Intrinsic relaxation in a supercooled ZrTiNiCuBe glass forming liquid

Abstract

We studied structural relaxation in the bulk metallic glass-forming alloy Zr46.8Ti8.2Cu7.5Ni10-Be27.5 on different time and length scales, with emphasis on the supercooled liquid state. Using X-ray photon correlation spectroscopy, we determined the microscopic structural relaxation time covering timescales of more than two decades in the supercooled liquid region, down to sub-second regime. Upon heating across the glass transition, the intermediate scattering function changes from a compressed to a stretched decay, with a smooth transition in the stretching exponent and characteristic relaxation time. In the supercooled liquid state, the macroscopic and microscopic relaxation time, as well as the melt viscosity all exhibit the same temperature dependence. This points to a relaxation mechanism via intrinsic structural relaxation of the majority component Zr, with its microscopic timescale controlling both the stress relaxation and viscous flow of the melt.

Disentangling structural and kinetic components of the α-relaxation in supercooled metallic liquids

“…4). This result contrasts with previous XPCS studies of metallic glass formers where β(T) has been found T-independent in all measured supercooled liquids allowing to superpose all the correlation curves in a single master curve [32][33][34] . Although the relationship between macroscopic and microscopic dynamics is not straightforward, also most metallic glasses show a T-independent shape of the α-relaxation peak in mechanical experiments.…”

“…This marked temperature dependence of β(Q FSDP ,T) in the Pt-based melt leads to the failure of the time-temperature superposition principle for the structural relaxation process (Supplementary Fig. 4), which contrasts with the usual law of invariance observed in previous studies on metallic glass formers at both microscopic [32][33][34] and macroscopic [35][36][37]72 scales. Interestingly, despite the different evolution of the dynamics during cooling, both alloys exhibit similar values of β(Q,T) at the glass transition suggesting the existence of a common degree of heterogeneities in metallic liquids at the dynamical arrest.…”

Delayed elasticity of metallic glasses: Loading time and temperature dependences of the anelastic relaxation

“…Above the glass transition, in the supercooled liquid (SCL) state, the relaxation dynamics of many disordered substances can be characterized by a stretched relaxation modulus described by a Kohlrausch-Williams-Watts (KWW) function. Recent studies on Zr 46.25 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 (Vit4) alloy have shown that, in the SCL, the relaxation time, obtained from stress relaxation and oscillation strain measurements, follows a Vogel-Fulcher-Tammann (VFT) temperature behavior in accordance with viscosity measurements and with the microscopic dynamics at the length scale of atomic-atomic * eloi.pineda@upc.edu distances as probed by x-ray photon correlation spectroscopy (XPCS) [3]. An important aspect is that the viscous liquid material above the glass transition temperature T g shows an invariant relaxation shape, with a KWW exponent between 0.5 and 0.6, indicating the validity of time-temperature superposition in this region and the participation of a broad relaxation time distribution in the process [3][4][5].…”

“…Complementary stress relaxation and mechanical spectroscopy experiments were already performed on Vit4 ribbons [3]. Stress relaxation was measured, applying a constant deformation step of ε = 0.1% and monitoring how the stress decays with time.…”

“…Therefore, the study of the relaxation dynamics is always affected by physical aging, and it becomes challenging due to the long timescales involved in both mechanical relaxation and physical aging [6]. Previous stress relaxation experiments in MGs show a progressive stretching of the relaxation modulus as the system is driven out of equilibrium, indicating a broadening of the relaxation time distribution in the glass state [3,5,7]. One important feature to understand glass dynamics is the contribution of anelastic relaxations [8,9], which may have a different temperature sensitivity than the viscous process governing the relaxation in the liquid.…”