What can be learnt from TEM in-situ straining experiments?

A few examples are given to demonstrate the key role of TEM in-situ straining tests in the investigation of dislocation mechanisms. This technique provides quantitative information on the kinetics of these phenomena, like dislocation velocities or mobile dislocation densities, but also in evidencing subtle mechanisms that would have left no record in post-mortem observations. In addition to individual behaviour controlled either by individual dislocation propagation or by dislocation nucleation, the collective behaviour of a large number of interacting dislocations also proved to be accessible by in-situ TEM through a statistical analysis of elementary events. These events (e.g. dislocation jump lengths) often reveal a scale invariance. Such a scale invariance is also observed at larger scales, e.g. by the measurement of dislocation avalanches using acoustic emission.