Effects Of The Surface Roughness And The Porosity On The High Cycle Fatigue Behaviour Of Ti-6al-4v Alloy Obtained By Additive Manufacturing Process

Abstract

This work focuses on the influence of defects, including porosity and surface roughness, on the high cycle fatigue behaviour of the Ti-6Al-4V titanium alloy fabricated by the Laser Power Bed Fusion (LPBF) Additive Manufacturing (AM) process. In particular, the scatter and the statistical size effect are investigated. vast fatigue test campaign has been undertaken, including two surface conditions (as-built and machined surfaces), and two specimen geometries. It was shown that a variety of crack initiation mechanisms, related to not only the pore type (gas and LoF pore) but also to the defect spatial position (surface or in-bulk) is the principal origin of the fatigue scatter for machined specimens. For the statistical scale or size effect, i.e., the change in the fatigue strength as a function of the loaded volume, it was shown that the changes in damage mechanisms are the first-order factor that governs the size effect observed for the machined specimens. For the as-built specimens, these effects are less significant. In the last section, two fatigue strength modelling approaches that take into account both defect types are proposed.