Environmental effect on the fatigue crack propagation of AM TiAl6V4 alloy specimens

Abstract

Additive manufactured (AM) parts made in TiAl6V4 alloy are increasingly used in medical devices and in the aeronautical industry, because of its high strength, low weight and excellent biocompatibility. Most of these components work under environmentally assisted cyclic loading, i.e. under corrosion-fatigue. Fatigue performance of additive manufactured alloys is significantly influenced by the porosities, residual stresses, which can be reduced by optimizing the process parameters, thermal treatments or hot isostatic pressing (HIP). Those parameters can also influence significantly to the propagation of cracks under corrosion-fatigue, but the understanding of this subject still needs significant research work. This paper presents the results of a fatigue crack propagation study in titanium TiAl6V4 specimens produced by selective laser melting (SLM), under corrosive ambient. The environment solutions studied were: artificial saliva and 3.5%wt NaCl solution. Tests were performed using standard 6 mm thick compact specimens (CT) tested at R=0.05 and with frequency 10 Hz. The main objective was to study the effect of the environment solution on da/dN-∆K curves and on the fatigue failure mechanisms. Current work shows a very important accelerating effect on the crack nucleation and fatigue crack propagation for tests under corrosion ambient, particularly for 3.5%wt NaCl solution. Fatigue path shows an irregular path. Secondary cracking was observed in air, but not detected in corrosive ambient.