Influence of similar atom substitution on glass formation in (La–Ce)–Al–Co bulk metallic glasses

The glass-formation range of bulk metallic glasses (BMGs) based on lanthanum and cerium was pinpointed in the La–Al–Co, Ce–Al–Co and pseudo-ternary (La–Ce)–Al–Co systems, 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. Compared 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 obviously improves the GFA of (LaxCe1−x)65Al10Co25 BMGs, and this cannot be explained by the conventional 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.