The slow transition from an out-of-equilibrium glass towards a supercooled liquid is a complex relaxation phenomenon. In this Letter, we study the correlation between mechanical relaxation and equilibration kinetics in a ${\text{Pd}}_{20}{\text{Pt}}_{20}{\text{Cu}}_{20}{\text{Ni}}_{20}{\mathrm{P}}_{20}$ high-entropy metallic glass. The evolution of stress relaxation with aging time was obtained with an unprecedented detail, allowing us to pinpoint new interesting features. The long structural relaxation towards equilibrium contains a wide distribution of activation energies, instead of being just associated to the $\beta$ relaxation as commonly accepted. The stress relaxation time can be correlated with the equilibration rate and we observe a decrease of microstructural heterogeneity which contrasts with an increase of dynamic heterogeneity. These results significantly enhance our insight of the interplay between relaxation dynamics and thermodynamics in metallic glasses.

One of the hallmarks of disordered matter is the large amplitude of the anelastic deformation, i.e., the fraction of reversible deformation that is not instantaneously recovered after the release of load but is delayed in time. In this paper, this delayed elasticity is studied for the glass-forming ${\mathrm{Zr}}_{46.25}{\mathrm{Ti}}_{8.25}{\mathrm{Cu}}_{7.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{27.5}$ alloy by means of stress step and recovery experiments. Even at high temperatures, not far from the glass transition, the delayed elasticity can recover an important fraction of the deformation and endure for a long time. Analyzing the effects of loading time and waiting time on the strain evolution, we reveal the presence of an anelastic response with a timescale dependent on loading time and an invariant shape, which indicates the presence of a distribution of reversible relaxation modes following a ${\tau }^{-n}$ law with exponent $n$ between 0.5 and 1. The underlying distribution of energy barriers activated at different temperatures is accordingly shape invariant. Moreover, we found that a distribution of reversible modes corresponding to the high-frequency side of the $\alpha \text{−}\mathrm{relaxation}$ peak can reproduce the experimental results. The results establish a direct link between the dynamical spectrum and the distribution of activation energies, revealing the origin of the transient creep and anelastic recovery behaviors of metallic glasses.

The two-tank molten salt thermal storage system is the most common storage solution in concentrated solar power (CSP) plants. Solar salt (60% NaNO₃ + 40% KNO₃) is the most widely used energy storage material in solar thermal plants. In solar tower technology, where the molten salts must operate at temperatures ranging from 290 °C to 565 °C, several issues related to tank failures have emerged in recent years, with some of these failures attributed to the welding process. The welding process of joints in 316L stainless steel (ASS) probes exposed to a moving flow of a binary mixture containing 60% NaNO₃ and 40% KNO₃ (solar salt) is analysed. The results were evaluated using scanning electron microscopy (SEM) at 120, 500, 1000, 1500, and 2300 h of exposure. It was identified that arc mechanical oscillations significantly improve the microstructural properties and geometrical characteristics of welded joints, reducing structural defects and improving corrosion resistance. The technique promotes uniform thermal distribution, refined dendrite morphology, and homogeneous alloying element distribution, resulting in lower mass loss in high-temperature molten salt environments. Additionally, oscillation welding optimises the bead geometry, with reduced wetting angles and controlled penetration, making it ideal for high-precision industrial applications and extreme environments, such as molten salt thermal storage systems.