NiCoCrAlYHf coating evolution through multiple refurbishment processing on a single crystal nickel superalloy
Mudith Karunaratne
Rachel Thomson
2134/14300
https://repository.lboro.ac.uk/articles/conference_contribution/NiCoCrAlYHf_coating_evolution_through_multiple_refurbishment_processing_on_a_single_crystal_nickel_superalloy/9233672
A combination of creep tests, ex-service blade samples, thermodynamic equilibrium calculations, combined thermodynamic and kinetic calculations, image analysis, chemical composition
mapping and heat treatments have been conducted on PWA1483 to determine if microstructural
rejuvenation can be achieved when taking the presence of oxidation coatings into account as part
of a blade refurbishment strategy.
The work has shown that the γˊ morphology changes during creep testing, and that through
subsequent heat treatments the γˊ microstructure can be altered to achieve a similar γˊ size and
distribution to the original creep test starting condition. Thermodynamic equilibrium calculations
have been shown to be helpful in determining the optimum temperatures to be used for the
refurbishment heat treatments.
The interaction of oxidation resistant coatings with the alloy substrate and refurbishment process
have been explored with both experimental measurements and coupled thermodynamic and
kinetic calculations. The predictive nature of the coupled thermodynamic and kinetic calculations
was evaluated against an ex-service blade sample which had undergone refurbishment and further
ageing. In general there was good agreement between the experimental observations and model
predictions, and the modelling indicated that there were limited differences expected as a result of
two different refurbishment methodologies. However, on closer inspection, there were some
discrepancies occurring near the interface location between the coating and the base alloy. This
comparison with experimental data provided an opportunity to refine the compositional
predictions as a result of both processing methodologies and longer term exposure. The improved
model has also been used to consider multiple processing cycles on a sample, and to evaluate the
coating degradation between component service intervals and the consequences of rejuvenation of
the blade with repeated engine exposure. The results from the experimental work and modelling
studies potentially offer an assessment tool when considering a component for refurbishment.
2014-03-12 15:14:57
Creep
Coating
Refurbishment
Gas turbine
Materials Engineering not elsewhere classified