Influence of the γ-phase volume fraction on the growth kinetics of discontinuous coarsening of the lamellar structure in Ti-(40-46)at.% Al intermetallic compounds

Abstract

The growth kinetics of the discontinuous coarsening of lamellar structure in Ti-(40-46)at.%Al intermetallic compounds was studied using optical microscopy, scanning electron microscopy and transmission electron microscopy. The growth rate of discontinuous coarsening shows a maximum near 44at.%Al. The interlamellar spacing of both primary and secondary lamellar cells also shows a minimum at about 43at.%Al. The growth rate calculated using solely the elastic strain energy as the driving force shows a linear relation with the measured value on a normalized scale. This kinetics analysis suggests that the driving force for the migration of grain boundaries is the elastic strain energy rather than the chemical or interfacial energies. The last two energies, being chemical in nature, are believed to be dissipated by the establishment of local equilibrium due to a comparatively rapid volume diffusion in front of the migrating grain boundary. The elastic strain energy depends on the elastic properties of constituent phases and, therefore, cannot be disappeared by chemical balance such as the local equilibrium at the boundary. The efficiency of the strain energy is consistent with the experimental observation that shows no planar αP2-αS2 and γP-γS interfaces under the condition of perfect dissipation of the chemical energy.