The early growth process of helium blistering in tungsten and molybdenum: First-principles and statistical model calculations

Abstract

Based on first-principles simulations combined with statistical physical model, we have performed systematically the investigations on the nucleation and the early growth process of helium (He) blistering in W and Mo. The thermodynamics and structural stability of He-vacancy complexes (HenVm) have been explored in detail. The energy-demand has been determined for He blistering nucleation, indicating that one mono-vacancy can capture up to eight He atoms. To trap more He atoms, the mono-vacancy must emit a Frenkel-pair to release the extensive stress in the vicinity of W/Mo lattice. In comparison with the HenV complex, the HenVm (e.g. HenV9) complex exhibits a relatively lower energy-demand for the nucleation and growth of He blistering. Based on statistical physical analysis, the chemical potential of He can significantly affect He blistering nucleation and growth. Two critical chemical potentials of He are found to be especially important. One indicates the transformation from a He atom to multiple He atoms trapped by one mono-vacancy, while the other illuminates He-caused superabundant vacancy formation which in turn attracts more He atoms to make the blistering grow even bigger, resulting into a cascading effect in both W and Mo.