nitinol wire experiment

Tips for working with nitinol wire

Here are some things I learned from working with the nitinol wire.

Accidentally increasing the transition temperature

I purchased the wire that I demonstrate above by shaping into an R and that I shape into a spring below from Kellogg's Research Labs . It is 0.01" thick. According to their forum, to set the wire's shape into it's memory you heat it to 500C (950F). Also, according the the specs for the one I bought, the transistion temperature at which it restores itself back to its remembered shape is 70C (160F). But I couldn't get it to go back to its remembered shape even by putting it in hot water up to 100C (212F). Instead I had to put it in a much hotter candle flame or run electrical current through it, producing a higher temperature.

My guess is that at some point I had unknowingly raised the transistion temperature. Again, according to Kellogg's forum, heating this wire to 350C (660F) will raise the transistion temperature. My guess is I'd done that by leaving it in the candle flame sometimes for too short a time when trying to set the shape. It's also possible I'd sufficiently heated part of the wire to set the shape but since I hadn't cut that part from the rest of my wire, the section of wire next to it got heated to a lower temperature around 350C (660F), raising the transistion temperature for that section. When I later went to use that section, it had a higher than expected transistion temperature.

So be careful of the temperatures you expose your wire to.

Accidentally reprogramming it

Since I didn't know the new transistion temperature for my wire, I sometimes used a candle flame to get it to go back to its programmed shape. If I left it too long in the flame then its temperature sometimes went as high at the required 500C (950F) to set a new shape. The remembered shape changed to whatever shape it happened to be in at the time.

So again, good temperature control helps. For my spring experiments, at least by using electrical current to get it to go back to its programmed shape, and since I had control of the current using my power supply and potentiometer, I had some control of the temperature that way.

Video - Nitinol wire - How to Use it

In the following video I start with the demonstration of making the letter R and then follow that with making the spring and measuring the force as the spring restores its shape using electric current to produce the heat.

“Nitinol: a shape memory alloy” experiment

Why it takes its initial shape

Can you re­mem­ber what you did last Tues­day? This al­loy can even re­mem­ber its shape af­ter 10 years!

Safe­ty pre­cau­tions

Ob­serve safe­ty rules when work­ing with flame and heat­ed ob­jects.

Warn­ing! Don’t try to re­peat this ex­per­i­ment with­out a pro­fes­sion­al su­per­vi­sion!

Reagents and equip­ment:

• niti­nol (clip, spring);
• hot wa­ter;
• Petri dish;
• heat­ing de­vice (hot­plate).

Step-by-step in­struc­tions

Take a niti­nol clip or spring and bend it. Now heat the de­formed item with a lighter, hot wa­ter and heat­ing de­vice . The clip and spring take their orig­i­nal shape!

Pro­cess­es de­scrip­tion

Niti­nol is an al­loy which is 55% nick­el and 45% ti­ta­ni­um. This al­loy is in­ter­est­ing be­cause it can re­mem­ber its shape. When a niti­nol item is heat­ed, the atoms in it “re­mem­ber” their po­si­tion, and so on re­peat­ed heat­ing they try to take this po­si­tion. If a niti­nol item is de­formed and then heat­ed, the atoms take their ini­tial po­si­tion, and the shape of the item is re­stored.

Dozens of experiments you can do at home

One of the most exciting and ambitious home-chemistry educational projects The Royal Society of Chemistry

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Magic Part 3 – Memory Wire

This wire has a better memory than i do..

This is cool stuff. It’s called memory wire, or more specifically, nitinol wire. To perform this trick, I “programmed” the wire by bending it into the shape of the word “LIME.” Then I heated the wire using a butane flame. It took a while, but when I was all done, I could bend the wire into any shape and then just put it in hot water and I get the word “LIME” right back! Scientists are finding way to create motors using the heating and cooling properties of nitinol.

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Casa Bouquet

let your joy bloom

Nitinol memory wire experiment for kids

April 25, 2020 by Lisa Grable 5 Comments

Safety note: Be sure to explain safety precautions to children. This experiment uses hot water. Eye and skin protection should be used. Disclaimer: All information provided on this site is for entertainment and education purposes only. Using any information from casabouquet.com is at your own risk.

Instructions for nitinol memory wire experiment

• Use tongs to carefully lower the nitinol wire into the room temperature water. Observe and record the results.

What questions can you answer with an experiment like this? Does the shape you bend in the metal make a difference? Can you think of how it could be useful to have a metal that can be easily returned to its original shape? What inventions already exist? What could you invent?

Affiliate links: if you make a purchase using these links, I’ll receive a small compensation towards maintaining this blog, at no extra cost to you.

• very hot water
• water with ice
• room temperature water
• paper towels,
• paper or notebook for recording results, pen

What is the science?

Content: thermal energy, elasticity, crystal structure

Resource links

• Science of Energy from need.org has a whole set of energy lab activities and worksheets
• Temperature sensors from Vernier Software & Technology
• Nitinol from Chemistry Learner
• Energy transfer from Physics 4 Kids
• Unit cells (crystals) from Purdue Chemistry
• General Lab Safety resources from Flinn Scientific. Be sure to check out the Student Safety Contract.

