In situTEM nanomechanics

Abstract

IntroductionThe mechanical properties of any material are highly correlated with its defect structure. Starting in the late 1950s, 1 in situ straining stages for use in transmission electron microscopes that could provide dynamic observations of dislocation motion in metals were developed. In the following years, research teams fabricated various transmission electron microscopy (TEM) straining holders, including some that could operate at low or high temperature. Since then, in situ TEM straining tests have been performed to study the behavior of dislocations and their interactions with other defects such as twins, grain boundaries (GBs), and interfaces.After early load sensor integration developments, 2 , 3 in situ TEM mechanical testing with quantitative load measurement expanded toward commercialization in the beginning of this century, including mechanical probing modes such as nanoindentation. 4 These developments are particularly useful for studying size effects in materials, whereby mechanical properties and microstructure can be tuned by the physical dimensions (internal such as grain size or external such as fi lm thickness) of materials. 5 -7 At the micrometer or nanometer scale, the sample dimensions can be of the same order as the defects that carry the deformation, such as the length of a dislocation line or the thickness or spacing of twins. When this occurs, strong size effects can change the deformation mechanisms and the corresponding mechanical properties. Quantitative in situ TEM mechanical testing is therefore an ideal tool for studying the origin and principles of these size effects. This review provides an overview of available in situ TEM techniques and recent studies performed on dislocation behavior, dislocation/boundary interactions, deformation twinning, and GB-mediated plasticity. We also provide a critical discussion of the effects of size on different deformation mechanisms and the correlated mechanical properties of materials. Some of these mechanisms are summarized in Figure 1 . In situ TEM straining techniquesVarious tools for mechanical testing by a transmission electron microscope that exist today 8 are briefl y detailed in this section. They span from simple motorized grips to elaborate mechanical testing units capable of returning values for load and displacement.In classical tensile holders for TEM, samples are attached to a pair of jaws, and one side is slowly pulled by an electric motor located in a housing unit outside the TEM instrument. A rigid shaft ensures strain transmission at speeds ranging from 10 nm/s to 10 µm/s. This simple technique 9 has various advantages because of its high versatility. Virtually any thin or thinned sample can be strained as soon as it is attached to In situ transmission electron microscopy (TEM) nanomechanical testing has benefi ted from a number of recent technical developments related to both how deformation is imaged and how deformation is induced and measured inside a TEM instrument. These developments have led to new insights into the ...

Disconnections kinks and competing modes in shear-coupled grain boundary migration

“…However, recent experiments have shown that under specific conditions (dislocation depletion, nanocrystalline materials, bicrystal...), grain boundaries (GBs) can themselves participate in plastic deformation [1][2][3][4][5]. Among the possible GB-based mechanisms, the shearcoupled GB migration is especially efficient compared to other mechanisms [6]: The GB migration over a distance m is accompanied by the relative in-plane translation d of the two grains forming the GB.…”

Local and transient nanoscale strain mapping during in situ deformation

“…3,4 In addition to the ex situ analysis of defects, in situ deformation in the TEM has provided great insight into the fundamental mechanisms occurring during deformation. 5 The development of in situ deformation holders allowing for high-resolution measurements of the loaddisplacement relationship with sufficient sensitivity to detect transient phenomena such as the nucleation of bursts of dislocations has enabled quantitative correlation with real-time diffraction contrast images revealing these mechanisms. 6,7 The development of compression and tension geometries with well-defined gauge sections has further enabled the measurement of time-resolved global stresses and strains from the load-displacement curve.…”

“…6,7 The development of compression and tension geometries with well-defined gauge sections has further enabled the measurement of time-resolved global stresses and strains from the load-displacement curve. 5 However, this measured plastic strain is not an intrinsic parameter of a material, but rather is a summed response of a volume of material based on a specific set of defects. Elastic strain is fundamentally the displacement of individual atoms from their relaxed positions; but a robust way to measure the local elastic strain, which subsequently drives defect propagation during deformation, has been lacking.…”

Review Article: Case studies in future trends of computational and experimental nanomechanics

“…The evolution of modern nanoscale 60 and microscale 61 mechanical testing has now made it possible to perform detailed and precise experiments where exact orientations, 62 environments, 63 and stress states 64 can be studied quantitatively and systematically. However, both the spatial and temporal resolutions of these techniques do not yet overlap with those of atomistic simulations.…”