Coincidence of collective relaxation anomaly and specific heat peak in a bulk metallic glass-forming liquid (original) (raw)
Related papers
Structural origin of dynamical relaxation in undercooled Cu50Zr50 metallic liquid
Journal of Non-Crystalline Solids, 2018
Molecular dynamics (MD) simulation has been performed to explore the correlation between dynamic characteristics and structural heterogeneity in undercooled Cu 50 Zr 50 melt based on the embedded atom method. It is found that atoms in the undercooled liquid can be classified into three groups in terms of the probability distribution of atoms' displacement, named 'fast atoms' (FAs), 'intermediate atoms' (IAs), 'slow atoms' (SAs). Meanwhile, the undercooled liquid can be divided into three temperature regime: as the temperature is higher than 1120 K, the distribution of FAs become network connectivity, in which the SAs region are surrounded; as the temperature is in the range from 1120 K to 900 K, the network of FAs region decompose into several isolated region gradually; after that the single relaxation separates into αand β-relaxation at temperature lower than 900 K, the FAs region become isolated islands, while the SAs have connected into networks where the FAs regions are surrounded, which cause the significant decreasing of atomic mobility and sharp increasing of the relaxation time. The FAs, located in loose packaging and isolated region, which corresponds to β-relaxation reflected by the timescale of intermediate plateau in mean-squared displacement (MSD) and intermediate scattering function (ISF). The SAs which develop into the backbone of the system and surround clusters formed by FAs, are responsible for the glass formation and have a connection with α-relaxation. The compressive deformation in the Cu 50 Zr 50 metallic glass shows that the 'fast atoms', anticipating in β-relaxation of undercooled liquid, mostly are located in large shear strain zones and the structural heterogeneity of undercooled liquid inherits into the glass. Since metallic glass (MG) can be regarded as frozen undercooled liquid, our study is helpful for understanding the structural origins of dynamical relaxation in MGs.
Acta Materialia, 2013
The relaxation spectrum of rapidly quenched Mg 65 Cu 25 Y 10 metallic glass ribbons is studied by mechanical spectroscopy at temperatures below and around the glass transition. The comparison between hyper-quenched and relaxed samples is used to examine the origin of the low temperature "excess wing" of internal friction commonly observed in mechanical spectroscopy of metallic glasses. The results show that the excess wing can be attributed to access of the system to the broad a-relaxation process while evidence of secondary relaxations is not found. This suggests that in this glassy system the activation energies of structural relaxation and low temperature deformation are directly related to the activation energy of the main relaxation process of the glassy state.
Journal of Non-Crystalline Solids, 2006
The relationship between the total relaxation time at the glass transition s tot T g and Glass Forming Ability (GFA) of Bulk Metallic Glasses (BMG) has been discussed. Subsequently s tot T g is applied to estimate the GFA of Zr 52.5 Al 10 Ni 14.6 Cu 17.9 Ti 5 and Zr 57 Al 10 Ni 12.6 -Cu 15.4 Nb 5 BMGs. The result indicates that the GFA of the former is greater than that of the latter, which is also demonstrated by the widely accepted criteria of both supercooled liquid region DT x and reduced glass transition temperature T rg . That testifies the relaxation time of glass transition (s tot T g ) is feasible for depicting GFA of BMGs. As a criterion estimating GFA, s tot T g could be easily obtained in practice, and then the occurrence of this criterion will promote exploring new bulk glassy composition. In addition, when s tot T g and DT x are calculated, the characteristic temperatures are determined by a electrical resistivity method besides DSC method. The values obtained from electrical resistivity method agree well with those from DSC method, which proves that the electrical resistivity method is applicable for determining the characteristic temperatures of BMGs.
On Relaxation Kinetics in Liquid and Glassy Ag-Cu Metallic Alloy
MRS Proceedings, 2002
ABSTRACTMolecular dynamics simulations of structure, thermodynamic and kinetic properties of model metallic AgCu alloy are performed to elucidate its behavior at glass transition. In spite of small variations of inherent structure of the alloy the relaxation kinetics undergo dramatic changes at the glass transition. The time dependences of the mean square displacements and the non-Gaussianity parameter show the signatures of anomalous diffusion in an intermediate time region. Analysis of time evolution of van Hove correlation function indicates the existence both jump displacements and short-range cooperative atomic rearrangements. Below Tg these cooperative rearrangements do not contribute to long-range diffusion but they still dominate the relaxation at short time.
Physical Review Letters
Lacking the structural information of crystalline solids, the origin of the relaxation dynamics of metallic glasses is unclear. Here we report the evolution of stress relaxation of high-entropy metallic glasses with distinct-relaxation behavior. The fraction of liquid-like zones, determined at each temperature by the intensity of stress decay, is shown to be directly related to both the aging process and the spectrum of relaxation modes obtained by mechanical spectroscopy. The results shed new light on the intrinsic correlation between the static and dynamic mechanical response in high-entropy and conventional metallic glasses, pointing towards a sluggish diffusion high-entropy effect in the liquid dynamics.
Intrinsic relaxation in a supercooled ZrTiNiCuBe glass forming liquid
Physical Review Materials, 2021
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.
Slow relaxations in deeply undercooled metallic liquids
Journal of Non-Crystalline Solids, 2002
Temperature-modulated calorimetry measurements on bulk glass forming Pd-rich alloys are reported that are unaffected by the structural glass transition or by irreversible relaxation phenomena, and that measure the relaxation time spectrum near the glass transition directly. The comparison of the temperature dependencies of the average relaxation times for two Pd-rich alloys with different thermal stability shows that the more stable alloy is more fragile, indicating that vitrification for these alloys is strictly governed by nucleation control. The comparison of the present data with results from static equilibrium measurements indicates further, that near the caloric glass transition the description of equilibrium thermodynamic properties, rheological quantities and relaxation times can be based on a common divergence limit.