Liquid-Liquid Structure Transitions In Eutectic And Solid-Solution Binary Alloys And Their Effects On Solidification

The knowledge on nature of liquid structures and properties is closely related to the development of science and technology in many fields; therefore, it has been becoming a common concern for condensed physics, materials science, life science, chemistry, metallurgy and so on. Although the knowledge on liquid structures and properties is more superficial than that of solid and gas, many respectable staggered achievements have been obtained in recent years, which provide abundant phenomenology basis for further exploration of the character of liquid structure from the theory point of view. The topological and chemical short-range orders, revealed by various diffraction method and computer simulations, enrich the intrinsic physical meaning on short-range order in liquid structure. The direct evidence of pressure-driven discontinuous liquid-liquid structure transition (L-LST) in liquid phosphorus breaks the traditional concept that liquid structure changes continuously and gradually with temperature and pressure changing. The discovery of temperature-induced L-LST in binary liquid alloys supplies a gap between the liquidus and liquid-gas critical point, which will play a profound effect on understanding of solidification mechanism, development of materials and its processing technology.However, the universality and essence of L-LST, including the temperature range, condition and rule, are still unknown. Moreover, although the technology of melt temperature treatment, melt overheating and thermal-rate treatment are not infrequently adopted to investigate the relation between the melt and solid, clear and systematic investigation is not found yet on the effect of L-LST on the solidification behavior and microstructure.In the present paper, the eutectic and solid solution binary alloys are chosen as the investigation object. The electrical transport properties and DSC analysis of liquid Pb-Sn, Sn-Bi, Pb-Bi and In-Sb eutectic-like alloys are systematically explored with temperature changing, and the result is compared with that of solid solution alloy Bi-Sb. Based on the experimental results, the characteristics, rules and mechanism of L-LST are also analyzed theoretically in this paper. For the first time, the reversibility and its character of L-LST in binary alloys are also discussed from the L-LST point of view.Furthermore, based on the prior study and from the new point view of L-LST, the effect of L-LST on solidification behavior and microstructure is investigated.The results are summarized as follows:â…  L-LIST exists in almost all investigated liquid binary alloys except In-Sb during heating process in the first cycle within measured temperature range, and the L-LST temperatures are all far above their liquidus;â…¡ It is observed that L-LST exists in Sn, Bi, Sb one-component system during heating process in the first cycle. For the first time, the characteristic of partial reversibility of L-LST is revealed...