Liquidmetal properties 3

[EnglishMuffin]

Does anyone know anything about "liquidmetal" ? After reading about it in Practical Mechanics, I was looking at this website:

http://www.liquidmetal.com/technology/dsp.creators.asp

which contains the following quote :

"Liquidmetal alloys solidify without crystallizing, which Drs. Johnson and Peker believe is why they are twice as strong as titanium, but softer and more malleable".

This statement strikes me as nonsense, unless they mean they have a high UTS and a low yield point, but what use would that be in practice from a strength point of view ? Maybe it would at least provide a metal forming advantage ?

 

[kenvlach]

Amorphous alloys (metallic glasses) have favorable properties in nearly every respect in comparison to normal (multicrystalline) alloys. Certainly, “more malleable” is correct; especially for titanium (every trace impurity or alloying makes Ti brittle, and its intermetallics are even worse). “Softness” may be an oversimplification of this to less engineering-astute investors; it isn’t fully consistent with the claimed properties for Liquidmetal® given in the ‘Our Technology’ link. Here they tout higher yield strength/hardness/elastic limit.

As you surmise, these properties would provide a metal forming advantage; e.g., be capable of a lot of work hardening whilst cold forming.

For less hype and more info, check out the metallurgical/materials science literature.
There is a good overview article Amorphous Aluminum Alloys—Synthesis and Stability online at

http://www.tms.org/pubs/journals/JOM/0203/Perepezko-0203.html

Ten articles from the ‘Symposium on Structure and Properties of Bulk Amorphous Alloys’ are in the July 1998 Metall. Trans. A. Table of contents at

http://www.tms.org/pubs/journals/MT/A/9807/contents-9807.A.html

Abstracts can also be viewed. There is one article on a Ti₆₅Cr₁₃Cu₁₆Mn₄Fe₂ alloy in which annealing causes a crystalline-to-amorphous phase transformation (it is usually the reverse).

 

[EnglishMuffin]

Do you think the bouncing ball demo on the site I mentioned is genuine ? The video part looked to me like an animation - but maybe the audio was real. I would imagine that this behavior might imply a material with very low structural damping.

 

[JimMetalsCeramics]

Liquidmetal is made through the rapid quenching of metal into an amorphous state. This is generally accomplished through quenching a molten stream of the metal with gas (e. g., He) or water (for less reactive metals) into a strip or into fine powder. If the quench through the solidification point (melting point) is adequately fast (million of degrees per sec.) the natural crystallization of the metal is suppressed. The powder is compacted into a bulk solid below the metal’s recrystallization temperature. By definition, an amorphous metal has no crystallinity, no slip planes and no crystalline grain boundaries. With the cited titanium alloy, this results in a material with almost perfect elastic recovery (highly efficient coefficient of return). In the demonstration at

http://www.liquidmetal.com

you see steel balls bouncing on different surfaces. The amorphous titanium one keeps the ball bouncing because the elimination of slip planes (and to a lesser extent, the elimination of crystalline grain boundaries) removes much of the plastic loss mechanism within the metal.

Some aluminum alloys have been formulated to have their crystallization kinetics suppressed. These have, in turn, been quenched into amorphous powders. The consolidation of these powders, leads to very high specific stiffness metal. Liquidmetal Golf exploits an aluminum alloy which is made into amorphous powder and then cold isostatically pressed into a bulk solid. [I've also seen it cold spray-formed]. The material makes for highly effective golf club head.

A great deal of work on amorphous metal powder manufacture is being conducted by Iver Anderson at Ames Lab.

"Twice as strong as titanium, but softer and more malleable", does sound like poor wording. They're possibly trying to say that soft metals can be made stronger through the production of amorphous structure.

 

[EnglishMuffin]

High specific stiffness huh? How high exactly? Most regular metals are around 10^8 lbf/in/lb. Sounds like it would make a great material for boring bars.

 

[EnglishMuffin]

Sorry - typo - I meant lbf.in/lb

 

[JimMetalsCeramics]

Not that I recommend the company below, but here is a link with data from Boeing:

http://www.inovati.com/pictures/graph2_large.gif

 

[JimMetalsCeramics]

For boring bars you want:

-raw strength,
-lower expansion coeff. than for Al (especially if you
intend on carbide tipping it), and
-high hardenability if it is not to be tipped.

 

[EnglishMuffin]

Whatever "DRA" is in that picture - it comes out to be 240*10^6 lbf.in/lb (in some cases) - amazing. But what is it?

 

[JimMetalsCeramics]

Discontinuously Reinforced Aluminum (e. g., SiC particles).

 

[EnglishMuffin]

Thanks.

 

[EnglishMuffin]

But that doesn't sound like "liquidmetal". Is it, in fact? All the other stuff on that diagram is pretty much like regular metal - stiffness wise.

 

[EnglishMuffin]

JimMetalsCeramics: I would say that static stiffness is often more important in a boring bar than strength - in most cases you would not be operating anywhere near the elastic limit. And you should find that high specific stiffness translates into improved dynamic stiffness, since the natural frequency will be higher. I am of course talking about bars with some kind of insert on the end, where the metal cutting capabilities are not an issue.

 

[EnglishMuffin]

JimMetalsCeramics Sorry - should have said "metal cutting capabilities of the bar material are not an issue".

 

[JimMetalsCeramics]

"Amorphous Al" is the liquid metal on that graph. Very high specific strength.
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I personally wouldn't use an aluminum composite for a boring bar. They have set diameters and I would definitely expect a bar with weaker strength than hardened steel to often distort (primarily tortionally). Even if the distortion is only elastic, it will drive the machinist crazy on runout and trueness issues, especially when taking heavy cuts.

There's also the separate issue of insert brazing.

 

[EnglishMuffin]

Well, I won't argue with you about the suitability for boring bars - having read some more, it looks as though the absolute stiffness of Liquidmetal is quite low, even though the specific stiffness is high - that's the problem. The strength appears perfectly adequate, however. The stresses in most boring bars are fairly low - don't get mixed up between strength and stiffness.
Take a look at this link - where they are using carbon fibre boring bars because of their high specific stiffness.

http://lacomrs6.kaist.ac.kr/main/thesis_abstract/hhy-2.htm

Actually, I wouldn't be surprised if the absolute stiffness of the carbon fibre composite was lower than that of pure tungsten carbide.

 

[JimMetalsCeramics]

It will depend on how heavy a cut the machinist will want to take. If the machining is of a high volume, fixed geometry part (e. g., automotive industry components) and set limits on cutting depths/stresses are maintained, then maybe these materials could be used. Changing siffness can affect susceptibility to chatter as it will shift resonance frequency. Boring, in particular gun-drilling, requires extreme trueness (minimal tool deflection).

The report, however, is not too detailed. New cutting tool materials are regularly rejected for 1 or 2 specific mechanical shortcomings.

 

[EnglishMuffin]

It was just a passing thought - an "off the cuff" comment, if you will. I've spent most of my life struggling with chatter problems, designing machine tools, cutting tools etc - even a few boring bars. At the moment, I haven't the slightest intention of doing anything like this personally. Thanks for the info.

 

[JimMetalsCeramics]

Wanna fight?

 

[EnglishMuffin]

No ! I gave you a star so stop complaining!