Related posts

Reader Interactions

May 3, 2020 at 7:26 pm

Thank you for sharing at #OverTheMoon. Pinned and shared. Have a lovely week. I hope to see you at next week’s party too! Please stay safe and healthy. Come party with us at Over The Moon! Catapult your content Over The Moon! @marilyn_lesniak @EclecticRedBarn

September 9, 2016 at 1:08 pm

September 12, 2016 at 7:08 am

Yes it is, Julie! It’s fun for kids to try and imagine how they would use the nitinol for an invention.

September 6, 2016 at 8:00 am

This is really neat! I’ve never heard of nitinol and can certainly see the happiness and excitement Monkey Boy would get if we did a project with it! Thank you so much for sharing! 🙂

September 6, 2016 at 2:00 pm

Thanks so much for coming by! As long as you follow safety procedure, this is a pretty enchanting lab to do!

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Solid State Motion System Using Nitinol!

Introduction: Solid State Motion System Using Nitinol!

- Work in progress -

Hello fellow makers,

In this instructable we will be exploring a motion system that does not use any mechanical parts that can wear out and break like motors, servos or solenoids., there are a couple of projects coming up where i will be using nitinol wire in and this served as an introduction for me into it's capabilities., unfortunately due to my location finding nitinol wire is very difficult, the only place that stocked it only had a single 10cm piece available and at a ridiculous price., so on a search i went to find alternative sources for the mythical memory wire, to my surprise there is a common source for nitinol, there might even be nitinol wire walking around in your house...braces, turns out you can easily buy 10 piece packets of niti (nitinol) orthodontic wire online and they are super cheap, the only drawback is their working temperature is human body temperature range which isn't a problem for most readers in the northern part of the globe but with the record breaking heatwave we are currently experiencing in south africa as i'm busy writing this it definitely had some drawbacks and i will need to source some industrial nitinol for future projects..

If you enjoy my Instructables and would like to support my future projects you can  Buy Me A Coffee .

Step 1: What You Will Need:

To make your own nitinol motion system you will need the following:.

• Nitinol wire

Amazon - Nitinol Sample Pack - 7 Varieties 0.5-1 - 2mm, 15-40 - 60-80ºC Transition

• Access to a 3D printer

I use a resin printer to get more accurate parts.

Amazon - Creality Halot-Mage Pro Resin 3D Printer

• 5mm brass tube

Amazon - Brass Tube Tubing - 2mm 3mm 4mm 5mm 6mm 7mm 8mm 10mm OD x 0.5mm

• 4mm brass rod

Amazon - 8 Pieces 4mm Brass Round Rods

• Tiger tail wire

Amazon - 0.45mm Steel Tiger Tail Beading Wire

• Long nose pliers preferably self locking

Amazon - Precision Kelly Forceps Locking Tweezers Clamp

• Butane torch
• Some PLA filament
• Lithium grease

Amazon - CRC 5037 White Lithium Grease

• 2-Part CA glue

Step 2: What Is Nitinol?

Nitinol is a type of shape memory alloy that is composed of nickel and titanium. The name "Nitinol" is derived from the combination of the elements symbols and the place of its discovery, the Naval Ordnance Laboratory (NOL) in the United States.

The unique property of Nitinol is its ability to "remember" its original shape and return to it when subjected to certain stimuli, such as heat.

Here's how the shape memory effect works in Nitinol:

• Martensitic Phase: At lower temperatures, Nitinol exists in a phase called martensite, which has a deformed or "memory" shape.
• Austenitic Phase: When heated above a certain transition temperature, known as the transformation temperature, Nitinol undergoes a phase change to austenite. In this phase, it reverts to its original, undeformed shape.

This ability to switch between two different crystal structures and maintain a memory of its original shape makes Nitinol useful in various applications. Some common applications include:

• Biomedical Devices: Nitinol is used in medical devices such as stents and guidewires, where its shape memory property can be employed for minimally invasive procedures.
• Eyeglass Frames: Some eyeglass frames are made from Nitinol, allowing them to return to their original shape even after being bent or twisted.
• Actuators and Robotics: Nitinol is used in actuators and robotics where a compact, lightweight, and precise shape change is required.
• Aerospace Applications: The unique properties of Nitinol make it useful in certain aerospace applications, such as deployable structures.

The ability to undergo a reversible phase transformation with changes in temperature makes Nitinol a fascinating material with diverse applications in various industries.

Step 3: Designing a Test Platform:

For my test platform I decided on this two digit bionic hand, in hindsight a simple claw would have been a lot easier!

Made in Fusion 360 I decided to leave the back of the hand open for easy tinkering as this is a test platform after all and will need a lot of adjustments.

The articulation of the joints are simply based around standard 1.75mm PLA filament as it is slippery enough to not bind up the joints and super easy to work with. For the motion system there is simply two holes running down both digits one for the pull/closure nitinol wire and the other for the spring/open action.

All parts were printed on a Creality Halot One with rigid resin.

