University of central Florida

Shape Memory Alloy (SMA)

ETG 6933 - Advanced Topics in Technology

Frederick Kaiser

7/5/2010

Abstract to be made

ContentsI. Executive Summery.............................................................................................................................3

II. Introduction.........................................................................................................................................4

III. History.............................................................................................................................................5

IV. Accidental Discovery........................................................................................................................6

V. Nitinol Phases and Properties..............................................................................................................7

VI. Introduction into the Market...........................................................................................................8

VII. Current State of the Technology....................................................................................................10

VIII. References.....................................................................................................................................12

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I. Executive Summery

There are two stories that are in circulating about the discovery of Smart Memory Alloy

(SMA). The commercial name for SMA is Nitinol.

The first story of the discovery of Nitinol is hard to verify, but there is a population of

people who believe. A study was conducted for Wright Patterson in the late 40’s that indicated a

more abstract explanation for the discovery of Nitinol. The study showed that first tine the metal

alloys that demonstrated shape recovery was being examined by the U.S. Military. These studies

were thought to have started shortly after the Roswell Crash where similar material was reported

to have been found. Importantly, even after decades, the Nickel-Titanium metal system (Nitinol)

remains the material that defines "morphing metal." Any earlier observation of "pseudo-

elasticity" was with a metal alloy that did not utilize Nickel and Titanium- and that was not

developed for that property. (Bragalia, 2009)

The Story of the discovery of Nitinol is easier to verify, sense there are witnesses who

were present, at the discovery of shape memory characteristics of Nitinol and they recorded what

they saw. The timeline and activities that led to the discovery was recorded by the metallurgists,

William J. Buehler and Dr. David S. Muzzey. (Kauffman, 1993) Nitinol (Nickel-Titanium Alloy)

was being developed as a durable metal to use for the nosecone for spacecrafts, the material that

was to be used on the nosecone was expected to be exposed to 1000’s of degree and violent

turbulence at the time a spacecraft is reentering the atmosphere from low space orbit. During a

demonstration meeting, fire from a pipe lighter was exposed to the accordion shaped strip of

Nitinol, and then something unexpected and amazing happened. The accordion shaped Nitinol

strip straightened out into its original flat shape. (Kauffman, 1996)

Even though, the shape memory alloy (SMA) may have been invented by

Extraterrestrials and left on Earth after a crash in the 1940’s. A more plausible explanation would

be an accidental discovery made by an engineer, looking to solve totally unrelated problem. We

will be focusing on the discovery made by William Buehler, and the further development of

Nitinol in the market place and the future of this shape memory alloy (SMA).

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II. Introduction

Shape Memory Alloy (SMA) is the generic name for this family of alloys, there are other

alloys that are considered a SMA, but it all started with the Nickel-titanium alloy. The other

SMA alloys include copper-aluminum-nickel, copper-zinc-aluminum, and iron- manganese-

silicon alloys. (Borden, 1991) Nickel-titanium alloy, also, generically called (Nitinol) derived

from (Nickel Titanium Naval Ordnance Laboratory), was discovered in 1961 by William J.

Buehler. Reference Figure 1. William J. Buehler was a researcher at the Naval Ordnance

Laboratory in White Oak, Maryland. (Kauffman, 1993) Like other discoveries the Nickel-

titanium alloy was come about by accident when a strip of Nickel-titanium alloy was bent out

shape and when heated stretch back into its original shape. This event was witnessed many times

by both William J. Buehler and Dr. David S. Muzzey. (Kauffman, 1993)

Figure 1 - William J. Buehler in 1968

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III. History

Between 1952 and 1958, at the Naval Ordnance Laboratory, Buehler a metallurgist, to

cure boredom experienced in between projects, would experiment on iron-aluminum alloy.

William J. Buehler had completed research on a series of iron-aluminum alloys, for the Naval

Ordnance Laboratory (NOL) in 1958. At NOL, Buehler was working on the in-house project

which was to find an appreciate metal that could handle the hot and turbulence experienced by a

spacecraft on reentry into the atmosphere from low space orbit. Buehler’s job on the in-house

project was to provide physical and mechanical property data on existing metals and alloys for

computer-assisted boundary layer calculations. These calculations were to simulate the heating,

etc. of a reentry body through the earth’s atmosphere. The job of working out calculation started

to become boring and Buehler started to think of different alloy conditions that may solve the

reentry problem. (Kauffman, 1996)

Buehler consulted Max Hansen’s recently published Constitution of Binary Alloys which

was the latest text available about binary constitution diagrams, showing the solid-state phase

relationships of two–component metallic alloys as a function of composition and temperature.

