RMIT Engineers 3D Print a Titanium Lattice That Floats in Seawater

Titanium is strong and corrosion resistant, but it sinks. A team at RMIT University found a way around that with a 3D printed lattice that stays buoyant even after serious damage.

The trick is simple in hindsight. Hollow titanium struts are filled with polyurethane foam. Water flows through the open lattice, but the sealed foam cells trap gas and keep the struts afloat. The result is a metal-polymer hybrid that defies the usual rule that metal lattices go under.

Samples floated in freshwater for more than two months. After two weeks in Port Phillip Bay seawater, the material lost just 0.15 percent of its mass and under one percent of its strength. A printed buoy stayed stable in tanks tilted to 45 degrees, with no casing, no coating, and no added flotation.

Jordan Noronha, the lead researcher at RMIT's Centre for Additive Manufacturing, introduced a new measurement called skeletal density. Instead of measuring total volume, skeletal density counts only the water-excluding parts: the titanium walls and the sealed foam-filled channels. If that density stays below the density of the surrounding liquid, the structure floats. Even when water flows through every opening.

At equal density, the lattice is 70 percent stronger than stainless steel or high-density polyethylene. That combination of strength and buoyancy opens possibilities in marine hardware, offshore platforms, and deep-sea equipment. Ma Qian, the distinguished professor leading the project, said changing the foam material could tailor the same structure for energy absorption, thermal management, or vibration control.

The team plans to scale up parts and test long-term marine performance. A floating titanium structure that survives damage without coatings could quietly change how engineers think about materials in saltwater environments.