Synopsis: Metals are supercool

Structural changes in an alloy may lead to a clearer picture of glass transitions in liquid metals.

Some metals stay liquid below their melting temperature (i.e., they can be supercooled) and eventually form a glass when cooled further. While metals are crystalline in solid form, metallic glasses are amorphous. Glassy metals⎯particularly metallic alloys that form thick bulk metallic glasses (BMG)⎯remain an attractive subject of study decades after their discovery.

In an article in Physical Review B, Victor Wessels at the Washington University in St. Louis and his collaborators demonstrate the existence of a rapid ordering process in a supercooled metallic liquid. The group used high-energy x rays from the Advanced Photon Source at Argonne National Laboratory to study structural changes in levitated $\text{Cu-Zr}$ alloys as they cool. A rapid chemical and topological ordering of the supercooled liquid begins just ${75}^{\circ }\text{C}$ below the melting temperature⎯a remarkable ${465}^{\circ }\text{C}$ above the BMG transition⎯suggesting that the atoms become more ordered well before they finally “slow down” to form a glass.

$\text{Cu-Zr}$ alloys, forming BMGs under different conditions, are an ideal system in which to test the physics of glassy metals as they form, pointing us to a clearer understanding of structural ordering prior to the glass transition in liquid metals. – Athanasios Chantis

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