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Metal Foams

Figure 1: INCO Open-cell nickel

Metals that float on water? What sort of fairy tale is that? Yet metal foams do – some have densities that are less that one tenth of that of H2O.

Metal foams are a new class of material, as yet imperfectly characterised, but with alluring properties.

They are light and stiff, they have good energy-absorbing characteristics (making them good for crash-protection and packaging) and they have attractive heat-transfer properties (used to cool electronic equipment and as heat exchangers in engines).

Some have open cells (Figure 1), very much like polymer foams but with the characteristics of metals (ductility, electrical conductivity, weld ability, and so forth).

Others have closed cells, like metallic cork.

And they are visually appealing, suggesting use in industrial design.

There are currently some 12 producers marketing a range of metal foams, mostly based on aluminum, but other metals – copper, nickel, stainless steel and titanium – can be foamed and are available on order.

We list, below, some of the potential applications, but at present few of these have been exploited profitably.

Like many other emerging materials, metal foams are a product looking for an application.

That is where this data module can help. It currently contains material, mechanical, thermal and other properties for 130 aluminum, nickel and copper foams, developed by the 8 suppliers in the table. Also included are 100 honeycomb materials.

With this data, you can apply Granta's CES Selector or GRANT MI tools to compare metal foams with all other materials including conventional metals and alloys, polymers and polymeric foams, ceramics, composites and natural materials. See Figure 2.

For a given application, you can see the advantages of these new materials over conventional ones.

You can select foams for specific energy absorbing tasks, for mechanical applications (cores for sandwich structures, for example) and thermal (heat transfer) applications.

Supplier	Trade Name
The Fraunhofer Institute, Bremen, Germany	“IFAM” (aluminum foam)
Alulight International, Austria	“Alulight” (aluminum foam)
INCO Special Products, Canada	“INCO” (nickel foam)
Cymat Corporation, Canada	“Cymat” (aluminum foam)
Shinko Wireco, Japan	“Alporas” (aluminum foam)
ERG, Oakland, CA, USA	“Duocel” (aluminum foam)
DMI, Ukraine	“Gasar” (copper foam)

The data module is fully customizable. You can add new foams to compare with those already present.

Because the actual measured properties available for metal foams are sparse, unknown properties have been filled using intelligent estimates.

The textbook referenced below describes models for property prediction of possible new foams. Properties for new ‘virtual materials’ may be predicted and entered into the database for analysis against real materials.

Please click on graph to see an enhanced image

Figure 2: Young’s modulus plotted against density for metal foams (red bubbles), compared with those for solid light alloys (purple), steels (dark green), polymers (blue), and polymeric foams (light green). Note the enormous range of modulus covered by the metal foams.

The most promising applications for metal foams appear to be as cores for light-stiff sandwich panels; as stiffeners to inhibit buckling in light shell structures; as energy absorbing units, both inside and outside of motor vehicles and trains; as efficient heat exchanges to cool high powered electronics (by blowing air through the open cells of the aluminum foam, like that of Figure 1, attached to the heat source) and as light cores for shell casting. Several industrial designers have seen potential in exploiting the reflectivity and light-filtering of open cell foams, and the interesting textures of those with closed cells.

The data in the database has been drawn from many sources. A comprehensive introduction to metal foams, listing sources of data and suppliers, can be found in Metal Foams - A Design Guide by M.F. Ashby, A.G. Evans, N.A. Fleck, L.J. Gibson, J.W. Hutchinson and H.N.G. Wadley, published by Butterworth Heinemann, Boston, USA (2000) ISBN 0-7506-7219-6.