Prominent β-relaxation and stress relaxation decoupling phenomenon in Gd-Ni-Al metallic glasses

Abstract

GdxNi20Al80−x (x = 50, 60, 65, 70 at%) metallic glasses (MGs) with prominent β-relaxation were developed, which provide a new model system for studying some controversial issues concerning β-relaxation. The relaxation behavior and thermal stability of GdxNi20Al80−x MGs were probed by dynamic mechanical relaxation, static stress relaxation, and differential scanning calorimetry. In view of the temperature and frequency dependence of the dynamic mechanical relaxation spectrum, we investigated the β-relaxation and α-relaxation separation phenomena of Gd50Ni20Al30 and Gd60Ni20Al20 MGs. With increasing Gd/Al ratio, the activation energy of the β-relaxation decreased, which was conducive to the flow units and prominent β-relaxation. The Gd70Ni20Al10 alloy had the most significant β-relaxation phenomenon, although some nanocrystalline Gd3Ni phase was distributed in the amorphous matrix. The Gd50Ni20Al30 glass had a crystallization activation energy of 476 kJ/mol, corresponding to the highest thermal stability. At a constant strain, the static stress relaxation process of the Gd70Ni20Al10 alloy was analyzed over a wide time window and temperature range. A decoupling phenomenon of the relaxation into a two-step process occurred in the Gd70Ni20Al10 alloy, namely, a fast relaxation process and a slow relaxation process, at different time scales. Analysis of the relaxation dynamics and time scales of the relaxation confirmed that the fast relaxation process differed from the β-relaxation process. This study elucidates the β-relaxation behavior and stress relaxation decoupling phenomenon in Gd-Ni-Al MGs and should, therefore, help clarify the mechanical relaxation behavior and intrinsic characteristics of MGs in future work.