Quantitative measurements in in situ straining experiments in transmission electron microscopy

Abstract

SummarySeveral examples of recent studies by in situ straining experiments in a transmission electron microscope performed in the Toulouse group (France) are presented. In particular, quantitative measurements of the features of the dislocation motion are described. These examples deal with individual or collective propagation of dislocations, which are submitted to various types of obstacle. Different metallic materials are investigated: magnesium, intermetallics, aluminium alloys and g phase of a superalloy.

In situ TEM observations of reverse dislocation motion upon unloading in tensile-deformed UFG aluminium

“…Rectangular microsamples, of size 3mm×1mm, were prepared by spark cutting, followed by mechanical and electro-polishing. They were fixed on a Gatan room-temperature straining device, and strained in a 2010HC transmission microscope [4]. The fixation was such that the stress could be released without inducing any compression.…”

TEM study of structural hardening in a new martensitic steel for aeronautic application

“…The choice of 0.2% plastic strain is usual for post mortem observations of dislocations, as it corresponds to plastically, but not heavily, deformed materials, as during in situ tests. Details on the TEM in situ deformation technique have been specified in previous studies [9,10]. The HREM observations were performed using a FEI-SACTEM (Tecnai F20) operating at 200 kV.…”

Glide and Mixed Climb Dislocation Velocity in γ-TiAl Investigated by In-Situ Transmission Electron Microscopy

“…The method to measure using the line tension of curved dislocations [20] could not be employed here, because the curved portions disappeared always rapidly. Nevertheless, the stresses induced by the thermal effects in the TEM thin foils is assumed to yield comparable values in all the experiments, because at the onset of the movement of the dislocations ( ), can be approximated to the critical resolved shear stress [20,21] or to the resolved climb stress . Furthermore, because and determined in the post-mortem experiments are close for glide and mixed climb (see Table 1), the same probably holds for the in-situ experiments.…”