New material: solid metal-foam composite

[Bob in a quantum-state-of-faith]

http://blog.makezine.com/archive/2010/02/new_material_composite_metal_foam.html

Watch the video-- it's very short.

Mechanical and aerospace engineer Dr. Afsaneh Rabiei has created a material that is very light, but very strong.  In addition, it has superior "crush-ability" as compared to other materials.

[Swatopluk]

I can't really see what's new with this particular metal foam apart from a seemingly more homogeneous bubble size distribution.

[Sibling Zono (anon1mat0)]

Couldn't listen to the video but if the title suggests anything we are talking about a composite material, so a titanium based alloy with bubbles is bound to be stronger than the typical aluminium metal foam, and I imagine the trick is also in the manufacturing.

[Bob in a quantum-state-of-faith]

Okay, sorry about the video not working-- it's the heart of the article.

Actually?  The material is both simple and cheap-- start with hollow spheres of steel-- that's right, simple steel.  Place into container, pour in powdered aluminum.  Heat the whole until the Al melts and bonds to the steel (presumably the surface of the steel hallow spheres is roughened, but they didn't say).

The advantage of this method over previous attempts, is the spheres create intact, non-intersecting hollow spaces in the metal-- previous attempts were more like a kitchen cellulose sponge.  The intersecting spaces are much weaker in such a structure.   But the non-intersecting spheres have the advantages that all complete spheres have-- strength.

Then the video shows a comparison of solid metal being crushed versus this stuff--- it crushes uniformly, and requires far more energy that it's weight would imply.   Strong and light.

The video did not talk about other materials than the steel/aluminum, but I imagine the method could easily be used with more exotic materials:  imagine hollow titanium spheres of varying sizes in a matrix of stainless steel?  The titanium would easily stand being heated to the melting point of nickel-steel.   Or, perhaps a matrix of platinum spheres in a titanium mix?  Again, as I recall, platinum's melting point is higher than titanium...

If you're just looking for strength?  Use ceramic hollow spheres to create the space-- then you could use about any metal you want as the matrix material.

The idea is a very clever one, I think.

[Aggie]

Ah! The spheres were hollow, that's how they do it (video worked, but I obviously wasn't paying attention  ).

Ingenious.  And possibly cheap enough to be commercially viable.

[The Meromorph]

Makes me wonder about the techniques being use with non-metals...
ABS with stainless balls in an injection moulded process?
Rubber with stainless balls as a tire filling? as a tire? for shoe soles?

Or constructing varable density material by using layers of differently sized balls...

[Bob in a quantum-state-of-faith]

Indeed.  One reason why I posted this, is that you guys are amazingly full of great ideas.

[Aggie]

  When you said platinum, all I could think about was booty jewelry. 

I was thinking about using a similar technique with small diamonds or other hard heat-resistant gemstones instead of the spheres, embedding them in a precious metal matrix, casting / shaping and then using an abrasive to expose the gems in the ring / whatever. No strength advantages, but it'd look cool. 

_{dunno about my pirate cred; it's all about gold and jools}

[Bob in a quantum-state-of-faith]

When you said platinum, all I could think about was booty jewelry. 

I was thinking about using a similar technique with small diamonds or other hard heat-resistant gemstones instead of the spheres, embedding them in a precious metal matrix, casting / shaping and then using an abrasive to expose the gems in the ring / whatever. No strength advantages, but it'd look cool. 

_{dunno about my pirate cred; it's all about gold and jools}

Take care:  diamonds *will* burn, if the temperature is hot enough-- certainly they will burn at less than the melting point of gold, for example.   I remember that from a stupid "crime drama" where they supposedly found these diamonds in the ashes from a fire, but no gold band.... riiiight.   Wikin on diamond here... go down about 1/2 way, and there is this:

Being a form of carbon, diamond oxidizes in air if heated over 700 °C.  In absence of oxygen, e.g. in a flow of high-purity argon gas, diamond can be heated up to about 1700 °C.  Its surface blackens, but can be recovered by re-polishing. At high pressure (~20 GPa) diamond can be heated up to 2500 °C,  and a report published in 2009 suggests that diamond can withstand temperatures of 3000 °C and above.

Thus, even the modest melting point of aluminum will potentially ruin the diamond-- it'd take special precautions, inert gas at high pressure.

Ruby is a bit better, according to wiki, again, with a melting point of 2044 ℃, which easily ought to withstand low temp materials, such as copper, lead, zinc and aluminum.

And, now that I've looked it up, gold melts at a much lower temperature than I remembered: 1064℃, well below the safe temp of a diamond if you use inert argon gas in your process.

(okay, now I'm on a sort of mission).  Sapphire melts at 2030–2050 °C. 