Bioprosthetic Hand (V1.0)

Attachments.

Step 4: Making a Nitinol Spring:

The whole motion system relies on a spring that will pulled apart by an external force and will contract when a current/heat is applied, now this step doesn't look that complicated but it took quite a few tries to get something that actually reassemble a spring.

To form a spring you simply need to wrap a wire around a cylinder right...the problem is with nitinol no matter how tight you bend it it will just spring back to its original shape...with force!

To form it it needs to be moulded around the cylinder and heated, but this also has some complications.

Heat it too much and it loses its amazing properties and as soon as you start heating it the force that it wants to return to its original shape with multiplies, so you need to have a way to keep it clamped onto the cylinder, heat it evenly and be able to quench it in water very quickly.

After a few tries I found the best way was to first drill a 1mm hole into a 5mm brass tube, this will hold onto the start of the nitinol wire and the brass tube will control the heating process.

Next I used a pair of self locking pliers to clamp onto the other end of the nitinol wire, I then tightly wound the wire around the tube to form a tight coil.

Holding the end of the brass tube tightly against the handle of the pliers we need to heat up the coil with a butane torch until the shiny silver wire turns golden (being titanium the wire will go from silver to gold,blue and then purple) as you bring the flame onto the coil you will immediately feel quite a strong force applied to the brass tube as it tries to unwind then as soon as it turns golden the force will stop and your coil would have formed, you will need to immediately quench the coil in water as soon as it changes color.

With it cooled you can now remove your coil and if everything went correctly you can pull it as much as you want and it will always return to its original coil.

Step 5: Refining the Test Platform Joints:

As with any motion system we need joints that slide smoothly and without binding and excessive friction.

As 3D printing always has some imperfections and distortion I used some wetted 400 grit sanding paper to sand each joint until I got smooth motion.

An easy way to spot problematic areas with resin prints is to temporarily assemble your joints (I used a drill bit as the hinge) and move it through its motions this will mark up the problematic areas which will be white and chalky.

Afterwards I used a 2mm drill bit and cleaned up all of the hinging holes, 2mm will give enough room for the filament piece but not big enough to cause binding.

Step 6: Nitinol Spring Negative Connection:

For this iteration of the motion system we will be using electrical current to contract the nitinol spring.

I decided that using a single ground/negative buss bar that the ends of the nitinol springs can clip onto will simplify assembly and the electrical setup.

There are two 4mm holes on the inside of the printed palm that I made to fit a 4mm brass rod in, I simply bent the the rod into an L and cut it down to size.

Onto the brass rod I soldered on some copper wire that was bent into circle to clip the nitinol springs onto.

Step 7: Assembly:

Now onto assembling our test rig.

First we need to assemble the digits, I started by applying some light Lithium grease to each of the joints contact points before sliding them into each other. The hinge is made by simple pushing through a piece of PLA filament and then heat up the end of the filament with a lighter until it starts to soften and push it flat against the resin part, next cut off the excess filament on the opposite side and heat it up and press it flat to create a collar that holds the filament piece in place.

Test your joints to make sure they move freely.

For cabling I use jewlers 0.45mm tiger tail wire which is a twisted stainless wire encased in nylon giving a stretch free slippery cable perfect for robotics. The cable is simply knotted on the finger tip side to avoid it slipping down the hole and on the palm side I tied a loop that can clip onto the nitinol spring.

Attach the nitinol spring to the end of the loop in the tiger tail and then the other end onto the bus bar and test out the motion.

Step 8: Joint Return:

This step is still a work in progress, we need a way to create pull force to pull the digit straight again.

A spring can be used but the force it provides gets larger as it stretches further and I want to minimize that.

Next I used the curve that the orthodontic nitinol wire has to my advantage and inserted that into the digit, this worked really well but I needed a slightly thicker wire to provide more spring plus the stainless steel orthodontic wire would be a better fit for this purpose.

Step 9: What's Next:

• Instead of using current through the nitinol wire to heat it up we can utilize miniature peltier modules as shown above attached to the coils to quickly heat and cool the wire, I will be exploring this method in a future Instructable.

Step 10: Enjoy!

To use this system you simply need to provide current across the nitinol spring (a single AA battery works well) this will cause it to heat up and return to its original shape which will pull the digit closed.

When current is removed the wire will cool back down making it malleable and streatch out from the opposite pulling force and the digits will open back up.

With this method you only need a single mosfet switch on each digit to control it creating a fully solid state motion system

I hope you guys find this Instructable useful and if you have any questions please feel free to leave me a message or comment bellow.

Thank you for taking the time to read through my project and as always..

Happy making!

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Cutting Edge Materials: Practicals

Six groups of practicals produced by the Institute of Physics (IOP) that help students to find out more about how science is applied to using and testing new materials.

In addition to the guidance included for specific activities, please refer to the generic health and safety information before commencing any practical activity.

The resource is accompanied by the Teacher and technicians' guide for both the practicals and activity sheets.

[b]Work on a coil[/b] This practical activity provides useful practice in using work done = force x distance and introduces students to memory metal in a dramatic way. It is suitable for mixed ability classes, with extension work on applications of memory metal.

