In this work, the fatigue behaviour of Ti6Al4V manufactured using electron beam melting, its dependency on porosity, distance from the base plate and build layer height were investigated. XCT scans of the fatigue sample gauge lengths were correlated to SEM investigations of the fracture surfaces. A comparison between the top and bottom halves of the builds in terms of defect population and fatigue behaviour was also made. Larger pores were detected in samples with a larger build layer height and lower position in the build chamber. Results also indicate that part geometry and pore location, specifically closeness to the surface, are important factors regarding the initiation location of fatigue fractures at 1 % strain. Furthermore, a fatigue critical lack of fusion defect was undetectable in the XCT scan.

Surfaces after chemical post-processing treatments of electron beam melting (EBM) produced Ti-6Al-4V have been studied. Targeted chemical treatment allowed the study of variation in surface quality with material removal depth. Characterization of surface and defect morphologies were made, comparing two chemical post-processing methods, Hirtisation® and chemical milling with different milling depths. Surface topography was characterized using white light interferometry and subsurface defect distribution was studied using X-ray computed tomography (XCT). The morphology of the surface at different milling depths was compared to the sub-surface information from XCT scans of the as-built material. Furthermore, Hot Isostatic Pressing (HIP) treated material was documented for comparison. Results show that post-processed surfaces contain a number of different defects of mixed morphology, position and origin. Post-processing deteriorates the surface quality with increased removal depth due to the presence of sub-surface defects. The position of sub-surface defects in relation to the material surface coincides with the depth at which contour-hatch interactions are likely to have occurred during the EBM building process. The distribution of this sub-surface defect population is anisotropic in the building (horizontal) plane and reasons for this are explored. Hirtisation® produces surfaces morphologically different from chemically milled surfaces. This difference was found to contribute to Hirtisation® producing surfaces with higher roughness (Sa) than chemically milled surfaces at comparable removal depth. HIP did remove all detectable sub-surface defects but microstructural artefacts indicating healed porosity were found.

Electron beam melting is a powder bed fusion (PBF) additive manufacturing (AM) method for metals offering opportunities for the reduction of material waste and freedom of design, but unfortunately also suffering from material defects from production. The stochastic nature of defect formation leads to a scatter in the fatigue performance of the material, preventing wider use of this production method for fatigue critical components. In this work, fatigue test data from electron beam melted Ti-6Al-4V specimens machined from as-built material are compared to deterministic fatigue crack growth calculations and probabilistically modeled fatigue life. X-ray computed tomography (XCT) data evaluated using extreme value statistics are used as the model input. Results show that the probabilistic model is able to provide a good conservative life estimate, as well as accurate predictive scatter bands. It is also shown that the use of XCT-data as the model input is feasible, requiring little investigated material volume for model calibration.