Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (9)
- Beitrag zu einem Sammelband (9)
- Vortrag (8)
- Posterpräsentation (2)
Schlagworte
- Creep (9)
- Superalloys (8)
- CMSX-4 (3)
- Nickel alloys (3)
- Nickel-base superalloys (3)
- Rafting (3)
- Creep damage (2)
- Dendritic structure (2)
- Misfit (2)
- Porosity (2)
Eingeladener Vortrag
- nein (8)
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.
Electron microscopy investigation of the structure of a compact extruded from nanopowder of nickel
(2007)
A new technique for investigation of interfacial dislocations in nickel-base superalloys by scanning electron microscopy is presented. At high temperatures the pressure of interfacial dislocations against the γ/γ'-interface causes grooves. This 'fingerprint of the dislocation network' is visualized by deep selective etching, which removes the γ'-phase down to the γ/γ'-interface. Compared with transmission electron microscopy, the proposed method has important advantages: observation of large sample areas, no superposition of dislocations lying in different specimen depths, possibility of three-dimensional view of dislocation configurations, information about the dislocation mobility, reduced time for preparation and visualization. The method can be applied for multiphase materials where the interface is grooved by interfacial dislocations.
The influence of small rhenium additions on the lattice spacing of a nickel solid solution was investigated using a nickelrhenium single crystal with an axial macrosegregation of rhenium. The effect of rhenium on the lattice spacing of the nickel solid solution was found to be similar to that of tungsten.
Changes in the structure of single-crystal (SC) superalloy SRR99 during creep at 980 °C and 200 MPa were investigated. Geometrical parameters of the y/y'-microstructure, y/y'-misfit, stresses in the phases and local misorientation of the structure were determined at defined points of the dendritic structure by use of X-ray diffraction (XRD), wavelength dispersive X-ray spectroscopy (WDXS), scanning (SEM) and transmission (TEM) electron microscopy. Correlation of the microstructural period and local misorientation of the structure with creep strain were found.
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.