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Table of contents
1 Introduction
1.1 Materials under study
1.1.1 Chemical composition
1.1.2 Effect of the main chemical elements
1.1.3 Grain size
1.1.4 Secondary phases
1.1.5 Microstructure evolution at high temperature
1.2 Creep background
1.2.1 Creep deformation
1.2.2 Phenomenological viscoplasticity laws
1.3 Creep deformation mechanisms
1.3.1 Diffusion creep
1.3.2 Grain Boundary Sliding
1.3.3 Dislocation creep
1.3.4 Deformation map
1.4 Damage mechanisms
1.4.1 Necking
1.4.2 Intergranular fracture
1.4.3 Physically-based lifetime prediction
1.5 Conclusion and summary of the manuscript
2 Modeling of creep cavity nucleation
2.1 Introduction
2.2 Experimental background and results
2.2.1 Material under study
2.2.2 Microscopic observations
2.3 Macroscopic and crystalline constitutive laws
2.3.1 Macroscopic isotropic creep flow rules
2.3.2 Crystal constitutive laws
2.4 Interfacial stress field calculations
2.4.1 Influence of the particle elasticity constants
2.4.2 Influence of the random orientations of the two neighbor grains
2.4.3 Time evolution of the normal stress fields
2.4.4 Influence of temperature and remote stress
2.4.5 Relationship between interface stresses and the orientation of each grain boundary with respect to the tensile axis
2.5 Interface fracture
2.5.1 The stress criterion
2.5.2 First prediction of cavity nucleation rate
2.6 Discussion
2.6.1 Local interfacial stress
2.6.2 The fracture criterion
2.6.3 Evaluation of the Dyson law prefactor
2.7 Conclusion
3 Effect of the particle geometry
3.1 Experimental observations
3.2 Interfacial stress field calculations
3.3 Precipitate shape factor effect
3.3.1 The Eshelby theory
3.3.2 Finite Element calculations
3.4 Precipitate sharp tip effect
3.4.1 Precipitate symmetric tip
3.4.2 Precipitate asymmetric tip
3.5 Discussion of the modeling assumptions
3.5.1 2D-3D comparison
3.5.2 Evolution of the average inclusion stresses during straining
3.5.3 Influence of the lattice rotation
3.6 Summary and conclusion
4 Lifetime prediction of 316L(N)
4.1 Introduction
4.2 Creep damage mechanisms
4.2.1 Necking
4.2.2 Intergranular damage
4.2.3 Thermally-activated nucleation of stable vacancy nuclei
4.2.4 Interface fracture
4.3 stress concentrators
4.3.1 Slip bands
4.3.2 Grain boundary sliding
4.3.3 Intergranular inclusion embedded in metallic grains
4.4 Long term lifetime prediction
4.4.1 Final evaluation of the Dyson law prefactor
4.4.2 lifetime predictions in 316 SSs
4.5 Discussion and conclusion
4.5.1 Cavity nucleation model
4.5.2 Evaluation of cavity nucleation rate
4.5.3 Lifetime predictions
4.5.4 Comparison of the long term creep resistance in Incoloy 800, 316L(N) and Grade 91 steel
5 Conclusions, work in progress and perspectives
5.1 Conclusions
5.1.1 Experimental investigation of damage mechanisms
5.1.2 Finite element calculations
5.1.3 Enhanced prediction of creep lifetimes
5.2 Work in progress
5.3 Perspectives
5.3.1 Local stress concentration
5.3.2 Intergranular Diffusion
5.3.3 Precipitation
A Uncertainty in 0
B Interface normal stress values
C Cohesive law: HINTE
