Thermomechanical relaxation and aging dynamics in La55Al25Co20 metallic glass.

Abstract

This study investigates the thermomechanical response of La55Al25Co20 metallic glass using Dynamic Mechanical Analysis (DMA) and differential scanning calorimetry, which revealed a stable supercooled liquid region (ΔT ≈ 50 °C) and a glass transition temperature (Tg) onset at 220 °C. Two distinct relaxation processes, α and β, were identified by DMA. The β-relaxation, which peaks at ∼180 °C, is notably sharp, intense, and highly strain-sensitive, a characteristic more prominent in this alloy than in other La-based alloys, and is linked to Co-induced dynamic heterogeneity. Stress relaxation analysis using the Kohlrausch-Williams-Watts model yielded a stretching exponent (βKWW ≈ 0.53), further indicating significant dynamic heterogeneity. These findings offer new insights into the interconnection of atomic mobility, structural frustration, and viscoelastic stability. Physical aging below Tg was found to reduce free volume and β-relaxation intensity, thereby increasing the structural rigidity and storage modulus of the material. The formation of La- and Co-centered icosahedral clusters not only aids relaxation at higher temperatures but also introduces geometric frustration, which contributes to residual stress and modulus fluctuations. Co-governed structural behavior directly impacts strain-activated relaxation dynamics, aging-driven rigidity, and frustration-mediated stress fluctuations. This work provides a pathway for compositional design to tailor the damping, thermal stability, and aging characteristics of rare-earth metallic glasses for thermomechanical applications.