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- Englisch (9)
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- Rafting (6)
- Creep (4)
- Nickel-base superalloys (4)
- Single crystal (3)
- Creep damage (2)
- Dendritic structure (2)
- Microstructural degradation (2)
- Residual stresses (2)
- Viscoplasticity (2)
- CMSX-4 (1)
Rafting during high temperature deformation in a single crystal superalloy: experiments and modeling
(2012)
A new experimental technique (repeated load annealing of flat wedge shaped specimens) was proposed for characterization of microstructural degradation under creep conditions. This technique was applied to investigate the microstructural degradation of the nickel-base superalloy CMSX-4 in a wide range of temperatures and stress levels. The results obtained allowed to describe analytically the kinetics of rafting, which is important to predict the reduction of fatigue lifetime and yield stress.
Experimental characterization and mechanical modeling of creep induced rafting in superalloys
(2012)
A constitutive model has been developed for the high temperature mechanical behavior of single crystal superalloys, including rafting and its consequences. The flow stress depends on the γ channel width via the Orowan stress. An evolution equation for channel widening during high temperature straining has been derived and calibrated with measurements. Therein, rafting is assumed to be driven by the relaxation of internal stresses. The model is able to represent the mechanical softening at high stresses consecutive to rafting. The model has been applied to simulate rafting during uniaxial creep in several crystal orientations, in notched specimens as well as in cyclically loaded specimens.
Creep damage of single-crystal nickel base superalloys: mechanisms and effect on low cycle fatigue
(2010)
The main mechanisms of creep damage of single-crystal nickel-base superalloys are the loss of the interface coherency, coarsening of the γ / γ'-microstructure, precipitation of topologically closed packed phases and growth of porosity. This degradation deteriorates the mechanical properties such as yield stress, creep lifetime and especially low-cycle fatigue life, which can be reduced nearly by a factor of 10. The degradation kinetics during creep was characterised quantitatively on the superalloy CMSX-4. A new non-destructive testing technique was applied to cover a wide test parameter range with few specimens in a relatively short time: repeated load annealing of wedge shaped specimens.
Constitutive modelling of creep degradation due to rafting in single-crystalline Ni-base superalloys
(2009)
A constitutive model for the mechanical behaviour of single-crystalline superalloys at high temperatures has been developed. The model relies on the slip system theory and is able to predict rafting and its influence on plastic flow. The kinetics of rafting are assumed to be driven by the reduction of the internal stresses represented by the macroscopic back-stress. The rafting effect is incorporated in the model through the dependence of the Orowan stress on the channel width. The model has been validated for the alloy CMSX-4 at 950 °C. The rafting part of the model has been calibrated by measurements of the channel widths after several levels of creep strains and for several loads.