Heat Transfer And Dendrite Growth Behaviour In Droplet Solidification Of Nickle-base Alloy

In the process of aerosolization, the liquid metal is atomized into tiny droplets,to achieve rapid solidification and then obain fine grain structures. As thesolid-liquid interface deviates from the equilibrium position, the heat and masstransfer phenomenas in the droplet solidification process are very complex. So farthere is no theory to describe the process of droplet solidification very acduratelyfrom the aspects of thermodynamics and kinetics. In this paper, the heat transfer anddendrite growth behavior in the process of aerosolized droplets of nickel-base alloyduring solidification has been numerically analyzed, and the effect of the relevantparameters on droplet solidification process has also been studied.A single point and multi-point nucleation heat transfer models of Nickel-basealloy during aerosolization have been developed based on the theory of energyconservation law. The results show that, the process of heat transfer is divided intothree stages: initial transient stage, recalescence stage and adiabatic approximationstage. The effect of the undercooling prior to nucleation and the value ofparameter K Bi on the process of heat transfer has been analyzed. The resultsindicate that increasing the undercooling prior to nucleation and the value ofparameter K Bi results a corresponding increase in recalescence rates. And gived areasonable explanation about the similarities and differences between thesingle-point nucleation model and multi-point model.Base on M-S theory, a planar interface stability criterion is proposed which isvalid for low as well as high growth rate conditions. While?the criterion is a bitcomplicated, so a simplified interface stability criterion is developed based on theassumptions of that the thermal diffusivity and thermal conductivity of liquid andsolid are equal, and no temperature gradient in solid.Characteristics of dendrite microstructure of the Nickel-base alloy droplet areanalyzed systematically, and a nondimensional model for dendritic growth isdeveloped. The relationships among the undercooling?radius and growth rate ofdendrite tip are established with the the numerical results. The results show thatincreasing the the undercooling of dendrite tip results a corresponding increase in dendrite growth rate and decrease in dendrite tip radius, and if the undercooling ofdendrite tip keeps constant, then with the increasing of the initial concentration ofsolute, the dendrite growth rate increases first and then decreases, the dendrite tipradius decreases. At the same time, the effects of solute distribution coefficient andthe ratio between thermal diffusivity and Solute diffusion coefficient on the processof dendrite growth are analyzed.The sizes of different real dendrite tip radius are achieved through throughprecise experimental measurements,and they are good for the the numerical results.