Corrosion-fatigue crack growth in titanium alloys

Fatigue crack growth data in the form of a da/dN-AK-curve can be used for component design and for prediction of residual lifetime. High-strength titanium alloys have proven themselves in aerospace applications and are being seriously considered for use in automotive technology. Depending on the type of alloy (a, (a+b)- or metastable b), microstructure and/or texture development reacts differently to thermomechanical processing, which is reflected in the mechanical properties. Fatigue crack growth in titanium can be more strongly affected by changes in microstructure than in steels or aluminum alloys. This depends in part on the anisotropic nature of the hexagonal ct-phase and in part on the extreme variation in microstructural morphologies (lamellar or equiaxed) which can be present in certain high-strength titanium alloys. Such effects can be exacerbated under the influence of a corrosive environment. The influence of loading frequency must be taken into account when corrosion-fatigue crack growth is considered. While high-strength (a + )-alloys react sensitively to the effect of loading frequency, a- and metastable -alloys tend to be insensitive. This behavior can be explained with the differing consequences of an increased level of hydrogen ahead of a crack tip.