Is plastic flow always controlled by dislocation mobility? An answer from in situ transmission electron microscopy straining tests.

In situ transmission electron microscopy (TEM) straining experiments are used to illustrate in two extreme cases the possible role of dislocation nucleation and exhaustion as a controlling factor in plastic flow. In the first example (FeAl intermetallic compounds), a thermally activated dislocation exhaustion is responsible for an anomalous stress-temperature dependence and an associated small strain rate sensitivity, the latter being evidenced during in situ experiments through unstable localized slip. The second example (heavily drawn pearlite) shows specific dislocation loop nucleation processes that may account for the Hall-Petch law breakdown characteristic of fine scale nanostructures.