The discontinuous coarsening reactions in the PbCd and the ZnCd lamellar eutectic alloys-I. The driving force, initiation and the morphology

Abstract

The morphologies of the discontinuous coarsening of the PbCd and the ZnCd lamellar eutectic alloys have been investigated at temperatures ranging from 353 to 483 K by scanning electron microscopy. Two types of coarsened cell morphology were observed and the terminology used by Frebel and Duddek [ Mater. Sci. Engng 32, 17 (1978)], namely, Type I and Type II has been adopted to describe them. A simple geometrical model is suggested for the Type II cell growth. The driving forces and the initiation of the reaction are discussed and the effects of lamellar faults and mismatch surfaces in the morphology of the secondary cells is described. The manner in which the microstructural features develop during the discontinuous coarsening reactions has been analysed and compared with the existing data.