PROCESS MODELING AND MICROSTRUCTURE

Among the many routes which are used for the processing of high-temper ature materials, solidification plays a key role. Several modelling to ols are now available for the simulation of the interconnected macrosc opic phenomena associated with any casting process (heat exchange, mou ld filling, convection, stress development, etc.). Based upon finite-d ifference (FD) or finite-element (FE) techniques; these models solve t he continuity equations of mass, energy, momentum, solute species, ave raged over the liquid and solid phases. As such, macroscopic models do not account for the detailed phenomena occurring at the scale of the microstructure. For that reason, a stochastic cellular automaton (CA) model has been developed recently for the prediction of the grain stru cture formation in solidification processes, in particular during the investment casting of superalloys. Such a microscopic model considers the heterogeneous nucleation of grains at the surface of the mould and in the bulk of the liquid, the growth kinetics and preferential growt h directions of the dendrites and the microsegregation. The microscopi c CA model has been coupled to FE heat flow computations in order to p redict the grain structure at the scale of a casting. It is shown that microstructural features and crystallographic textures can be simulat ed as a function of the casting conditions and alloy composition.