Improved green and sintered density of alumina parts fabricated by binder jetting and subsequent slurry infiltration

Abstract

Additive Manufacturing (AM) of ceramics is a constantly emerging field of interest both in research and in industry. Binder jetting-based AM of ceramics in particular offers the opportunity to produce large ceramic parts with a high wall thickness at a high throughput. One limitation is that it requires flowable powders, which are generally coarse and thus exhibit only limited sintering activity. The resulting low sintered densities impede the commercial binder jetting-based production of dense oxide ceramics. We present an approach to efficiently increase the green density of binder jetted alumina parts by optimized slurry infiltration, which also leads to a significant increase in the sintered density. In a first step, alumina parts were fabricated via binder jetting, using a 20-µm-sized alumina powder, yielding relative green densities of about 47–49%. Initial sintering studies with powder compacts showed that sintering even above 1900 °C is not sufficient to achieve acceptable densification. Therefore, green samples were infiltrated with a highly filled ceramic slurry to fill the remaining pores (about 2–5 µm in size) with smaller particles and thus increase the packing density. Particle volume content (40–50 vol%), particle size (100–180 nm) and the infiltration procedure were adapted for tests on cuboid samples to achieve a high penetration of the green bodies and a high degree of pore filling. In this way, the relative green density could be increased starting from about 47% after binder jetting, to 73.4% after infiltration and drying. After sintering at 1675 °C densities above 90% could be achieved, yielding three-point bending strengths up to 145 MPa. As a conclusion, this approach can be regarded as a promising route for overcoming the drawbacks of the binder jetting process on the way to denser, mechanically more stable sintered alumina parts.

A review on the ceramic additive manufacturing technologies and availability of equipment and materials

“…On the other hand, infiltration has been used to improve sintered parts properties. For example, Vogt et al [49] reached alumina samples with densities above 90% and improved bending strength from 60 to 145 MPa with infiltration of nanometric alumina powder. Also, Maleksaeedi et al [50] showed that infiltration can also improve surface quality, reducing surface roughness (Ra) from 13.2 to 0.9 μm.…”

“…It is usually water-based with some additives for surface tension and viscosity adjustment [41] as isopropyl alcohol [41,45,48], diethyleneglycol [48], polyvinyl alcohol [56], and glycerol [45]. Also, some related works [38,44,49,51] used a commercial aqueous binder (BA005, ExOne). Table II shows the additive manufacturing systems available for binder jetting of ceramics.…”

“…Moreover, ExOne company has been working on the development of ceramic feedstock for binder jetting presenting advanced ceramics aluminum oxide, zirconium oxide, silicon carbide, and boron nitride under development [61]. Also, some researchers have used non-dedicated ExOne 3D printers to process ceramics [38,44,49].…”

Tailoring α-alumina powder morphology through spray drying for cold consolidation by binder jetting

“…Spray-drying granulation was successful in producing a feedstock that could be easily deposited during printing starting from ultrafine feedstocks with limited flowability. Further densification by thermal treatment alone proved to be challenging, however density can be increased by slurry infiltration as observed in literature [22,43]. In this perspective, the preparation of a stable suspension with an optimal rheology is a dual advantage: can be employed for granulation and, on the other hand, for post-processing after sintering.…”