A Review of the Fatigue Behaviour of Laser Powder Bed Fusion Ti6Al4V

Fatigue in metals has been recognized since the early 1800s, after several cases of fatigue failure were reported. It is described as a material's deterioration brought on by repeated loading that causes progressive, localised structural damage. Fatigue is a problem that affects engineering components that are under the action of cyclic stresses. In these components fatigue failure always occurs at significantly much lower stresses than the yield strength of material. Unlike in the early days of failure, the causes of failure in engineering structures have been studied thoroughly and are nowadays well known. The theory of fatigue allows engineers to design components with the aim of minimizing the possibility of failure. However, it is not possible to guarantee that fatigue failure will not occur, and therefore, the recourse to damage tolerance approach in design for cyclically loaded components. The last few years have seen a pickup of the various additive manufacturing (AM) technologies. This is because AM leads to shorter manufacturing times and is capable of producing parts with complicated geometries and assemblies of interconnected parts. Unlike traditional manufacturing methods, AM does not require post-machining processes thus leading to minimal wastage of material. The microstructures of additively manufactured parts are finer than those of traditional methods, and the strength is higher on the AM parts, but ductility is lower. As in traditionally manufactured metallic components, fatigue failure in parts manufactured by laser powder bed fusion (LPBF) occurs, mainly due to inherent defects such as residual stresses, internal flaws and surface roughness. An insight into the fatigue behaviour of the LPBF Ti6Al4V alloy is presented here.