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Mechanical Characterisation of CMSX-3 and CMSX-4 with Pt and PtAl Coatings Under Thermo-Mechanical Fatigue Loading Conditions

Key Information

Supervisors: Dr R Lancaster and Prof M Whittaker

Expected Interview Date: March 2020

The approach for the assessment of fatigue damage from cyclic variation of stress, strain and temperature as experienced in the hot section of a gas turbine uses the range of stress or strain and the maximum temperature attained in the cycle against which to predict the damage from fatigue curves. This results in a fatigue life based on an elastic prediction which is then assessed against the engine life requirements. Recent methods have proposed the generic use of analyses with plasticity and creep included to determine the relaxed stress and strain state with a revised fatigue damage assessment approach.

In the case of hot section components, the stress or strain may vary in-phase with the temperature, or there may be a phase difference which at its extreme would be completely out-of-phase with the temperature. This case occurs in a hotspot where the maximum temperature condition generates a significant compressive stress.

In other types of cycle where transient effects occur due to the boundary conditions of the external hot gas temperature and the internal cooling temperature combined with the mechanical loading due to rotational and gas loading forces, the peak stress or strain may develop on the rise or fall to the peak temperature condition, and would correspond to a much lower temperature than the peak.

Such components do have the added benefit of thermal barrier coatings, but to date, little understanding is currently available that truly captures how the mechanical behaviour differentiates across the two materials.

The work proposed in this project is to investigate thermo-mechanical fatigue damage in high temperature coated systems through a thorough review of existing data available on single crystal materials, to develop a TMF lifing model that can represent the true service behaviour observed including the influence of creep and oxidation that occurs at high stresses and temperatures, to validate this model with targeted TMF tests and to investigate the fracture behaviour of the TMF experiments in comparison with predicted stress fields from finite element models.
The work could investigate how damage is accumulated in a range of TMF cycles, predicting the first cycle and stabilised cycle responses under these conditions. The incremental accumulation of damage around the cycle may generate an understanding of the driving behaviours in TMF. In particular, a holistic knowledge of the damage evolution experienced in a counter-clockwise -135° cycle is of great interest. Research could also incorporate the use of PD crack monitoring and Digital Image Correlation (DIC) for advanced characterisation of the TMF behaviour.

The materials of choice would be the nickel based single crystal superalloys CMSX-3 and CMSX-4 with Pt and PtAl coating systems.
TMF test data from Rolls-Royce would be made available in addition to that available from open literature.
Outline Plan:

(1) Familiarisation with previous work, literature and fatigue data on TMF in single crystals, with particular emphasis on coated materials
(2) Develop TMF testing capability and propose validation tests
(3) Perform validation tests including fractographic studies
(4) Demonstrate application to an engine component
The Materials and Manufacturing Academy (M2A) in the College of Engineering is a Swansea University initiative which provides postgraduate research training in partnership with industry; providing access to world-class laboratories and a wealth of academic and industry expertise.
Sponsoring Company Rolls Royce plc
Company Website Eligibility
We welcome applications from candidates with an Engineering or Physical Sciences degree (minimum level 2:1), or a combination of degree and equivalent experience to the same level.
Normally, we would expect candidates to have met the University’s English Language requirements (e.g. IELTS 6.5 overall with 5.5+ in each component) by point of application. 
Full eligibility can be found at https://www.materials-academy.co.uk/eligibility
Fees at UK/EU rate and a stipend of £20000 per annum for a period of four years.
For full details on funding eligibility, please refer to the Materials and Manufacturing Academy (M2A) Website.
Due to funding restrictions, this scholarship is not open to ‘International’ candidates.
Closing Date 1 April 2020

Start Date October 2020

Apply Now

Informal enquiries about this studentship are welcome and may be directed by email to: M2A@swansea.ac.uk