The Research On Faceted Dendritic Growth Using Phase-field Method

Casting production as a processing include such procedures:pouring liquid melt into casting model, cooling and solidification, and getting a melt product which has a certain shape and size. After a solidification process a certain shape and size was given on the microscopic dimension to a melt work and it’s organization, structure and performance also was demanded on microcosmic dimension. Having a better or worse integrated mechanical performance and property of a metal casting was influenced by changing of microstructure in solidification directly, so effective controlling or guiding the development of microstructure in solidification process had a meanful significance in producing good casting products which had the best comprehensive mechanical properties.As a useful numerical modeling method in predicting solidification process of supercooled melt, phase-field method was applied in simulating the dendrite growth extensively. Nucleation and growth of metallic and alloying crystal would follow the mechanism of faceted dendritic evolution under the conditions of strong anisotropy or extra fields. The faceted dendritic morphology of pure substance and binary alloys were displayed and the different simulation results were also discussed in this paper. In this paper, based on the phase-field model given by Kim et al, a phase-field model of faceted dendrite growth in binary alloy was built by adjusting interface energy, and the faceted dendritic growth of Si-10%Ni lean solution binary alloy was simulated, and the further studying directions in future were demonstrated.The simulation results showed that, when the anisotropic strength coefficient x> exceeded the critical value1/15, the morphology of dendritic growth performed as a faceted dendrite, and the curvature effect disappeared, then a discontinuous angular contracture was presented; and a large number of side-branches generated in the spine of the primary dendrite. In order to verify the availability of the faceted dendritic phase-field model, the simulation results was analyzed and compared with the experimental observation. The growth morphology, solute-field redistribution and growth velocity of faceted dendrite were influenced by interfacial thickness significantly. A thinner diffusive boundary was conducive to releasing latent heat of solidification and good for slid phase advancing into liquid phase,and increasing of thermal perturbation because of those comprehensive effort was beneficial to forming of secondary or high secondary dendrite. Lower interface width is favorable to diffusion of solute atom and releasing of latent heat of crystallization, so that with increasing of interface thickness dendritic growing speed was decreasing. As a precondition of melt solidification process, the value of degree of supercoiling also had a direct influence to faceted dendritic morphology and growth velocity. With increasing of supercoiling degree the dendritic growth speed increased and the number of secondary dendrite arm increased too. With the value of anisotropy strength coefficient added, the secondary dendrite developed increasingly and it’s number and volume increased also, and those resulted a solute trapping obviously, while a more obvious macroscopic feature of faceted dendrite and crystal shape characteristics occurred. Before the value of v was lower than the critical value, the growth speed is an increasing function of v, but when the value of v surpassed the critical value the function between v and dendritic growth velocity was a decreasing function and it’s decreasing tendency was slower than increasing function’.