Glass formation of containerless levitated Zr55Al10Ni5Cu30 alloy containing oxygen

Although Zr-Al-Ni-Cu bulk metallic glasses exhibit high glass forming ability (GFA), the glass formation is highly sensitive to low oxygen contents. Even ppm contents are sufficient to decrease drastically the GFA. The crystallization behavior of the amorphous matrix is also dependent on oxygen content and phases can be formed or suppressed depending on its content. In the present work, an arc-melted Zr55Al10Ni5Cu30 alloy was processed by a containerless levitation technique. Zr sponge, known to have high contents of oxygen due to its high surface area, was used to produce arc-melted samples, which were subsequently levitated under high pure argon/helium atmospheres for different hold times. The final microstructures of the samples contained quenched-in Zr4Cu2O type crystals enriched in aluminum in an amorphous matrix. With increasing hold times under levitation, the amorphous volume fraction increased from ∝58% up to ∝99%. This increase in amorphous phase indicates that the oxygen content is reduced during levitation melting thereby increasing the GFA of the material. Since the atomic movement is difficult due to the high viscosity and random packed structure of the supercooled liquid, the formation of the complex oxide phase (with 112 atoms per unit cell) rather than more simple structures during quenching is a surprise; this is discussed based on the assumption of a clustered or short-range-ordered structure of the supercooled liquid, which makes the crystal growth of the complex phase easier. (orig.)