The morphology of fracture surfaces in complex metallic alloys is analysed. The simultaneous use of Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) allows the measurement of the universal roughness exponent ζ┴ = 0.78 over five decades of lengthscales (0.5 nm - 0.5 mm). Furthermore, a small lengthscales regime (lnm - 1 μm) is shown to be characterised by a roughness index ζ┴QS ≃ 0.5.
On the other hand, cracks fronts stopped during their propagation at pinning microstructural obstacles in two different metallic alloys is analysed, and their “in-plane” roughness index is determined for the first time. In the case of the 8090 Al-Li alloy, which has a very anisotropic microstructure, the roughness of the tensile crack front propagating along the grains length is equal to ζ ≃ 0.60. On the other hand, the roughness of the purely three-dimensional fatigue crack front in the Superα2 Ti3Al-based alloy is equal to ζ ≃ 0.54.