Emeralds is not listed, because they tend to shatter when heated, instead of melting-- although I don't see why they couldn't see if the pieces would then melt.... but I couldn't find a definitive answer.

Pearls were a surprise-- they melt quite easily, 318.4 ℃.  I would not suggest using any pearls in your mix... they'd melt. 

Okay, that's enough of that, except for completeness, here's some melting points of metals, just to compare all this to:  (everything in ℃, due to my chemistry bias... )

Silver: Melting Point: 961.78 °C
Copper: Melting Point: 1083.0 °C
Aluminum:  Melting Point: 660.37 °C
Lead:  Melting Point: 327.46 °C
Iron:  Melting Point: 1535.0 °C
Steel, and alloy of Iron and other things, mostly carbon: often melts at around 1370 °C.  "around" because the properties of the alloy will change this quite a bit, although typically lower than pure iron, above.
Titanium:melting point of 1725°C
Platinum:   Melting Point: 1768.3 °C

[Aggie]

That old false-diamond standby, cubic zirconia, would fit the bill nicely (mp = 2750°C), as would the newer simulant on the block, moissanite (decomposes 2730 °C).  Sapphires/ruby (and other magmatic gems) is what I had in mind, but as you suggest, there may be damages at lower temperature.  Hardness is important for exposing with abrasives, too... moissanite, sapphire or diamond would be fine, zirconia should be OK.

Gold alloys have lower melting points as well - how about a ruby-studded pink gold heart for Valentine's day?

In any case, one would want to use tiny, imperfect gems, not large-carat whoppers.

[Sibling Zono (anon1mat0)]

Sounds like a business model. 

IIRC the toolkit to handle jewelry gold isn't too sophisticated and if the product is nice I'm sure you can find lots of buyers.

[Bob in a quantum-state-of-faith]

That old false-diamond standby, cubic zirconia, would fit the bill nicely (mp = 2750°C), as would the newer simulant on the block, moissanite (decomposes 2730 °C).  Sapphires/ruby (and other magmatic gems) is what I had in mind, but as you suggest, there may be damages at lower temperature.  Hardness is important for exposing with abrasives, too... moissanite, sapphire or diamond would be fine, zirconia should be OK.

Gold alloys have lower melting points as well - how about a ruby-studded pink gold heart for Valentine's day?

In any case, one would want to use tiny, imperfect gems, not large-carat whoppers.

Sounds like it would work.

The only caveat now, that I can think of, is density issues:  steel spheres will sink in molten aluminum, as the specific gravity of steel is much higher than aluminum.

Googling the specific gravity of your gems, versus gold and gold alloy (which should be less dense-- gold being one of the most dense and any addition would make it lighter) should yield good results-- it's what I did.

If the gems want to float?  Make your molds "upside down" and pour the molten gold-alloy in from the side-- forcing it if needed with a steel piston-pump (hand operated).   Or, you could epoxy your gems into a fine steel wire matrix, which is anchored into your mold with more epoxy.  Sure, the epoxy will burn, but it ought to hold just long enough for the gold to form around your assembly.  Or you could use silver wire or copper.  Or, you might epoxy your gems to the face of your mold-- if you're using a plaster mold, this won't matter, you would break it apart anyway.  Then, the epoxy would be on the outer part, to be ground away.

There is one more consideration:  miscibility of your alloy with respect to your gemstones.   Or, in other words?  The oil and water effect.  The video did not say how the good Doctor addressed this issue-- and if the steel spheres are heated to the melting point of aluminum, it may not even be a problem.

And that may plague your project as well-- you may find that you must heat your gems carefully, slowly, so they are not damaged, up to the melting point of your alloy (and beyond a bit) to let the molten metal flow properly around the gemstones-- so that it 'wets' it enough to form a bond.

Good luck!

[Aggie]

LOL, need to go plunder some gold and jewels first - I'm no goldsmith.

[Sibling Zono (anon1mat0)]

you may find that you must heat your gems carefully, slowly, so they are not damaged, up to the melting point of your alloy (and beyond a bit) to let the molten metal flow properly around the gemstones-- so that it 'wets' it enough to form a bond.

And that the stress from the temperature change doesn't shatter them.

[Bob in a quantum-state-of-faith]

you may find that you must heat your gems carefully, slowly, so they are not damaged, up to the melting point of your alloy (and beyond a bit) to let the molten metal flow properly around the gemstones-- so that it 'wets' it enough to form a bond.

And that the stress from the temperature change doesn't shatter them.

That's why pre-heating the gems to the same, or a bit above the melting point of the alloy is a good idea-- you can take the gems' temperature up slowly, say over several hours, to help avoid shattering them.  Same for allowing the mix to cool-- over several hours, like what is used for glass, would be a good idea.