Solidification of binary hypoeutectic alloy matrix composite castings

We consider a binary hypoeutectic alloy casting which solidifies in dendritic form in an unreinforced engineering casting and seek to predict its microstructure in a metal matrix composite, where the reinforcement is fixed in space and fairly homogeneously distributed, and it does not catalyze heterogeneous nucleation of the solid. The reinforcement can cause several microstructural transitions in the matrix alloy, depending on the matrix cooling rate, the width of interstices left between reinforcing elements, and the initial velocity of the solidification front. These transitions comprise (1) coalescence of dendrite arms before solidification is complete, causing solidification to proceed in the later stages of solidification with a nondendritic primary phase mapping the geometry of interstices delineated by reinforcement elements; (2) sharp reduction or elimination of microsegregation in the matrix by diffusion in the primary solid matrix phase; and (3) a transition from dendrite to cell formation, these cells featuring significant undercoolings or a nearly plane front configuration when reinforcing elements are sufficiently fine. (Author)