Nucleation of a second solid phase along dislocations

Abstract

A model for the nucleation of a second solid phase along dislocations is proposed and analyzed. The elastic distortions caused by the difference in the specific volume of the two phases in the elastic field of a dislocation are calculated following Eshelby’s transformation problem and assuming that both phases have the same moduli, but some modifications are introduced to account for the presence of the dislocation. The nucleation rateJ is expressed in terms of the dislocation density π, the free energy of formation of the critical embryo δG ^*_d and other quantities. It is found that the nucleation barrier δG ^*_d is only slightly shape dependent and therefore the critical shape can be approximated by that of the family with the lowest nucleation barrier. Then δG ^*_d andJ are calculated numerically for incoherent nucleation along edge and screw dislocations. It is found that: i) the nucleation barrier is smaller for edge than for screw dislocations, ii) the higher the shear modulus, the stronger the catalytic effect of dislocations, iii) metastable embryos may exist in undersaturated systems.