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Liquidmetal

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Liquidmetal and Vitreloy are commercial names of a series of amorphous metal
Amorphous metal
An amorphous metal is a metallic material with a disordered atomic-scale structure. In contrast to most metals, which are crystalline and therefore have a highly ordered arrangement of atoms, amorphous alloys are non-crystalline...

 alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

s developed by a California Institute of Technology
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...

 research team, now marketed by a firm that the team organized called Liquidmetal Technologies. Despite the name they are not liquid, but solid at room temperature, and the maker claims they are hard wearing and withstand thermal cycling. Liquidmetal alloys combine a number of desirable material features, including high tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

, excellent corrosion resistance, very high coefficient of restitution
Coefficient of restitution
The coefficient of restitution of two colliding objects is a fractional value representing the ratio of speeds after and before an impact, taken along the line of the impact...

 and excellent anti-wearing characteristics, while also being able to be heat-formed in processes similar to thermoplastic
Thermoplastic
Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...

s. Liquidmetal was introduced for commercial applications in 2003. It is used for, among other things, golf club
Golf club (equipment)
A golf club is used to hit a golf ball in a game of golf. Each club is composed of a shaft with a grip and a clubhead. Woods are mainly used for long-distance fairway or tee shots; irons, the most versatile class, are used for a variety of shots; Hybrids that combine design elements of woods and...

s, watch
Watch
A watch is a small timepiece, typically worn either on the wrist or attached on a chain and carried in a pocket, with wristwatches being the most common type of watch used today. They evolved in the 17th century from spring powered clocks, which appeared in the 15th century. The first watches were...

es and covers of cell phones.

Background


The qualities of Liquidmetal can be discussed by comparing the alloy to the common metal iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

. Iron has a relatively large atom, which forms into an open crystal structure given the proper conditions. The atoms can "slide" along the planes of the structure, meaning that pure iron is fairly ductile, while still being very strong in tension. To improve the strength of iron, impurities can be added to "lock in" the structure to prevent it from sliding. The most common alloying agent is carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, which results in steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

.

When steel solidifies from a liquid after being smelted
Smelting
Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...

, it starts to form small crystals of various forms. These crystals grow until they come into contact with other crystals seeded at other points, which have different orientations, and sometimes different mechanical arrangements. When the process is complete, these crystals form a large lattice structure of individual "grains", which are sometimes visible to the naked eye.

Although the alloying process prevents the sort of sliding motions of pure iron, the inter-grain strength is fairly low compared to the strength of the bonds inside the grains. This leads to another form of ductility where the grains themselves slide along their boundaries, or the grains are broken apart from each other. Mechanical cracks formed during the cooling process are another source of potential weakness. Under repeated loading the grains can be forced apart and the cracks forced open; this process, known as crack propagation, leads to metal fatigue
Metal Fatigue
Metal Fatigue , is a futuristic science fiction, real-time strategy computer game developed by Zono Incorporated and published by Psygnosis and TalonSoft .-Plot:...

.

Numerous processes can be used to reduce this problem. Wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...

 is repeatedly worked to mechanically force these cracks shut during the forming of an item such as a horse shoe, and the famed Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

ese katana
Katana
A Japanese sword, or , is one of the traditional bladed weapons of Japan. There are several types of Japanese swords, according to size, field of application and method of manufacture.-Description:...

 swords use a similar process to produce high quality steels. More modern techniques like cold rolling and forging
Forging
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: '"cold," "warm," or "hot" forging. Forged parts can range in weight from less than a kilogram to 580 metric tons...

 are able to remove these imperfections on industrial scales. Alternately it is possible to grow single very large crystals that are free from such inter-grain boundaries by definition, but these processes are slow, energy intensive, and fairly expensive. Such materials are typically limited to aerospace roles, for instance the blades of turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

s in jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

s which are subject to repeated heat cycling, which is a perfect environment for causing metal fatigue.

Molten metals generally have fairly low viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 and flow easily, but this has disadvantages as well as advantages in terms of the sorts of casting processes that can be used. There are limitations on the complexity of shapes that can be formed in metal casting. Most metals shrink as they cool, which means that they have to be finished after casting to obtain a quality surface, because they do not remain in contact with the mold as the metal cools. Cast metals retain the mechanical imperfections that the forging and rolling processes remove, making them considerably less strong. Metals are simply not ideal for forming complex shapes except for machining and other post-forming processes, which are more expensive and time consuming.

Most of the "problems" with metals are a side effect of their crystalline structure, so producing a non-crystalline amorphous metal would solve many of them. Crystal growth in a cooling mass of metal is strongly favored, so using any sort of "normal" process will lead to crystal formation. A variety of methods can be used to quickly chill the metal before this can take place, but these are suitable only for small batches.

By comparison, thermoplastics are highly viscous in their molten state and have no crystalline structure, and avoid these difficulties. Although they are far less strong than steel, about fifty times less, they can be easily formed into complex shapes and retain a good finish. They can be created from raw materials and formed into a product in a continuous process, something that metals cannot generally match.

