Influence of Similar Atom Substitution on Glass Formation in (La-Ce)-Al-Co Bulk Metallic Glasses

TL;DR

This study investigates how substituting similar atoms La and Ce in La-Ce-Al-Co bulk metallic glasses enhances their glass-forming ability, with a thermodynamic model explaining the observed improvements beyond traditional criteria.

Contribution

It introduces a thermodynamic model to explain how similar atom substitution improves GFA in La-Ce-Al-Co BMGs, surpassing traditional size mismatch and mixing criteria.

Findings

Coexistence of La and Ce enhances GFA of BMGs.

Fully glassy rods up to 25 mm diameter achieved.

Thermodynamic model explains substitution effect.

Abstract

The glass-formation range of bulk metallic glasses (BMGs) based on lanthanum and cerium was pinpointed in La-Al-Co, Ce-Al-Co and pseudo-ternary (La-Ce)-Al-Co system respectively by copper mold casting. Through the stepwise substitution of La for solvent Ce in (LaxCe1-x)65Al10Co25 alloys (0<x<1), the fully glassy rods of the (La0.7Ce0.3)65Al10Co25 alloy can be successfully produced up to 25 mm in diameter by tilt-pour casting. Comparing with the glass-forming ability (GFA) of single-lanthanide based alloys, La65Al10Co25 and Ce65Al10Co25, the coexistence of La and Ce with similar atomic size and various valence electronic structure can obviously improve the GFA of (LaxCe1-x)65Al10Co25 BMGs, which can't be explained by the former GFA criteria for BMGs, e.g. atomic size mismatch and negative heats of mixing. A thermodynamic model was proposed to evaluate this substitution effect, which gives a reasonable explanation for the obvious improvement of GFA induced by the coexistence of similar atoms.