[b]Muscle metal[/b] An activity accessible to foundation tier students.They use a shape memory alloy called Nitinol (muscle metal) to explore energy transformation and mechanical work.The investigation which is the central part of the activity requires students to consider the reliability of their evidence before they can state a conclusion.The final experiment allows them to select one of two possible models of the agent responsible for the contraction of hot muscle metal.

[b]Muscle wire[/b] An activity designed for higher tier students. As well as comparing the behaviour of a smart material with its biological equivalent, it invites students to use their evaluation of experimental evidence to make judgments about the fitness of scientific theories. After following a procedure to measure the work done by a loop of Nitinol wire when heated by an electric current, students are required to: • consider two alternative theories for the wire • carry out experiments to test those theories • decide which theory is best • devise another experiment to test the best theory.

[b]Muscle wire efficiency[/b] An activity aimed at higher tier students. It requires them to perform calculations with the following formulae: • power = voltage x current • energy = power x time • work = force x distance *effciency = useful energy output/energy input They are introduced to Nitinol wire, a shape memory alloy which can transform electrical energy into mechanical work, albeit with an efficiency of less than 1%.The extension activity requires students to perform an extra experiment to test a theory about the low efficiency.

[b]Circuit training[/b] This activity can be used to assess the construction, testing and evaluation of an electronic device. Students should work individually and may need extra guidance to achieve assessment requirements as set out in the relevant awarding board specifications.

[b]High temperatures[/b] An ordinary household light bulb is adapted as a temperature probe for measuring high temperatures, demonstrating the increase in electrical resistance of a metal when heated. It has a thin metal filament, usually made out of tungsten, which has a very high melting point (3422 degrees C).

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Please be aware that resources have been published on the website in the form that they were originally supplied. This means that procedures reflect general practice and standards applicable at the time resources were produced and cannot be assumed to be acceptable today. Website users are fully responsible for ensuring that any activity, including practical work, which they carry out is in accordance with current regulations related to health and safety and that an appropriate risk assessment has been carried out.

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Precision flexinol position control using arduino.

Flexinol, also known as Muscle Wire, is a strong, lightweight wire made from Nitinol that can be made to contract when conducting electricity. In this article I'll present an approach to precision control of this effect based on controlling the voltage in the Flexinol circuit. In addition, taking advantage of the fact that the resistance of Flexinol drops predictably as it contracts, the mechanism described here uses the wire itself as a sensor in a feedback control loop. Some advantages of eliminating the need for a separate sensor are reduced parts count and reduced mechanical complexity.

The information here follows on earlier discussions: Flexinol and other Nitinol Muscle Wires and Flexinol Control Circuit Using PIC 16F690 and ULN2003A . You might want to refer back to those articles for an introduction to using Flexinol in design and an overview of the properties of this unique alloy.

Built around an Arduino Uno, the setup I've put together to experiment with is very simple, and hopefully easily repeatable. To drive the Flexinol, it makes use of a homebrew digital to analog converter (DAC) that can be assembled from common parts. To calculate the resistance, the Arduino's native analog to digital (ADC) peripheral is used to measure the voltage drop across the Flexinol. The control code for the circuit first self-calibrates, and then steps through a set of targets attempting to hold positions across the range from fully relaxed to fully contracted. Throughout the run, data is sent to the Arduino serial monitor for observation and study.

Achieving precise, low-jitter position control of a Flexinol mechanism turns out to be surprisingly difficult. Although in robotics projects, Flexinol's contraction is usually driven by electricity, the shape memory effect that causes the contraction is actually a function of temperature. In an aptly named phenomenon called resistive heating, electric current makes the wire get hot and it contracts. All by itself, controlling resistive heating in a thin length of wire is elusive, involving variables such as ambient temperature, air flow, altitude and even humidity. Beyond those environmental basics however, controlling the Flexinol requires a reasonably thorough understanding how the wire will actually respond to changes in temperature.

In the on-off model of Flexinol control used in most hobby projects, we typically give the wire more than enough electric current to heat it and fully transition to the contracted Austenite phase. We then remove electricity entirely to allow the wire to cool and transition to the relaxed Martensite phase. Fortunately for the effort at hand, Flexinol does not simply transform at a particular temperature, but rather the effect is incremental across a rather wide temperature range. The full temperature span varies by the formulation but is typically between 40-70 degrees Celsius.

Adapted from the Flexinol specifications document, the above chart shows temperatures in Celsius plotted against the percentage of contraction for high temp Flexinol. Immediately apparent is the fact that the temperature response of Flexinol is non-linear. It begins gradually, accelerates to the point where most of the useful physical transformation takes place over about a 10 degree change in temperature, and then tapers off. A second observation is that there is a significant difference in the transformation temperatures when Flexinol is heating to the Austenite phase compared to when it is cooling to the Martensite phase. When heating, the mid-point between fully contracted and fully relaxed is at about 100 degrees; when cooling, the mid-point is about 70 degrees. This 30 degree gap is known as the transformation temperature hysteresis.

