Nickel titanium
Encyclopedia
Nickel titanium, also known as nitinol, is a metal
alloy
of nickel
and titanium
, where the two elements are present in roughly equal atomic percentages.
Nitinol alloys exhibit two closely related and unique properties: shape memory and superelasticity (also called pseudoelasticity
). Shape memory refers to the ability of nitinol to undergo deformation at one temperature, then recover its original, undeformed shape upon heating above its "transformation temperature". Superelasticity occurs at a narrow temperature range just above its transformation temperature; in this case, no heating is necessary to cause the undeformed shape to recover, and the material exhibits enormous elasticity, some 10-30 times that of ordinary metal.
in 1962.
While the potential applications for nitinol were realized immediately, practical efforts to commercialize the alloy did not take place until a decade later. This delay was largely because of the extraordinary difficulty of melting, processing and machining the alloy. Even these efforts encountered financial challenges that were not really overcome until the 1990s, when these practical difficulties finally began to be resolved.
The discovery of the shape-memory effect in general dates back to 1932 when Swedish researcher Arne Olander first observed the property in gold-cadmium alloys. The same effect was observed in Cu-Zn in the early 1950s.
At high temperatures, nitinol assumes an interpenetrating simple cubic crystal structure referred to as austenite
(also known as the parent phase). At low temperatures, nitinol spontaneously transforms to a more complicated “monoclinic” crystal structure known as martensite
. The temperature at which austenite transforms to martensite is generally referred to as the transformation temperature. More specifically, there are four transition temperatures. When the alloy is fully austenite, martensite begins to form as the alloy cools at the so-called martensite start, or Ms temperature, and the temperature at which the transformation is complete is called the martensite finish, or Mf temperature. When the alloy is fully martensite and is subjected to heating, austenite starts to form at the As temperature, and finishes at the Af temperature.
Crucial to nitinol’s properties are two key aspects of this phase transformation. First is that the transformation is “reversible,” meaning that heating above the transformation temperature will revert the crystal structure to the simpler austenite phase. Upon heating, however, there is a slight upward shift in the temperatures, now beginning at the As temperature, and finishing at the Af temperature. The second key point is that the transformation in both directions is instantaneous.
Martensite's crystal structure (known as a monoclinic, or B19' structure) has the unique ability to undergo limited deformation in some ways without breaking atomic bonds. This type of deformation is known as twinning, which consists of the rearrangement of atomic planes without causing slip, or permanent deformation. It is able to undergo about 6-8% strain in this manner. When martensite is reverted to Austenite by heating, the original austenitic structure is restored, regardless of whether the martensite phase was deformed. Thus the name "shape memory" refers to the fact that the shape of the high temperature austenite phase is "remembered," even though the alloy is severely deformed at a lower temperature.
A great deal of force can be produced by preventing the reversion of deformed martensite to austenite - in many cases, more than 100,000 psi. One of the reasons that nitinol works so hard to return its original shape is that it is not just an ordinary metal alloy, but what is known as an intermetallic compound. In an ordinary alloy, the constituents are randomly positioned on the crystal lattice; in an ordered intermetallic compound, the atoms (in this case, nickel and titanium) have very specific locations in the lattice. The fact that nitinol is an intermetallic is largely responsible for the difficulty in fabricating devices made from the alloy.
The scenario described above (cooling austenite to form martensite, deforming the martensite, then heating to revert to austenite, thus returning the original, undeformed shape) is known as the thermal shape memory effect. A second effect, called superelasticity or pseudoelasticity is also observed in nitinol. This effect is the direct result of the fact that martensite can be formed by applying a stress as well as by cooling. Thus in a certain temperature range, one can apply a stress to austenite, causing martensite to form while at the same time changing shape. In this case, as soon as the stress is removed, the nitinol will spontaneously return to its original shape. In this mode of use, nitinol behaves like a super spring, possessing an elastic range some 10 to 30 times greater than that of a normal spring material. There are, however, constraints: the effect is only observed some 0-40 degrees C above the Af temperature.
Nitinol is typically composed of approximately 50 to 51% nickel by atomic percent (55 to 56% weight percent). Making small changes in the composition can change the transition temperature of the alloy significantly. One can control the Af temperature in nitinol to some extent, but convenient superelastic temperature ranges are from about -20 degrees to +60 degrees C.
