COHERENCY STRAIN-ENERGY AND THE DIRECTION OF CHEMICALLY-INDUCED GRAIN-BOUNDARY MIGRATION IN AL2O3-CR2O3 AND AL2O3-FE2O3

Using various pairs of Al2O3 crystals of known surface orientation and two solute species of Cr2O3 and Fe2O3, the direction of chemically induced grain boundary migration has been investigated on the basis of a calculation of coherency strain energy. For all the grain boundaries studied, the chemically induced migration always occurred in the direction of the grain with the surface orientation corresponding to higher coherency strain energy. The migration directions of some grain boundaries were different depending on the solute species because of different strain energy for the same orientation. The zigzag migration was also observed but only in grain boundaries between grains whose coherency strain energies were comparable to each other. These observations have confirmed the prediction of the migration initiation by the coherency strain theory.