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Simulation Of Liquid Phase-separated Cu-Co Alloy Using Cellular Automata (CA) Model

Posted on:2015-12-19Degree:MasterType:Thesis
Country:ChinaCandidate:M LiuFull Text:PDF
GTID:2191330473453685Subject:Materials engineering
Abstract/Summary:PDF Full Text Request
There is a metastable miscibility gap in the undercooled liquid of an immiscible alloy in binary alloy phase diagram. When a homogeneous liquid is undercooled to the bimodal temperature, it is separated into two liquid phases. Since their densities are much different, it is prone to form segregation during usual casting conditions under gravity. This limits the application of this kind of alloy. As known, the liquid-liquid phase transformation during solidification affects the final microstructure of the alloy. So the liquid-liquid phase separation in immiscible alloy should be studied in order to improve the segregation.In this paper, a CA model is developed to simulate the growth of a dispersed phase droplet during the liquid-liquid phase separation of a Cu-Co alloy. It is found that,1). The constitutional and curvature undercooling are considered in CA model. The equilibrium partition coefficient decreasing with the increase of Cu content, which is distinguished to the dendrite growth process, is also considered in the model.2). The factor which eliminates the anisotropy of CA grid system is adopted to keep the round shape of the droplet in 2D simulation.3).The growth mechanics of a single droplet is explained. Under deep undercooling, liquid-liquid phase separation occurs. The driving force for the growth of a droplet is the difference between local and equilibrium concentration in liquid matrix. The growth rate of the droplet decreases, correspondingly, the changing rate of the radius of the droplet also decreases till to final stable state.4). When two droplets grow up and merge, a liquid bridge forms between them. The individual concentration field interacts and finally combines into one. Since the effects of surface tension and interaction between two drops are not considered presently, the droplet continues to grow while keeping the shape at merging.
Keywords/Search Tags:Cu-Co alloy, liquid-liquid phase separation, solute diffusion, droplet growth, Cellular Automata
PDF Full Text Request
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