Modeling of transport phenomena during solidification of metal-matrix particulate composites

A multiphase model for the solidification of metal-matrix particulate composites is developed using the continuum approach and techniques of volume averaging. Macroscopic conservation equations and associated transfer terms are developed that are pertinent to the solidification of a binary alloy matrix containing a stationary solid phase and a generally non-stationary spherical particulate reinforcement. Macroscopic particle rejection is included in the model as well as the possibility of particle clustering with and without solidification. The conservation equations are reduced to a form suitable for implementation into a two-phase CFD code, and are solved numerically using an established finite-volume scheme. An algorithm is developed to calculate the solid volume fraction in the presence of particles.; Simulations are conducted for one-dimensional sedimentation and one- and two-dimensional composite solidification in various Al-7wt.%Si/SiC systems. Good agreement is found between one-dimensional sedimentation results and available analytical solutions and numerical and experimental data from the literature, and reasonable agreement is found between experiments and one-dimensional composite solidification results. One-dimensional case study results indicate a larger amount of particle settling in clustering particle systems, and a transition between macroscopic rejection and engulfment in systems containing an impenetrable growth front.; Two-dimensional results for the unreinforced alloy show significant thermosolutal convection in the mush leading to widespread macrosegregation. Particle entrapment is predicted in all reinforced alloy cases. Relatively small particles are found to result in negligible particle settling prior to entrapment whereas large denuded and packed zones are formed for relatively large particles. Macrosegregation is found to be negligible in reinforced regions of the casting due to substantially reduced fluid flow after particle entrapment, and the eutectic formation approaches that predicted by the reinforced Scheil model. Macroscopic rejection studies with fluid flow indicate a breakdown of the rejection model due to the large drag force exerted on a large volume fraction of particles.; Future research includes the development of more advanced particle rejection criteria, the inclusion of a non-stationary solid phase, as well as solidification experiments designed to provide experimental validation of future models.