Effect of build height on structural integrity of Ti-6Al-4V fabricated via laser powder bed fusion

The additive manufacturing process involves layer-by-layer fabrication of parts, where each layer potentially experiences unique thermal histories, including cooling rates and thermal gradients. These variations can impact the microstructure and, subsequently, mechanical properties of the final product, especially as the height of the build increases. This research aims to investigate the influence of build height on the structural integrity of Ti-6Al-4V specimens fabricated via laser powder bed fusion (LPBF). The microstructural features, microhardness values, and defect characteristics, such as size, location, and distribution of defects, were analyzed along the build direction. Tensile and fatigue tests were conducted to determine the potential height-dependency of fatigue and tensile failures. The findings of this study indicated influence of build height on the structural integrity of parts subjected to cyclic loading, as the majority of the fatigue specimens failed in the upper half of the gage section (with respect to the build direction). Microstructure characterizations and microhardness testing revealed consistent grain morphology along the build direction, with uniform hardness distribution throughout the build height. However, more process-induced defects were detected within the top half of the gage section, compared to the bottom half. The results suggest that as the build height increases, there is a higher likelihood of process-induced defect formation, ultimately leading to a reduction in the structural integrity at greater build heights.