One often-encountered complication regarding nitinol is the so-called R-Phase
. The R-Phase is another martensitic phase that competes with the martensite phase mentioned above. Because it does not offer the large memory effects of the martensite phase, it is, more often than not, an annoyance.
While both methods have advantages, there are no substantive data showing that material from one process is better than the other. Other methods are also used on a boutique scale, including plasma arc melting, induction skull melting, and e-beam melting. Physical vapor deposition
is also used on a laboratory scale.
Hot working
of nitinol is relatively easy, but cold working is difficult because the enormous elasticity of the alloy increases die or roll contact, leading to tremendous frictional resistance and tool wear. For similar reasons, machining is extremely difficult—to make things worse, the thermal conductivity of nitinol is poor, so heat is difficult to remove. Grinding (abrasive cutting)
, Electrical discharge machining
(EDM) and laser cutting
are all relatively easy.
Heat treating nitinol is delicate and critical. It is the essential tool in fine-tuning the transformation temperature. Aging time and temperature controls the precipitation of various Ni-rich phases, and thus controls how much nickel resides on the NiTi lattice; by depleting the matrix of nickel, aging increases the transformation temperature. The combination of heat treatment and cold working is essential in controlling the properties of nitinol.
Nitinol is half nickel, and thus there has been a great deal of concern in the medical industry regarding the release of nickel, a known allergen and possible carcinogen. (Nickel is also present in substantial amounts in stainless steel
and cobalt-chrome alloys.) When properly treated (via electropolishing
and/or passivation
), nitinol forms a very stable protective TiO2 layer that acts as a very effective and self-healing barrier against ion exchange. It has been repeatedly shown that nitinol releases nickel at a slower pace than stainless steel, for example. With that said, very early medical devices were made without electropolishing, and corrosion was observed. Today's nitinol vascular self-expandable metallic stent
s, for example, show no evidence of corrosion or nickel release, and the outcomes in patients with and without nickel allergies are indistinguishable.
There are constant and long-running discussions regarding inclusions in nitinol, both TiC and Ti2NiOx. All metals contain inclusions, and nitinol cannot be melted without inclusions—they are omnipresent. The size, distribution and type of inclusions can be controlled to some extent. Theoretically, smaller, rounder and few inclusions should lead to increased fatigue durability. All studies done to date, however, have failed to show measurable differences.
A major limitation to further use of nitinol has been its difficulty to weld, both to itself and other materials. In the past ten years, laser welding nitinol to itself has become a relatively routine process. More recently, strong joints between NiTi wires and stainless steel wires have been made using nickel filler. More research is ongoing into other processes and other metals nitinol can be welded to.
Recent advances have shown that processing of Nitinol can expand thermomechanical capabilities; allowing for multiple shape memories to be embedded within a monolithic structure. Research on multi-memory technology is on-going and promises to deliver enhanced shape memory devices in the near future.
In 1989 a survey was conducted in the United States and Canada that involved seven organizations. The survey focused on predicting the future technology, market, and applications of SMA's. The companies predicted the following uses of nitinol in a decreasing order of importance: (1) Couplings, (2) Biomedical and medical, (3) Toys, demonstration, novelty items, (4) Actuators, (5) Heat Engines, (6) Sensors, (7) Cryogenically activated die and bubble memory sockets, and finally (8) lifting devices.
A process of making parts and forms of Type 60 Nitinol having a shape memory effect, comprising: selecting a Type 60 Nitinol. Inventor G,Julien CEO of Nitinol Technologies, Inc. (Washington State)
Science Digest articles - Miracle Metal 1982 - PDF
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
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...
of nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
and 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....
, where the two elements are present in roughly equal atomic percentages.
Nitinol alloys exhibit two closely related and unique properties: shape memory and superelasticity (also called pseudoelasticity
Pseudoelasticity
Pseudoelasticity, sometimes called superelasticity, is an elastic response to an applied stress, caused by a phase transformation between the austenitic and martensitic phases of a crystal. It is exhibited in shape-memory alloys...
). Shape memory refers to the ability of nitinol to undergo deformation at one temperature, then recover its original, undeformed shape upon heating above its "transformation temperature". Superelasticity occurs at a narrow temperature range just above its transformation temperature; in this case, no heating is necessary to cause the undeformed shape to recover, and the material exhibits enormous elasticity, some 10-30 times that of ordinary metal.
