Evolution of residual stress in environmental barrier coatings for ceramic matrix composites

Ceramic matrix composites (CMCs) are exciting new materials for use in gas turbine engines, in which an environmental barrier coating (EBC) is needed to protect the CMCs from water vapour attack.  The coating also serves as a thermal barrier coating (TBC).  The EBC is a prime reliant coating (unlike a TBC), without which CMC components would have very limited life in the harsh gas turbine engine operating environments.

One major factor governing the life of an EBC is its residual stress state, which results from the quenching process of its manufacture via the thermal spray process and the cooling after spraying.  The coating stress state also changes with thermal excursions such as heat-treatment and engine operations.  This is because of factors that include the mismatch of coefficients of thermal expansion (CTE), thermal gradients, coating crystallization, phase change and sintering, among others.

This iCASE project, supported by Rolls-Royce Plc, aims to develop new understanding and models for coating stress evolution including the effects of EBC crystallization, phase change, sintering, and thermal mechanical loading.  Both testing such as hole-drilling using focused ion beam with image correlation, and the finite element method that incorporates creep of the Si bond coat, for example, will be part of the project scope.

This is a 4-year EPSRC Industrial CASE studentship in conjunction with Rolls Royce Plc and will provide full fees and maintenance for a student who has Home/Republic of Ireland or Islands fee status.  The stipend will be at least £17,285 per year.  Information on fee status can be found at http://www.ox.ac.uk/admissions/graduate/fees-and-funding/fees-and-other-charges 

Candidates will be considered in the November 2020 admissions field which has an application deadline of 13 November 2020 and, if the studentship is unfilled, in the January 2021 admissions field which has an application deadline of 22 January 2021.  

Any questions concerning the project can be addressed to Professor James Marrow (james.marrow@materials.ox.ac.uk).  General enquiries on how to apply can be made by e‑mail to graduate.studies@materials.ox.ac.uk.  You must complete the standard Oxford University Application for Graduate Studies.  Further information and an electronic copy of the application form can be found at http://www.ox.ac.uk/admissions/postgraduate_courses/apply/index.html.

X-ray computed nano-tomography image of a SiC-SiC composite

X-ray computed nano-tomography image of a SiC-SiC composite

 

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