Various forms of the plastic deformation in single crystals were studied in pure nickel and nickel alloys oriented for single slip [135] and multiple slip [001]. Particular attention was paid to the heterogeneity of deformation observed at two distinct scales: the slip bands and the dislocation organizations. The slip bands emerging at the surface could be studied using the atomic force microscopy (AFM). The height of extrusions and inter-band spacing depends on the orientation of tensile axis, the strain level and the nature of the alloy. At another scale, dislocation organizations typical of face-centered cubic crystals were observed, which depended upon the orientation of tensile axis and on the stacking fault energy. A study by transmission electronic microscopy permitted the dimensional characteristics of these structures to be approached. In the case of mono-crystal oriented for single slip strained in stage III (γ ~ 0.8) a correlation was observed between the inter-band spacing (d) and the inter-wall spacing (δ) of the type I dislocation pattern. This result suggests that this kind of walls act as a screen to the mobility of dislocations unlike equiaxed cells that would be only an obstacle to the dislocation mobility. This internal length was lower for Ni16%Cr alloy than for nickel. Consequently, stacking fault energy was probably a parameter which affects the internal length in relation with cross-slip capability. On the other hand, results, obtained of the [001] direction in nickel, were more complex due to multiple slip. Indeed, only equiaxed cells were observed for this orientation with cell size magnitude (δ) far lower than those observed for inter-band spacing (d). As in the case of samples oriented for single-slip, the equiaxed cells observed for samples oriented for multiple-slip seem to be only obstacles to the mobility of dislocations. However, there were probably walls associated with this kind of cells which act as barriers to the movement of dislocations.

Some Correlations between Slip Band Emergence and Dislocation Pattern. C.Huvier, E.Conforto, H.El Alami, D.Delafosse, X.Feaugas: IOP Conference Series - Materials Science and Engineering, 2009, 3[1], 012012