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Communication Dans Un Congrès Année : 2019

Creep Mechanisms in Advanced Superalloys

Loic Nazé

Résumé

Nickel base superalloys are widely used to manufacture critical mobile and static components of the high‐temperature jet engines, as well as ground turbines. The mechanical criteria which govern the dimensioning of high performance engineering parts are ever more demanding and must be taken into account when trying to improve the creep, fatigue and corrosion resistance of Ni or Co base superalloys. The elementary physical mechanisms of plasticity and their evolution with temperature and strain rate will be summarized and related to microstructural patterns and their alteration during service. At low temperature, under high stress the ceep rate goes through two minimum values, below 1% strain, in most Ni base superalloys with adequately low stacking fault energy. The first minimum is associated with the movement of a first generation of dislocations, confined to definite matrix channels, the essential function of them is to compensate and cancel out the elastic pre‐strain of these channels, caused by the γ‐γ’ misfit. This mechanism, under very low stress, is responsible for negative creep. Under higher stresses, after several slip systems have been activated, shear and twinning of the ordered γ’ precipitates can take place incompatibility with that of the matrix and the development of planar defects, on several slip planes, leads to the second minimum. At high temperature, under low stress, the initially isotropic microstructures rapidly tend to become rafted. The origin of this phenomenon, the role of the misfit parameter in the development of rafted structures and the consequences of these patterns on the mechanical resistance of the material will be examined. At intermediate temperatures, all the mechanisms described above can be simultaneously activated and interact with one another in various ways depending on the stress level and the strain rate. The differences in chemical compositiion of alloys and the various engineering microstructures obtained after optimized thermo mechanical treatments or single crystal growth will be considered in relation with their ability to enhance or deteriorate the creep resistance of a number of currently used and/or recently developed high‐performance alloys.
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Dates et versions

hal-02427025 , version 1 (03-01-2020)

Identifiants

  • HAL Id : hal-02427025 , version 1

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Fivel Marc, Loic Nazé, Jean-Loup Strudel. Creep Mechanisms in Advanced Superalloys. International Conference on Advanced Materials and Processes for Defence Applications, Sep 2019, Hyderabad, India. ⟨hal-02427025⟩
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