Abnormal behavior of supercooled liquid region in bulk-forming metallic glasses

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We report the formation of a primitive icosahedral quasicrystal with increased stability in Al±Mn±Be alloys close to the compound Al 15 Mn 3 Be 2 by melt spinning and injection casting. The crystal structure of this compound was unknown. We show that in as-cast as well as heat treated condition the intermetallic phase H1 has a hexagonal structure with lattice parameters aˆ1:2295 nm and cˆ2:4634 nm. The space group is P6 3 =mmc. In the injection-cast samples, the quasicrystal coexists with another closely related hexagonal phase H2 with aˆ1:2295 nm and cˆ1:2317 nm with a possible space group of P6=mmm. This phase exhibits speci®c orientation relationships with the icosahedral quasicrystal given by ‰0001Š hex ==2f QC and ‰011 10Š hex ==5f QC , where 2f QC and 5f QC represent twofold and ®vefold axes respectively. Electron diOE raction patterns from both phases exhibit a close resemblance to the quasicrystalline phase. It is shown that the H1 phase is closely related to m-Al 4 Mn with the same c parameter while the a parameter is reduced by ½. Following Kreiner and Franzen, it is postulated that both structures (H1 and H2) can be understood by a simple hexagonal packing of I13 clusters.

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