Pressure-less spark plasma sintering of 3D-plotted titanium porous structures

Additive manufacturing of titanium porous structures by direct ink writing involves the removal of the binder needed for powder extrusion and subsequent sintering to consolidate the 3D-plotted body. In this work, pressure-less spark plasma sintering (PL-SPS) was systematically studied for fast consolidation of titanium porous structures. Furthermore, poloxamer 407 was used as the binder and the lowest temperature possible was identified for its thermal elimination. The results show for the first time that PL-SPS generated sintering conditions similar to those generated by conventional pressure-less sintering, producing hierarchical titanium porous structures with equivalent densification, shrinkage, and surface roughness, but with minimal grain growth. The thermal responses of the die and material showed efficient radiation heat transfer, allowing fast heating (100 °C/min) of one sample per run, promoting the formation of sintering necks and powder densification in 10 min, which is much faster than conventional sintering that requires at least 2 h of dwell time. However, the process operates at a sintering temperature 200–300 °C above the conventional sintering temperature, and at the expense of high consumption of electrical energy to achieve such a high heating rate. The mechanical strength of the resulting titanium structures increases with increasing strand densification at nearly constant strand separation, resulting in strong and plastic porous structures.