Structural Transitions Of Binary Compound-Forming Melts And Their Effects On Solidification

By measuring structure-sensitive parameters (for example, resistivity), it has been found that some topology and chemical short-range orders (CSRO) existed in liquid alloys. Especially for compound-forming melts, there are more complex interactions between like-atoms and unlike-atoms.In some compound-forming melts, it has been found that CSROs will change on dependence of composition. However, do CSROs exist in all compound-forming melts? And especially, do they change as a function of temperature? Furthermore, whether and how do these abnormal transitions with temperature of CSROs affect the solidification behavior of compound-forming melts? The investigations of abnormal transition in compound-forming melts are of real significance in researching the universality of liquid-liquid structure transition. Furthermore, it will help us to understand the mechanism of solidification and the effects of liquid-liquid structure transition on the solidification behavior and microstructure.In this paper, the temperature-induced liquid-liquid structure transitions of compound-forming melts and their effects on solidification are investigated systematically and the results are as follows:Ⅰ. Liquid Bi-In, Cu-Sn and Bi-Te alloys are selected for studying electronic transformation characters of compound-forming melts. Some significant phenomena are discovered.(1) Temperature-induced liquid-liquid structure transitions occure above liquidus in binary compound-forming melts: Cu-Sn, Bi-In and Bi-Te. It is shown that some CSROs with crystal structure remain through the melting process and they are broken suddenly at certain higher temperature, which results in abnormal transition in ρ-T curves. The results have been proved by DSC experiments.(2) In Bi-In melts, a turning point occurs in ρ-concentration curve and this point is corresponding to the concentration with the strongest interaction between unlike-atoms. Similarly in ρ-concentration curves of Cu-Sn and Bi-Te melts, maximum values of ρ reflect the strong chemical interaction between the components.(3) There are more than one kind of CSRO at some concentration of compound-forming melts, such as Cu-30wt.%Sn and Bi-80wt.%Te. These kinds of CSROs have different structure and they are broken at different temperature, which results in several abnormal transitions in ρ-T curves.Ⅱ. Further research, which focuses on the effects of temperature-induced liquid-liquid structure transition on solidification behavior and solidification structures, is performed in Bi-Te and Cu-Sn melts. The results show that the CSROs have significant effects on solidification. Especially, the...