Growth kinetics of discontinuous coarsening of lamellar structure in Ti-44 at.% Al (-0.5 at.% Cr) intermetallic compounds

Abstract

The growth kinetics of a discontinuous coarsening of lamellar structure in Ti-44at.% Al(-0.5 at.% Cr) intermetallic compounds was studied using an optical microscope, X-ray diffractometer, and transmission electron microscope. The growth rate is linear during the initial period of the reaction and reaches a maximum near the eutectoid temperature. The migrating grain boundary plane maintains no definitive geometrical angular relationship to the lamellar interface. The discontinuous coarsening occurs through the grain boundary diffusion and its activation energy is estimated to bit about 230 kJ/mol. This kinetic analysis suggests that the driving force for grain boundary migration is the elastic strain energy rather than the chemical and interfacial free energies, despite the comparatively larger value of the last two. The reasons for this are not clearly understood. However, the possibility of dissipation of the chemical free energy in front of the migrating grain boundary was evaluated. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. Ali rights reserved.