Assessment Of Fatigue Sensitivity To Defects Of A Tial Alloy Produced By Electron Beam Melting (Ebm)

The fatigue properties of a Ti-48Al-2Cr-2Nb alloy obtained by electron beam melting (EBM) has been examined by conducting high cycle fatigue tests performed at different R ratios both at room temperature and at high temperatures, comparable to those experienced by the components during service. Additionally, a fairly large set of specimens with artificially introduced defects, has been used to conduct fatigue tests with the objective of studying the growth behavior of small cracks. Artificial defects with different sizes have been generated in the gauge section of the specimens by EDM (Electro Discharge Machining). After EDM defects were produced, the specimens have been pre-cracked in cyclic compression, so that small cracks could be generated at the root of the EDM starter defects. Fatigue tests have been conducted by applying the staircase technique with the number of cycles of censored test (runout) fixed at 10(7) cycles. By employing the Murakami model for the calculation of the range of stress intensity factor, the threshold stress intensity factor range dependence on the loading ratio R and on the defect size has been evaluated, and a modified El-Haddad model describing the dependence of the fatigue endurance strength on the defect size has been established, highlighting the relevant parameters that govern the specific mechanisms of failure of the gamma TiAl alloy studied in the present work.