The thermal evolution and dynamics properties of small clusters in melt are investigated by molecular dynamics simulation with 500 particles. The interatomic ineraction is described by a well-fitted semiempirical tight binding potential. We have studied some solidlike clusters and structural properties of liquid aluminum. The atomic volume, internal energy, pair correlaion function, and bonded pairs in liqiud are obtained from quick cooling and slow cooling simulation. A comparison between the slow and quick cooling process reveals that the cooling rate significantly affects the evolution route of various clusters in liqiud aluminum. Our results show that glass contains a lot of 1551 and 1541 five-fold symmetry clusters. On the contrary, the crystal has some 1421 and 1422 clusters corresponding to a face-centered cubic structure and hexagonal closing-packedstructure. This work gives clear physical insight of the structure evolution form liquid to solid.

By means of constant pressure molecular dynamics simulation technique, a series of simulations of the Fe50Al50 alloy have been carried out. The atoms interact via semi-empirical n-body noncentral potential. The pair correlation functions and the pair analysis technique is applied to reveal the cluster evolution in the process of quick solidification. By using the bond orientaion order parameters, we have measured both local and extended orientaion symmetries for computer-generated models of dense liquid and glass. A lot of polyhedra in liquid systems, e.g., icosahedra, are also obtained. In order to test the reliance of the computational results, corresponding x-ray diffracion experiments have been performed on the material.

The effects of rapid solidification on the microstructure of Al-8Ce, Al-20 Ce and Al-36.6 Ce (wt%) alloys has been invesigated using X-ray diffraction, canning electon microscopy and transmisson electron microscopy. A microstructure selecion map has been esbablished for the rapidly solidified Al-rich Al-Ce alloys. Rapid solidification has no effect on the phase constitution but has a marked effect on the microstructure of the Al-8 Ce and Al-20 Ce alloys. For the Al-36.6 Ce alloy, however, rapid solidification has a significant effect on both the microstructure and the phase constitution.

Investigations of the thermal evolution of the structural and dynamic properties of small cobalt clusters in melt are performed using molecular-dynamics simulations with a Finnis-Sinsclaire potemtial. The mean square displacements, atomic volume, and inernal energy, as well as the pair correlation function and bonded pairs, are obtained from quick and slow cooling simulations, respectively. The splitting of a second peak of pair correlation funcion is due to the presence of icosahedron-type clusters. The results demonstrate that the transition from a supercooled-liquid to a crystal is a discontinuous transition in structure, while the supercooled-liquid to glass transition is a continuous transiton in tructure. The physical picture of the tructure of metallic glass is a disrdered entanglement with a lot of icosahedar.

Empirical tight binding model potentials have been used in molecular dynamics simulations of local order and defects in liquid and glass under high and normal pressures. Results are reported for some solidilike cluster and for structural properties of liquid and glass. Not only are Frank-Kasper polyhedra and Bernal hole polyhedra detected, but also a varity of defective icosahedra. Adramatic split of the second peak of g (r) is associated with the glass transition. The split of the second peak is caused by the fluidity of the liquid phase in glass. The nearest distance is shortened, and the nearest-neighbor corrdination number increase under high pressure. High pressure favors glass formation. The microstructure of glass is very similar to medium range order icosahedra structure.

The structure and dynamic viscosity of molten metal In in the temperature range from 280 to 750℃ and investigated by using a high-temperature X-ray diffractometer and a torsional oscillation viscometer. The experiments show that the nearest interatomic distance r1 and the corrdination number Ns of In melt decrease with increasing temperature from 280 to 750℃. The viscosity of In melt drops as temperature increases and meets on the whole the whole the exponential relation. Thermal contraction of atom clusters can be found in the heating process. The sudden change in structure or noticeable contraction occurs in the range of 390-550℃. The anomalous change of viscosity is measured at about 430 and 470℃, which is in good accordance with that of structure. A theoretical discussion on the correlation of struture and viscosity of In melt is given in this paper.

The effects of thermkal-rate treatment technique on the critical thickness of glass formation for an Al85Ni10Ce5 alloy melt have been investigated. The amorphous ribbon of the alloy with a thickness of 300μm is obtained using a single-roller melt-spinning technique by the thermal-rate tteatment, while that of 50μm is obtained at conventional melt superheavitn condition. The experiment shows that the coordiantion numbers of the Al85Ni10Ce5 alloy melt decreases from 12 to 9 with increasing melt temperature from 900 to 1200℃. The relationship between the corrdination numbers, the first position of the main peak of the alloy melt and the critical cooling rate for getting amorphous alloys has been discussed.

The structrues of molten Cu-23% Sn alloy at different temperatures have determined by using a high-teperature X-ray diffractometer. It has been found that there exist not only short-range order (SRO) structure but also medium-range order (MRO) structure in the molten alloy. The medium-range order structure in the alloy melt is a function of temperature. There exist obvious medium-range order structure at the range of temperatures from 900 to 1200℃. The medium-range order structure disappears when the temperature reaches 1300℃. the temperature dependence of the dynamic viscosity of the alloy melt has been measured using a torsional oscillation viscometer. It has been found that there is an abnormal change in the relationship between the temperature and the viscosity of the alloy melt. The abnormity change is consistent with the transformation from medium-range order to short-range order in the alloy melt.

Viscosities of Al85Ni15 alloy melt and the Al-Ni-based melts with the addition of Ce, Cu, and Mn have been measured by an oscillating vessel viscometer. Liquidus temperatures of those alloys have been determined using differential scanning calorimetry (DSC). A high temperature area (HTA) and a low temperature area (LTA) can be used to describe the viscosity behavior. LTA is in the range of 100℃ above liquidus. The activation energy of LTA is much higher than that of HTA. Variation of activation energy with temperature of Al-Ni-based melts was found for the first time. The relationship between the glass formability and viscosity of the alloy melts has been discussed.