Activation of dislocation sources in γ-phases of nickel-base superalloys studied by use of atomic-force microscopy and transmission electron microscopy

Using in situ atomic force microscopy (AFM) and post-mortem transmission electron microscopy (TEM), the activation of dislocation sources in γ-phases of nickel-base superalloys has been investigated. Sources, at the origin of slip bands containing numerous pile-ups of several tens of dislocations, are heterogeneously distributed. They are a few micrometers apart. The physical reason for such an heterogeneity is the presence of short-range order which induces a high friction stress acting against the dislocation movement. A description of the solid solution as a combination of soft and hard areas is proposed. Dislocation sources can be activated in areas where the friction is low while the presence of hard zones hinders their operation. This distribution of hard and soft zones results from the local variations of short-range order. The distribution of the sources indicates that soft regions are a few micrometers apart.