On the influence of specimen build orientation on the fatigue crack growth resistance of selective laser melted Ti-6Al-4V

Abstract

A challenge in developing an in-depth understanding of the crack growth resistance of ALM materials is the fact that mechanical properties of additive manufactured materials have been shown to be both process and part-geometry dependent. Up to now, no studies have investigated the influence of off-axis (beyond the three orthogonal build orientations) orientations on the fatigue crack growth behaviour of selective laser melted Ti-6Al-4V. Furthermore, the widespread use of compact tension specimens for investigating the material behaviour generates data more suitable for plane-strain conditions, rather than the plane-stress state which is more applicable to many lightweight aerospace structures. To address this gap in knowledge, a comprehensive study was carried out to investigate the influence of off-axis build direction in thin SLM Ti-6Al-4V plates, with a focus on the influence of microstructure anisotropy on the fatigue crack growth behaviour. It was found that although an anisotropic grain structure is visible on the specimens, it had no discernible influence on the crack growth resistance when the specimen had undergone a stress relieving heat treatment.