Hardness and plastic deformation in a bulk metallic glass

Determination of the mechanical properties of amorphous materials through instrumented nanoindentation

“…The material pile-up, indicative of indentation dominated by plastic deformation, was clearly identified. The images also show the semi-circular shear bands, in the form of overlapping layers of upwardly displaced material, typical of indentations in bulk metallic glasses [16]. The pile-up behaviour makes the sides of the residual imprint bow out, leading to the concavity found in the indentation edges.…”

“…Keryvin et al [15], Lewandowski and Lowhaphandu [44] and Yuan et al [45] suggested that Zr-based glass shows limited pressure sensitivity with f$ < 10°. Others authors [16,46] maintain that these materials present a moderate pressure dependence with f> « 20°. The present results (fi K, 14°) and the good agreement in the estimation of the compressive strength support the validity of the method for determining the mechanical properties of metallic glasses from instrumented indentation.…”

“…Finally, the finite element results in the elastic regime follow the analytical expression for the elastic contact of a conical indenter on a semi-infinite half space [37] H tan y E* a r o> (16) It should be noted, however, that it is extremely unlikely that real materials will lie within this region in the case of a blunt indenter (such as the one used here).…”

“…Further loading leads to the localization of the deformation within the shear band (or in an array of parallel bands) without any strain hardening. There is a wide body of experimental evidence showing that the yield criterion for shear band formation in metallic [13][14][15][16] and ceramic glasses [17,18] as well as in polymers [19][20][21][22] depends on the hydrostatic stress and that the yield surface of these materials is adequately represented by either the Mohr-Coulomb or the Drucker-Prager yield criterion. Mathematically, the yield surface (<P -0) is given by [23] #= v / 3^2-^+^tan^ = 0…”

Formation, thermal stability and deformation behavior of graphite-flakes reinforced Cu-based bulk metallic glass matrix composites

“…More recently, bonded interface technique through Vickers indentation were used as a very useful method to study the deformed plastic zone beneath an indentation of different kinds of as-cast BMG alloys or as-annealed alloys, which can help image the deformation pattern directly and provides insights into the governing deformation mechanisms [14][15][16][17]. In this paper, we report the preparation of graphite-flakes reinforced Cu 47 Ti 34 Zr 11 Ni 8 BMG composites.…”