Notch effect and fatigue performance of Ti-6Al-4V sheets in saline environment

Ti-6Al-4 V grade is a well-known and largely employed alloy for many critical applications, especially when high mechanical and corrosion properties are needed. In the technical literature one of its negative aspects, i.e., its notch sensitivity in case of fatigue loading, especially in aggressive environments, is well described. The present experimental work is, hence, aimed at studying the fatigue behavior of notched Ti-6Al-4 V alloy samples (machined from a 5-mmthick sheet) in standard laboratory conditions and in a saline solution with 3.5 wt. % NaCl. Axial fatigue (R¼0.1) loading was chosen and different notches were machined to obtain Kt values ranging from 2.55 to 13.34 [calculated by finite element method (FEM)]. By the step-loading technique, the fatigue limits for a constant life of 2x105 cycles varying the Kt factor and the test environment were determined. Finally, by replicas, the fatigue-crack lengths were measured and, by scanning electron microscopy (SEM), the fracture surfaces were observed and related with the fatigue-crack propagation rates.