Dendritic Growth In Undercooled Melt Research Articles

A Stable Mode of Dendritic Growth in Cases of Conductive and Convective Heat and Mass Transfer

In this paper, we develop a theory of stable dendritic growth in undercooled melts in the presence of conductive and convective heat and mass transfer boundary conditions at the solid/liquid interface of a dendrite. To simplify the matter and construct the analytical theory, conductive and convective mechanisms are considered separately. Namely, the laws for total undercooling and selection criterion defining the stable growth mode (dendrite tip velocity and diameter) are derived for conductive and convective boundary conditions. To describe the case of simultaneous occurrence of these heat and mass transfer mechanisms, we sew together conductive and convective laws using power stitching functions. The generalised selection theory is compared with experimental data for Al24Ge76 and Ti45Al55 undercooled melts.

Influence of tiny amounts of impurity on dendritic growth in undercooled melts

An influence of small amounts of impurity on the dendrite growth is investigated analytically and numerically. For investigations, a model for anisotropic dendrites rapidly growing in pure and binary melts is used. The dependence of the dendrite growth velocity and of the dendrite tip radius from undercooled melt from amounts of impurity is analyzed. Calculations are carried out for the pure nickel and binary nickel-zircon diluted melts.

A New Growth Kinetics in Simulation of Dendrite Growth by Cellular Automaton Method

A modified cellular automaton model was proposed to simulate the dendrite growth of alloy. Different from previous models, this model used neither an analytical equation(such as KGT model) nor an interface solute gradient equation to solve the velocity of solid-liquid interface, but used the interface solute and energy conservation and thermodynamic equilibrium condition to describe the solid/liquid interface growth kinetics process. In present model, once the temperature field and solute field were solved by finite different method in the entire domain, the material thermodynamic properties can be substituted into four algebraic equations to easily determine the variation of solid fraction, interface temperature and solute concentration, instead of calculating interface moving velocity. As a result, the complexity of the calculation can be largely reduced. The simulated dendrite growth was in a good agreement with the Lipton–Glicksman–Kurz (LGK) model for free dendritic growth in undercooled melts.

Dendritic Growth in Undercooled Melt with Forced Convection

Dendritic Growth in Undercooled Melt with Forced Convection

Nucleation and Dendritic Growth in Undercooled Melts

ABSTRACTTechniques of containerless processing are applied to undercool and solidify metals and alloys. These techniques allow direct measurements of both the undercooling and the crystal growth velocity. Experimental results are presented for studies of nucleation of metastable crystalline phases and quasicrystals. Measurements of the dendrite growth velocity as a function of undercooling are exemplified for dilute Ni-based alloys and intermetallics. The results are analysed within current theories of rapid crystal growth. Their consequences on the formation of grain refined microstructures are highlighted. In addition, recent experiments on the undercooling of magnetic alloys are discussed revealing the existence of long-range magnetic ordering in an undercooled melt.

Dendritic Growth in Undercooled Melt with forced Convection: Theory.

Analytical solutions for melt flow with Oseen viscous flow approximation are obtained for the Navier-Stokes equations in the region near the tip of a dendrite of which shape is approximated to be a paraboloid of revolution. Temperature is also analyzed in the presence of flow in a melt. A theory of dendritic growth is proposed with flow in the undercooled pure melt. Local equilibrium condition at the interface is applied in the theory. The predicted growth rate of the tip of dendrite as functions of the melt undrcooling with and without forced flow velocity is successfully compared with the experimental results for the pure succinonitrile.

Dendritic Growth in Undercooled Melt with Forced Convection: Experiment for Pure Succinonitrile.

The flow in the melt will affect to the morphology of solidification but has rarely been studied quantitatively, because of difficulties in how to bring the controlled flow of melt to the region near the tip of dendrite. In order to realize the flow of melt, the undercooled melt in a cylindrical circular loop cell is partially heated to drive the melt and is forced to flow by the buoyancy. The dendritic growth in this forced melt flow is studied for dendrites growing horizontally in the undercooled melt of pure succinonitrile. The flow affects more significantly to the growth rate of dendrite in lower undercooling than in higher undercooling in the melt. The growth rate of the dendrite tip increases with the increase of forced melt flow when the flow is coming to the tip. When the velocity of the forced flow becomes small, the growth rate of the tip of dendrite approaches one predicted by the theory, where the dendritic growth is studied by the diffusion of heat alone under the marginal stability assumption.

On dendritic growth in undercooled melts

The role of gravity-dependent convection in the steady-state growth of dendrites in undercooled melts is investigated theoretically. The model described by Huang and Glicksman (1981) is extended and refined, using the concept of a thermal diffusion boundary layer (Burton et al., 1987) to characterize the dendritic interface. Theoretical predictions are presented in graphs and shown to be in good general agreement with published experimental data on succinonitrile. The need for careful space experiments to clarify the role of nongravity-dependent convection is indicated.

Effect of growth rate dependent partition coefficient on the dendritic growth in undercooled melts

The theory of alloy dendritic growth at large undercoolings is extended to include the effect of growth rate dependent partition coefficient on the growth rate, tip radius and composition of dendrites. Three distinct behaviors are observed depending on the value of the dimensionless rate v. For small values of v, k ≅ k 0. For the intermediate range, when v is between 0.01 and 100, a significant effect of the velocity dependent partition coefficient is found. When v > 100, k → 1 and the dendrite behavior in an alloy is found to approach that for the pure material. In undercooled alloy melts segregation free zones could then be obtained by dendrite growth.