Intra-build stability and inter-build repeatability of porosity, tensile properties and fatigue performance in laser powder bed fusion of Ti–6Al–4V

This study investigated the intra-build stability and inter-build repeatability of porosity, tensile properties and fatigue performance in laser powder bed fusion additive manufacturing of Ti–6Al–4V. Location on the building platform and repeated builds were the studied variables on porosity and fatigue life, while the influence of 40 and 80 μm layer thickness parameter sets and specimen surface conditions were additionally evaluated for tensile properties. It was shown that variability in the properties between identically processed specimens is dominated by variability in internal defects, and that build location was the major source of this variation. Center of the building platform consistently provided the best performance. Upstream locations close to the gas flow inlet performed better than downstream locations close to the gas flow outlet. Tensile strength met the ASTM F2924-14 requirements for each specimen condition, while ductility requirements were met consistently only for machined specimens produced with 40 μm layer thickness parameters at favorable build locations. Specimens produced with identical process parameters showed high variation in fatigue lives, with logarithmic standard deviation of 1.163 for 66 specimens produced over four different builds. Within one build with build location as the only variable, logarithmic standard deviation was 0.899. On a fixed optimal location (center of the building platform) over three repeated builds the logarithmic standard deviation was 0.762, showing better inter-build repeatability than intra-build stability.