INITIATION AND GROWTH OF SOLIDIFICATION SHRINKAGE VOIDS

Solidification void formation results from the unavoidable density changes that accompany freezing of most liquids. Predicting the void distribution and artificially modifying it when necessary are vital to a wide variety of applications ranging from high-performance thermal energy storage to advanced materials processing. This chapter discusses in detail the current state-of-the-art research on void formation over the complete life cycle of a void. The thermodynamics of void nucleation in a constant-volume environment are reviewed, as well as the heat transfer and fluid dynamic phenomena that determine which nucleation centers grow to macroscopic sizes. Once the initial nucleation pattern has been established, other heat transfer and fluid flow models can be invoked to determine void growth rates, while volume accounting and minimizing the interfacial energy are used to track the void profile. Further migration of voids that become frozen-over in the solid can be analyzed by a similar numerical heat transfer and volume conservation approach. This chapter also considers several techniques for void control and suggests some topics for future research on void formation.