Dislocation loop punching in bubble arrays

Abstract

High densities of inert gas bubbles can be produced in metals by ion implantation or nuclear transmutations. At low temperatures, these bubbles grow by repeated emission of prismatic dislocation loops. An analysis is presented for loop punching considering the effects of the stress fields between bubbles and the presence of retained loops. It is shown that the retained loops increase the pressure required for further loop growth dramatically as the interbubble spacing decreases. At a critical helium content, further bubble growth ceases by one of two mechanisms: equilibration of the chemical potentials for gas atoms in the bubble and in interstitial solution, or interbubble fracture when the average ligament stress exceeds the theoretical tensile strength of the material. The critical concentrations predicted for gas release or blistering are shown to agree with experimental findings. Furthermore, the influence of retained loops on bubble growth also leads to a natural explanation for bubble superlattice formation. The prediction of bubble swelling and lattice parameter changes with helium content is shown to be in excellent agreement with experimental data.