Abstract
A commonality between nanocrystalline metals and metallic glasses is their dependence of structure and properties upon preparation history and postprocessing. Depending on preparation conditions, stored excess enthalpy and volume—relative to the crystalline ground state—can vary significantly. Annealing of material states of elevated enthalpy or volume induces structural relaxation and concomitant depletion of excess energy and volume. We analyzed the kinetics of volume relaxation in nanocrystalline PdAu alloys by partitioning the overall process into a set of independent and parallel reactions for arbitrary time-temperature protocols. The obtained spectra of kinetic parameters imply a complex relaxation behavior that violates time-temperature superposition and time aging-time superposition. The analysis will enable to reconstruct the effective energy landscape underlying the relaxation dynamics.
Highlights
It is well established that glassy materials change their properties years after the time of manufacture
Glassy materials are usually generated by cooling the material fast enough to avoid crystallization so entering the regime of the supercooled liquid to eventually—when the temperature falls below the liquid-to-glass transition temperature Tg—condense into the state of an amorphous solid.[3,4,5]
This disordered matter resides in a nonequilibrium state that proceeds to spontaneously evolve toward a temporally distant equilibrium state
Summary
It is well established that glassy materials ( polymers, silica glasses, metallic glasses, and molecular systems) change their properties years after the time of manufacture. Glassy materials are usually generated by cooling the material fast enough to avoid crystallization so entering the regime of the supercooled liquid to eventually—when the temperature falls below the liquid-to-glass transition temperature Tg—condense into the state of an amorphous solid.[3,4,5] This disordered matter resides in a nonequilibrium state that proceeds to spontaneously evolve toward a temporally distant equilibrium state (metastable, confined, or unconfined/true) During this course, the state variables of the system, e.g., volume or enthalpy, alter.[2] Concomitantly, it is observed that macroscopic properties, such as mechanical,[6,7] transport,[8] dielectric,[9] etc., properties, change with time.[1] Aging affects these properties through changes in the respective relaxation times of microscopic processes manifesting the system’s structural relaxation dynamics toward lower-energy states at a given temperature.[10,11] We note that there is a reverse process, termed rejuvenation,[12] entailing an evolution of materials into higherenergy states through application of external forces, e.g., thermomechanical processing or irradiation.[13,14]. We note that aging is a general phenomenon, which is not restricted to the glassy state but should be found in all kinds of disordered materials irrespective of their chemical nature and of their atomic structure or microstructure.[20]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
