Effect of the α-γ phase transition on the stability of dislocation loops in bcc iron

Body-centered-cubic iron develops an elastic instability, driven by spin fluctuations, near the alpha-gamma phase transition temperature T(c)=912 degrees C that is associated with the dramatic reduction of the shear stiffness constant c(')=(c(11)-c(12))/2 near T(c). This reduction of c(') has a profound effect on the temperature dependence of the anisotropic elastic self-energies of dislocations in iron. It also affects the relative stability of the a < 100 > and a/2 < 111 > prismatic edge dislocation loops formed during irradiation. The difference between the anisotropic elastic free energies provides the fundamental explanation for the observed dominant occurrence of the a < 100 >, as opposed to the a/2 < 111 >, Burgers vector configurations of prismatic dislocation loops in iron and iron-based alloys at high temperatures.