Porous Nickel is as Strong as Titanium and Five Times Lighter

Researchers have built a sheet of nickel with nanoscale pores that make it as strong as titanium but four to five times lighter.

Titanium is as strong as steel but about twice as light. This new material is strong as steel but ten times lighter.

The empty space of the pores, and the self-assembly process in which they’re made, make the porous metal akin to a natural material, such as wood.

The work was by researchers at the University of Pennsylvania’s School of Engineering and Applied Science, the University of Illinois at Urbana-Champaign, and the University of Cambridge.

Read more at: https://phys.org/news/2019-01-metallic-wood-strength-titanium-density.html#jCp

And just as the porosity of wood grain serves the biological function of transporting energy, the empty space in the researchers’ “metallic wood” could be infused with other materials. Infusing the scaffolding with anode and cathode materials would enable this metallic wood to serve double duty: a plane wing or prosthetic leg that’s also a battery.

Even the best natural metals have defects in their atomic arrangement that limit their strength. A block of titanium where every atom was perfectly aligned with its neighbors would be ten times stronger than what can currently be produced. Materials researchers have been trying to exploit this phenomenon by taking an architectural approach, designing structures with the geometric control necessary to unlock the mechanical properties that arise at the nanoscale, where defects have reduced impact.

They call the porous nickel metallic wood because of its low density and its cellular nature.

The struts in the researchers’ metallic wood are around 10 nanometers wide, or about 100 nickel atoms across. Other approaches involve using 3D-printing-like techniques to make nanoscale scaffoldings with hundred-nanometer precision, but the slow and painstaking process is hard to scale to useful sizes.

The new manufacturing methods can make samples that are 400 times larger than before.

The start with tiny plastic spheres, a few hundred nanometers in diameter, suspended in water. When the water is slowly evaporated, the spheres settle and stack like cannonballs, providing an orderly, crystalline framework. Using electroplating, the same technique that adds a thin layer of chrome to a hubcap, the researchers then infiltrate the plastic spheres with nickel. Once the nickel is in place, the plastic spheres are dissolved with a solvent, leaving an open network of metallic struts.

The material is 70% empty space.

Scientific Reports – High strength metallic wood from nanostructured nickel inverse opal materials

Nanostructured cellular material based on electroplated nickel (8,900 kg/m3 bulk density), which has the strength of titanium and the density of water (1,000 kg/m3). The high strength arises from size-dependent strengthening of load-bearing nickel struts whose diameter is as small as 17 nm and whose strength is as high as 8 GPa. We refer to this material as a “metallic wood,” because it has the high mechanical strength and chemical stability of metal, as well as a density close to that of natural materials such as wood.

The high strength of the metallic wood results from the size-dependent strengthening of the inverse opal struts, which have up to 4X the yield strength of bulk electrodeposited nickel and enable high specific strengths of 230 MPa/(Mg/m3). The cellular structure can be controlled to tune the modulus and strength each by a factor of 10X.

The metallic wood can be easily fabricated over 100 mm2 areas, can be processed at room temperature, and can be combined with additional functional materials, as demonstrated with the rhenium coatings. The high strength continuous metallic architecture with isotropic elasticity, high hardness, and high strain energy storage could be important for a variety of applications such as energy storage heat transport, and sensors. Future work could explore improvements in specific strength above 230 MPa/(Mg/m3) by incorporating lightweight metals such as titanium or aluminum and developing roll-to-roll processing of high strength porous metals from self-assembly.

Abstract

This paper describes a nickel-based cellular material, which has the strength of titanium and the density of water. The material’s strength arises from size-dependent strengthening of load-bearing nickel struts whose diameter is as small as 17 nm and whose 8 GPa yield strength exceeds that of bulk nickel by up to 4X. The mechanical properties of this material can be controlled by varying the nanometer-scale geometry, with strength varying over the range 90–880 MPa, modulus varying over the range 14–116 GPa, and density varying over the range 880–14500 kg/m3. We refer to this material as a “metallic wood,” because it has the high mechanical strength and chemical stability of metal, as well as a density close to that of natural materials such as wood.

Written by: Brian Wang. Nextbigfuture.com

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