Framebuilders - Liquidmetal?

hi there,

this is something random that i thought of. Has anybody used this type of metal before? ive seen it used on tennis rackets (head) but nothing else.

I doubt it's available to hobbyists or small scale manufacturers yet.

Also looks like when they fail they do so catastrophically, "shattering to bits."^1

1.) http://en.wikipedia.org/wiki/Liquidmetal

There's JB Weld; you're not talking about that, are you?

hi there,

this is something random that i thought of. Has anybody used this type of metal before? ive seen it used on tennis rackets (head) but nothing else.

Metallic glasses have a number of applications which are suited to their lack of grain boundary deformation mechanisms and their high stiffness, but damage-tolerant designs are not one of them. Despite brochure bullsh*t suggesting that such materials can be quite tough, the truth is that it's a nonsense.

You could cast a tube, perhaps, but unfortunately there's no way in heck you could draw one. Welding or other fusion-jointing techniques cause the molten metal to begin to crystallise, especially if there's any contaminiation accidentaly introduced to the weldpool.

So, 'fraid not, chap.

Falanx - thanks for responding here, I have another question. I see many references to these materials being very stiff but I don't understand why and I suspect that it's more marketing. Do you have any figures for the modulus of glassy metals / metallic glasses compared to an equivalent crystalline metal? Surely someone has measured propagation velocities in these materials?

I was under the impression that modulus was largely independent of grain structure: there is very little difference between a martensitic and austenitic steel for instance, especially when the higher alloy level of the typical austenitic steel is taken into account. Also with silica glass the stiffness of your actual glass is very similar to that of crystalline silica (quartz). Even the highest modulus glass fibre, which I assume is subjected to some form of melt drawing to improve molecular alignment, is less than 20% higher than crystalline quartz.

The stiffness of amorphous metal alloys is merely a function of their composition, and is often lower than that of polycrystalline metals of similar base. A number of amorphous metal alloys have been developed to extremely low Young moduli for biomedical applications, but nonetheless, even in alloys not developed for such extreme disparities between UTS and E, their Young Modulus is often noticeably lower than the same base metal in polycrystalline forms.

Ti40Cu36Pd14Zr10 for example is listed as three times as strong as CP titanium, suggesting a UTS of about 1.5GPa, but with a Young Modulus approaching that of cortical bone, about 20GPa. CP polycrystalline titanium is of the order of 115GPa.

Some iron-rich alloys demonstrate Es in the region of half what a polycrystalline metal possesses, but with bulk hardnesses suggesting strengths well over 3GPa, some as high as 4GPa +.

You're correct in the understanding of the lack of causation between grain size or geometries and Young and Bulk Moduli. The only exception being extremely fine grain sizes where the sheer volume of grain boundary and disorder causes the Hall-Petch behaviour to no longer hold. One other thing to bear in mind that not only do these materials usually have lower Young Moduli than similar polycrystalline metals, their elastic extension is greater, and when viewed at a sensible scale, shows a behaviour similar to elastomers.

Falanx

thanks for that, off to the books to look up Hall-Petch behaviour.

BTW I assume "polycrystalline glasses" in the last sentence was actually "polycrystalline metals".

Falanx

thanks for that, off to the books to look up Hall-Petch behaviour.

BTW I assume "polycrystalline glasses" in the last sentence was actually "polycrystalline metals".

Yep, apologies. I was at work and, well there's only so many materials science things you can do at once before the states of matter become confused ;-) FTFM

Essentially, Hall-Petch behaviour describes the relationship in polycrystalline materials between the mean free linear intercept - half the average grain diameter, and the materials' yield strength and ability to do work during fracture.

In strain-rate sensitive metals, which are usually bound by a high activation energy for their slip systems, or merely in possession of a few slip systems because of their particular crystallography, there is usually a purely inversely proportional relationship between strength and toughness - strong metals are brittle, weak metals are ductile.

The lattice friction stress, which is a major contributor of the yield strength, is dependent on the availability of slip systems. Grain boundaries are disordered and have no long-range structure which means as their volume increases - the grain size is decreased - the lattice friction stress rises, increasing yield strength. Yet at the same time, the increase in grain boundary area toughens the material by a combination of grain boundaries being stronger than grains and increasing the work done on fracture by forcing cracks to propagate across more grains.

This is why everyone and his dog is after routes to refine the grain of most metals. However, what most don't fully appreciate is that grain refinement is a bit of waste of time in metals with plentiful low energy slip systems - the FCC metals, like aluminium or nickel or copper because their lattice friction stress is permanently affected by plentiful slip. You can see it in the 300 series, austenitic, FCC stainless steels. Temperature has essentially no effect on their strength or toughness, and altering the test temperature is the most practical way of observing the Hall-Petch behaviour of a material.

Falanx

Thanks for the concise and comprehensible explanation. That is the neatest explanation of why the stainless steels with which I'm most familiar never attain the strength or hardness of alloy steels.

I'm a winemaker so I work with a lot of 304 and 316, I started out as a trainee aeronautical engineer in the Navy, I retain a strong interest in materials and engineering but that training was a long time ago so much of it is forgotten.

You're a real asset to this place.

No worries. As a friend on mine once said; "..because this is what I do for a living." :-)

Now, don't get me wrong, you can get some pretty astounding strength out of those 300 series steels, but they have to be in small sections and you have to work them near to death. half and quarter millimetre 300 series wires reach 2GPa UTS and you can make yarn from them even stronger, in a similar way to how Scifer steel wire is drawn.

Whoah... most of this is over my head, but the Wiki page had me wondering if you could possibly do carbon fibre in a liquid metal matrix...

Wouldn't that create a sea of galvanic corrosion?

I dunno...I spose it could....

How about reinforcement with another metal?

Whoah... most of this is over my head, but the Wiki page had me wondering if you could possibly do carbon fibre in a liquid metal matrix...

No.


Wouldn't that create a sea of galvanic corrosion?

Yes and no.



I dunno...I spose it could....

How about reinforcement with another metal?

No.

I often find the simplest answers are best :-)