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RMIT researchers 3D print super strong titanium structure

The material’s unique lattice structure design makes it 50% stronger than the next strongest alloy of similar density used in aerospace applications

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According to RMIT University, researchers have created a new metamaterial – a term used to describe an artificial material with unique properties not observed in nature – from common titanium alloy. The material’s unique lattice structure design makes it 50% stronger than the next strongest alloy of similar density used in aerospace applications.

Lattice structures made from hollow struts were originally inspired by nature – strong hollow-stemmed plants like the Victoria water lily or the hardy organ pipe coral (Tubipora musica) showed us the way to combine lightness and strength. However, as RMIT’s Distinguished Professor Ma Qian explains, decades of trying to replicate these hollow ‘cellular structures’ in metals have been frustrated by the common issues of manufacturability and load stress concentrating on the inside areas of the hollow struts, leading to premature failures.

“Ideally, the stress in all complex cellular materials should be evenly spread,” said Qian. “However, for most topologies, it is common for less than half of the material to mainly bear the compressive load, while the larger volume of material is structurally insignificant.”

By pushing metal 3D printing design to its limits, the RMIT team optimized a new type of lattice structure to distribute the stress more evenly, enhancing its strength or structural efficiency.

RMIT researchers 3D print super strong titanium structure. The material’s lattice structure makes it 50% stronger than the next alloy.
Compression testing shows (left) stress concentrations in red and yellow on the hollow strut lattice, while (right) the double lattice structure spreads stress more evenly to avoid hot spots.

“We designed a hollow tubular lattice structure that has a thin band running inside it. These two elements together show strength and lightness never before seen together in nature,” said Qian. “By effectively merging two complementary lattice structures to evenly distribute stress, we avoid the weak points where stress normally concentrates.”

The researchers 3D printed this design at RMIT’s Advanced Manufacturing Precinct using laser powder bed fusion. Testing showed the printed design – a titanium lattice cube – was 50% stronger than cast magnesium alloy WE54, the strongest alloy of similar density used in aerospace applications. The new structure had effectively halved the amount of stress concentrated on the lattice’s infamous weak points. The double lattice design also means any cracks are deflected along the structure, further enhancing the toughness.

Study lead author and RMIT PhD candidate Jordan Noronha said they could make this structure at the scale of several millimeters or several meters in size using different types of printers. This printability, along with the strength, biocompatibility, corrosion, and heat resistance make it a promising candidate for many applications from medical devices such as bone implants to aircraft or rocket parts.

“Compared with the strongest available cast magnesium alloy currently used in commercial applications requiring high strength and lightweight, our titanium metamaterial with a comparable density was shown to be much stronger or less susceptible to permanent shape change under compressive loading, not to mention more feasible to manufacture,” said Noronha.

RMIT researchers 3D print super strong titanium structure. The material’s lattice structure makes it 50% stronger than the next alloy.
Professor Martin Leary, Professor Ma Qian, Jordan Noronha, and Professor Milan Brandt at RMIT’s Centre for Additive Manufacturing.

The team plans to further refine the material for maximum efficiency and explore applications in higher-temperature environments. While currently resistant to temperatures as high as 350°C, they believe it could be made to withstand temperatures up to 600°C using more heat-resistant titanium alloys, for applications in aerospace or firefighting drones. As the technology to make this new material is not yet widely available, its adoption by industry might take some time.

“Traditional manufacturing processes are not practical for the fabrication of these intricate metal metamaterials, and not everyone has a laser powder bed fusion machine in their warehouse,” said Noronha. “However, as the technology develops, it will become more accessible and the printing process will become much faster, enabling a larger audience to implement our high-strength multi-topology metamaterials in their components. Importantly, metal 3D printing allows easy net shape fabrication for real applications.”

Technical Director of RMIT’s Advanced Manufacturing Precinct, Distinguished Professor Milan Brandt, said the team welcomed companies wanting to collaborate on the many potential applications. “Our approach is to identify challenges and create opportunities through collaborative design, knowledge exchange, work-based learning, critical problem-solving, and translation of research,” he said.

Titanium Multi-Topology Metamaterials with Exceptional Strength’ was published in Advanced Materials.

The authors acknowledge the scientific and technical support of the RMIT Advanced Manufacturing Precinct and the RMIT Microscopy and Microanalysis Facility, especially the technical staff Simon Brudler and Paul Spithill. The project was funded by the Australian Research Council.

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