Abstract
The first stage of the solidification of metal alloys is nucleation, during this stage is defined the number of grains present in the final structure, just as the conditions in which the same will grow. The application of pressure in the solidification is mostly studied as an operational parameter, and its effects are described and commented extensively in literature. The objective of this paper is to study the effect of pressure on nucleation, still not to describe but to explain it, for this purpose the pressure is treated as a thermodynamic variable. From this analysis it was possible to determine the real influence of pressure on the activation energy, being clear that its effect is equivalent and co-dependent to that of the undercooling, and can thus cause considerable variations in the activation energy, much larger than what is proposed in previously published papers that approach the subject, causing a considerable stimulus on nucleation. It was also observed that the curve that represents the effect of pressure on the activation energy proposed in this paper, has a similar form to the curves that describe how the pressure refines structures, resulting from the process of solidification under pressure reported in literature.
Highlights
Casting is one of the main manufacturing processes used in the production of metal parts, and the effects of the solidification process on these parts is most evident when casting is the final operation
The mechanical properties of a metal alloy have a strong dependence on the structure produced during solidification, both on the macro and micro scale, and what controls the structural parameters are the thermal variables and the process dynamics, which in practice are controlled by the composition of the alloy, and by operational parameters such as mold preheating temperature, casting temperature, mold geometry, cooling mechanism and others
Where r is the radius of the nucleus, which suggests that the dependence of surface energy density on pressure is proportional to the size of the nucleus and the mechanical properties of the material
Summary
Casting is one of the main manufacturing processes used in the production of metal parts, and the effects of the solidification process on these parts is most evident when casting is the final operation. The mechanical properties of a metal alloy have a strong dependence on the structure produced during solidification, both on the macro and micro scale, and what controls the structural parameters are the thermal variables and the process dynamics, which in practice are controlled by the composition of the alloy, and by operational parameters such as mold preheating temperature, casting temperature, mold geometry, cooling mechanism and others. Each of these operational parameters changes the way the system evolves to its final state in a different fashion, causing variations in the structure of the resulting alloy. When calculating its effects on the physical properties involved in the nucleation process, a set of equations was obtained and its implications were compared with the results published in the literature, making it clear that the effect of pressure on nucleation contemplates a much greater magnitude than what is proposed so far
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