Oxidation behaviour of single crystal nickel-based superalloys: intermediate temperature effects at 450–550°C

ABSTRACT

The oxidation behaviour of two single crystal Ni-based superalloys has been investigated at 450°C and 550°C. Isothermal oxidation was carried out for varying times and it was found that exposure resulted in a sub-micrometre thick oxide. The external and internal oxide kinetics were studied via high-resolution image analysis and both showed sub-parabolic growth rates. Thermogravimetric tests indicated that the overall oxidation growth obeys a near quartic power law while parabolic kinetics can describe the transient oxidation period. Characterisation of the resulting oxides was carried out using electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Results from thermodynamic modelling of the oxide formation are also presented to further assess the postulated mechanism of low-temperature oxidation in these Ni-based superalloys.

KEYWORDS:

• Oxidation
• Ni superalloy
• low temperature
• single crystal
• sub-parabolic kinetics

Acknowledgements

This work was supported by Uniper Technologies. Thanks are due to Rugby Labs – GE Power (formerly Alstom) for materials supply. The authors also would like to thank Dr Adriana Encinas-Oropesa and Dr Nigel Simms at Cranfield University for use of the TGA facilities, Dr Geoff West from Warwick University for access to the STEM-EDX and Dr Shan Jin from Thermo-Calc Software for the thermodynamic calculations.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Engineering and Physical Sciences Research Council (EPSRC) [grant number 512444116].