Starting with sixty intermetallic compound alloys and then narrowing down to twelve, Buehler,

was able to select an alloy that exhibited considerably more impact resistance and ductility than

the other eleven alloys. That metal combination was an equiatomic nickel–titanium alloy.

(Kauffman, 1996)

In 1959, Buehler, decided to concentrate his research efforts on nickel-titanium alloy

which he gave new name (Nitinol). Nitinol exhibited favorable attributes that were needed for

the nose cone of spacecraft during orbital reentry. (Kauffman, 1996)

Following the startling acoustic damping discovery, other seemingly related unique

changes were observed. More interestingly, these changes also occurred in about the same

temperature range as the acoustic damping change. Examples of some of these correlatable

phenomena were: (Kauffman, 1996)

Polished plane metallographic alloy surface when heated slightly (100 °C to 200 °C; 212

°F to 392 °F) exhibited an obvious eruption or recon touring of the surface. Plate-like surface

shearing occurred and appeared to form along certain crystallographic planes.

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Microhardness indentations made at room temperature remained stable in size at room

temperature. However, when heated slightly (100 °C to 200 °C; 212 °F to 392 °F), they tended to

significantly reduce in size.

Metallography specimens polished using standard Al2O3 abrasive followed by etching

always revealed a typical acicular martensitic structure that one would typically find in quench-

hardened steel. It was only after very careful diamond polishing (with minimal surface strain)

that the true NITINOL base structure was revealed.

Acoustic damping, strain, and microstructure combined with minor temperature variation

were all, in their way, trying to tell me that this was an overtly dimensionally mobile alloy

capable of major atomic movement in a rather low temperature regime—near room temperature.

IV. Accidental Discovery

In 1961, preparing for meeting to demonstrate the fatigue-resistant properties of Nitinol,

Buehler, prepared a (.010 inch thick) strip. At room temperature he bent the strip into an

accordion shape, so it could be pulled out of shape and bounce back. Buehler gave the Nitinol

strip to his assistant to bring to the laboratory management meeting, because he was able to

attend. At the laboratory management meeting, the strip was passed around the members of the

meeting, as a prop. The members of the meeting pulled and twisted the nickel–titanium alloy.

One of the Associate Technical Directors, Dr. David S. Muzzey, who was a pipe smoker, applied

heat from his pipe lighter to the compressed strip. To everyone’s amazement, the Nitinol

stretched out longitudinally. The mechanical memory discovery, while not made in Buehler’s

metallurgical laboratory, was the missing piece of the puzzle of the earlier mentioned acoustic

damping and other unique changes during temperature variation. The unattended actions during a

management meeting made accidental discovery of an amazing alloy, that will be used many

new and innovative inventions. (Kauffman, 1996)

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V. Nitinol Phases and Properties

Nitinol has phase change while still solid; these phase changes are known as martensite

and austenite. Martensite and austenite phase changes "involve the rearrangement of the position

of particles within the crystal structure of the solid" the discovery of the shape-memory effect.

Dr. Frederick E. Wang. (Kauffman, 1993) Nitinol is in the martensite phase under the shift of

temperature. The alteration temperature varies from different compositions from -50 °C to 166

°C. (Jackson, 1997) Nitinol can be bend into varies shapes in the martensite phase, to reshape the

Nitinol back into its original character the Nitinol must held into position and heated to

approximately 500 °C. By heating the Nitinol the atoms are realigned into a compact and regular

pattern resulting into a rigid cubic arrangement known as the austenite phase. (Kauffman, 1993)

The parent shape is achieved in the austenite phase. The Nitinol can phase shifted back and forth

from martensite to austenite for millions of cycles with no breakdown on the composite alloy.

