Australian engineers at RMIT University have developed a lightweight titanium material that floats in water even after suffering severe structural damage.
The research, led by Dr Jordan Noronha at RMIT’s Centre for Additive Manufacturing, was published this week in the journal Advanced Materials.
The 3D-printed titanium lattice was created and tested in Melbourne in collaboration with the Conservatoire National des Arts et Métiers in France.
The team designed the material to solve a longstanding problem in marine engineering: how to make ultra-light metal structures that do not sink once water penetrates their internal spaces.
The lattice is built from hollow, interconnected titanium struts filled with polyurethane foam.
Testing found the resulting structure not only floats but is also stronger than the stainless steel and high-density plastic currently used in jetties, buoys and floating sensors.
According to the researchers, this marks the first reported demonstration of a floating metal-hybrid lattice metamaterial, with buoyancy confirmed by samples that stayed afloat in freshwater for more than two months.
Metallic lattices have long been prized for their strength-to-weight ratio, but their open, porous structure has historically worked against them in marine settings.
Noronha said the interconnected spaces that make these lattices so light are also what allows them to fill with water and sink, which had ruled them out for use in ocean infrastructure until now.
To get around this, the researchers introduced a new engineering concept called skeletal density, which calculates buoyancy based only on the solid titanium walls and sealed, foam-filled channels rather than the full open volume of the lattice.
This offers a straightforward design principle for engineers going forward: as long as the skeletal density of a structure is lower than that of the surrounding liquid, it will stay afloat even when water moves freely through its outer openings.
The foam filling proved central to the material’s resilience.
“By filling only the hollow titanium struts with polyurethane foam, we created a structure that allows water to flow through it while remaining buoyant even after significant cracking and damage,” said Noranha.
In lab testing, the lattice withstood cracking, the failure of key connection points and even the fracture of an entire structural layer while still remaining buoyant.
It only sank once it was severely crushed and compacted, a result the researchers say demonstrates its potential to retain flotation despite major structural damage in real-world conditions.
Short-term corrosion trials using seawater from Melbourne’s Port Phillip Bay also showed strong durability, with the lattice losing just 0.15 per cent of its mass and less than 1 per cent of its strength after two weeks of immersion.
Noronha explained that tiny sealed cells within the foam trap gas and stop water from flooding the hollow struts, unlike conventional hollow marine structures that can rapidly fill with water once cracked.
“Tiny, sealed cells in the foam trap gas and prevent water from flooding the hollow struts,” said Noronha.
The team also built a working prototype, a 3D printed marine buoy that stayed stable in a turbulent seawater tank tilted up to 45 degrees, without requiring a sealed casing, protective coating or additional flotation aids.
Project leader Distinguished Professor Ma Qian said the next phase of research will involve scaling up the technology and testing its long-term performance in realistic marine and deep-sea environments.
He added that the material’s design is highly adaptable beyond marine use.
“By changing the material inside the titanium framework, we could tailor a similar structure for energy absorption, thermal management, vibration control and other applications,” said Ma Qian.
The project was supported by the Australian Research Council and RMIT’s School of Engineering.
