Numerical Simulation Of Liquid-Liquid Phase Separation And Coarsening In Immiscible Cu-Co Alloy

The liquid-liquid phase separation of immiscible alloy has an important impact on the final solidified microstructure and properties.An immiscible alloy,once deeply undercooled to the position of bimodal,will separate from a homogeneous liquid into two liquids with different concentrations.Cu-Co alloy is an immiscible alloy that has been widely used as magnetic material in electronics industry due to its excellent giant magneto-resistance effect.However,it is prone to form serious segregation under usual casting conditions due to the fact that their densities are much different under gravity.Thus the application of these kinds of alloys is limited.With the development of computer technology,the numerical simulation method can help us to predict microstructure evolution during the solidification of immiscible alloy,so as to provide the foundation for improving the solidification structure of the alloy through process control.A two-dimensional lattice Boltzmann method(LB method)and relevant program are developed to simulate liquid-liquid phase separation of Co84Cu16.The LBM for liquid-liquid phase separation is applied to simulate diffusion,collision,coagulation,and Ostwald ripening at 1400K(undercooling is 300K).The main finished work is as follows.(1)The method of several important parameters' determination is introduced,such as ?0,?0,G and their values.In addition,the relationship that the surface tension ? increases with the increasing of G is gotten.(2)The growth process of single droplet is simulated.When the initial concentration C0 increases to 0.20 from 0.16,the growth rate of droplet increases to 11m/s from 6m/s and the final size of droplet increases from 451u to 491u(11u is 0.04 ?m).When interaction strength G increases from 109 to 112,the matrix equilibrium concentration reduces,the growth rate of droplet increases from 6m/s to 11.5m/s and droplet's final size increases from 451u to 501u.(3)The law of coagulation process of two droplets is simulated.The coagulation of two droplets depends on the surface spacing ds.When dc is too large,increasing of radius can make two droplets coagulate.Meanwhile,increasing of interaction strength can accelerate the coagulation of two droplets.(4)The law of Ostwald ripening process is simulated and the differences between coagulation and Ostwald ripening are compared.Whether Ostwald ripening occurs or not depends on the degree of supersaturation.Two droplets will coagulate when the degree of supersaturation is larger than 0.05.So C0 and G can't be too large.The larger droplet radius ratio improves the occurrence probability of Ostwald ripening and the smaller value of ds improves the occurrence probability of droplets coagulation.(5)The law of the growth process of multi-droplets is studied.The average diameter of the droplets increases and the number of droplets is decreased with the increasing of C0 and G,and G has a more remarkable impact effect.In the early stage,the growth of droplets is mainly affected by diffusion and coagulation.However,in the final stage,it is mainly influenced by Ostwald ripening.