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 (La x Ce 1− x ) 65Al 10Co 25 alloys (0 < x < 1), the fully glassy rods of the (La 0.7Ce 0.3) 65Al 10Co 25 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, La 65Al 10Co 25 and Ce 65Al 10Co 25, the coexistence of La and Ce with similar atomic size and various valence electronic structure obviously improves the GFA of (La x Ce 1− x ) 65Al 10Co 25 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.