From AdvancedScienceNews
Recently, the 3D printing technology reference noted that the team of Professor Ma Qian of the Melbourne University of Technology used 3D printing technology to develop titanium alloy lattice topological metamaterialsThe resulting structure has the same density as a magnesium alloy (185g cm), but the yield strength is greatly improved。On December 31, 2023, the researchers published an article titled "Titanium multi-topology metamaterials with exceptional strength" in Advanced Materials**. It should be noted thatThe team led by Professor Ma Qian also published a blockbuster study of Nature in 2023(Click).
doi:10.1002/adma.202308715
Mechanical metal metamaterials consist of interconnected pillars, plates, sheets, or shells with cavities or pore sizes ranging from sub-millimeters to millimeters, typically arranged in repeating units. They are an emerging class of multifunctional materials with versatility that cannot be achieved with solid materials or traditional porous materials. However, few metallic lattice metamaterials are able to achieve significantly better mechanical properties than magnesium, such as similar densities (18g cm), but the yield strength can exceed 200mpa. This makes it impossible for these new lightweight materials to be used in a wider range of applications, such as those that require significant load-bearing and heat- or corrosion-resistant properties.
with sub-millimeter to millimeter channel diametersHollow pillar lattice (HSL) metal metamaterialIt is a new research direction of the mechanical metamaterial family. Manufacturing challenges have been eliminated with the advent of powder bed fusion (PBF) additive manufacturing technology, which can greatly simplify and manufacture more complex topologies. One example of this is throughLPBF technology 3D printing Ti6Al4V metamaterial with complex hollow pillar lattice。This type of structure exhibits excellent structural efficiency, and its mechanical properties exceed those of solid strut lattice (SSL) materials of the same density, making them highly efficient pillar-based lattice topologies.
3D printed conventional lattice structure with hollow pillar lattice.
However, there are still serious structural defects that arise from complex stress concentrations in hollow node regions. These stress concentrations can lead to local elliptiness and cracking, resulting in premature failure of the lattice structure. The introduction of joint reinforcement can effectively reduce the stress distribution in the nodal area, but it is found that this strategy still results in a significant near-zero stress area for the load misaligned hollow pillars**.
The traditional solid strut lattice (SSL) is weaker than the hollow strut lattice (HSL) of the same density, and it is not suitable for HSL-based multi-topology designs for strengthening. Recent studies have found that tapplet structures (TPLs) can effectively distribute stresses. In order to improve the mechanical envelope of the hollow pillar lattice (HSL) without hindering its multifunctional topology, the researchers propose to integrate the TPL topology into the internal hollow space of the HSL topology to create a synergistic thin plate hollow pillar lattice (TP-HSL) topology to take advantage of the structural advantages of each lattice. This strategy differs from previous multi-topology lattice designs by randomly or determinizing the placement of various unit cell cells in the lattice design space. It creates a two-stage coherent architecture that provides high mechanical strength while being open-pore to retain the versatility of HSL topologies, such as for fluid control or mixing, enhanced biomimicry, and thermal conductivity control.
The researchers propose a variety of topology integration strategies.
The researchers proposed a variety of topological integration strategies, in which a simple cubic TPL unit composed of sub-millimeter-thick Ti-6Al-4V lamellar layers was embedded into the hollow space of the simple cubic Ti-6Al-4V hollow pillar lattice HSL to form a single Ti-6Al-4V thin plate integrated hollow pillar lattice (TP-HSL). Co-topologies can be easily achieved by choosing a consistent unit cell design, such as a simple cubic lattice cell, as the pillars and plates follow a consistent orientation, eliminating the need for unit cell manipulation. In addition, this TP-HSL topology is designed to securely interconnect all load-misaligned horizontal struts to load-aligned plates, ensuring efficient stress distribution and thus high structural efficiency.
The HSL (left column) and TP-HSL (right column) continuum models were used for isotropic linear elasticity analysis.
Ti-6Al-4V was selected as TP-HSL material because of its medium density, high strength, excellent corrosion resistance, cost-effectiveness in a wide range of corrosive media (seawater, oxidizing acids, chlorides, rocket propellants), it can be printed using the LPBF process, and it has a rich database for a wide range of application conditions. These properties make it the material of choice for many critical applications and the most widely studied alloy in metal additive manufacturing.
Ti-6Al-4V TP-HSL specimen fabricated by LPBF process.
The mechanical response of Ti-6Al-4V TP-HSL and HSL specimens with different densities to uniaxial compression and its failure modes.
Comparison of performance with existing metal lattices.
Finally, the density distribution of the integrated hollow pillar lattice metamaterial printed by Ti-6Al-4V 3D was 10–1.8G cm, its relative yield strength far exceeds the empirical upper limit of all honeycomb metals, including hollow strut lattice (HSL) and solid strut lattice (SSL) metamaterials made of various metal alloys. In addition, their absolute yield strength greatly exceeds that of magnesium alloys with comparable densities, while inheriting the high corrosion resistance, biocompatibility, heat resistance, and other unique properties of Ti-6Al-4V. Overall, titanium porous lattice topological metamaterials extend the boundaries of lightweight multifunctional metal materials.
Due to their low density and high yield strength (>250 MPa), coupled with the intrinsic properties of Ti-6Al-4V, such as good heat resistance (up to 350 °C), significant corrosion resistance, and biocompatibility, the Ti-6Al-4V designed in this study can be used as the core structure of demanding thermal protection systems such as hypersonic vehicles. In particular, when printed with the high-temperature titanium alloy TI-SF61, they can be further used at temperatures up to 600°C. These important properties also make them a potential material of choice for titanium drones for close-range and extended flight time monitoring or extinguishing bushfires or severe industrial fires. Other applications include lightweight construction (lighter, stronger, more heat-resistant, and more corrosion-resistant) to replace magnesium alloy components in the defense and aerospace sectors. However, for applications that require efficient fluid flow, these TP-HSL designs may not be the optimal solution as they compromise fluid flow. From a design point of view, the structural efficiency of the current TP-HSL architecture can be further improved.
Note: The content of this article is **Frontier of additive manufacturing technology.