Bulk stiffnesses of metallic glasses

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Abstract
Determinations of density, Vickers microhardness, Young’s modulus, and Poisson’s ratio are reported for a series of Fe-B glasses, for glassy Fe40Ni38Mo4B18, and for glassy Cu68Zr32. From the last two parameters, one may calculate the shear and bulk stiffnesses of the glasses. For the Fe-B series the shear stiffness decreases by ∼13% when the B concentration decreases from 23 to 15 at.%; the bulk stiffness simultaneously decreases by ∼45%. As a result, the bulk stiffness of the near-eutectic alloy Fe85B15 (≃111 GPa) is strongly depressed relative to that for pure crystalline Fe (≃169 GPa) and that for crystalline Fe3B (≳163 GPa). The ratios of bulk stiffness to shear stiffness for Cu68Zr32 (≃4.7) and Fe40Ni38Mo4B18 (≃2.6) are relatively large and similar to those previously observed for other metallic glasses. For Fe85B15 the observed ratio is ≃1.9, which is quite close to that ( (5)/(3) ) expected for a solid bonded by centrally directed interatomic forces (a Cauchy solid). For the glasses examined here, as well as those examined previous, there is a linear proportionality between microhardness (H) and shear stiffness (μ); on average H≃μ/6.1.