Amorphous Zr–Al–TM (TM=Co, Ni, Cu) Alloys with Significant Supercooled Liquid Region of Over 100 K

TLDR

High stability of the supercooled liquid in this alloy system is attributed to dense random packing of optimally sized atoms and a large negative enthalpy of mixing. Melt‑spun Zr65Al7.5Cu2.5(Co1−x−yNixCuy)25 alloys exhibit a supercooled liquid region exceeding 100 K across a broad compositional window, with ΔTx reaching 127 K for Zr65Al7.5Ni10Cu17.5; increasing Co raises Tg and hardness but lowers Tx, reducing ΔTx, and the data show no direct link between bonding strength and supercooled liquid stability.

Abstract

Amorphous alloys exhibiting a wide supercooled liquid region above 100 K were found to form in a compositional range from 0 to 3%Co, 0 to 15%Ni and 10 to 23%Cu in Zr65Al7.5Cu2.5(Co1−x−yNixCuy)25 system by melt spinning. The temperature span ΔTx(=Tx−Tg) between glass transition temperature (Tg) and crystallization temperature (Tx) reaches as large as 127 K for Zr65Al7.5Ni10Cu17.5. The Tg and hardness (Hv) increase from 622 to 685 K and 426 to 502 with increasing Co content while the Tx decreases from 749 to 690 K, resulting in the decrease of ΔTx from 127 to 30 K with increasing Co content. The compositional effect on Tg, Tx, ΔTx and Hv indicates that there is no close relation between the magnitude of the attractive bonding force and the stability of the supercooled liquid. The high stability of the supercooled liquid against the nucleation and growth of a crystalline phase in the limited composition range seems to result from a highly dense random packing structure consisting of atoms with an optimum atomic size ratio and a large negative enthalpy of mixing.