
|HIGH TEMPERATURE BRAZING OF GAS TURBINE COMPONENTS
SAE Technical Papers | 1956
|