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Microstructural features and short crack growth behavior were characterized and linked in a Ti-6Al-4V by employing X-ray micro-tomography combined with EBSD serial sectioning. Statistical analysis was used to rank the contributing features to the crack behavior. Afterwards, by creating surrogate models, the microstructural mechanism controlling the short crack behavior were revealed. Short crack preferably grows inside the predominant α phase above the average microstructural fraction. A high number of grains in contact with cracked α grains elongated in the loading direction may impose a constraint on the crack opening resulting in low crack growth rates. As the crack front becomes larger, the increase in the shear stress field away from the cracked grain leads to crack bifurcations, resulting in a decrease in crack driving forces with low crack growth rates. This leads to a preferable growth in α+β phase and along the interface above the average microstructural fractions.

Synchrotron X-ray microtomography was utilized to observe the complex 3D crack morphology and the closure behavior of a short crack in Ti-6Al-4V alloy. The aim of the study was to investigate the effect of the crack path evolution on the 3D short crack closure behavior. In situ fatigue tests at R = 0.1 were carried out using microtomography with a spatial resolution of 1 μm. The 3D crack morphology was observed in detail consisting of non-facets (zigzag), branching, and facets with deflection angles indicating the presence of mode II and mode III displacements. The crack grows with facet-like paths mainly in α grains as compared to the non-facet paths in the α+β grains. The change in the crack path from facet-like paths to non-facet-like paths in the larger crack front induces an increase in the fractional area of closed patches.