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_xCe_1-x)₆₅Al₁₀Co₂₅ alloys (0 < x < 1), the fully glassy rods of the (La_0.7Ce_0.3)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 (La_xCe_1-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.