Nickel Titanium Alloy-Nitinol - Heanjia Super-metals Co., Ltd.

Learning Gallery

Nickel Titanium Alloy-Nitinol

Nickel titanium Alloy

Introduction

Nickel titanium, also known as nitinol, is a metal of 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 super-elasticity (also called pseudo-elasticity). Shape memory refers to the ability of Nitinol to undergo deformation at one temperature, and 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.

Nitinol's extraordinary ability to accommodate large strains, coupled with its physiological and chemical compatibility with the human body has made it one of the most commonly used materials in medical device engineering and design.

History

The term Nitinol is derived from its composition and its place of discovery: (Nickel Titanium Naval Ordnance Laboratory). William Buehler along with Frederick Wang, discovered its properties during research at the Naval Ordnance Laboratory in 1962.

While the potential applications for Nitinol were realized immediately, practical efforts to commercialize the alloy didn't take place until a decade later.

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 (also known as the parent phase). At low temperatures, Nitinol spontaneously transforms to a more complicated "monoclicic" crystal structure known as martensite. 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.

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.

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.

The effect of Nitinol composition on the Ms temperature.

The scenario described above (cooling austenite to form martensite, deforming the martensite, and 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.

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.

Predicted uses

l Couplings

l Biomedical and medical

l Toys, demonstration, novelty items

l Actuators

l Heat Engines

l Sensors

l Cryogenically activated die and bubble memory sockets, and finally

l lifting devices

Pre Page: Nickel-Chromium-alloys Next Page: Hastelloy

Product (745)

Product Forms (14)

Quality Certificate (11)

Learning Gallery (30)

Incoloy News (9)

Inconel News (22)

Molybdenum News (7)

Nikrothal News (4)

Nichrome News (13)

Titanium News (2)

Nickel News (8)

Alloys House (30)

Tools (27)

Nickel alloy News (30)

Latest Buzz (30)

nickel chrome copper iron alloys news (28)

Credit Report

Products Index

Company Info

Learning Gallery