In this work we are presenting new effective manufacturing approaches towards the synthesis of ceramic and metallic objects with complex shapes, combining the potential of 3D printing with the rapid densification allowed by Spark Plasma Sintering (SPS). 

Two different approaches have been developed. The first technique is based on a material extrusion (MEX) approach. A water-based colloid with a high load of inorganic powder (over 80wt.% or 60%vol.) is used as a precursor for the 3D printing process. The colloid includes water, the powder of interest, and a small amount of an organic binder (Pluronic), with no other chemicals involved. The formulation of the colloid is controlled to produce the appropriate rheological properties, characterized by a strong non-Newtonian behavior showing shear thinning at high shear rates. The use of a syringe-to-syringe mixing procedure allows for avoiding any waste of chemicals during the preparation of the colloid and any modification of its rheological properties due to loss of the solvent or air inclusion. In addition, our custom printer allows the extrusion and combination of up to 4 different materials, some of them suitable as a support. Also, not continuous geometries are possible because a retraction system is implemented.

After desiccation the green body is densified using a FAST/SPS apparatus. In order to maintain the original shape, the sintering is performed in a pseudo-isostatic mode, using an inert coarse ceramic powder (generally alumina or silicon carbide) as a pressure transfer medium. No debinding is required before the sintering, as the small amount of organic binder (less than 3%wt.) is degraded during the sintering process.

The second approach is based on an innovative direct powder deposition. In this case, two different extruders deposit the powders of the material of interest together with the inert pressure transfer-medium one are deposited directly within the SPS graphite. The deposition of the two powders is controlled by ultrasonic dispensers. No chemicals are involved since only the powders of the two materials are handled. As a result, the process is particularly simple and environmentally friendly. At the end of the deposition process the die containing the two powders is directly transferred to a standard SPS apparatus for the densification. This combination of direct powder deposition and SPS allows great versatility, as no chemicals other than the starting powders are required. As a result, the approach can be easily adapted to a wide range of materials and composites.

With both approaches, the entire sintering process can be completed in less than an hour, allowing to drastically reduce times required for the realization of complex geometries of advanced materials.