Transport phenomena during solidification processing of functionally graded composites by sedimentation

A combined experimental and numerical investigation of the solidification process during gravity casting of functionally graded materials (FGMs) is conducted. Focus is placed on understanding the interplay between the freezing front dynamics and particle transport during solidification. Transparent model experiments were performed in a rectangular ingot using pure water and succinonitrile (SCN) as the matrix and glass beads as the particle phase. The time evolutions of local particle volume fractions were measured in situ by bifurcated fiber optical probes working in the reflection mode. The effects of important processing parameters were explored. It is found that there exists a particle-free zone in the top portion of the solidified ingot, followed by a graded particle distribution region towards the bottom. Higher superheat results in slower solidification and hence a thicker particle-free zone and a higher particle concentration near the bottom. The higher initial particle volume fraction leads to a thinner particle-free region. Lower cooling temperatures suppress particle settling. A one-dimensional multiphase solidification model was also developed, and the model equations were solved numerically using a fixed-grid, finite-volume method. The model was then validated against the experimental results and subsequently used as a tool for efficient computational prototyping of an Al/SiC FGM.