Coarsening of Lamellar Structures at Elevated Temperatures

Abstract

The coarsening of lamellar eutectic alloys is controlled by faults in the as-grown structure. A model, based on the use of In cosh cylinder co-ordinates, is proposed to calculate the rate of shrinkage of lamellar terminations. It is found that for high volume fractions and diffusion through the continuous phase around the fault, the fault shape remains approximately constant and a value can be obtained for the rate of shrinkage of an isolated fault. For the case of interface diffusion, the shape is not preserved and only the initial shape changes can be calculated. The problem of coarsening of an array of faulted lamellae is considered. The important variables in the coarsening rate are the lamellar spacing and fault density. These results are compared to the experimental observations of Graham and Kraft on unidirectionally solidified Al–CuAl₂ alloys.