Effects of laser power on geometry, microstructure and mechanical properties of printed Ti-6Al-4V parts

This study investigated the effect of laser power on the properties of Ti-6Al-4V alloy parts produced by additive manufacturing. The printing study was carried out using the laser beam powder bed fusion (PBF-LB) technique (Renishaw RenAM 500M). The laser power was altered in the range of 100-400 W, in order to evaluate the effects of changing the input energy received by the powder particles on the as-built parts. The impact of changing laser power was investigated based on printed part dimensions, porosity, morphology, micro/nanostructure, wear, hardness and tensile properties. It was determined that laser power has a direct influence on part dimensional accuracy, with larger dimensions compared with CAD design under the processing conditions used, obtained at higher powers i.e. 2 % at 250 W, while 4 % at 400 W. The border thickness for rounded edges was found to be similar to 0.2 +/- 0.06 mm greater than that obtained for straight edges, printed on the same quarter circle samples. A more homogeneous morphology, along with an improved surface finish, was obtained for parts printed using the higher laser powers. The microstructure of the high power alloy, was characterised by wider prior beta grains with longer and finer alpha' needles, along with superior as-built mechanical properties, when compared to parts produced using lower laser power (100 W). Additionally, shifts in the XRD peak position for parts printed at the lower and higher laser powers, indicate some reduction in the level of residual stress for parts produced at higher powers.