Session BB2.4

3:15 PM BB2.4
MODELING OF MICROSTRUCTURE DEVELOPMENT OF A SINGLE SPLAT IN PLASMA THERMAL SPRAY DEPOSITION. G.-X. Wang and V. Prasad, Process Modeling Laboratory; S. Sampath and H. Herman, Center for Thermal Spray Research, State University of New York, Stony Brook, NY.

In plasma thermal spray deposition, millions of molten particles impinge on a solid substrate to form a coating or a deposit layer, whose properties are ultimately controlled by the microstructure of individual splat formed and by the bonding and connection between the splats. It is therefore essential to understand the microstructure formation mechanism of each individual splat. We have developed an integrated method for modeling the microstructure development of a single splat on a solid substrate or a predeposit layer. This method is based on a one-dimensional heat and mass transfer model, but including the classic nucleation theory, the non-equilibrium crystal growth kinetics, and the linear stability theory of a planar interface. The model calculates the nucleation rate from which one can determine the nucleation temperature, grain density and size distribution at the end of the nucleation. The kinetic melt undercooling is introduced at the solid/liquid interface based on a linear crystal growth kinetics. The solidification morphology, i.e., planar or dendritic, is determined by comparing the model predicted solid/liquid interface velocity with the absolute stability velocity obtained from the stability theory. Once dendritic morphology is selected, the heat transfer model introduces the dendrite tip growth kinetics based on a single dendrite tip growth model available in the literature, that includes the solute diffusion around the tip, capillarity undercooling, and kinetic undercooling. The marginal stability criterion is used to determine the dendrite tip velocity and the tip radius. A supplement microsegregation model with local recalescence and solute trapping is also employed to calculate the solute redistribution and solute segregation. This integrated model has been applied to investigate the microstructure development in thermal sprayed AlCu, Mo, and Al2O3 splats under varying process conditions. Selected results are presented to explain the controlling mechanisms of structure formation in plasma thermal spray.
* This work was supported by the MRSEC Program of the National Science Foundation under Award Number DMR-9632570