The Investigation Of The Melt Structure Transition Of Cu-Sb Alloys And Their Correlation With Solidification

The structures and properties of liquid metals and alloys do have much effect on solidification, phase transitions, as well as the final solidified microstructures and their qualities. In recent years, the phenomena of liquid polyamorphism bring great interest to relevant realms, and pressure or temperature induced liquid-liquid structure transitions (TI-LLST) were found could occur in liquids. All these present challenges to our conventional picture of liquid as entity with a continuously varying averaged structure, and provide new breakthrough to further recognize liquid substances. The overheating treatment of alloy melts has been widely studied for many years, and it has been verified that the structures and properties of some alloys could be obviously improved by such proper treatment. Generally, people think that the effects of over-heating treatments on solidification must attribute to some changes of melt's structures states, however, the essence and rule of these phenomena are not anatomized very well by now. And although the detection and investigation of liquid-liquid structure transitions provide a new way for deeper understanding the relationship of liquid-solid structures, the nature and rule of the melt structure transition and its effect on solidification still need to be explored further.In this paper, the compound forming alloy is chosen as the investigation object. The characters, mechanism and also their correlation of TI-LLST in three components Cu(100-x)Sbx (x=70,76.5,90) alloy are systematically explored with electrical resistivity method. In addition, based on the prior results, from the new viewpoint of TI-LLST, the effects of TI-LLST (both reversible and irreversible) on the solidification of Cu-Sb alloys are studied further. The major contents and conclusions are as follows:First, the electrical resistivities of liquid Cu-Sb alloys are measured as the function of temperature continuously in several heating and cooling cycles. The results show that the resistivity-temperature (ρ-T) curves of the melt change abnormally in a relatively high-temperature zone above the liquidus in several experimental. It indicates that there are TI-LLST in Cu-Sb alloys, moreover the structure transition contain both irreversible and reversible ones. These new phenomena verify that the temperature behavior of melt another kind of alloy—Sb-based alloy could also be reversible, except the Sn-based alloy.Second, from the viewpoint of melt structure transitions, through different melt overheating treatments, the effects of both reversible and irreversible TI-LLST on the solidification of Cu-Sb alloys were studied. The results show that larger undercooling, higer nucleus forming rates, faster solidification rates could be obtained after the melt experienced the TI-LLST, in consequence, finer grain sizes as well as different microscopic patterns of solidified structures would be gained. In other sides, amending the melt processing methods in response to the reversible structure changes could catch hold of the melts states effectively, and resulting in different solidification microstructures.Third, in research methods, the resisitivity method was still used to investigate the solidification process of the melt, associated with the thermal analysis method. The results reflected in this paper show that the the resisitivity method could not only display the solidified behavior very validly, such as the more visible solidification parameters but also supply more imformations of the solidification behavior than thermal analysis method.The new phenomena and results reflected in this paper suggest that grasping the rules of melt structure change with temperature before material processing will give help for controlling the solidification more effectively, finally resulting in more ideal microstructures. It provides a new basis for deeper understanding the essence of heat treatment, and is also of significance for promoting the innovation of material processing.