Papers by Keyword: Supercooled Liquid

Abstract: The molecular dynamics simulations on the isothermal relaxation properties of supercooled liquid and glassy Pb have been performed. The calculated diffusion constant of Pb is well agreed with the experimental result. Results indicate that the relaxations of supercooled and glassy Pb present more and more pronounced heterogeneity with decreasing temperature. The appearance of the second plateau of mean square displacement (MSD) and the non-zero plateau of Non-Gaussian parameter (NGP) is corresponding to the rest of structure rearrangement.

Abstract: Viscous flow behaviour of supercooled liquids and mechanical properties in Zr55+XCu30-XNi5Al10 (X=0, 5 and 10 at. %) and Zr65Cu18Ni7Al10 bulk metallic glasses (BMGs) have been examined. Viscosity has been measured by using a penetration viscometer at a high-speed heating rate of 400 K/min. With increasing Zr-content, Tg tended to decrease and Tx tended to increase, resulting Tx (=Tx-Tg) increaseing up to about 170 K under a heating rate of 400 K/min by the DSC analysis. The viscosity lowered about one order of magnitude, e.g., minimum value of the viscosity decreased from 3~4x106 Pa-s for the Zr55Cu30Ni5Al10 and Zr60Cu25Ni5Al10 BMGs down to 5~6x105 Pa-s for the Zr65Cu20Ni5Al10 and Zr65Cu18Ni7Al10 BMGs under the same heating condition. Compression tests were also carried out at a slow strain rate of about 1 x 10-4 s-1 at room temperature. With increasing Zr-content, the apparent yield stress was decreased but the total strain at fracture was increased significantly, suggesting that there is a strong relationship between viscosity and the mechanical properties in these BMGs.

Abstract: It is well known that multi-component alloys form bulk metallic glasses (BMGs) from the supercooled liquid state without rapid quenching. However, the mechanism of phase selection between crystal and glass states has not been fully clarified. To obtain an insight into the glass-forming processes, we carried out in-situ observation on the solidification of Zr-based BMG-forming alloys from its supercooled liquids by time-resolved X-ray diffraction combined with the conical nozzle levitation (CNL) technique to achieve a containerless melting. For Zr-based alloys, we succeeded in detecting the X-ray diffraction patterns during glass formation from the supercooled liquid state as well as the crystallization from the liquid state. Furthermore we performed the precise structure analysis of supercooled state of Zr-based binary liquids. Based on the liquid structure and in-situ observation results, we discussed about the phase selection mechanism between crystal and glass states.

Abstract: An overview is given of recent advances in the experimental physics of supercooled liquids and glasses. These are described in the context of measurements of non-ergodicity, viscosity and low frequency dynamics. Particular attention is paid to recently reported correlations between melt fragility and the vibrational and mechanical properties of the ensuing glass. Low frequency vibrations are discussed in relation to the Boson peak that characterises the glassy state. Throughout the over-arching role of density fluctuations in glass formation is stressed together with the experimental tools now available to characterise heterogeneity.

Abstract: Viscous flow behavior in supercooled liquid region of as-cast and pre-annealed Zr55Cu30Al10Ni5 bulk metallic glasses has been examined by using a penetration viscometer under high-speed heating rate of 20, 200 and 400 °C/min. Applied load for the cylindrical-shaped penetration indenter with a diameter of 1 mm was varied from 0.049 N to 0.294 N. Viscosity was quite independent of these applied loads. By pre-annealing the bulk metallic glasses at 400 °C, the density of the glasses increased, while the viscosity and the activation energy for viscous flow in their soopercooled liquid decreased with the pre-annealing treatments. Corresponding measurements of the differential thermal calorimetry (DSC) have been also done.

Abstract: Viscosity of a Zr55Cu30Al10Ni5 supercooled liquid alloy having bulk metallic glass forming ability has been measured by using a penetration viscometer with a cylindrical probe under high speed heating conditions at rates between 20°C/min and 400°C/min in the temperature range from the glass transition temperatures (Tg) up to above the crystallization temperatures (Tx). The viscosity of the alloy decreased with increasing the heating rate and tended to saturate at the heating rate of 200°C/min and above. Corresponding measurements of the differential thermal calorimetry (DSC) under the high-speed heating conditions have been also done.

Abstract: Formation of the icosahedral order in supercooled liquids and glassy phases is investigated for a model alloy system by using molecular dynamics simulations. The simulation results show that the short-range icosahedral order grows in the supercooled liquids as well as in the glassy phases. Structural analyses reveal that the icosahedral clusters form a network in which the clusters are connected via the pentagonal-bicap sharing. Geometrical property of the network formed by the icosahedral clusters is an origin of medium-range order in the glassy phases