Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.748897
Title: Environmentally-assisted fracture events in high strength nickel-based superalloys
Author: Németh, André Anjou Nordine
ISNI:       0000 0004 7232 6675
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
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Abstract:
There is significant interest in defining and quantifying the performance of polycrystalline Ni-based superalloys - particularly high strength ones produced via powder processing for turbine disc applications - at temperatures between 700 and 800°C. This is because the outer rims of a high pressure turbine disc in turbine applications for jet propulsion can experience such temperatures during a significant portion of the flight cycle while also being exposed to oxidative/corrosive gases which cause intergranular environmentally-assisted crack growth. In this work, a testing methodology involving slow strain-rate tensile tests on a electro-thermal mechanical testing device is presented which is capable of the rapid assessment of an alloys susceptibility to environmentally-assisted cracking. It makes use of miniature test pieces which are shown to be of sufficient size to characterise macroscopic properties. This approach is first validated and then utilized to perform systematic experimentation involving the control of the important microstructural and compositional variables such that the effects of others can be isolated, identified and confirmed. The need to better understand the embrittlement mechanism was addressed at the most appropriate lengthscale using high resolution characterisation techniques which are capable of providing the most revealing information including scanning and transmission electron microscopy and nanoscale secondary ion mass spectrometry. Our results have implications for alloy design efforts – rationalising the effect of heat treatment and demonstrating that for a given strength level, both more and less damage tolerant variants can be designed.
Supervisor: Crudden, David J. ; Armstrong, David E. J. ; Reed, Roger C. Sponsor: EPSRC ; Rolls-Royce
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.748897  DOI: Not available
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