Also to be considered is the fact that when the current being supplied to the Flexinol is changed, the temperature doesn't change immediately, it needs time to either warm or cool. Therefore, when current is changed Flexinol will not move immediately to the new position, but will continue contracting or relaxing for a number of seconds. If we continue to change the current while the Flexinol is still settling, then we overshoot the target and the mechanism ultimately swings back and forth across the target rather than holding steady. Overshoot is further complicated by transformation hysteresis and heat dissipation issues. Typical approaches to feedback control where the current is proportionately increased or decreased until the desired position is reached won't work very well here.

In the solution presented here, transformation temperature hysteresis is accounted for by calibrating such that for a given position there is both a predetermined warming voltage value and a predetermined cooling voltage value. If the Flexinol is too relaxed to hold the target position then the warming value is fed to the DAC. If the Flexinol is too contracted for the position then the cooling value is fed to the DAC.

The warming and cooling values are determined in a calibration process each time the program is run. The first step in the calibration is to establish a baseline by measuring the resistance of the Flexinol when it is fully relaxed and fully contracted. In the second step, voltage to the Flexinol is steadily increased and then steadily decreased, all the while calculating the resistance of the Flexinol. When certain target resistance values are reached, the DAC values are stored in a lookup table. In making the calibrations, the current is changed at a moderate pace, a compromise between giving the Flexinol time to settle at the new position while still moving quickly enough to be useful. Although this approach does not completely eliminate overshoot, by sampling relatively continuously at high resolution and switching between warming and cooling current as needed, jitter in the mechanism can be reduced to trivial levels.

On the electronics side, current to the Flexinol is controlled by varying voltage. Because we'll be measuring resistance in the circuit, we need a nice clean voltage. To control the voltage I've setup a resistor ladder DAC (frequently written R-2R). An R-2R DAC is a clever construct that enables you to build up a DAC of theoretically any resolution simply by adding "rungs" to the ladder - 8 rungs equals an 8-bit DAC. Binary values are fed into the ladder by toggling eight digital pins from the Arduino, and a proportionately corresponding voltage is available at the output. The ladder is a resistor network built up of two values, one the double of the other. Here I've used 10K and 22K values, which it turns out is close enough. The other components of the DAC portion of the circuit are an LM358 operational amplifier and the PN2222 transistor. They are both setup as voltage followers in order to get enough current gain to supply the Flexinol. In my test circuit, I'm powering the Arduino through the USB programming cable and feeding the DAC with a separate 6 volt supply. Finally, the circuit feeds a voltage divider made up of a fixed value resistor (2.7 ohms) and the Flexinol which acts as a variable resistor.

Calculating the Resistance

In a voltage divider, when the value of the first resistor is known, the value of the second resistor can be calculated based on the voltage drop across the circuit using the following formula:

R2 = (R1 * VOut) / (VIn - VOut)

This calculation is pretty easy to code on the Arduino. The first step is to take readings using analogRead at A0 and A1. Those readings can then be converted to voltages by multiplying the values by 0.004883, which is equivalent to 5/1024 or reference voltage/ADC resolution.

Although the calculation itself is simple enough, it is here that we run into the limitations of both the test circuitry and the 10-bit ADC of the Arduino. According to the specifications the difference in resistance between Austenite and Martensite phase should be about 20%. Experimentally I've determined that in this particular circuit the actual useful range will be closer to 15% or about 1.5ohms for this length of wire. Therefore in order to produce useful results, measurements need to be accurate to within a tenth of an ohm, or better yet several hundredths. With this setup we just barely get there.

The Results

Although not perfect, the results of the experiment are quite good. According to data culled from test runs, the setup is able to reliably hold the Flexinol to a variance of <0.1ohm from the target value. Observing the mechanism while testing, there is occasional jitter when moving to a new position, but overall the arm is held solidly with no discernable movement. As it stands the technique could be applied in numerous projects where incremental positioning is needed, but extreme precision is not required. There are many opportunities for improvement, some of which are simply a matter of substituting higher quality components and building permanent rather than prototype circuitry. It seems likely that continued experimentation and refinement of the approach in both hardware and software will enable greater precision.

The sketch I used in this experiment is provided in its entirety below. or it can be downloaded as a zip file here: FlexinolResist.zip

Although there is probably limited value in reproducing the experiment exactly, the code is reasonably well commented and a carefully read should help make some of the notions described in the body of this article a little more clear.

About the Author: Ralph Heymsfeld is the founder and principal of Sully Station Solutions . His interests include artificial intelligence, machine learning, robotics and embedded systems. His writings on these on other diverse topics appear regularly here and across the Internet.

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Nitinol Memory Wire and Demonstration Kits

• Item #: FAM_753255

Description

Specifications.

What do elephants and nitinol wire have in common? A good memory! Introduce students to a shape memory alloy that changes phases near 50° C and can be easily heat-treated to "remember" a certain shape. Then challenge students to explain the contradiction with metal properties when a straight piece of wire dropped in hot water contracts (not expands) to form a new shape. Nitinol wire can be reused an unlimited number of times. Kit includes a special tool to make intricate wire patterns.

