In Situ Quantitative Tensile Testing of Antigorite in a Transmission Electron Microscope

Abstract

The determination of the mechanical properties of serpentinites is essential toward the understanding of the mechanics of faulting and subduction. Here we present the first in situ tensile tests on antigorite in a transmission electron microscope. A push‐to‐pull deformation device is used to perform quantitative tensile tests, during which force and displacement are measured, while the evolving microstructure is imaged with the microscope. The experiments have been performed at room temperature on 2 × 1 × 0.2 μm3 beams prepared by focused ion beam. The specimens are not single crystals despite their small sizes. Orientation mapping indicated that several grains were well oriented for plastic slip. However, no dislocation activity has been observed even though the engineering tensile stress went up to 700 MPa. We show also that antigorite does not exhibit a purely elastic‐brittle behavior since, despite the presence of defects, the specimens accumulate permanent deformation and did not fail within the elastic regime. Instead, we observe that strain localizes at grain boundaries. All observations concur to show that under these experimental conditions, grain boundary sliding is the dominant deformation mechanism. This study sheds a new light on the mechanical properties of antigorite and calls for further studies on the structure and properties of grain boundaries in antigorite and more generally in phyllosilicates.

Deformation of Antigorite and Its Geological Implications

“…(2020) and Idrissi et al. (2020) showed a total lack of dislocation activity in antigorite, where strain occurs only by shear cracks and cataclasis at grain boundaries, which are observed in our samples (e.g., Figure 7). The development of CPOs was proposed to occur through the formation and progressive rotation of antigorite blades by sliding along the basal plane (i.e., the [001] plane; Hansen et al., 2020); a similar mechanism has also been considered responsible for the formation of CPOs in calcite deformed in the brittle regime (Demurtas et al., 2019).…”

“…Furthermore, it is unlikely that antigorite has five independent slip systems (i.e., the Von Mises criterion cannot be met). The two most recent studies (Hansen et al, 2020;Idrissi et al, 2020) actually show that the dislocations observed in antigorite may not even truly contribute to deformation. These facts suggest that completely plastic flow of antigorite cannot be achieved in the deformation of antigorite.…”

Creep Rheology of Antigorite: Experiments at Subduction Zone Conditions

“…Transmission electron microscopy investigations of naturally and experimentally deformed samples highlight kink bands which have orientations consistent with slip along both a and b directions of intact sheets (Auzende et al., 2015, Figures 4e and 4f). However, during tensile in‐situ transmission electron microscopy experiments (Idrissi et al., 2020), movement of dislocations was not observed ‐ as it was for other materials deformed using the same technique (Idrissi et al., 2016); instead evidence for grain boundary sliding parallel to grain cleavage is observed.…”

“…The systematic variation of our data during individual tests and consistency with the LTP flow law suggest that the creep rate is limited by the same underlying plastic mechanism over the explored range of conditions. For layered materials like antigorite, previous work shows that deformation is accommodated by basal shear mechanisms, which can involve sliding along shear microcracks or grain boundaries (e.g., “asperity friction” Escartin et al., 1997; Hansen et al., 2020; David et al., 2020; Idrissi et al., 2020), basal and sub‐basal dislocations (e.g., (001), (101), and (10$$\overline{1}$$) systems (Amiguet et al., 2014; Auzende et al., 2015)), or ripplocations (Gruber et al., 2016). The mechanical basis for the LTP law suggests that moving defects along these crystallographic planes encounter a “barrier” which can be overcome by stress or thermal activation.…”

Fracture behavior and characterization of free-standing metal silicide thin films

“…In the uniaxial tension test [41][42][43][44][45][46], which is schematically illustrated in Fig. 1.2 b, deformation and failure of the thin film specimen occur under uniform stress acting along a single axis.…”