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Title: Thermo-mechanical fatigue of the single crystal nickel based superalloy CMSX-4
Author: Drew, G. L.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2004
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This thesis has been to develop the understanding of, and capability to accurately model, the response of the commercial single crystal nickel-based superalloy turbine blade material CMSX-4TM1, and like-alloys, under thermo-mechanical fatigue, for the range of near-<001> orientation corresponding to the primary turbine blade axis. Thermo-mechanical fatigue (TMF) testing was conducted together with creep and isothermal low cycle fatigue (LCF) testing, and analysed in order to investigate inelastic deformation, microstructural evolution, crack growth and oxidation damage phenomena. Based on the results obtained selected contemporary semi-empirical and mechanistic approaches to material behaviour and lifetime modelling were assessed. Isothermal uniaxial tensile creep tests were performed and compiled for orientation q>20°, at 750°C under a constant nominal stress of 750 MPa, in parallel with uniaxial tensile creep tests stepped in temperature and stress between 950°C/500 MPa and 750°C/750 MPa conditions. The interaction of high and low temperature creep deformation mechanisms, as may be expected during TMF under constant varying temperature and stress, and the orientation dependent phenomenological behaviour were discussed in light of a detailed microstructural analysis. This work was used in the assessment of a continuum damage mechanics approach to modelling of the stress-relaxation behaviour during TMF. Isothermal LCF test specimens deformed between 550°C and 950°C over a wide range of loading conditions were analysed to determine the temperature and stress dependence of fatigue crack initiation and propagation, and the role of oxidation in these processes. Quantitative parameters were determined for use in an oxidation-fatigue crack growth model, which was shown to compare well with both 950°C LCF and TMF fatigue crack growth rate and life to failure data. In-Phase (IP), Clockwise (CW) and Counter-Clockwise (CCW) TMF cycles, chosen to simulate the behaviour at critical locations in the turbine blade, were performed between 500-950°C. The phenomenological behaviour was discussed in conjunction with fractographic, morphological and microstructural analysis, and compared with the continuum damage mechanics and oxidation-fatigue models for material behaviour and life prediction.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available