What do elephants and nitinol wire have in common? A good memory! Introduce students to a shape memory alloy that changes phases near 50° C and can be easily heat-treated to "remember" a certain shape. Then challenge students to explain the contradiction with metal properties when a straight piece of wire dropped in hot water contracts (not expands) to form a new shape. Nitinol wire can be reused an unlimited number of times. Kit includes a special tool to make intricate wire patterns. Materials support at least 3 demos. Includes instructions.

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• Published: 20 April 2003

Crystal structures and shape-memory behaviour of NiTi

• Xiangyang Huang 1 ,
• Graeme J. Ackland 1 , 2 &
• Karin M. Rabe 1  

Nature Materials volume  2 ,  pages 307–311 ( 2003 ) Cite this article

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Shape-memory alloys (SMAs) are a unique class of metal alloys that after a large deformation can, on heating, recover their original shape 1 . In the many practical applications of SMAs, the most commonly used material is NiTi (nitinol). A full atomic-level understanding of the shape-memory effect in NiTi is still lacking, a problem particularly relevant to ongoing work on scaling down shape-memory devices for use in micro-electromechanical systems. Here we present a first-principles density functional study of the structural energetics of NiTi. Surprisingly, we find that the reported B 19′ structure 2 , 3 , 4 of NiTi is unstable relative to a base-centred orthorhombic structure that cannot store shape memory at the atomic level. However, the reported structure is stabilized by a wide range of applied or residual internal stresses. We propose that the memory is stored primarily at the micro-structural level: this eliminates the need for two separate mechanisms in describing the two-way shape-memory effect.

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Nanocomposite NiTi shape memory alloy with high strength and fatigue resistance

Science and technology of shape-memory alloys: new developments. Mater. Res. Bull. 27 , (2002).

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Acknowledgements

We thank R. D. James, K. Bhattacharya and I. I. Naumov for valuable discussions. This work was supported by AFOSR/MURI F49620-98-1-0433. The calculations were performed on the SGI Origin 3000 and IBM SP3 at ARL MSRC.

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Huang, X., Ackland, G. & Rabe, K. Crystal structures and shape-memory behaviour of NiTi. Nature Mater 2 , 307–311 (2003). https://doi.org/10.1038/nmat884

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Received : 18 September 2002

Accepted : 25 March 2003

Published : 20 April 2003

Issue Date : 01 May 2003

DOI : https://doi.org/10.1038/nmat884

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A Complete Guide to Nitinol Wire 

Over the years, there has been considerable growth in the adoption of nitinol – especially in the product development and manufacturing spaces. Thanks to its unique ability to conform to any shape and return to its original form if necessary, many manufacturers have found different uses for it. 

This article will look into the intricate details of this transformative material, as well as how to get your hands on some of it for your manufacturing project.

Table of Contents

What Is The Nitinol Wire? 

Nitinol is one of the most interesting metal alloys on the market today. Known for its ability to adapt its physical shape based on the requirements, the alloy – which is actually pronounced as “night in all” – has become one of the most popular on the planet. 

In most cases, nitinol is applied in the medical field. But, that doesn’t mean it can’t be used for other things. In fact, as time goes on, more functionalities of the wire have been found, with more people asking “What is Nitinol wire and how can I get some of that?”

How Was Nitinol Created?

Nitinol is a simple alloy that is made from a combination of nickel and titanium. The ratio of both materials is usually equal, although adjustments can always be made to this combination. So, when constituent materials are adjusted, there is a significant chance that you see changes in the property’s features as well – from its physical appearance to its temperature of transformation.

Nitinol’s creation was actually a happy accident. While scientists had been working on shape memory alloys for a long time, they hadn’t necessarily made any progress.

In 1959, however, William Buehler – a metallurgist at the Naval Ordinance Labs – came upon an accidental breakthrough. While working on a new missile cone nose, Buehler was working on different metal alloy options. He eventually found nitinol as part of one of his many experiments. 

When he discovered that this new material could deliver the shape memory effect, Buehler decided to name it after its composite materials – Nickel (Ni) and Titanium (Ti), as well as the name of his workplace (the Naval Ordinance Labs). This combo eventually formed NITINOL.

Most nitinol ingots are processed via melting- whether it is vacuum induction melting or vacuum arc melting. Following the manufacturing, a nitinol wire experiment can also be made to ascertain its efficiency and properties. 

The Shape Memory Effect

In metallurgy, a shape memory alloy (SMA) is a type of metal alloy that can lose its form and return to its original form based on what you want. Most SMAs get deformed when in their cold state or room temperature, then get confirmed to their original state when you apply some heat to them. This capability is what metallurgists call the shape memory effect . 

So, how does Nitinol wire work with this physical adaptability?

We’ve already cleared the composition part of nitinol – the material usually contains mostly nickel and titanium.

When stored at room temperature, the material easily loses its form and can be twisted into just about any shape you need. Once you apply heat to it, nitinol will return to its original form, essentially “remembering” its initial shape. The material’s adaptability and flexibility make it especially perfect for a range of applications.

