“It demonstrates that liquid metals can be used for structural applications with multiple interesting functionalities”Pu Zhang

Researchers at the State University of New York at Binghamton have produced the first ever liquid metal lattice to help develop prototypes that can regain their shape after being heated to melting point, such as web-like mesh antennas, honeycombs and soccer balls, and even a hand that slowly opens as the metal lattice melts. This new class of materials hold promise for applications in aerospace, robotics and tunable metamaterials.

The lattice is made from Field's metal, a fusible alloy that is a mixture of bismuth, indium and tin, and which turns to liquid at the relatively low melting point of 62°C. Field's metal, already employed as a liquid metal coolant in the nuclear engineering industry, was shown here to have other uses, with a range of structures demonstrating the functionalities of liquid metal lattice materials, such as recoverable energy absorption, tunable rigidity and reconfigurable behaviors.

As described in the journal Additive Manufacturing [Deng et al. Addit. Manuf. (2020) DOI: 10.1016/j.addma.2020.101117], the material was combined with a rubber shell based on a new hybrid manufacturing process that integrates 3D printing, vacuum casting and conformal coating techniques taken from electronics technology. The skeleton of the shell maintains structural integrity to confine the liquid metal in the channels after melting. The core-shell lattice materials have relatively high energy absorption capacity and strength due to the metallic feature.

When the liquid metal is in a solid state it is extremely strong and safe, and can absorb a great deal of energy when crushed. After heating and cooling, it returns to its original shape and can then be reused, making it deployable in shape memory cushion structures in aerospace engineering and soft robotics. For instance, a spacecraft that crashes will normally involve aluminum or steel in its cushion structures, but on landing the metal absorbs the energy and deforms, and so can only be used once. With the Field's alloy, it is possible for it to crash but then be heated up later to recover its shape.

The study introduces a novel area of research into liquid metal and architected materials. As group leader Pu Zhang told Materials Today, “It demonstrates that liquid metals can be used for structural applications with multiple interesting functionalities”. Further research will be around improving the durability, strength and energy absorption capacity of the materials, and to develop scaled-up and defect-free manufacturing processes. The team are also investigating different structure types and improved coating materials, and even hope one day to build a complete liquid metal lattice robot.

Hybrid manufacturing process produces liquid metal lattice structure
Hybrid manufacturing process produces liquid metal lattice structure