Abstract
AbstractBoundary heat flux has a significant effect on solidification behavior and microstructure formation, for it can directly affect the interfacial heat flux and cooling rate during phase transition. In this study, a phase field model for non-isothermal solidification in binary alloys is employed to simulate the free dendrite growth in undercooled melts with induced boundary heat flux, and an anti-trapping current is introduced to suppress the solute trapping due to the larger interface width used in simulations than a real solidifying material. The effect of heat flux input/extraction from different boundaries was studied first. With heat input from boundaries, the temperature can be raised and the dendritic morphology changed with gradient temperature distribution caused by the heat flux input coupling with latent heat release during the liquid-solid phase transition. Also, the concentration distribution can be also influenced by this irregular temperature distribution. Heat flux extraction from the boundaries can decrease the temperature, which results in rapid solidification with small solute segregation and concentration changes in the dendrite structures. Also, dendrite growth manner changes caused by undercooling variation, the result of competition between heat flux and latent heat release from phase transition, are also studied. Results indicate that heat flux in the simulation zone significantly reduces the undercooling, thus slowing down the dendrite formation and enhancing the solute segregation, while large heat extraction can enlarge the undercooling and lead to rapid solidification with large dendrite tip speed and small secondary dendrite arm spacing, while solute segregation tends to be steady. Therefore, the boundary heat flux coupling with the latent heat release from the solidification has an effective influence on the temperature gradient distribution within the simulation zone, which leads to the morphology and concentration changes in the dendritic structure formation.
Highlights
The mechanical properties of many materials have a significant relationship with the microstructure formation process [1], but in practice, it is difficult to observe the microstructure formation process with experimental methods, and computer simulations can visually show the phase transition process and provide much more information to calculate many other parameters that are related to the mechanical properties with the data achieved from simulations
With heat extraction from the boundary, we find that the solute distribution along the primary dendrite arm near the north boundary keeps steady unlike that without heat flux; this is because the heat extraction partly balances the latent heat release from the liquid-solid phase transition, which keeps the temperature almost unchanged at the solid-liquid interface and makes the solute diffusion approximately steady
A phase field model for simulating solidification in binary alloys under non-isothermal conditions is implemented to study the effect of heat flux input/extraction from boundaries on the dendrite structure forming process in a Ni-Cu alloy
Summary
The mechanical properties of many materials have a significant relationship with the microstructure formation process [1], but in practice, it is difficult to observe the microstructure formation process with experimental methods, and computer simulations can visually show the phase transition process and provide much more information to calculate many other parameters that are related to the mechanical properties with the data achieved from simulations. The phase field model has been used for computing solidification morphologies to avoid the explicit boundary tracking needed to solve the classical sharp-interface model With this advantage, phase field methods have attracted considerable interest in the last decades as a means of simulating the solidification process. Kobayashi [6] developed a simple phase field model for one-component melt growth including anisotropy and used this model to study the formation of various dendritic patterns He found that the qualitative relations between the shapes of crystals and some physical parameters and noises gave a crucial influence on the side branch structure of dendrites. Distributions of the concentration change as the result of temperature change caused by different boundary heat flux couplings with latent heat release are given and analyzed in detail
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