The Reversibility Of The Liquid-Liquid Structure Transition And Its Effect On The Solidification Of Sn-Bi And Pb-Sb30% Alloy

In the practice and investigation about material solidification and crystal growth, the liquid-solid heredity and the correlation between the structure, properties of solid and the liquid's heat history have been early discovered . Recently, overheating, melt thermal treatment, melt thermal-rate treatment have become the most active areas in condensed matter physics and material processing, and some achievements have been acquired. However, the different solidification structure is often owed to the difference of the melt's structure, and the essence of the effect need to be further studied. It has been accepted that the temperature can induce the Liquid-Liquid structure transition (L-LST), but the reversibility of the L-LST and its effect on the solidification are seldom studied. In this paper, we carry out investigation of the temperature dependence of electrical resistivity (ρ-T) using DC four-probe method for Sn-Bi and Pb-Sb30% alloy systems, moreover, the reversibility of the L-LST and its effect on the solidification are further studied. It is helpful to explore the mechanism of solidification and the effects of the L-LST on the solidification behavior and microstructure.The L-LST was suggested to occur in Sn-Bi alloys, within a certain range of 500-800°C above the liquidus. By analyzing theρ-T curves of Sn-Bi alloys systems and pure Sn, it is found that the L-LST are partial reversible, which has main connection with the structure of pure Sn. There are two different kinds of short-range order in Sn melt, one is irreversible structure namely metastable state cluster, the other is reversible structure namely tetrahedral Sn-Sn covalent bond cluster.Based on the L-LST, two temperature (before the L-LST and after the L-LST ) were chosen as the melting and heat preservational temperature. The results of the solidification show that the undercooling of the primary and eutectic phase increases and the microstructure becomes finer after solidifying from the melt experienced the L-LST.In the present paper, the reversibility of the L-LST in Pb-Sb30% alloy was further studied, and the results showed that the structural transition is irreversible. Moreover, the L-LST had a visible effect on the solidification behaviors and morphologies of Pb-Sb30% alloy. Associated to the liquid structural transition, the undercooling increased, and the primary phase and eutectic phase became fine, and the Vickers hardness of the sample increased about 30%.The experiment investigations of the two alloy systems suggest that the reversibility of the L-LST doesn't exist in every alloy system, and the L-LST affects the solidification remarkably.