(Jackson, 1997)

The production method of Nitinol varies existing current techniques of producing nickel-

titanium alloys include vacuum melting techniques such as electron-beam melting, vacuum arc

melting or vacuum induction melting. The Nitinol is made into cast ingot in a press forge or

rotary forge into in to rods or wire. The working temperature for Nitinol is between 700 °C and

900 °C. The cold working method for Nitinol is similar to the fabrication of titanium wire. To

produce wires ranging in size from .075mm to 1.25mm in diameter carbide and diamond dies

must be used to produce the wire. A change to the mechanical and physical properties of Nitinol

will occur when the alloy is cold worked. (Jackson, 1997)

General the properties of Nitinol is comparable to other alloys, its melting point is around

1240 °C to 1310 °C, and its density is around 6.5 g/cm³. Other physical properties due differ

from other alloys such as temperatures with various compositions of elements include electrical

resistivity, thermoelectric power, Hall coefficient, velocity of sound, damping, heat capacity,

magnetic susceptibility, and thermal conductivity. (Jackson, 1997) The large force generated

upon returning to its original shape is a very useful property. Other useful properties of Nitinol

are its "excellent damping characteristics at temperatures below the transition temperature range,

its corrosion resistance, its nonmagnetic nature, its low density and its high fatigue strength"

these properties translate into many uses for Nitinol. Reference Table 1. (Jackson, 1997)

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PHYSICAL PROPERTIESMelting Point 2390°F 1310°CDensity 0.234 lb/in3 6.5 g/cm3

Electrical Resistivity 30 μohm-in 76 μohm-cmModulus of Elasticity 4-6 x 106 psi 28-41 x 103 MPaCoefficient of Thermal Expansion 3.7 x 10-6/°F 6.6 x 10-6/°CMECHANICAL PROPERTIESUltimate Tensile Strength (min. UTS)

160 x 103 psi 1100 MPa

Total Elongation (min) 10% 10%SHAPE MEMORY PROPERTIESLoading Plateau Stress @ 3%/ strain (min)

15 x 103 psi 100 MPa

Shape Memory Strain (max) 8.0% 8.0%Transformation Temperature (Af) 140° F 60° C

Table 1 - Nitinol SM495 Wire Properties (Nitinol, 2010)

VI. Introduction into the Market

The first successful product that used Nitinol was created for the Grumman Aerospace

Corporation by Raychem Corporation. Raychem Corporation Cryofit “shrink-to-fit” coupler was

used as a coupler to tightly fit hoses together. Grumman Aerospace was having a problem with

the hydraulic lines in the F-14 jet fighter, the existing hydraulic line couplers would leak (below

–120 °C; –184 °F). Raychem Corporation found that when a Nitinol tube is placed into liquid

nitrogen between (−196 °C; −321 °F) and (−210 °C; −346 °F), the tube size could be easily be

expanded with a tapered mandrel rod. The ends of the hydraulic pipe were inserted into the

Nitinol coupler tube and the assembly was then allowed to warm, to a temperature lower than –

120 °C; –184 °F. The Nitinol tube would revert back to its original shape coupling the hydraulic

tubes together. The Nitinol tube applied very high associated force, provided a continuously

clamping and totally sealed joint at well below the required –120 °C (–184 °F) temperature. The

Cryofit Nitinol coupler was used on the F-14 jet fighter from that point on. The same coupler or

similar couplers are being used air craft that require that specifications. (Kauffman, 1996)

Nitinol has a variety of applications some are used in military, medical, safety, and

robotics. The military have been using Nitinol coupler since the late 60’s, these coupler are used

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for hydraulic lines. (Kauffman, 1993) In the medical field Nitinol is used for tiny tweezers and

heart stints and catheters through blood vessels. Nitinol is used in Orthodontic to help straighten

teeth. Eyeglass frames are made of Nitinol, so if they bend they spring back in to shape. A safety

application for Nitinol is in fire sprinklers as an anti-scaling device and also water faucets and

shower heads. (Kauffman, 1993) Fire sprinklers using Nitinol achieve more reliable water flow

starts and stops. (Kauffman, 1993) To simulate human muscle motion, Nitinol components are

being used in robotics actuators and micromanipulators. (Rogers, 1995) Other applications for

Nitinol would include household appliances such as thermal sensitivity deep frying baskets,

woman bras making them comfort to the bodies shape for better comfort, Nitinol engine mounts

and suspension parts that control vibration more efficiently, and structure members for bridges

and building. Reference Figures 2, 3, 4, 5. (Falcioni, 1997)(Rogers, 1995)