For many people wondering how to use nitinol wire, it is important to note that the transition temperature of nitinol – essentially, the temperature and physical condition needed for nitinol to change its shape – can be repeated. This means that the shape memory nitinol wire can be used over multiple cycles without stress. 

Many nitinol wire manufacturers tout the wire’s ability to withstand different deformation and realignment cycles as a huge benefit. It essentially means that the material is a great choice for making products that need to be used in the long term. 

Usually, the nitinol material transforms when it is put under temperatures of about 180°F. However, you should note that these values can vary based on a number of factors – including and especially the combination of materials and the hat treatment method used in manufacturing it. 

Nitinol: Physical Properties

As you would expect, Nitinol’s most touted properties are its impressive elasticity and ability to adapt to different shapes. It is flexible enough to be transformed and then revert to its original state, but it can also be stretched significantly – leaps and bounds more than the average metal.

Besides these, however, nitinol has several other physical properties. Some of those include: 

• Appearance: In its most undiluted state, nitinol comes with a bright silver look. The appearance is the same as any other metal, so the material isn’t necessarily unique. Of course, this is what you’d expect since the nitinol wire composition is primarily nickel and titanium. 
• Melting point: Nitinol’s melting point is important because it plays a role in signifying the point at which the material starts to transform. In most cases, nitinol would need to be subjected to about 1310 °C for it to melt. You should note, however, that this isn’t necessarily accurate. The nitinol wire composition affects its melting point, and that number could also change based on the wire’s manufacturing process. 
• Resistivity: Thermal resistivity for nitinol stands at 82 ohm-cm in higher temperature. When temperatures drop lower, the thermal resistivity of the  material also goes low – to about 76 ohm-cm. 
• Conductivity: As for thermal conductivity, nitinol holds a rating of 0.1 W/ cm-°C.
• Heating Details: Nitinol withstands up to 0.077 cal/ gm-°C in heat capacity, while its latent heat stands at 5.78 cal/ gm.

Mechanical Properties Of Nitinol 

With an ultimate tensile strength that  ranges between 103 and 1,100 MPa, it’s safe to say that nitinol isn’t necessarily the strongest material on Earth. Still, it definitely does its best. Of course, you should note that the content of titanium in nitinol is one of the biggest determinants of this. 

To get a proper picture of how strong nitinol is, consider the fact that stainless steel has a tensile strength rating between 300 MPa and 2,400 MPa. While this number can vary based on the material composition of the steel as well, the fact that nitinol has a comparable rating shows that it can provide considerable durability. 

Once nitinol is taken above its transformation temperature, it adds density and strength. Still, its formability is what makes nitinol so useful – especially for medical applications.

Nitinol also has impressive corrosion resistance – even more than stainless steel – and, it is biocompatible; meaning that you can put it in a human’s body without posing a threat to them. 

Besides those, the material also has the following mechanical properties: 

• Elongation To Fracture: With a 15.5% elongation-to-fracture ratio, Nitinol has an impressive ability to withstand change without cracking its formation or shape.  
• Yield Strength: Typically, nitinol comes with a yield strength of 560 MPa in high temperatures. The number reduces drastically to 100 MPa in low temperatures. 
• Elastic Modulus: In high temperatures, nitinol has an approximate elastic modulus of 75 GPa – a number which reduces to just 28 in low temperatures. 

The Nitinol Cable Construction Process

How To Shape Nitinol Wires

In the next module, we’ll look into how to shape the nitinol wire perfectly.

As explained earlier, the features that most people look into when working with nitinol wires are the shape memory effect and the pseudo-elasticity. 

In high temperatures, nitinol becomes incredibly stiff. However, when it is cooled, the alloy takes on a flexible and rubbery shape that allows it to easily be deformed. This is the point where you form it into your desired shape. When nitinol is heated to the transformation temperature, the metal easily goes back to its initial shape.

Remember that you can always make adjustments to the temperature where nitinol’s shape memory kicks in. However, for these adjustments to be made, you also need to change the alloy’s chemical composition and switch the hat treatment method. 

All in all, keep in mind that the transformation effect in nitinol is reversible – and that this transformation happens instantly, regardless of the direction. 

You should also note that nitinol itself isn’t usually the only thing that’s in the wire. Due to its propensity for deformation, wire manufacturers tend to add other materials to a nitinol strand – stainless steel being one of the most popular.

This addition provides more strength to the cable, while also improving its longevity.

When using nitinol wire, you’d need to start by defining the shape you want it to be in and setting the wire. The process that is employed is primarily through heating, where you constrain the nitinol element on a fixture of the desired shape and apply the right heat treatment. 

As you consider how to make a nitinol wire, you should know that the heat treatment method you use in setting shapes for it are similar, whether the nitinol is in its superelastic or shape memory form.

Finally, you also want to pay special attention to the treatment parameters you choose when setting the shape – as well as the physical properties of the nitinol wire you have. In general, you can set shapes with temperatures as low as 400°C. But, based on the wire’s composition and properties, that temperature could easily change.

When the time comes to cool the wire, this can usually be done through a simple water quench or a quick air cooling sequence. 

