Kinetics of void-lattice formation in metals

Abstract

Since the discovery¹ that voids form in neutron-irradiated stainless steel and that these could form into a three-dimensional lattice², void-lattices have been observed in some b.c.c. metals^2,3 such as Mo, W, Nb, and Ta, and in f.c.c. metals^4,5 such as Al and Ni. The irradiation conditions in which a void-lattice is formed are not understood⁶, but several explanations^7–11 of the stability of the void-lattice have been given on the basis of void–void elastic interaction^9–11. Our present approach regards the void-lattice formation as a phase transition associated with the bifurcation of the homogeneous steady state in the mean field theory^12,13. The void-lattice is an interesting example of a class of phase transitions manifested by open, nonequilibrium, dis-sipative structures and have an inherent capability of self-organization. Although void-lattice formation has already been examined on this basis^14,15, we show here that the transition is induced in certain microstructural conditions where vacancy loop dynamics has an important role. The theory generally agrees with experimental features and predicts that another spatially dependent state exists which can influence irradiation-induced phenomena that have important technological implications for the development of fast reactor materials.