Diffusive healing of internal fatigue micro-cracks in pure titanium

The internal micro-cracks with the critical length about 30 μm and thickness less than 1μm were introduced into the pure titanium samples by uniaxial tension-compression low cycle fatigue method. The experimental results indicate that the internal fatigue micro-crack clearly evolves from the original penny-shaped crack into a string of spherical voids in the longitudinal section plane of the fatigue sample after the vacuum diffusive healing at the high temperature. The quantitative relationship between the radius and the spacing of spherical voids depends on the crack position (with grains, on grain boundaries or transgranular sites) and its orientations within the grain. The diffusive healing, the related thermodynamics and mechanism, and the effect of the surface tension anisotropy on the relationship between void diameter and void spacing are also discussed.