The theory of void nucleation in metals

Abstract

A general theory of void nucleation in irradiated metals is developed via the nodal line/critical point formalism of Poincaré. The theory reduces to several simple subcases, depending on the experimental conditions, in particular the damage rate, temperature, and gaseous and non-gaseous impurity concentrations. The most important of these subcases are: 1. (1) Spontaneous (i.e. no activation barrier) void nucleation driven by inert gas. 2. (2) Heterogeneous nucleation on metastable gas:vacancy clusters. 3. (3) Heterogeneous nucleation on clusters of non-gaseous impurities. 4. (4) Homogeneous nucleation with or without the assistance of mobile, surface active impurities. Simple nucleation rate equations are presented for each of these cases. Equations for void number density are derived for the various steady state nucleation cases on the basis of a simple void growth equation. The predictions of void number densities are found in reasonable agreement with measurements on pure Ni, type 316 stainless steel, and on the Nimonic alloy, PE-16. The theory also reproduces the shape of the void number density vs 1 T curves—including the activation energies.