Al-based metallic glasses are potential industrial materials due to their excellent properties such as high specific strength and high corrosion resistance. However, bulk Al-based amorphous alloys are not obtained until now, which limits their applications greatly. It is of significance for us to improve their glass forming ability (GFA) and locate the best glass former in such marginal GFA systems. So the objective of this thesis is to understand some key theories and parameters associated with GFA of Al-based metallic glasses, from which, we expect to present new insights into developing bulk Al-based metallic glasses.
The main results are presented as follows:
(1)Similar to atomic size distribution, electronegativity in Al-based metallic glasses was also found to have a single peak distribution with a concave downward shape. For Al-Ni-RE (RE= Gd，Y，Ce，La), there is a critical electronegativity difference (Δxcr), which can determine supercooled liquid region existed or not, roughly distinguish the crystallization types and locate the best glass former. The tendencies of Δxcr and λ are similar in ternary compositional triangle. This reveals that electronegativity also has important influence on glass forming ability and supercooled liquid region.
(2)Ternary Al-based metallic glasses with good GFA can be developed by plotting two simple cluster stability lines in ternary composition triangle and restraining the intersectional point of the lines with average electronegativity. With this understanding the Al-Ni-Y alloy system in Ni-rich side was re-examined, as a result, Al86Ni9Y5 alloy with glass forming ability of about 500 μm was successfully fabricated by wedge casting.
(3)The GFA of quenched amorphous phase are evaluated at different wheel speed in Al85Ni9La5TM1(TM=Fe, Ti, Cu, Zr) and Al86Ni9La5 with addition of B, Zr and Cu alloys. XRD results showed the addition of Fe, Ti, B deteriorate GFA of Al86Ni9La5, while minor Cu, Zr retain GFA of base alloy. This can be explained by Inoue’s empirical criterion and cluster theory. When annealed at 268 oC and 355 oC, the same crystalline formations were obtained for Al85Ni9La5TM1. The first crystallization stage is due to the formation of fcc-Al. The final crystallization stage corresponds to the formation of Al11La3 and Al3Ni. There also exists a critical electronegativity difference for these four alloys, but the criterion is different from ternary alloys.
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