Al-La-Cu Amorphous Alloys with a Wide Supercooled Liquid Region

Amorphous Al-La-Cu alloys exhibiting a wide supercooled liquid region and a high reduced glass transition temperature (T_g/T_m) were formed over a compositional range from 25 to 85 at% La and 0 to 60%Cu by melt spinning. The temperature span ΔTx (= T_x-T_g) between T_g and crystallization temperature (T_x) reaches as large as 59 K for Al₂₀La₅₅Cu₂₅. The T_g/T_m is also as high as 0.68 for Al₂₀La₅₅Cu₂₅ and the Al-La-Cu alloys are concluded to have a high glass-forming ability. The T_x and hardness (H_v) increase with increasing Al and Cu contents in the range from 430 to 575 K and 140 to 300 and the tensile strength also has a similar compositional dependence in the range of 535 to 880 MPa. The compositional effect on T_x and H_v was presumed to originate from the variation of the atomic configuration which reflects the compounds of La₃Al, La(Al, Cu) and La(Al, Cu)₂. The high stability of the supercooled liquid against the precipitation of crystalline phases in the vicinity of the stoichiometric composition Al₁La₂Cu₁, i.e., large ΔT_x and high T_g/T_m, seems to result from an optimum bonding state of the constituent atoms for the stoichiometric alloy.