The evolution of dislocation substructures formed in single crystals of NiAl by tension creep testing at temperatures between 1123 K and 1473 K has been studied. Significant differences in the dislocation structure are evident in samples tested in different orientations.
For samples tested in soft orientations, where glide of (001) dislocations is easy, some interacting (001) dislocations can be found. In hard oriented samples, the density of dislocation networks is high and low angle subgrain boundaries are observed. The subgrain size in hard oriented crystals is strongly stress dependent.
In hard oriented crystals, (001) dislocations have no resolved shear stress for glide and must move by the slower process of climb; or by glide of (110) dislocations. The (001) dislocations are captured in networks, leading to a high total dislocation density in hard oriented samples compared to soft oriented crystals, whereas the dislocation density within the volume of subgrains is constant for all orientations.
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