In situ deformation in T.E.M.: recent developments

In situ straining experiments in weak-beam conditions

“…The compatibility between results of weak-beam observations at 100 kV and bright field observations at 1 MeV is a first indication that the surface effects may not be very large. It is however necessary to check whether the criterium explained in § 1 is met or not.…”

“…As discussed in [1,4], most artefacts originate from the use of thin foils, owing to the elastic interaction between dislocations and the free surfaces. Several critical sample thickness can be defined, depending on the physical process studied.…”

“…For instance, in pure aluminium, the thickness should be larger than 0.2 Mm to enable cell formation, and larger than 0.8 03BCm to generate the same dislocation density as in the bulk material (see [3,4] In situ experiments in weak-beam conditions have been performed on two electron microscopes, a Philips EM-300 operating at 100 kV and more recently a JEOL 200 CX operating at 200 kV Commercial straining holders have been used at room temperature, and straining holders designed in our laboratory have been used at lower and higher temperatures. Microspecimens are also described in [1] (same issue).…”

“…Observations are always made around the thin areas near the perforation of micro-specimens, where the stress is concentrated [1]. Under such conditions, the local tensile axis is close to the tensile holder axis.…”

Quantitative in situ experiments and possible artifacts

“…Sometimes, dislocation motion is not smooth but jerky. In some cases (HCP metals, intermetallics), this behaviour is ascribed to a locking-unlocking mechanism, and activation parameters are also obtainable by measuring flight times and waiting time [5]. When dislocation motion is no more controlled by a double kink mechanism, glide is controlled by localized obstacles.…”