Australian engineers develop floating titanium material for marine infrastructure

Engineers at RMIT University have solved a problem that has long plagued designers of lightweight metal structures: how to keep them from sinking. They've created a 3D-printed titanium lattice—a framework of hollow, interconnected struts—that floats in water and stays afloat even after cracking, puncturing, or other damage. The material could reshape how marine infrastructure is built and maintained.

The breakthrough came from a deceptively simple idea. Metallic lattices are extraordinarily light, with densities less than one-tenth that of water. But their open, interconnected geometry is also their fatal flaw: water flows through the empty spaces and fills the hollow struts, making the entire structure sink. For decades, this contradiction meant that the strongest, lightest metal structures available were unsuitable for any application that required them to stay afloat. The RMIT team, led by Dr Jordan Noronha at the Centre for Additive Manufacturing, filled those hollow titanium struts with polyurethane foam. The foam traps gas in tiny sealed cells, preventing water from flooding the metal framework even when seawater flows freely through the external openings. The result is a hybrid structure that maintains buoyancy under conditions that would destroy conventional designs.

The researchers also developed a new measurement called "skeletal density" to predict whether an open structure will float. Unlike traditional density calculations, which average the entire volume of a material, skeletal density considers only the solid parts—the metal itself—and ignores the empty space. The principle is elegant: if the skeletal density is lower than the surrounding liquid, the structure will float, regardless of how much water can flow through it. This gives engineers a simple design rule where none existed before.

Testing revealed the material's practical advantages. The titanium lattice proved 70 percent stronger than stainless steel or high-density polyethylene at the same overall density. When exposed to natural seawater from Melbourne's Port Phillip Bay for two weeks, the structure lost only 0.15 percent of its mass, and its strength declined by less than 1 percent. The team demonstrated the concept with a 3D-printed marine buoy that remained stable in a turbulent seawater tank tilted up to 45 degrees, without a sealed casing, protective coating, or any additional flotation device. Samples of the material stayed afloat in freshwater for more than two months. The hybrid lattice continued to float even after cracking, connection-point failures, and the fracture of an entire lattice layer.

The study, published in Advanced Materials, is described as the first reported demonstration of a floating metal-hybrid lattice metamaterial. RMIT conducted the research in collaboration with the Conservatoire National des Arts et Métiers in France, with support from the Australian Research Council and RMIT's School of Engineering. Distinguished Professor Ma Qian, the project leader, said the next phase involves scaling up the components and testing their long-term performance under realistic marine and deep-sea conditions. The researchers also see potential applications far beyond marine buoys. By changing the material inside the titanium framework, they could tailor similar structures for energy absorption, thermal management, vibration control, and other specialized uses. The technology opens a path toward lightweight, durable structures that can withstand both the demands of the ocean and the unexpected damage that comes with real-world use.