Figure 2 - Wire for Braces Figure 3 - Stent for Clogged Arteries

Figure 4 – Frames for Eyeglasses Figure 5 - Clot Trapping Filter for blood Vessels

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VII. Current State of the Technology

The use of Shape Memory Alloy in the future is wide open, possible application could be

engines in cars and airplanes, and a motor for generating electricity. Nitinol can be used in

automobile frame and replace body panels, so if in an impact the original shape can be returned

with else. (Kauffman, 1993) Nitinol can be used to form smart louvers for eliminate engine heat

more efficiently. SMA’s is ideal for fasteners, seals, connectors, and clamps. Tighter connections

and easier and more efficient installations result from the use of shape memory alloys. (Borden,

1991)

Nitinol has the mechanical and electrical properties that will allow it to be used to make

more efficient electric motors. Dynalloy Inc. is a 20-year-old company that markets a line of

SMA wire called Flexinol that is used as actuators by a wide variety of manufacturers. Flexinol

is made of nickel-titanium alloy. It comes wrapped on spools like traditional wire, with diameters

ranging from 0.001 to 0.02 inch. Dynalloy claims that one 100- meter spool of Flexinol can

replace approximately 1,000 electric motors. The wire contracts anywhere from 2 percent to 5

percent of its length, like muscles, when it is heated. (Weber, 2010) Nitinol motors are planned

as addition power source for future electric and hybrid cars. Reference Figure 6.

Figure 6 – SMA Wire Motor Used for Additional Force

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The aerospace industry is also searching for new SMA applications. By using the

material, engineers at Boeing, General Electric Co. and Goodrich Corp. developed a variable

geometry chevron that reduces commercial aircraft engine noise. Chevrons are zigzag or saw

tooth shapes at the back end of the nacelle and the engine exhaust nozzle, with tips that are bent

slightly into the airflow. This creates vortices that form at each chevron, enhancing the mixing

rate of the adjacent flow streams. When the chevrons enhance mixing by the right amount, jet

engine noise diminishes. (Weber, 2010)

Traditionally, automakers use hundreds of cable actuators, small electromagnetic motors

and other mechanical devices to adjust mirrors, seats and headrests; operate windows and door

locks; raise antennas; and release latches. Many of these components can be replaced with SMA.

(Weber, 2010) Using Nitinol wire automaker will be able to make louvers the open when, when

the engine heat is high enough to make the alloy react. Reference Figure 7.

Figure 7 – SMA Controlled Louvers

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VIII. References

Borden, Tom. "Shape-Memory Alloys: Forming a Tight Fit." Mechanical Engineering. Oct. 1991, p67-72.

Bragalia, Anthony. “The Final Secrets of Roswell's Memory Metal Revealed.” UFODigest.Com. June 8, 2009, http://www.ufodigest.com/news/0609/memorymetal.php, retrieved on July 2, 2010.

Falcioni, John G. "Shape Memory Alloys." Mechanical Engineering. April 1992, p114.

Jackson, C.M., Wagner, H.J. and Wasilewski, R.J. “55-Nitinol-The Alloy with a Memory: Its Physical Metallurgy, Properties, and Applications: A Report.” Washington: NASA. 1972.

Kauffman, George and Isaac Mayo. "Memory Metal." Chem Matters. Oct. 1993, p4-7.

Kauffman, George and Isaac Mayo. “The Story of Nitinol: The Serendipitous Discovery of the Memory Metal and Its Applications.” The Chemical Educator. 1996. VOL. 2, NO. 2, S 1430-4171 (97) 021 11–0.

“Nitinol Devices & Components.” Nitinol SM495 Wire Material Data Sheet. www.nitinol.com, SDS-SM495, Rev. B., http://www.nitinol.com/media/files/material-properties-pdfs/sm495_wire_data%20%5BConverted%5D_v2.pdf, retrieved on 4 July 2010.

Rogers, Craig. "Intelligent Materials." Scientific American. Sept. 1995, p154-157.

Weber, Austin. “Smart Materials Have a Bright Future.” www.assemblymag.com. March 26, 2010. http://www.assemblymag.com/Articles/Feature_Article/BNP_GUID_9-5-2006_A_10000000000000788627. Retrieve on 5 July 2010.

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