Papers by Keyword: Solute Trapping

Abstract: Through solving an extended Fick’s diffusion equation for the solidification front of a paraboloid of revolution, a generalized Ivantsov function is obtained. The relaxation effect of nonequilibrium liquid diffusion is taken into account. The solute profile in the interfacial region and in the bulk liquid during steady-state dendritic solidification is uniquely determined. It is concluded that the consideration of the relaxation effect and the diffuse interface of finite thickness which decreases with increasing of velocities are necessary for achieving the good model predictions.

Abstract: During rapid solidification, interfaces are often driven far from equilibrium and the "solute trapping" phenomenon is usually observed. Very recently, a phase field model with finite interface dissipation, in which separate kinetic equations are assigned to each phase concentration instead of an equilibrium partitioning condition, has been newly developed. By introducing the so-called interface permeability, the phase field model with finite interface dissipation can nicely describe solute trapping during solidification in the length scale of micrometer. This model was then applied to perform a phase field simulation in a Al-Sn alloy (Al-0.2 at.% Sn) during rapid solidification. A simplified linear phase diagram was constructed for providing the reliable driving force and potential information. The other thermophysical parameters, such as interface energy and diffusivities, were directly taken from the literature. As for the interface mobility, it was estimated via a kinetic relationship in the present work. According to the present phase field simulation, the interface velocity increases as temperature decreases, resulting in the enhancement of solute trapping. Moreover, the simulated solute segregation coefficients in Al-0.2 at.% Sn can nicely reproduce the experimental data.

Abstract: Vacancies are the simplest type of lattice defect. However, they play a major role in the kinetics of diffusional processes, such as solid-state precipitation, where mass transport is directly proportional to the concentration of vacancies. We present a physical modelling framework, where we simulate the evolution of excess vacancies on the example of Al-alloys during simplified time-temperature treatments. Interaction energies between solute atoms and vacancies are evaluated by first-principle analysis. Assuming that the escape of vacancies from existing traps is dependent on temperature and binding energies, we explore the life-time of non-equilibrium vacancies and the natural and artificial aging response of Al alloys. The predictions of the model are finally compared to experimental data.

Abstract: The evolution of interface morphology for a single-phase Nickel-Copper binary alloy in directional solidification is studied by using a phase-field model cooperated solute concentration gradient corrections. The effect of pulling velocity V and strength of the crystalline anisotropy γ on interface morphology and the solute segregation is formulated. The results indicate that, the transition from plane to cells/fine cellular structures, then to planar structures(plane-cell-plane) will happen with the increment of V, and the level of solute trapping becomes stronger. When the crystal grows with cellular structures, γ crucially influences the interface pattern formation at the lower growth velocity, but the solute partition ratio is not significantly affected by the anisotropy strength. Then, the operating behavior for planar growth is hardly any affected by the crystalline anisotropy.