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Loss of crystallinity under the influence of mechanical stress has been documented mainly in the context of shock metamorphism. Recently, however, it has become apparent that amorphization can result from quasi-static deformation, particularly in the case of grain boundaries in olivine loaded under high stress, thus promoting grain boundary sliding [1]. Stress-induced amorphization has thus emerged as a potential deformation mechanism in minerals and rocks, among other materials [2]. The prevailing view is that activation of stress-induced amorphization is promoted when conventional plasticity, e.g. driven by dislocations, is inhibited, however the underlying mechanisms are still unclear.

We propose to use nanomechanical testing to investigate the mechanisms of stress-induced amorphization. We utilize the PI-95 TEM Pico-indenter holder and the Push-to-Pull (PTP) device (Bruker, Inc.) to conduct quantitative tensile tests at room temperature, in situ in a transmission electron microscope.

In this contribution, we present the results of two studies on minerals with very contrasting mechanical properties: olivine, for which evidence of amorphization under stress has already been reported, and talc, a much softer mineral. We demonstrate that stress-induced amorphization can be activated under high stresses at room temperature in small-sized olivine bi-crystals. Amorphized grain boundaries are then subject to sliding and the resulting constitutive equation of such a sliding boundary has been determined. We show by Molecular Dynamics that this phenomenon can be considered as a case of transformation plasticity. We present also some preliminary results of amorphization in talc loaded in tension perpendicular to the basal plane.

[1] V. Samae et al., 2021, Stress-induced amorphization triggers deformation in the lithospheric mantle. Nature 591, 82–86.

[2] H. Idrissi et al, 2022, On amorphization as a deformation mechanism under high stresses. Current Opinion in Solid State & Materials Science. 26(1), 100976.