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.

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.

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.

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.