Nanostructured metals: light but strong

  • 03-Oct-2008 02:46 EDT
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Through Severe Plastic Deformation (SPD) processing, Metallicum can reduce the grain size of conventional metals from the typical range of 10 to 50 µm to a range between 20 and 500 nm.

Metallicum Inc., an offshoot of Los Alamos National Laboratory that was recently acquired by Manhattan Scientifics, has figured out a way to manufacture nanostructured metals and alloys—“to change the internal structure of virtually any polycrystalline metal so it is much stronger than its conventional counterpart,” said Terry Lowe, co-inventor of the nanostructuring process and President of the Metallicum division.

The process, called Severe Plastic Deformation (SPD), creates metals 30 to 100% stronger than conventional grades. “A lightweight industrial metal, like aluminum, can be manufactured to have the strength of steel,” said Lowe. “So all of the sudden you can use aluminum for things that you would never even conceive of it being used for.”

The improvement in strength, as well as other enhanced properties, can be attributed to reducing the size of a material’s grains (or crystals)—comparable to the diameter of a human hair to begin with—by a factor of 500 to 1000. “We devised methods that deform metals, but without changing their geometry,” Lowe explained. “We subject materials to intense, localized shearing, which basically causes the grains to want to rotate or spin. As they rotate, what really happens is they break up into smaller grains, and you form new boundaries.”

The characteristics of the grain boundaries then can be altered to increase metal ductility, the ability to resist failure, and to customize the properties of the metal at its surfaces. “The limiting property in many [transportation] applications…is not strength; it’s fatigue—the ability to resist cyclic loadings,” Lowe said, adding that the SPD process results in “dramatically” increased fatigue resistance—by an amount comparable to the increase in strength.

The main “green” benefit of the technology lies in the fact that if you enhance the strength and other characteristics of a material, then you can use less of it in the final component design. “Basically, you’re just moving around a lot less metal,” Lowe said, positively impacting the amount of fuel used. “A big airplane like a B747 has about 100,000 lb of titanium in its construction. We believe our nano metals could reduce that weight by about 5% or 5000 lb.”

Lowe referred to nanostructured metals as “drop-in technology” because they can simply replace their conventional form in current applications while meeting or exceeding all specs. “It isn’t some novel, fancy material; it’s the same material,” he said.

Another green aspect is that the process is performed at low temperatures. “For alloys that you would typically process at elevated temperatures—titanium, for example, typically above 800°C—we can process at room temperature or up to 500°C,” said Lowe, noting that tool life and surface finish improve because of the material’s ease of machineability. And nanostructured metals are ideal for complex shapes, he added, because they are super plastic at low temperatures.

“Typically, super plasticity is expensive. You’ll spend 20 minutes to four hours pressing a single part, but with our material you do the same thing in a matter of seconds because they’re super plastic at 10 to 100 times greater rates,” said Lowe. “So you can do near-net-shape forming, but really quickly. And you can do that with materials that aren’t traditionally even super plastic.”

Beyond aluminum and titanium, Metallicum has used its SPD process on a variety of materials including steel, beryllium, magnesium, nickel, cobalt-chromium, and even polymers and silicon. “It’s a deliberate choice to focus on titanium [first],” said Lowe, with initial application in the biomedical field. “The first day on the market, you want to address the smaller-volume applications, which have a very high margin. Generally in the transportation industry, your manufacturing practice has to be very mature to be cost effective, and that’s probably more than a year off.”

“It’s really just a matter of scale,” Lowe continued. “And there’s nothing that prevents us from adjusting that scale; the question is, when is it most appropriate to do that?”

Metallicum has identified more than 100 different applications for the technology and is currently in the second generation of the continuous processing methodology. The process is capable of producing rod and bar up to 40 mm in diameter to be formed into anything from car parts to heart stents.

Cost should not be a deal-breaker, believes Lowe, because “our methods are intrinsically mechanical processing methods; they’re not fundamentally different from rolling, extrusion, and other similar technologies.” Savings that result from using less material help, too.

Currently, the company is in different stages of development and evaluation with at least two major automakers, one heavy-equipment manufacturer, and two major aerospace companies.

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