The dynamic viscosity of Al-Yb and Al-Ni-Yb superheated melts was measured using a torsional oscillation viscometer. The results show that the temperature dependence of viscosity fits the Arrhenius law well and the fitting factors are calculated. The amorphous ribbons of these alloys were produced by the melt spinning technique and the thermal properties were characterized by using a differential scanning calorimetry (DSC). E (the activation energy for viscous flow), which reflects the change rate of viscosity, has a good negative relation with the GFA in both Al-Yb and Al-Ni-Yb systems. However, there is no direct relation between liquidus viscosity ( L ) and GFA. The superheated fragility M can predict GFA in Al-Yb or Al-Ni-Yb alloy system.Al-based amorphous alloys, glass-forming ability, viscosity, fragility of superheated melt PACS: 81.05. Kf, 66.20.+d From a physical point of view, viscosity is the micro-shear stress for a velocity gradient unit in fluid flow. Probing the viscosity starts a dynamic description of the structure of liquid metals. Thus the viscosity is regarded as a macro-performance of the micro-atomic interaction and is sensitive to the change in the structure [1]. Viscosity is one of the most important factors that affect the glass forming process. It is demonstrated that the three GFA factors, i.e. critical cooling rate R c , the reduced glass transition temperature T rg and supercooled liquid range T x , can be deduced only from the equations of temperature dependence of viscosity [2]. However, the interrelationship between the viscosity behavior of superheated liquid and the GFA of metallic glasses is poorly understood because of the difficulty of viscosity measurement at high temperatures.The concept of fragility m first proposed by Angell [3] is defined as the deviation of temperature dependence of viscosity approaching T g (the glass transition temperature). It is widely used to classify the dynamic behavior of supercooled liquids and glasses. However, for the alloys with low GFA (such as Al-based alloys belonging to marginal glass forming alloys [4]), it is difficult to obtain T g as well as m. Recently a new concept, the fragility of superheated melts M [5] defined as the viscosity variation rate of superheated liquids towards the liquidus temperature, has been proposed by Bian. A negative correlation between M and GFA was found in Al-Ni-Ce, Al-Co-Ce and Al-Fe-Ce alloy systems [5]. However, a further study [6,7] found that there is no good relationship between M and GFA in multi-alloy systems including Pr-based, Al-R (rare earth metal) and Al-Co-Ce alloys simultaneously. Al-R and Al-R-M (transition metal) systems are two of the fundamental Al-based amorphous alloy systems [4]. In order to further clarify the correlation between GFA and M in Al-based metallic glasses, we chose the Al-Yb of Al-R and the corresponding Al-Ni-Yb of Al-R-M alloys in the present work. We measured the viscosity of the melts at high temperatures above liquidus and calculated the fitting factors according...

The atomic structures of liquid Ag-based binary alloys have been investigated in the solidification process by means of X-ray diffraction. The results of liquid structure show that there is a break point in the mean nearest neighbor distance r 1 and the coordination number N min for glass-forming liquid, while the correlation radius r c and the coordination number N min display a monotone variational trend above the break point. It means glass-forming liquids have a steady changing in structure above liquidus and more inhomogeneous state at liquidus. We conclude that there is a strong correlation between liquid structure and glass forming ability in Ag-based binary alloys. liquid structure, glass forming ability, Ag-based binary alloys PACS: 81.05.Bx, 07.85.Nc, 61.20.-PThe liquid structure is known to be more complicated and mysterious in the three states of matter. As people's understanding of liquid structures has stagnated, it remains an open question in condensed state physics that has attracted investigations into the liquid structure through the methods of X-ray diffraction, neutron diffraction, X-ray absorption spectroscopy, and computer simulations [1][2][3][4]. Bulk metallic glass is generally obtained by rapid quenching from melts, and consequently its atomic distribution is very close to that of the liquid state. Whether the liquid structure of melt affects glass forming ability or not attracts the attention of researchers. Due to its theoretical and applied values, many researchers looked into this matter [5][6][7][8][9]. Mattern et al.[10] found a continuous development of structural change between liquid state and glass state. However, the direct relationship between liquid structure and glass forming ability has not been reported by now.In this paper, we study the differences in liquid structure between glass and crystal in Ag-based binary alloys, in which Ag 50 Cu 50 , Ag 60 Cu 40 and Ag 70 Ge 30 are glasses reported in refs. [11][12][13], while Ag 70 Cu 30 is crystal, aiming to give insight into the effect of liquid structure on glass forming ability.