Comparison of Ti-6Al-4V and 316L Stainless Steel Diamond Lattice Structures Fabricated by Additive Manufacturing

Laser Based Powder Bed Fusion (PBF-LB) is an additive manufacturing process, which can be used for the manufacture of geometrically complex metallic structures. The focus of this thesis is to evaluate the properties of PBF-LB fabricated Ti-6Al-4V and 316L stainless steel lattice structures, obtained using multiple laser scanning strategies. Amongst the investigations carried out was to determine the effect of both strut diameter and overhang angle, two key lattice design parameters, on the lattice morphology and internal porosity. Ti-6Al-4V structures were manufactured using a point-based approach, in which laser parameters were varied in order to control strut diameter, 316L stainless steel structures were manufactured with a hatch and contour approach, in which strut diameter is varied via. CAD. Evaluation of the structures showed limitations of the minimum achievable overhang angle for both structures of approximately 20°. Porosity formation within the titanium alloy structures was found to be largely associated with keyholing defects, while stainless steel porosity was attributed to lack of fusion defects, both of which were attributed to the selected laser process parameters. In-process monitoring used in the manufacture of the titanium alloy struts, demonstrated that reduced optical emission intensities were obtained from melt pools, from which higher levels of strut failures occurred. A further study evaluated the morphological and compressive mechanical properties of diamond lattice structures fabricated from the titanium and stainless steel alloys. The diamond lattice structure was selected for its noted ease of manufacture and its application within the biomedical sector. Samples fabricated in titanium alloy were found to be of higher quality, with lower amounts of external particle adhesion and more cylindrical struts in comparison to the stainless-steel samples. Both titanium and stainless steel were found to have similar relative compressive strengths, while stainless steel samples were found to have higher relative elastic modulus. Despite the same lattice structures differences in failure modes between the two alloys were obtained. Titanium samples were found to deform in a brittle manner, showing failure through sudden rupture of struts along parallel planes, while stainless steel samples underwent ductile failure where struts and nodes were found to deform consistently without rupture.