Structural basis for supercooled liquid fragility established by synchrotron-radiation method and computer simulation

Abstract

International audienceMetallic melts above the liquidus temperature exhibit nearly Arrhenius-type temperature dependence of viscosity. On cooling below the equilibrium liquidus temperature metallic melts exhibit a non-Arrhenius temperature dependence of viscosity characterized by liquid fragility phenomenon which origin is still not well understood. Structural changes and vitrification of the Pd(42.5)Cu(30)Ni(7.5)P(20) liquid alloy on cooling from above the equilibrium liquidus temperature are studied by synchrotron radiation X-ray diffraction and compared with the results of first-principles calculations. Subsequent analysis of the atomic and electronic structure of the alloy in liquid and glassy states reveals formation of chemical short-range order in the temperature range corresponding to such a non-Arrhenius behavior. The first-principles calculations were applied to confirm the experimental findings

A structural signature of liquid fragility

“…2b). Essentially, no accelerated evolution occurs in the intermediate region for Vit 106a, a behaviour that has been previously presented for a few bulk metallic glass-forming alloys, but not analysed in this manner [17][18][19] . The very different behaviours of Ni 62 Nb 38 and Vit 106a are analogous to the fragile/strong characterization of viscosity proposed by Angell.…”

Role of different factors in the glass-forming ability of binary alloys

“…The formation of partly covalent bonds leading to large mixing enthalpy may be responsible for lower GFA of the Si-and Ge-rich glasses. On the other hand, the structural changes and vitrification of the Pd-Cu-Ni-P liquid alloy on cooling from above the equilibrium liquidus temperature studied in situ by synchrotron radiation X-ray diffraction, and the results of ab initio computer simulation clearly indicated intensification of covalent bonding close to glass-transition which is responsible for large fragility of the melt [68]. It allows us to anticipate that the Si-and Ge-rich glasses can also be fragile which deteriorates their GFA.…”

Computational modeling sheds light on structural evolution in metallic glasses and supercooled liquids

“…Aside from the structural metrics above, other structure parameters may also show correlation with the liquid fragility, such as the peaks in pair distribution functions (PDFs), [71][72][73] volume or density variations, 74,75 bond orientational order 76 and interatomic repulsion softness. 77 In a nutshell, these structural indicators suggest that the liquid fragility does correlate with how and how fast the local structural ordering takes place upon cooling.…”