Morphological healing evolution of penny-shaped fatigue microcracks in pure iron at elevated temperatures

This letter reports a joint experimental and numerical investigation of high temperature morphological healing of micron-sized intragranular microcracks in pure iron. Irregular penny-shaped microcracks were first created by low-cycle fatigue and then subjected to annealing in vaccum at $1173\mathrm{K}$ . It is shown theoretically that, depending on its initial aspect ratio, a penny-shaped microcrack may evolve via surface diffusion into an isolated spherical void, or a doughnut-shaped channel pore with or without a central spherical void. Subsequent evolution causes the doughnut-shaped channel pore to break up into a ring of spherical voids via Rayleigh’s instabilities. These results were confirmed with experimental observations of typical configurations of voids that result from the crack healing process. The experimentally observed evolution time is also in good agreement with the predictions of finite element simulations of the evolution process.