Lamellar and Rod Eutectic Growth

A general theory for the growth of lamellar and rod eutectics is presented. These modes of growth depend on the interplay between the diffusion required for phase separation and the formation of interphase boundaries. The present analysis of these factors provides a justification for earlier approximate theories. The conditions for stability of rod and lamellar structures are considered in terms of the mechanisms by which the structure can change. The mechanisms considered include both small adjustments to the lamellar spacing due to the motion of lamellar faults, and catastrophic changes due to instabilities. It is concluded that stable growth occurs at or near the minimum interface undercooling for a given growth rate. The consequences of the existence of a diffusion boundary layer at the interface are discussed. The experimental results for the variation of growth rate, undercooling, and lamellar spacing are compared with the theory. We believe that the theory presented in this paper provides an adequate basis for understanding the complex phenomena of lamellar and rod eutectic growth.