Materials Science

The Yttrium Solution

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Science  17 Oct 2003:
Vol. 302, Issue 5644, pp. 359
DOI: 10.1126/science.302.5644.359d

When metal alloys are cooled, they tend to form crystalline arrays, but for some it can be technologically advantageous to induce them to adopt an amorphous structure instead. These metallic glasses can be formed via extremely rapid cooling, but this method of fabrication only works for wires and ribbons, which have high surface-to-volume ratios.

Two groups, looking at different alloys, have found that yttrium (Y) can enhance the formation of glasses significantly and thus make it feasible to fabricate components in bulk form. Guo et al. started with a group of rare earth alloys based on La-Al-Ni and La-Al-Cu and added Y as the base element (the majority component). The addition of an additional element raised the complexity of the alloy and hence its glass-forming ability, and the specific choice of Y worked well because its atomic size falls between those of La and Al, leading to an improvement in packing efficiency. Replacement of some of the yttrium with scandium, which has a similar atomic size, further enhanced the glass-forming ability, and fully amorphous rods could be produced by cooling in water. Lu et al. found that the addition of small amounts of Y vastly improved the glass-forming ability of iron-based metallic glasses. The Y not only scavenged free oxygen and thus stabilized the melt, but moved the processing conditions closer to the eutectic point and prevented the formation of secondary iron-based crystallites. — MSL

Appl. Phys. Lett. 83, 2575; 2581 (2003).

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