Nanomechanical Testing Journal Club

Highly ductile amorphous oxide at room temperature and high strain rate

by Erkka J. Frankberg, Janne Kalikka, Francisco García Ferré, Lucile Joly-Pottuz, Turkka Salminen, Jouko Hintikka, Mikko Hokka, Siddardha Koneti, Thierry Douillard, Bérangère Le Saint, Patrice Kreiml, Megan J. Cordill, Thierry Epicier, Douglas Stauffer, Matteo Vanazzi, Lucian Roiban, Jaakko Akola, Fabio Di Fonzo, Erkki Levänen, and Karine Masenelli-Varlot

Science, 2019, 366, 6467, pp. 864-869

Oxide glasses possess several attractive properties for current electronics and energy applications, including resistance to thermal and chemical degradation, optical transparency and dielectric properties. However, their low toughness has limited their use, both from the perspective of restricting processing routes and mechanical reliability during their service life. This low toughness is predicated upon a lack of active plastic deformation processes, which, although generally true at conventional stresses and strains, is not necessarily the case at elevated stress/strain. One way to achieve this is reduction of inherent material flaws through testing of small, more controlled, sample volumes.

This study reports on the in situ TEM tensile and compressive properties of amorphous aluminum oxide. This is coupled with detailed atomistic simulations to gain new insight into plastic deformation processes in oxide glasses. Of particular interest, this plastic deformation was observed to be time-dependent, where the elevated strain rates of the simulation produced comparatively very low viscosity values versus the experiments. Two bond switching mediated plasticity mechanisms were identified: density changes, occurring predominantly at lower strains, and steady state viscous creep. The overall distribution of the plastic strain was homogeneous, but localized and brief fluctuations were identified where weaker groups of atoms yield through accumulated bond switching. Overall, these results indicate higher ductility in amorphous aluminum oxide than previously expected. Some important conditions for achieving this ductility were identified, which may aid in the search for new, more damage tolerant oxide materials and processing routes. Specifically, these are a dense and low defect material with low activation energy for plasticity.