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- Creep (1)
- Deformation mechanisms (1)
- Dislocation reactions (1)
- Dislocation theory (1)
- Lattice distortion (1)
- Microstructural degradation (1)
- Nickel-base alloys (1)
- Nickel-base superalloys (1)
- Rafting (1)
- Superalloys (1)
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.
α(1 0 0) Dislocations are observed in nickel-base superalloys after creep deformation at high temperatures and low stresses. They are formed in the γ/γ´ interfaces by a three step mechanism. First, primary dislocations with Burgers vector α/2(1 0 1) and 60° character are left behind in the interfaces when dislocation loops glide through the γ channels. The 60° dislocations move into edge orientation and react forming secondary dislocations α/2(1 1 0). In the third step, new primary dislocations are knit into the already existing meshes of primary and secondary dislocations, which results in hexagonal misfit dislocation networks consisting of secondary dislocations α/2(1 1 0) and tertiary dislocations α(1 0 0), both of edge type. This self-organisation process is explained by dislocation theory and crystallography.
Creep deformation accelerates when the α(1 0 0) interfacial dislocations enter the γ´ phase. During their climb towards the opposite interface, they attain a characteristic rectangular shape. This shape and the importance of the α(1 0 0) super dislocations for creep deformation are discussed.
Moiré fringes for misfit measurements at incoherent y/y'-interfaces of nickel-base superalloys
(1998)
The shape of X-ray reflections from the cuboidal γ/γ'-microstructure was investigated. The measurements were performed on the 4th generation single-crystal nickel-base superalloy TMS138. It is shown that reflections from non-cubic crystallographic planes split not only in d-scale due to the different spacing of the γ- and γ'-lattices but also in the pole figure due to the tilting of γ-lattice planes. This tilting results from the elastic distortion of the γ-lattice caused by the γ/γ'-misfit. The results obtained are discussed under the methodical aspect of misfit measurement.