Glass Transition and Viscoelastic Behaviors of La₅₅Al₂₅Ni₂₀ and La₅₅Al₂₅Cu₂₀ Amorphous Alloys

Abstract

It has been found that amorphous La₅₅Al₂₅Ni₂₀ and La₅₅Al₂₅Cu₂₀ alloys exhibit a distinct glass transition and the temperature span between T_g and T_x, ΔT_x(=T_x−T_g) exceeds 50 K. This is the first evidence for the formation of an amorphous phase with ΔT_x above 50 K in a metal-metal type system. With the aim of clarifying the glass transition behavior and the properties of supercooled liquid in the metal-metal type amorphous alloys, the changes in fundamental properties of specific heat (C_p), viscosity (η), tensile yield strength (σ_y), tensile elongation including elastic elongation (ε_f) and viscoelasticity in the glass transition region were examined for both amorphous alloys. The transition brought about significant changes in the above-described properties, i.e., for the La₅₅Al₂₅Ni₂₀ alloy, an increase of C_p by 12 J/mol·K and ε_f from 2.43 to 188% and a dramatic decrease of η to below 10¹² Pa·s and σ_y from 710 to 3.47 MPa. In addition, the complex modulus decreased from 33.5 to 1.79 GPa and the loss tangent increased rapidly from 9×10⁻³ to 3.32. Similar significant changes in the fundamental properties were also observed for another La₅₅Al₂₅Cu₂₀ amorphous alloy and hence these amorphous alloys were concluded to be typical glassy materials.