History
The term nitinol is derived from its composition and its place of discovery: (Nickel Titanium Naval Ordnance Laboratory). William J. Buehler along with Frederick Wang, discovered its properties during research at the Naval Ordnance LaboratoryNaval Ordnance Laboratory
The Naval Ordnance Laboratory , now disestablished, formerly located in White Oak, Maryland was the site of considerable work that had practical impact upon world technology. The White Oak site of NOL has now been taken over by the Food and Drug Administration.-History:The U.S...
in 1962.
While the potential applications for nitinol were realized immediately, practical efforts to commercialize the alloy did not take place until a decade later. This delay was largely because of the extraordinary difficulty of melting, processing and machining the alloy. Even these efforts encountered financial challenges that were not really overcome until the 1990s, when these practical difficulties finally began to be resolved.
The discovery of the shape-memory effect in general dates back to 1932 when Swedish researcher Arne Olander first observed the property in gold-cadmium alloys. The same effect was observed in Cu-Zn in the early 1950s.
How it works
Nitinol's unusual properties are derived from a reversible, solid state phase transformation known as a martensitic transformation.At high temperatures, nitinol assumes an interpenetrating simple cubic crystal structure referred to as austenite
Austenite
Austenite, also known as gamma phase iron, is a metallic non-magnetic allotrope of iron or a solid solution of iron, with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of ; other alloys of steel have different eutectoid temperatures...
(also known as the parent phase). At low temperatures, nitinol spontaneously transforms to a more complicated “monoclinic” crystal structure known as martensite
Martensite
Martensite, named after the German metallurgist Adolf Martens , most commonly refers to a very hard form of steel crystalline structure, but it can also refer to any crystal structure that is formed by displacive transformation. It includes a class of hard minerals occurring as lath- or...
. The temperature at which austenite transforms to martensite is generally referred to as the transformation temperature. More specifically, there are four transition temperatures. When the alloy is fully austenite, martensite begins to form as the alloy cools at the so-called martensite start, or Ms temperature, and the temperature at which the transformation is complete is called the martensite finish, or Mf temperature. When the alloy is fully martensite and is subjected to heating, austenite starts to form at the As temperature, and finishes at the Af temperature.
Crucial to nitinol’s properties are two key aspects of this phase transformation. First is that the transformation is “reversible,” meaning that heating above the transformation temperature will revert the crystal structure to the simpler austenite phase. Upon heating, however, there is a slight upward shift in the temperatures, now beginning at the As temperature, and finishing at the Af temperature. The second key point is that the transformation in both directions is instantaneous.
Martensite's crystal structure (known as a monoclinic, or B19' structure) has the unique ability to undergo limited deformation in some ways without breaking atomic bonds. This type of deformation is known as twinning, which consists of the rearrangement of atomic planes without causing slip, or permanent deformation. It is able to undergo about 6-8% strain in this manner. When martensite is reverted to Austenite by heating, the original austenitic structure is restored, regardless of whether the martensite phase was deformed. Thus the name "shape memory" refers to the fact that the shape of the high temperature austenite phase is "remembered," even though the alloy is severely deformed at a lower temperature.
A great deal of force can be produced by preventing the reversion of deformed martensite to austenite - in many cases, more than 100,000 psi. One of the reasons that nitinol works so hard to return its original shape is that it is not just an ordinary metal alloy, but what is known as an intermetallic compound. In an ordinary alloy, the constituents are randomly positioned on the crystal lattice; in an ordered intermetallic compound, the atoms (in this case, nickel and titanium) have very specific locations in the lattice. The fact that nitinol is an intermetallic is largely responsible for the difficulty in fabricating devices made from the alloy.
The scenario described above (cooling austenite to form martensite, deforming the martensite, then heating to revert to austenite, thus returning the original, undeformed shape) is known as the thermal shape memory effect. A second effect, called superelasticity or pseudoelasticity is also observed in nitinol. This effect is the direct result of the fact that martensite can be formed by applying a stress as well as by cooling. Thus in a certain temperature range, one can apply a stress to austenite, causing martensite to form while at the same time changing shape. In this case, as soon as the stress is removed, the nitinol will spontaneously return to its original shape. In this mode of use, nitinol behaves like a super spring, possessing an elastic range some 10 to 30 times greater than that of a normal spring material. There are, however, constraints: the effect is only observed some 0-40 degrees C above the Af temperature.
