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Ni- and Cu-free Zr-Al-Co-Ag bulk metallic glasses (BMGs) with diameters up to 20 mm were synthesized by copper mold casting. The effects of Ag alloying on the superior glass-forming ability (GFA) of Zr-Al-Co-Ag alloys were studied based on the localized atomic structure and crystallization behavior. High-energy synchrotron radiation x-ray diffraction result reveals that Ag addition in Zr-Al-Co system results in a more homogeneous local atomic structure, which could be an origin for the improved GFA of the Zr-Al-Co-Ag alloy. Crystallization products of the Zr-Al-Co-Ag glassy alloy are more complex than those of the Zr-Al-Co glassy alloy. The Zr-Al-Co-Ag BMGs free from highly toxic elements Ni and Cu exhibited a combination of superior GFA, high compressive fracture strength over 2000 MPa, low Young's modulus of 93 to 94 GPa, and good corrosion resistance in phosphate-buffered solution (PBS), inspiring their potential biomedical applications. [ABSTRACT FROM AUTHOR]

Using a cold graphite mold casting method, bulk AlNiY chill-zone alloys were prepared at hypereutectic compositions with Al content from 85 at.% to 94 at.%. It was found that ultra-hard surface layers with a thickness of about 200 µm and submicron grain size form when the melt can be undercooled without heterogeneous nucleation at the mold contact surface. This hard chill-zone forming in contact with the mold possesses Vickers microhardness Hv about 350-420 and is thus harder than fully amorphous Al alloys. In compression, ultimate strength more than 1.1 GPa and true strain more than 150% without failure were achieved simultaneously. The combination of high strength and good plasticity will be discussed in relation to the special structure of the chill-zone alloy. [ABSTRACT FROM AUTHOR]