Assessment of the fatigue performance of heat-treated addictive manufactured TiAl6V4 specimens

Abstract

Titanium Ti6Al4V alloy has excellent mechanical properties and corrosion resistance combined with low specific weight, and is commonly used in biomedical applications, automotive and aerospace components, involving fatigue loadings. Current work studies the fatigue behavior under strain amplitude control of titanium TiAl6V4 specimens, intending to characterize fatigue strength from low to high life range after different heat treatments. Fatigue tests were carried out at room temperature, using round dog bone specimens produced by selective laser melting (SLM), where laser powder deposition occurred in layers perpendicular to the loading direction. Two batches of specimens were tested: one subjected to a stress relieve treatment and a second one treated by the hot isostatic pressing process (HIP). The material was characterized in terms of the tensile mechanical properties, cycle curve, Basquin and Coffin equations. Additional analysis of the hardness and scanning electron microscopy was carried out to complement the discussion of the results. The obtained dada showed that the stress relieved specimens exhibits significantly cyclic softening, increasing with applied strain, while HIP specimens show a practically stable cyclic behavior in relation to the monotonic curve. Material response for both treatments is well fitted by Basquin and Coffin-Manson formulations. The transition life was 187 reversals and 326 reversals, for stress relieved and HIP specimens, respectively. Fatigue life for a given strain is governed by the strain value, independently of the post manufacturing heat treatment.