A SYNTHESIS OF MECHANISMS FOR INITIATION OF THE CELLULAR (OR DISCONTINUOUS PRECIPITATION) REACTION

摘要

To provide a basis for understanding mechanisms for initiation of the cellular reaction, the junc- tion of an incoherent grain boundary with microfaceted interfaces at both the rationally and the irration- ally oriented interfaces of grain boundary allotriomorphs is examined with the Cahn--Hoffman formalism. When relative values of the three { vectors are appropriate, the angle between the grain boundary and a facet at the allotriomorph edge can vary from 0 to 90 and still be in equilibrium throughout this range. Also, the same vector applies everywhere on a given planar facet. With the aid of DIGM. these consider- ations can permit a grain boundary to migrate part way along the broad face of an allotriomorph to in- itiate the cellular reaction via the Tu Turnbull mechanism, or migrate to the allotriomorph end and isolate it a la Hillert Lagneborg, or entirely fail migration, thereby allowing operation of the Fournelle Clark mechanism, depending upon relative values of the; vector components.