Nitinol is typically composed of approximately 50 to 51% nickel by atomic percent (55 to 56% weight percent). Making small changes in the composition can change the transition temperature of the alloy significantly. One can control the Af temperature in nitinol to some extent, but convenient superelastic temperature ranges are from about -20 degrees to +60 degrees C.
One often-encountered complication regarding nitinol is the so-called R-Phase
R-Phase
The R-Phase is a phase found in Nitinol. It is a martensitic phase in nature, but is not "the" martensite that is responsible for the shape memory and superelastic effect. When one uses the word martensite in connection with Nitinol, one is invariably referring to the B19' monoclinic martensite...
. The R-Phase is another martensitic phase that competes with the martensite phase mentioned above. Because it does not offer the large memory effects of the martensite phase, it is, more often than not, an annoyance.
Making nitinol and nitinol devices
Nitinol is exceedingly difficult to make due to the exceptionally tight compositional control required, and the tremendous reactivity of titanium. Every atom of titanium that combines with oxygen or carbon is an atom that is robbed from the NiTi lattice, thus shifting the composition and making the transformation temperature that much colder. There are two primary melting methods used today:- Vacuum Arc RemeltingVacuum Arc RemeltingVacuum arc remelting is a secondary melting process for production of metal ingots with elevated chemical and mechanical homogeneity for highly demanding applications...
: This is done by striking an electrical arc between the raw material and a water-cooled copper strike plate. Melting is done in a high vacuum, and the mold itself is water-cooled copper, so no carbon is introduced during melting.
- Vacuum Induction MeltingVacuum Induction MeltingVacuum induction melting is a process for melting metal under vacuum conditions using electromagnetic induction. It works by creating electrical eddy currents in the metal which heats the "charge" to melt it...
: This is done by using alternating magnetic fields to heat the raw materials in a crucible (generally carbon). This is also done in a high vacuum, but carbon is introduced during the process.
While both methods have advantages, there are no substantive data showing that material from one process is better than the other. Other methods are also used on a boutique scale, including plasma arc melting, induction skull melting, and e-beam melting. Physical vapor deposition
Physical vapor deposition
Physical vapor deposition is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin films by the condensation of a vaporized form of the desired film material onto various workpiece surfaces...
is also used on a laboratory scale.
Hot working
Hot working
Hot working refers to processes where metals are plastically deformed above their recrystallization temperature. Being above the recrystallization temperature allows the material to recrystallize during deformation. This is important because recrystallization keeps the materials from strain...
of nitinol is relatively easy, but cold working is difficult because the enormous elasticity of the alloy increases die or roll contact, leading to tremendous frictional resistance and tool wear. For similar reasons, machining is extremely difficult—to make things worse, the thermal conductivity of nitinol is poor, so heat is difficult to remove. Grinding (abrasive cutting)
Grinding (abrasive cutting)
Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.A wide variety of machines are used for grinding:* Hand-cranked knife-sharpening stones * Handheld power tools such as angle grinders and die grinders...
, Electrical discharge machining
Electrical discharge machining
Electric discharge machining , sometimes colloquially also referred to as spark machining, spark eroding, burning, die sinking or wire erosion, is a manufacturing process whereby a desired shape is obtained using electrical discharges...
(EDM) and laser cutting
Laser cutting
Laser cutting is a technology that uses a laser to cut materials, and is typically used for industrial manufacturing applications, but is also starting to be used by schools, small businesses and hobbyists. Laser cutting works by directing the output of a high-power laser, by computer, at the...
are all relatively easy.
Heat treating nitinol is delicate and critical. It is the essential tool in fine-tuning the transformation temperature. Aging time and temperature controls the precipitation of various Ni-rich phases, and thus controls how much nickel resides on the NiTi lattice; by depleting the matrix of nickel, aging increases the transformation temperature. The combination of heat treatment and cold working is essential in controlling the properties of nitinol.
