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Author: Caron, Arnaud × Type: Text ×

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    Lower nanometer-scale size limit for the deformation of a metallic glass by shear transformations revealed by quantitative AFM indentation
    (Frankfurt am Main : Beilstein-Institut, 2015) Caron, Arnaud; Bennewitz, Roland
    We combine non-contact atomic force microscopy (AFM) imaging and AFM indentation in ultra-high vacuum to quantitatively and reproducibly determine the hardness and deformation mechanisms of Pt(111) and a Pt57.5Cu14.7Ni5.3P22.5 metallic glass with unprecedented spatial resolution. Our results on plastic deformation mechanisms of crystalline Pt(111) are consistent with the discrete mechanisms established for larger scales: Plasticity is mediated by dislocation gliding and no rate dependence is observed. For the metallic glass we have discovered that plastic deformation at the nanometer scale is not discrete but continuous and localized around the indenter, and does not exhibit rate dependence. This contrasts with the observation of serrated, rate-dependent flow of metallic glasses at larger scales. Our results reveal a lower size limit for metallic glasses below which shear transformation mechanisms are not activated by indentation. In the case of metallic glass, we conclude that the energy stored in the stressed volume during nanometer-scale indentation is insufficient to account for the interfacial energy of a shear band in the glassy matrix.
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    Importance of surface oxide for the tribology of a Zr-based metallic glass
    (Heidelberg : Springer, 2017) Kang, S.J.; Rittig, Kai Thomas; Kwan, S.G.; Park, H.W.; Bennewitz, Roland; Caron, Arnaud
    Thermally grown surface oxide layers dominate the single-asperity tribological behavior of a Zr60Cu30Al10 glass. Increase in oxidation time leads to an increased contribution of shearing and a corresponding decreased contribution of ploughing to friction. This change in the dominating friction and wear mechanism results in an overall minor decrease of the friction coefficient of oxidized surfaces compared to the metallic glass sample with native surface oxide. Our results demonstrate the importance of creating a stable oxide layer for practical applications of metallic glasses in micro-devices involving sliding contact.