Scientists create world's first floating titanium
By
Etiido UkoSeptember 20, 2026
Scientists create world's first floating titanium
Dr. Jordan Noronha holding a sample of the floating titanium
Sara Tan, RMIT
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The scientists created simple cubic lattices from Ti-6Al-4V, consisting of 4 x 4 x 4 arrays of 10-mm cells
Sara Tan, RMIT
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The 3D-printed buoy used in testing
Sara Tan, RMIT
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Cross sections of the titanium lattice cube showing before and after being filled with polyurethane foam for buoyancy
Sara Tan, RMIT
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The project team: Professor Andrey Molotnikov, Distinguished Professor Ma Qian, Distinguished Professor Milan Brandt, Dr. Jordan Noronha and Professor Martin Leary at RMIT's Centre for Additive Manufacturing
Sara Tan, RMIT
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Dr. Jordan Noronha holding a sample of the floating titanium
Sara Tan, RMIT
View gallery - 5 imagesThey say a drowning man is willing to grasp onto just about anything to stay afloat, but he would most likely think twice if you offered a titanium buoy. Yet, scientists have created a titanium structure that floats without compromising the metal’s strength.
A team of researchers at Australia's RMIT University has created what they call a “buoyant metal–polymer open-cell lattice metamaterial,” a 3D-printed titanium structure that can float despite titanium itself being more than four times denser than water. To achieve this, they 3D-printed a titanium alloy skeleton and left the individual beams hollow. They then filled the hollow beams with lightweight polyurethane foam. During testing, the structure remained buoyant even after cracks developed, connection points fractured, and an entire lattice layer broke apart.
There are plenty of reasons to want something both extremely strong and buoyant.
Buoys, floating sensors, offshore platforms, and other marine infrastructure must survive repeated wave impacts and corrosive seawater without disappearing beneath the surface when damage occurs. Metals such as stainless steel and titanium provide the strength and fatigue resistance these jobs require. Ti-6Al-4V, the titanium alloy used here, also offers particularly good resistance to seawater corrosion. However, the obviousleak in the boatis its density. Ti-6Al-4V has a density of around 4.43 g/cm³, compared with about 1 g/cm³ for freshwater, meaning it typically sinks to the bottom.
But humans, being the crafty species that we are, devised a couple of solutions ages ago, when we first became seafarers. UnderArchimedes’ principle, an object floats when the weight of the water it displaces can support its own weight. A ship may therefore be made from dense steel but still float because its hollow hull encloses an enormous volume of air. Alternatively, engineers can add low-density materials such as foam to provide flotation.
Metal lattices may offer another route. 3D printing can turn a relatively small amount of metal into a large, lightweight network of beams, producing structures with impressive strength-to-weight ratios. Some metallic lattices even have an apparent bulk density less than one-tenth that of water. Unfortunately, their open architecture works against them in the water.
“Their open, interconnected spaces allow water to enter, causing them to sink,” explains lead researcher Dr. Jordan Noronha.
This explanation highlights a slightly deceptive aspect of density. Calculating the mass of a lattice against its entire outside volume counts all those large empty gaps as part of its volume. Once submerged, however, water simply flows into them. They no longer contribute useful displacement, and the structure sinks.
The RMIT researchers therefore developed another measure called “skeletal density,” which ignores the externally accessible space and counts only the parts of the structure that actually exclude water. If that skeletal density is lower than the density of the surrounding liquid, the structure should float.
The researchers designed simple cubic lattices from Ti-6Al-4V, consisting of 4 x 4 x 4 arrays of 10-mm cells. Instead of printing conventional solid beams, they printed hollow struts with walls only 0.2 mm (0.39 inches) thick and internal channels ranging from 2.5 to 4 mm (0.1 to 0.16 inches) in diameter. The structures were manufactured using laser-based powder bed fusion, in which a laser selectively melts successive layers of titanium powder to gradually build the complex geometry.
They then injected expandable polyurethane foam through the interconnected channels running inside the titanium struts. As it expanded, the foam filled the beam interiors while leaving the large spaces between them completely open.
Under a microscope, the foam formed a tightly integrated interface with the rough inner titanium walls, and contained mostly closed cells around 10 to 200 micrometers across. Those sealed microscopic bubbles trap gas and keep water out. The result is effectively a skeleton made of tiny, foam-filled titanium pipes. The titanium carries the load and provides strength, while the foam provides buoyancy.
Now, previous metal-polymer lattices generally fill the spaces between the beams with polymers such as epoxy, PEEK, or silicone. The resulting structures can gain useful properties including vibration damping or thermal regulation, but filling the external cells removes the very openness that made the lattice interesting in the first place. Here, water can still flow freely through the structure, leaving its permeability and large exposed surface area intact.
The foam also barely affected the titanium’s mechanical performance. Compared with equivalent empty hollow-strut lattices, adding polyurethane increased bulk density by only about 5.9% to 7.3%, while producing similarly small changes in yield strength, ultimate compressive strength, and stiffness. The hybrid also achieved a higher specific strength than two conventional marine materials used for comparison, HDPE plastic and 316L stainless steel.
For the first buoyancy tests, the researchers submerged several designs in freshwater for more than two months. Every unfilled titanium lattice sank as water flooded its hollow channels. The foam-filled versions behaved exactly as the skeletal-density model predicted: samples with skeletal densities above the 0.997-g/cm³ density of the test water sank, while those below it floated.
Then the researchers started breaking them. After all, it’s not enough for the structure to sit pretty in calm water; In practice, it still has to continue functioning as intended after taking multiple beatings from the sea.
They placed floating samples under compression, and periodically returned to the water as the damage progressively worsened. They still floated after exceeding their ultimate compressive strength, after individual nodes fractured, and even after cracks propagated far enough to fracture an entire layer of the lattice. Only once the structures were severely crushed and entered the densification stage did they finally sink. By then, compression had reduced their volume enough to push their skeletal density above that of water.
The closed-cell foam proved particularly valuable here. A completely hollow titanium structure could also be made buoyant by sealing air inside its struts, but a single serious crack could let water flood through the connected channels. The foam instead acts as a “distributed barrier.” It prevents damage in one location from giving water an open highway through the whole structure.
The team also immersed the material in natural seawater from Melbourne’s Port Phillip Bay for two weeks. It remained buoyant, lost just 0.15% of its mass and suffered less than a 1% reduction in strength.
Finally, they turned the material into something recognizably useful, a 100-mm-high, 85-mm-wide prototype marine buoy. The 3D-printed buoy floated in natural seawater while turbulent flow repeatedly rotated it by up to 45 degrees, all without a sealed outer casing, protective coating, or separate flotation material, proving the structure’s viability in real-life conditions.
For next steps, the researchers plan to scale the technology into larger structures and prove its long-term durability in real marine and deep-sea conditions. They also see the hollow titanium framework as a much broader materials platform. Swapping the polyurethane for another filler would tailor the same basic architecture for energy absorption, vibration damping, thermal management, or other applications. In other words, engineers create objects with a mix-and-match of unconventional properties by combining the 3D-printed hollow structure with different filler materials.
A paper on the study was recently published in the journalAdvanced Materials.
Source:RMIT