Hot topics
Fatigue failures of nitinol devices are a constant subject of discussion. Because it is the material of choice for applications requiring enormous flexibility and motion (e.g., peripheral stents and heart valves), it is necessarily exposed to much greater fatigue strains than are other metals. While the strain controlled fatigue performance of nitinol is superior to all other known metals, fatigue failures have been observed in the most demanding applications. There is a great deal of effort underway trying to better understand and define the durability limits of nitinol.Nitinol is half nickel, and thus there has been a great deal of concern in the medical industry regarding the release of nickel, a known allergen and possible carcinogen. (Nickel is also present in substantial amounts in stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
and cobalt-chrome alloys.) When properly treated (via electropolishing
Electropolishing
Electropolishing, also known as electrochemical polishing or electrolytic polishing , is an electrochemical process that removes material from a metallic workpiece. It is used to polish, passivate, and deburr metal parts. It is often described as the reverse of electroplating...
and/or passivation
Passivation
Passivation is the process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. Passivation of metals is usually achieved by the deposition of a layer of oxide...
), nitinol forms a very stable protective TiO2 layer that acts as a very effective and self-healing barrier against ion exchange. It has been repeatedly shown that nitinol releases nickel at a slower pace than stainless steel, for example. With that said, very early medical devices were made without electropolishing, and corrosion was observed. Today's nitinol vascular self-expandable metallic stent
Self-expandable metallic stent
A self-expandable metallic stent is a metallic tube, or stent, used in order to hold open a structure in the gastrointestinal tract in order to allow the passage of food, chyme, stool, or other secretions required for digestion...
s, for example, show no evidence of corrosion or nickel release, and the outcomes in patients with and without nickel allergies are indistinguishable.
There are constant and long-running discussions regarding inclusions in nitinol, both TiC and Ti2NiOx. All metals contain inclusions, and nitinol cannot be melted without inclusions—they are omnipresent. The size, distribution and type of inclusions can be controlled to some extent. Theoretically, smaller, rounder and few inclusions should lead to increased fatigue durability. All studies done to date, however, have failed to show measurable differences.
A major limitation to further use of nitinol has been its difficulty to weld, both to itself and other materials. In the past ten years, laser welding nitinol to itself has become a relatively routine process. More recently, strong joints between NiTi wires and stainless steel wires have been made using nickel filler. More research is ongoing into other processes and other metals nitinol can be welded to.
Recent advances have shown that processing of Nitinol can expand thermomechanical capabilities; allowing for multiple shape memories to be embedded within a monolithic structure. Research on multi-memory technology is on-going and promises to deliver enhanced shape memory devices in the near future.
Applications
There are four commonly used types of applications for nitinol.- Free Recovery: nitinol is deformed at a low temperature, and heated to recover its original shape.
- Constrained Recovery: The same, except that recovery is rigidly prevented, and thus a stress is generated.
- Work Production: Here the alloy is allowed to recover, but to do so it must act against a force (thus doing work).
- Superelasticity: As discussed above, here the nitinol acts as a super spring.
In 1989 a survey was conducted in the United States and Canada that involved seven organizations. The survey focused on predicting the future technology, market, and applications of SMA's. The companies predicted the following uses of nitinol in a decreasing order of importance: (1) Couplings, (2) Biomedical and medical, (3) Toys, demonstration, novelty items, (4) Actuators, (5) Heat Engines, (6) Sensors, (7) Cryogenically activated die and bubble memory sockets, and finally (8) lifting devices.
- In colorectal surgery http://www.nitisurgical.com/patient_education.htm, the material is used in devices for reconnecting the intestine after removing the pathology.
- In dentistry, the material is used in orthodonticsOrthodonticsOrthodontics, orthodontia, or orthodonture is the first specialty of dentistry that is concerned with the study and treatment of malocclusions , which may be a result of tooth irregularity, disproportionate jaw relationships, or both...
for brackets and wires connecting the teeth. SuresmileSuresmileSureSmile is a type of braces used by orthodontists to straighten teeth. With SureSmile the orthodontist combines 3-D imaging, treatment planning software and a robot to create the wires. The technique is reported in The World Journal of Orthodontics to decrease the time required to complete...
is one example of an orthodontic application. Once the SMA is placed in the mouth its temperature rises to ambient body temperature. This causes the nitinol to contract back to its original shape applying a constant force to move the teeth. These SMA wires don't need to be retightened as often as they can contract as the teeth move unlike conventional stainless steel wires. Additionally, nitinol can be used in endodonticsEndodonticsEndodontics is one of the dental specialties recognized by the American Dental Association, Royal College of Dentists of Canada, and Royal Australasian College of Dental Surgeons, and deals with the tooth pulp and the tissues surrounding the root of a tooth...
