Impact of High Pressure on Reversible Structural Relaxation of Metallic Glass

The temperature dependence of the reversible structural relaxation time and diffusion constant of metallic glasses under pressure is theoretically investigated. The compression not only changes the glassy dynamics, but also generates a metastable state along with a higher-energy state where the system can rejuvenate. The relaxation times for forward and backward transitions in this two-state system are nearly identical and much faster than the relaxation time without accounting for barrier recrossing. At ambient pressure, the expected irreversible relaxation process is recovered, and the numerical results agree well with prior experimental results. An increase in pressure has a minor effect on the relaxation time and diffusion constant that one computes without considering the influence of the metastable state, but it leads to a large reduction of the reversible relaxation time computed upon considering the metastable state. The presence of external compression is also shown to trigger a fragile-to-strong crossover in metallic glasses.