Vitreloy


Vitreloy was the end result of a long research program into amorphous metals carried out at Caltech. It was the first of a series of experimental alloys that could achieve an amorphous structure at relatively slow cooling rates. Amorphous metals had been made before, but only in small batches because cooling rates needed to be in the millions of degrees per second. For example, amorphous wires could be fabricated by splat cooling a stream of molten metal on a spinning disk. Because Vitreloy allowed such slow cooling rates, production of larger batch sizes was possible. More recently, a number of additional alloys have been added to the Liquidmetal portfolio. These alloys also retain their amorphous structure after repeated re-heating, allowing them to be used in a wide variety of traditional machining processes.

Liquidmetal alloys contain atoms of significantly different sizes. They form a dense mix with low free volume. Unlike crystalline metals, there is no obvious melting point at which viscosity drops suddenly. Vitreloy behaves more like other glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

es, in that its viscosity drops gradually with increased temperature. At high temperature, it behaves in a plastic manner, allowing the mechanical properties to be controlled relatively easily during casting. The viscosity prevents the atoms moving enough to form an ordered lattice, so the material retains its amorphous properties even after being heat-formed.

The alloys have relatively low softening temperatures, allowing casting of complicated shapes without need of finishing. The material properties immediately after casting are much better than of conventional metals; usually, cast metals have worse properties than forged or wrought ones. The alloys are also malleable at low temperatures (400 °C (752 °F) for the earliest formulation), and can be molded
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....

. The low free volume also results in low shrinkage during cooling. For all of these reasons, Liquidmetal can be formed into complex shapes using processes similar to thermoplastics, which makes Liquidmetal a potential replacement for many applications where plastics would normally be used.

Due to their non-crystalline (amorphous) structures, Liquidmetals are harder than alloys of titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

 or aluminum used in similar applications. The zirconium and titanium based Liquidmetal alloys achieved yield strength
Yield (engineering)
The yield strength or yield point of a material is defined in engineering and materials science as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed...

 of over 1723 MPa, nearly twice the strength of conventional crystalline titanium alloys (Ti6Al4V is ~830 MPa), and about the strength of high-strength steels and some highly engineered bulk composite material
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...

s (see tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

 for a list of common materials). However, the early casting methods introduced microscopic flaws that were excellent sites for crack propagation, and led to Vitreloy being fragile, like glass. Although strong, these early batches could easily be shattered if struck. Newer casting methods, adjustment to the alloy mixtures and other changes have improved this.

The lack of grain boundaries may contribute to the high coefficient of restitution (close to 1) these alloys exhibit. In a demonstration, ball bearing
Ball bearing
A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races.The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit...

s dropped on plates of metal will bounce three times as long on Liquidmetal.

The lack of grain boundaries in a metallic glass eliminates grain-boundary corrosion — a common problem in high-strength alloys produced by precipitation hardening and sensitized stainless steels. Liquidmetal alloys are therefore generally more corrosion resistant, both due to the mechanical structure as well as the elements used in its alloy. The combination of mechanical hardness, high elasticity and corrosion resistance makes Liquidmetal wear resistant.

Although at high temperatures, plastic deformation occurs easily, almost none occurs at temperature before onset of catastrophic failure
Catastrophic failure
A catastrophic failure is a sudden and total failure of some system from which recovery is impossible. Catastrophic failures often lead to cascading systems failure....

. This limits the material's applicability in reliability-critical applications, as the impending failure is not evident. The material is also susceptible to metal fatigue with crack growth; a two-phase composite structure with amorphous matrix and a ductile dendritic crystalline-phase reinforcement, or a metal matrix composite
Metal matrix composite
A metal matrix composite is composite material with at least two constituent parts, one being a metal. The other material may be a different metal or another material, such as a ceramic or organic compound. When at least three materials are present, it is called a hybrid composite...

 reinforced with fibers of other material can reduce or eliminate this disadvantage.

Uses


Liquidmetal combines a number of features that are normally not found in any one material. This makes them useful in a wide variety of applications.

One of the first commercial uses of Liquidmetal was in golf clubs made by the company, where the highly elastic metal was used in portions of the face of the club. These were highly rated by users, but the product was later dropped, in part because the prototypes shattered after fewer than 40 hits. Since then, Liquidmetal has appeared in other sports equipment, including the cores of golf ball
Golf ball
A golf ball is a ball designed to be used in the game of golf.Under the Rules of Golf, a golf ball weighs no more than 1.620 oz , has a diameter not less than 1.680 in , and performs within specified velocity, distance, and symmetry limits...

s, ski
Ski
A ski is a long, flat device worn on the foot, usually attached through a boot, designed to help the wearer slide smoothly over snow. Originally intended as an aid to travel in snowy regions, they are now mainly used for recreational and sporting purposes...

s, baseball
Baseball bat
A baseball bat is a smooth wooden or metal club used in the game of baseball to hit the ball after the ball is thrown by the pitcher. It is no more than 2.75 inches in diameter at the thickest part and no more than 42 inches in length. It typically weighs no more than 33 ounces , but it...

 and softball bats, and tennis racquets.

