Comparative study of nanoindentation on melt-spun ribbon and bulk metallic glass with Ni<inf>60</inf>Nb<inf>37</inf>B<inf>3</inf> composition
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This paper describes the mechanical properties under nanoindentation of a new glassy alloy with a nominal composition of Ni60Nb 37B3, in the form of melt-spun ribbons and 1-mm-thick copper mold-cast sheets. The alloy composition was designed based on the synergy between the topological instability criterion and the difference in electronegativity among the elements. X-ray diffraction and scanning electron microscopy analyses confirmed that both ribbon and sheet samples possess totally amorphous structures with relatively high thermal stability (supercooled liquid region of about 60 K), as evaluated by differential scanning calorimetry (DSC). Nanoindentation tests revealed that the hardness of this alloy, about 15 GPa, is among the highest reported for metallic glasses. The elastic modulus of the cast sheet is higher and its hardness is similar to that of the ribbon. This correlates well with the different amounts of frozen-in free volume in both types of samples detected by DSC. © Materials Research Society 2013.