VHCF response of heat-treated SLM Ti6Al4V Gaussian specimens with large loaded volume

Among the materials used for the production of components through Additive Manufacturing (AM) processes, the Selective-Laser-Melting (SLM) Ti6Al4V alloy is widely employed in aerospace applications for its high specific strength and in biomedical applications for its good biocompatibility. Actual structural applications are generally limited to static loading conditions where the large defects originating during the SLM process do not play a significant role for the static failure. On the contrary, the same defects strongly affect the fatigue response of the parts since they act as crack initiation sites that rapidly lead to fatigue failure. In the literature, a lot of research has been carried out to investigate the quasi-static and the High-Cycle Fatigue properties of the SLM Ti6Al4V alloy but there are still few studies on its Very-High-Cycle Fatigue (VHCF) response. In the paper, the VHCF response of Ti6Al4V specimens, which are vertically orientated during the SLM building and then subjected to a conventional heat treatment (2 hours heating in vacuum at 850°C), is experimentally assessed. Ultrasonic VHCF tests are carried out on Gaussian specimens with a large risk-volume (2300 mm^3). Fracture surfaces are investigated for revealing the defect originating the fatigue failure. The Stress Intensity Factor Threshold associated to the experimental failures is finally estimated.