METHODOLOGY FOR STUDYING THE EFFECT OF OVERHEATING ON SUPERCOOLING OF METALS AND THEIR ALLOYS

Procesi littâ, 2024, Vol 3 (157), 19-27

Abstract

This work is devoted to the development of a physical modeling technique to study the effect of overheating of metal melts on their supercooling before crystallization, since melting and crystal- lization are important technological processes for obtaining high-quality castings. Due to the fact that the processes involved in casting metals and their alloys operate at very high temperatures, are opaque and sometimes take place in aggressive environments, direct study of such processes is extremely difficult. In this regard, we have applied the method of physical modeling to conduct these studies, in which low-temperature metal alloys and organic compounds are used as objects of study. To conduct the research, a special experimental setup was created and a physical mod- eling technique was developed. At the beginning of the experiments, three prototypes of equal weight were prepared from each model alloy on an electronic balance (with a weighing accuracy of 0.01 g). To ensure the absolute identity of the melting and crystallization conditions of the model alloys, all three test samples were simultaneously placed in a chamber in which they were gradually heated to a certain level in order to melt and superheat. After appropriate exposure of the melt in the superheated state, it was cooled at a certain rate by cooling to the temperature of nucleation, which was recorded using thermocouples. The signal from the thermocouples in the form of absolute temperature values in digits and temperature curves of the cooling of the melts of the test media was observed on the screens of the potentiometer and laptop. The magnitude of melt supercooling, at which crystals nucleate, was determined by characteristic features on the cooling temperature curve of the model medium, such as the appearance of boards on them due to the release of crystallization heat. Transparent model environments allowed us to observe the nucleation of crystals visually. As a result of the researches, it was found that the effect of overheating on supercooling of the studied alloys is most likely due to a change in the concentration of limitedly soluble impurities. This assumption is based on the fact that the dissolution of impurities in the melt of any metal occurs as a result of diffusion, which is a relatively time-consuming process, and to obtain greater homogeneity of the metal melt, it is necessary either to increase the temperature of its overheating or to ensure its longer exposure to the overheated state. Ultimately, the results of the studies confirmed these assumptions, when, with an increase in the degree of dissolution of impurities, the supercooling of model melts changes, at which crystals are formed, and this was most likely due to a change in their physical and chemical properties.