The ability to be cast and molded, combined with high wear
Wear
In materials science, wear is erosion or sideways displacement of material from its "derivative" and original position on a solid surface performed by the action of another surface....

 resistance, has also led to Liquidmetal being used as a replacement for plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

s in some applications. It has been used on the casing of a late-model SanDisk
SanDisk
SanDisk Corporation is an American multinational corporation that designs, develops and manufactures data storage solutions in a range of form factors using the flash memory, controller and firmware technologies. It was founded in 1988 by Dr. Eli Harari and Sanjay Mehrotra, non-volatile memory...

 "Cruzer Titanium" USB flash drive
USB flash drive
A flash drive is a data storage device that consists of flash memory with an integrated Universal Serial Bus interface. flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g...

s as well as their Sansa
SanDisk Sansa
The SanDisk Sansa is a line of 2 to 16 gigabyte flash memory-based digital audio players and portable media players produced by SanDisk.- Sansa Fuze+:...

 line of flash
Flash memory
Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...

-based MP3 player, and casings of some mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...

s, like the luxury Vertu
Vertu (company)
Vertu is a British-based manufacturer and retailer of luxury mobile phones. Formerly a wholly owned subsidiary, the business is now an independently run division of the Finnish mobile phone manufacturer Nokia.- Concept :...

 products, and other toughened consumer electronics. Liquidmetal has also notably been used for making the SIM ejector tool of some iPhone
IPhone
The iPhone is a line of Internet and multimedia-enabled smartphones marketed by Apple Inc. The first iPhone was unveiled by Steve Jobs, then CEO of Apple, on January 9, 2007, and released on June 29, 2007...

 3Gs made by Apple Inc., shipped in the US. This was done by Apple as an exercise to test the viability of usage of the metal. They retain a scratch-free surface longer than competing materials, while still being made in complex shapes. The same qualities lend it to be used as protective coatings for industrial machinery, including petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

 drill pipes
Drill string
A drill string on a drilling rig is a column, or string, of drill pipe that transmits drilling fluid and torque to the drill bit. The term is loosely applied as the assembled collection of the drill pipe, drill collars, tools and drill bit...

 and power plant
Thermal power station
A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this...

 boiler tubes
Water-tube boiler
A water tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes...

.

It is also considered as a replacement of titanium in applications ranging from medical instruments and cars to military and aerospace industry. In military applications, rods of amorphous metals are considered as a replacement of depleted uranium
Depleted uranium
Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...

 in kinetic energy penetrator
Kinetic energy penetrator
A kinetic energy penetrator is a type of ammunition which, like a bullet, does not contain explosives and uses kinetic energy to penetrate the target....

s. Plates of Liquidmetal were used in the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

 ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

 collector array in the Genesis space probe
Genesis (spacecraft)
The Genesis spacecraft was a NASA sample return probe which collected a sample of solar wind and returned it to Earth for analysis. It was the first NASA sample return mission to return material since the Apollo Program, and the first to return material from beyond the orbit of the Moon...

.

Although Liquidmetal has very high strength and an excellent strength to weight ratio, its commercial success as a structural material may be limited. Work continues on amorphous iron-based alloys that would combine at least some of the advantages of Liquidmetal with even greater strength, estimated to be two to three times the strength of the best steels made today. This would give such an alloy a strength to weight ratio that would easily beat the best lightweight materials such as aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 or titanium, and be much less expensive than composite materials.

Commercial alloys


A range of zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...

-based alloys have been marketed under this trade name. Some example compositions are listed below, in molar percent:
  • An early alloy, Vitreloy 1:
: 41.2 : 22.5 : 13.8 : 12.5 : 10
  • A variant, Vitreloy 4, or Vit4:
: 46.75 : 27.5 : 8.25 : 7.5 : 10
  • Vitreloy 105, or Vit105:
: 52.5 : 5 : 17.9 : 14.6 :10
  • A more recent development (Vitreloy 106a), which forms glass under less rapid cooling:
: 58.5 : 15.6 : 12.8 : 10.3 : 2.8

Business facts


Various news media reported
"Liquidmetal Technologies Inc., a Caltech spinoff in Rancho Santa Margarita, Calif., filed a regulatory notice recently that it's granted Apple a perpetual, exclusive license to use its technology in consumer electronics. Liquidmetal retains the rights for other applications."
"Liquidmetal Technologies Inc. and The Swatch Group Ltd. announced that they have dropped an exclusive licensing agreement, allowing the Swiss watches manufacturer to utilize the Liquidmetal alloy technology worldwide."

External links