Effects of stress ratio on small crack growth behavior in titanium alloys with different microstructures under corrosion fatigue condition

This study systematically examines the influence of corrosion on small crack growth in TC4 ELI titanium alloys with equiaxed, bimodal, and lamellar microstructures under varying stress ratios. At low stress ratios, corrosion-induced crack tip blunting was found to retard crack propagation and extend fatigue life. Conversely, at high stress ratios, the increased crack tip opening promotes Cl⁻ ingress, accelerating crack growth and significantly reducing fatigue resistance. Elevated current densities further amplify corrosion-driven crack growth. Corrosive environments also weaken the microstructural effects on crack propagation, as evidenced by reduced crack deflection, straighter crack paths, and alterations in the dominant slip systems near the crack tip. Among the microstructures, lamellar structures exhibit more severe corrosion damage under high stress ratios than equiaxed or bimodal ones. Finally, by incorporating the total charge transfer into a modified Santus model, fatigue life predictions for all three microstructures in both air and corrosive environments show good agreement with experimental results.