Interrelationship of Manufacturing, Surface Morphology, and Properties of Titanium

Manufacturing of titanium parts modifies the surface morphology mostly with the goal of a functionalization like grooves to change the wettability or to act as reservoirs for lubricants, for instance. While the function of the surface is adapted to special efforts, it must be considered how the new surface morphology acts on mechanical properties like the fatigue limit. Therefore, it is necessary to know which hardening mechanisms are activated during the change of the morphology. To do so, we analyzed the processes during manufacturing and measured the modified morphology of the surface with classical and new methods. The main influence on the fatigue limit is given by the changed roughness or newly introduced notches at the surface. These imperfections must be taken into account when calculating the consequences on the fatigue limit. Thereby, it is of high relevance to be aware of the interaction between the size of the imperfection and the governing microstructural dimensions, i.e., the grain size in titanium because the same imperfection can reduce the fatigue limit in a fine-grained metal while it has no influence on the fatigue limit in a coarse-grained metal.