As the proud owner of my very own personalised Liquidmetal USB stick, made back in 2008, I was thrilled to hear this extraordinary material mentioned at the MMTA’s recent conference. Liquidmetal, a name straight out of the Terminator films, is, however, unlikely to be used to make the time travelling cyborgs of the movies.
My USB stick dates back to my undergraduate placement year for a well-known car manufacturer, where I was working on a project to make small, complex components directly out of metal rather than making plastic components and then coating the exposed surfaces with zinc and chrome. At that time, the most well-known uses of this material were in golf clubs, baseball bats and other sporting equipment. Unfortunately, Liquidmetal had some well publicised issues with impact brittleness and some rather impressive failures after a certain number of hits. These public failures resulted in the business going into substantial debt.
Since then, the consumer electronics market has been the main growth area for Liquidmetal. For example the SanDisk Cruzer Titanium USB drives, with the slide-out connector, is not made of titanium, but rather Liquidmetal. This type of small, complex part is ideally suited to this metal, an alloy of zirconium, titanium, copper, nickel, and aluminium.
As mentioned, the driver for my own research project was the processing characteristics of this metal, the key quality that makes it interesting to materials engineers looking to design innovative metal parts and to fabricate them more simply than with traditional metalworking technologies.
The positive characteristics of Liquidmetal:
- Exceptional dimensional control and repeatability
- Excellent corrosion resistance
- Brilliant surface finish
- High strength
- High elastic limit
- High hardness, scratch & wear resistance
- Complex shapes that can be moulded
However, it looks like there will soon only be one company using Liquidmetal in its electronic parts: Apple. Rumour has it that, as well as the iPhone 7 having a longer battery life, potentially a water-resistant cover and the elimination of antenna lines, the chassis may be made of Liquidmetal. A very small quantity of Liquidmetal will be used in place of the aluminium currently used in older phones to achieve the same degree of strength but with less weight, keeping the iPhone 7 thin and light.
Apple has gone to the effort of purchasing the rights to Liquidmetal, so it cannot be used by others in the consumer electronics industry, so it seems likely that they have big plans for the material. It is important to note that Apple will be able to license the material to other industries and applications.
Why is Liquidmetal different from other metals?
When conventional metal alloys cool from their molten state to a solid, atoms naturally form a crystalline structure consisting of many small crystalline grains (see diagram below) The specific ratio of elements slows crystallization. When cooled quickly enough, the alloy solidifies in an amorphous (glass-like) state, precluding crystallization. As a result, the alloy retains the extremely dense amorphous atomic structure that characterizes glass and gives Liquidmetal alloys their mechanical and chemical properties. Perhaps a more appropriate description of Liquidmetal is bulk metallic glass.
As well as its positive forming characteristics, there are some negatives too. There is the impact brittleness we have already touched upon, but there is also a gradual loss of integrity at high temperatures rather than a set melting temperature. Liquidmetal is far from the only bulk metallic glass, with any number of alloys processed in the correct way being able to form an amorphous structure. The key is to cool the alloy extremely quickly.
What makes Liquidmetal special compared to other amorphous alloys is that it is easier to make. To simplify, it doesn’t need to be cooled as quickly as other similar materials, meaning the process is cheaper and easier, and greater quantities can be produced.
What is Liquidmetal like?
From the images, Liquidmetal looks very much like a regular metal, and more the colour of steel than aluminium. Look closely and you will see polished areas which could be used to make the whole part shiny if required. In USB form, If you were to bend a thin piece of Liquidmetal, it would feel more flexible than steel or aluminium, but will reach a point where it suddenly becomes very difficult to deform further.
Experiments with Liquidmetal
This material does lend itself well to exciting experiments!
NASA are generally quite keen on Liquidmetal, having used it in several projects, as well as publishing a report following experimentation on the material.
In one experiment, three marble-sized balls made of steel were dropped from the same height into their own glass tubes. Each tube had a different type of metal plate at the bottom: steel, titanium, and Liquidmetal. Once each ball was dropped, they were left to bounce. The balls hitting the steel and titanium plates bounced for 20 to 25 seconds. The ball hitting the Liquidmetal plate bounced for 1 minute and 21 seconds! During the experiment, this was also the only ball that bounced right out of its tube.
In another experiment (not performed by NASA!), a Porsche was driven over a Liquidmetal component causing no damage.
It seems that although technically a very interesting material, Liquidmetal’s main uses (ignoring its golf club application that actually did offer mechanical advantages before the shattering moment) have been as ‘premium’ or ‘luxury’ additions to a product, similar to the use of the word ‘titanium’ in many unnecessary products (which often don’t even contain any titanium).
The incredibly expensive luxury phone brand Vertu, was at one time made of Liquidmetal. (The price is mostly due to the 24hr concierge service included)
Current iPhone Application
So what essential and critical part is currently made of Liquidmetal on the iPhone? Yes, the SIM card ejector pin.
It seems an unusual choice, but it does prove that there is a factory somewhere with the ability to make millions of Liquidmetal components, making the iPhone 7 rumours about Liquidmetal having a more prominent use both more credible and practically achievable.
In an ideal materials world, Liquidmetal would be used as a hard, non-deforming, non-corroding and generally scratch resistant case.
Plastics are flexible but not strong, and while metals are much stronger than plastics, they’re not as flexible. Liquidmetal alloys can provide a more durable casing than plastic, which is much more resistant to dents, nicks, scratches and breakage.
Liquidmetal is useful anywhere you could imagine an extremely hard, somewhat flexible, easily mouldable component to be useful. It is conceivable that Apple will soon also be in business with the military, aerospace companies, and deep-sea drilling companies, as they have the ability to now license this material out to these types of industries (all of which have used or researched Liquidmetal in the past).
Liquid metal in the Terminator Films… Not to be confused with the branded Liquidmetal alloy!
In the Terminator 2 storyline, the T-1000 cyborg is made of liquid metal. T-1000 is a more advanced Terminator than the first film, and is composed entirely of a ‘mimetic polyalloy’, rendering it capable of rapid shapeshifting, near-perfect mimicry and rapid recovery from damage. Furthermore, it can use its ability to quickly liquify and assume forms in innovative and surprising ways, including fitting through narrow openings, morphing its arms into solid metal tools or bladed weapons, walking through prison bars, and flattening itself and capable of imitating the pattern and texture of the ground to hide or ambush targets.
The polyalloy cannot function unless it is programmed with specific instructions or controlled. The mimetic polyalloy can harden as solid as any steel.
The mimetic polyalloy can be destroyed by the following factors:
Temperatures in excess of 1535 degrees Celsius, such as those needed to smelt iron, could permanently alter the bonding processes of the mimetic polyalloy. The molten iron (or any other element) could then mix with the elements of the alloy and physically alter its molecular structure, thus rendering it inoperative. High temperatures added with collision damage, such as a crashing helicopter, can also destroy the mimetic polyalloy.
When a T-1000 is exposed to liquid nitrogen, it freezes its morphing processes long enough for an enemy to shatter it with a single gunshot. The effect is only temporary; heat can thaw the scattered fragments and the T-1000 is able to reform itself.
A T-X can be temporarily incapacitated by charging up a particle accelerator and triggering a magnetic field. The mimetic polyalloy is pulled from the metallic endoskeleton by the magnetic field.
Tamara Alliot, MMTA