Alumina powder breakthrough in 3D printing materials
Walking into the laboratory of Northwestern Polytechnical University, a light-curing 3D printer is humming slightly, and the laser beam is moving precisely in the ceramic slurry. Just a few hours later, a ceramic core with a complex structure like a maze is fully presented – it will be used to cast the turbine blades of aircraft engines. Professor Su Haijun, who is in charge of the project, pointed to the delicate component and said: “Three years ago, we dared not even think about such precision. The key breakthrough is hidden in this inconspicuous alumina powder.”
Once upon a time, alumina ceramics were like a “problem student” in the field of 3D printing – high strength, high temperature resistance, good insulation, but once it was printed, it had a lot of problems. Under traditional processes, alumina powder has poor fluidity and often blocks the print head; the shrinkage rate during sintering can be as high as 15%-20%, and the parts that were printed with great effort will deform and crack as soon as they are burned; complex structures? It’s even more of a luxury. Engineers are troubled: “This thing is like a stubborn artist, with wild ideas but not enough hands.”
1. Russian formula: Putting “ceramic armor” on the aluminum matrix
The turning point first came from the revolution in material design. In 2020, material scientists from the National University of Science and Technology (NUST MISIS) of Russia announced a disruptive technology. Instead of simply mixing aluminum oxide powder, they put high-purity aluminum powder into an autoclave and used hydrothermal oxidation to “grow” a layer of aluminum oxide film with a precisely controllable thickness on the surface of each aluminum particle, just like putting a layer of nano-level armor on the aluminum ball. This “core-shell structure” powder shows amazing performance during laser 3D printing (SLM technology): the hardness is 40% higher than that of pure aluminum materials, and the high-temperature stability is greatly improved, directly meeting aviation-grade requirements.
Professor Alexander Gromov, the project leader, made a vivid analogy: “In the past, composite materials were like salads – each one was in charge of its own business; our powders are like sandwiches – aluminum and alumina bite each other layer by layer, and neither can do without the other.” This strong coupling allows the material to show its prowess in aircraft engine parts and ultra-light body frames, and even begins to challenge the territory of titanium alloys.
2. Chinese wisdom: the magic of “setting” ceramics
The biggest pain point of alumina ceramic printing is sintering shrinkage – imagine that you carefully kneaded a clay figure, and it shrank to the size of a potato as soon as it entered the oven. How much would it collapse? In early 2024, the results published by Professor Su Haijun’s team at Northwestern Polytechnical University in the Journal of Materials Science & Technology set off the industry: they got a nearly zero-shrinkage alumina ceramic core with a shrinkage rate of only 0.3%.
The secret is to add aluminum powder to alumina and then play a precise “atmosphere magic”.
Add aluminum powder: Mix 15% of fine aluminum powder into the ceramic slurry
Control the atmosphere: Use argon gas protection at the beginning of sintering to prevent aluminum powder from oxidizing
Smart switching: When the temperature rises to 1400°C, suddenly switch the atmosphere to air
In-situ oxidation: Aluminum powder instantly melts into droplets and oxidizes to aluminum oxide, and volume expansion offsets contraction
3. Binder revolution: aluminum powder turns into “invisible glue”
While the Russian and Chinese teams are working hard on powder modification, another technical route has quietly matured – using aluminum powder as a binder. Traditional ceramic 3D printing binders are mostly organic resins, which will leave cavities when burned during degreasing. A domestic team’s 2023 patent takes a different approach: making aluminum powder into a water-based binder47.
During printing, the nozzle accurately sprays “glue” containing 50-70% aluminum powder on the aluminum oxide powder layer. When it comes to the degreasing stage, vacuum is drawn and oxygen is passed through, and the aluminum powder is oxidized to aluminum oxide at 200-800°C. The characteristic of volume expansion of more than 20% allows it to actively fill the pores and reduce the shrinkage rate to less than 5%. “It is equivalent to dismantling the scaffolding and building a new wall at the same time, filling your own holes!” an engineer described it this way.
4. The art of particles: the victory of spherical powder
The “appearance” of alumina powder has unexpectedly become the key to breakthroughs – this appearance refers to the particle shape. A study in the journal “Open Ceramics” in 2024 compared the performance of spherical and irregular alumina powders in fused deposition (CF³) printing5:
Spherical powder: flows like fine sand, the filling rate exceeds 60%, and the printing is smooth and silky
Irregular powder: stuck like coarse sugar, the viscosity is 40 times higher, and the nozzle is blocked to doubt life
Even better, the density of the parts printed by spherical powder easily exceeds 89% after sintering, and the surface finish directly meets the standard. “Who still uses “ugly” powder now? Fluidity is combat effectiveness!” A technician smiled and concluded5.
Future: Stars and seas coexist with small and beautiful
The 3D printing revolution of alumina powder is far from over. The military industry has taken the lead in applying near-zero shrinkage cores to manufacture turbofan blades; the biomedical field has taken a fancy to its biocompatibility and started printing customized bone implants; the electronics industry has targeted heat dissipation substrates – after all, the thermal conductivity and non-electrical conductivity of alumina are irreplaceable.
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