Novel microstructural features of selective laser melted lattice struts fabricated with single point exposure scanning

Abstract

Single point exposure scanning strategy is a largely unexplored selective laser melting (SLM) technique to fabricate lattice structures without an STL file. In this work, we used a series of >50 sets of processing parameters to systematically study the SLM fabrication of vertical struts made of Ti-6Al-4 V. In addition, the effects of (partial) re-melting and latent heat on hardness and developed microstructure were investigated. We demonstrate that the strut dimensions could be controlled by the processing parameters with higher energy inputs, resulting in larger strut diameters up to a saturation point (i.e. 520 μm corresponding to 0.5 J energy). The single point exposure method yielded keyhole shaped pores that were up to 4 times smaller than those observed, typically when the hatching and contour technique is used. Transmission electron microscopy (TEM) images revealed ultrafine (˜200–300 nm) and homogeneous microstructure in the double-melted specimens as compared to the classic microstructure of SLM Ti6Al4V observed in the single melted strut: hierarchical α'-laths with varying sizes (0.1–1 μm). Finally, we investigated the texture and identified the retained β phase, which enabled us to check the Burgers orientation relationship (BOR) between α' and β phases. This is the first attempt to systematically study the microstructural features resulting from the single point exposure SLM technique for lattice structures made from Ti6Al4V, and exhibits the processability window that could be used to engineer the microstructure of such structures.