, where nitinol files are used to clean and shape the root canals during the root canalRoot canalA root canal is the space within the root of a tooth. It is part of a naturally occurring space within a tooth that consists of the pulp chamber , the main canal, and more intricate anatomical branches that may connect the root canals to each other or to the surface of the root.-Root canal anatomy:...
procedure. - Due to the fact it can change shapes it is also used as a golf clubGolf 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...
insert. - Another significant application of nitinol in medicine is in stentStentIn the technical vocabulary of medicine, a stent is an artificial 'tube' inserted into a natural passage/conduit in the body to prevent, or counteract, a disease-induced, localized flow constriction. The term may also refer to a tube used to temporarily hold such a natural conduit open to allow...
s: A collapsed stent can be inserted into a vein and heated (returning to its original expanded shape) helping to improve blood flow. Also, as a replacement for sutures where nitinol wire can be weaved through two structures then allowed to transform into its preformed shape which should hold the structures in place. - Nitinol is highly biocompatibleNitinol BiocompatibilityMetal implants containing a combination of biocompatible metals or used in conjunction with other biomaterials are often considered the standard for many implant types. When materials are introduced to the body it is important not only that the material does not damage the body, but also that the...
and has properties suitable for use in orthopaedic implants. - Nitinol is also popular in extremely resilient glasses frames. It is also used in some mechanical watch springs.
- It can be used as a temperature control system; as it changes shape, it can activate a switch or a variable resistor to control the temperature.
- It is used in cell-phone technology as a retractible antenna, or microphone boom, due to its highly flexible & mechanical memory nature.
- It is used in some novelty products, such as self-bending spoonsSpoon bendingSpoon bending is the apparent deformation of objects, especially metal cutlery, either without physical force, or with less force than normally necessary...
which can be used by amateur and stage magicians to demonstrate "psychic" powers or as a practical jokePractical jokeA practical joke is a mischievous trick played on someone, typically causing the victim to experience embarrassment, indignity, or discomfort. Practical jokes differ from confidence tricks in that the victim finds out, or is let in on the joke, rather than being fooled into handing over money or...
, as the spoon will bend itself when used to stir tea, coffee, or any other warm liquid. - It can also be used as wires which are used to locate and mark breast tumours so that following surgery can be more exact.
- Nickel titanium can be used to make the underwires for underwire braUnderwire braAn underwire bra is a brassiere with a wire built into the underside of the cup intended to lift, separate, shape, and provide additional support for a woman's breasts...
s. - Demonstration model heat engineHeat engineIn thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...
s have been built which use nitinol wire to produce mechanical energy from hot a cold heat sources.
Further reading
- H.R. Chen, ed., Shape Memory Alloys: Manufacture, Properties and Applications, Nova Science Publishers Inc., 2010, ISBN 978-1-60741-789-7.
- Y.Y. Chu & L.C. Zhao, eds., Shape Memory Materials and Its [sic] Applications, Trans Tech Publications Ltd., 2002, ISBN 0-87849-896-6.
- D.C. Lagoudas, ed., Shape Memory Alloys, Springer Science+Business Media LLC, 2008, ISBN 978-0-387-47684-1.
- K. Otsuka & C.M. Wayman, eds., Shape Memory Materials, Cambridge University Press, 1998, ISBN 0-521-44487-*
- Gerald Julien, Nitinol Technologies,Inc Edgewood, Wa. Us patent" 6422010 Manufacturing of Nitinol Parts & Forms
A process of making parts and forms of Type 60 Nitinol having a shape memory effect, comprising: selecting a Type 60 Nitinol. Inventor G,Julien CEO of Nitinol Technologies, Inc. (Washington State)
External links
- Society of Shape Memory and Superelastic Technologies
- Nitinol Resource Library
- Physical properties of nitinol
- Nitinol technology
- Nitinol Technical Resource Library
- Literature on Nitinol Wire
Science Digest articles - Miracle Metal 1982 - PDF
- http://www.colorsproject.com/nitinol_articles_science_digest_1982_sanders.pdf