SHAPE OF GRAIN-BOUNDARIES DURING PHASE-TRANSFORMATIONS

A simple and general formalism for the analysis of the grain boundarie s in specimens solidified under local conditions of uniform temperatur e is presented. It is applied to two specific cases: the solidificatio n of regular eutectics for which the growth rate is the same for all t he grains and the solidification of nodular cast iron where the growth kinetics is inversely proportional to the radius of the grain. In the first situation, hyperbolic grain boundaries typical of different nuc leation times are obtained. For the second case, it is shown that the specific growth kinetics leads to planar grain boundaries regardless o f the nucleation times and cooling conditions. Quenched and fully soli dified grain structures observed in a lead-tin alloy and in nodular ca st iron are compared with the predictions of a stochastic solidificati on model. Copyright (C) 1996 Acta Metallurgica Inc.