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Imagine printing a ceramic part in seconds and then sintering it to full density in minutes instead of days. That is the challenge at the heart of my PhD research on robocasting, a 3D printing technique that extrudes ceramic paste layer by layer to build complex geometries and conducted under the supervision of Charles Manière and Sylvain Marinel.

Technical ceramics (alumina, silicon nitride, boron carbide …) are prized for their excellent properties, but they are difficult to shape into intricate geometries using conventional processes. Additive manufacturing offers a way around these constraints, provided the ceramic "ink" shows shear-thinning behavior with a sufficiently high yield stress: fluid enough to flow through a nozzle, yet stiff enough to hold its shape once deposited.

I started by developing water-based alumina suspensions using a single, simple binder (carboxymethylcellulose - CMC) instead of the complex multi-additive formulations often used in the field. This stripped-down recipe produced stable, printable pastes compatible with fast printing speeds of up to 100 mm/s, without sacrificing print quality.

Printing fast is only half the story: densifying the printed parts is traditionally the slowest step, often taking many hours in a furnace. To address this, I turned to UHS-SPS (Ultrafast High Temperature Sintering - Spark Plasma Sintering), a technique that dramatically compresses sintering times.

Finally, I pushed the method beyond alumina to two much more refractory, non-oxide ceramics: silicon nitride and boron carbide. Boron carbide, in particular, required reconfiguring the sintering process into an Ultra High Temperature Pressureless SPS (UHTP-SPS) to reach the 2350°C needed for densification, one of the highest sintering temperatures reported for this route.

The result is a robust, transferable formulation-to-sintering strategy. It works across very different ceramic chemistries, from oxide to non-oxide. This opens new possibilities for rapidly manufacturing complex ceramic components for different applications, without the usual trade-off between shape complexity and processing time. There is still plenty to explore, scaling up part size, refining microstructural control, testing new ceramic systems. But this work shows that speed and precision do not have to be at odds, even for some of the toughest materials we know how to shape.

Flavie Lebas

CRISMAT Laboratory (Caen, France)

lebas.flav@orange.fr

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