How Nitinol Wires Can Be Cut 

When a nitinol wire is being cut, you need to ensure that you have the right wire cutters. Whether it’s an automatic nitinol wire cutter or a manual one, ensure that the cutter’s blades are strong enough and more robust than the wire itself. 

Most nitinol wire cutters are made of carbon steel with tungsten carbide layering. You can find them in different shapes including: 

• Round-head wire cutters
• Oval head wire cutters
• Taper head wire cutters

Get the right option, and you’ll find that crimping a nitinol wire will be as easy as possible. 

Nitinol Industrial Applications 

So, you might be thinking – why should I buy a nitinol wire? Well, nitinol is one of the most versatile materials available right now, with functionalities that vary significantly. Some of them include:

Medical Industry Applications

Amongst its many applications, nitinol has gained the most prominence from its use in the medical field. Thanks to the material’s biocompatibility, shape memory, and elasticity, the material helps in the manufacturing of multiple devices and medical components. Some of these include:

• Orthodontic Archwires: In the field of orthodontics, nitinol is used in manufacturing archwires. A nitinol orthodontic wire is applied in the orthodontics field to apply extensive forces to help move and align teeth in the desired position. 
• Developing Stents: Nitinol is used in building surgical stents that are broadly used in conducting minimally invasive surgical procedures. These surgical procedures primarily look to treat narrowed or blocked blood vessels. These nitinol stents can easily be pressed into small diameters for delivery, then they can be expanded back into their original shape when they are deployed. With their flexibility, nitinol stents help to improve the overall efficiency and delivery of surgical procedures. 
• Surgical Tools: Thanks to its superelasticity, nitinol is also applied in the production and use of surgical equipment across the board. From stone retrieval baskets to retrievable filters and biopsy forceps, nitinol wire uses are incredibly extensive. 
• Dental Instruments: Like the general medical field, nitinol wire applications also extend to the dental space. The material is used in different applications, from endodontics (shaping and treating root canals during procedures) to creatine endodontic files and other dental implants. Dentists and manufacturers rely on its flexibility a great deal, and they use the material for a myriad of applications. 

Aerospace and Automotive Manufacturing 

Away from the medical space, nitinol wires have also found significant use in the aerospace and automotive sectors. Some of its most significant uses include: 

• Developing Motors & Actuators: In general electrical engineering, it is almost impossible to overstate the use of actuators and sensors. Nitinol actuators can help to convert thermal energy into mechanical work, allowing them to be used in applications such as flap and valve control – as well as manufacturing engine components for different aerospace and automotive systems. 
• Building Vibration Dampers: Nitinol strips and wires can also be integrated into structures that help them to provide optimal vibration dampening and noise reduction. This provides a base for aerospace and automotive components to work better and more seamlessly across the board. 

Consumer Goods Production 

Nitinol is also applied in developing different new-age consumer products, thanks again to its unique qualities. Some examples of products that the material has been used to make include: 

• Smart Materials: Nitinol is applied in developing smart products and electronics, with applications such as smart textiles, foldable displays, self-repairing phone cases, and much more.   
• Eyeglasses: Nitinol frames are renowned for their flexibility and ability to withstand squeezing or deformation. They are also durable and resilient, meaning that they don’t break easily and can hold in a lot of contact. 
• Electronics: Mobile phones require components such as cameras, optical image stabilizers, antennas, and microphones. All of these can be made using nitinol. 

You should note that these are just some of the many applications of nitinol. With its unique properties, the material is incredibly versatile and able to handle different forms of applications. And, as time goes on, there is no doubt that more manufacturers will be looking to buy nitinol wire for its different uses.

Why Are Nitinol Wires So Advantageous? 

The benefit of nitinol comes from its elasticity and shape-changing ability. This allows it to be very flexible – a property that materials such as stainless steel just don’t have. 

The nitinol wire composition remains a major factor for you to consider when using it, but all in all, it is a good option for different functionalities. 

Another benefit of nitinol wire medical functionalities is the material’s strength. Consider in the dentistry profession, for instance – nitinol is used to make braces, and thanks to its shape adjustment, it holds on to its tension over time. Materials like stainless steel that lose tension won’t be able to last, and patients would need to get new braces every now and then. With nitinol, you never have to worry about this. Fewer trips to the dentist mean you get to save money and energy in the long run. 

Possible Cons Of Nitinol Wires

If you’re a manufacturer or a user, attachment will most likely be the biggest issue you face with nitinol wires. Depending on their current phase, nitinol wires can be stiff or flexible. So, welding or bonding them can be a bit of a challenge. 

You could try crimping a nitinol wire mechanically to the other, with materials like stainless steel helping to ease the attachment. The next step will be simple welding, which would aid in creating the final product.

To do this, however, it is important that you work with a skilled and experienced wire manufacturer. This is why we recommend giving us a call at Tuolian Metal . We can develop the right techniques for using nitinol wires, thus helping your project. If you need further advice, feel free to reach out to us as well.  

Conclusion 

Nitinol is one of the most fascinating materials out there. With its pseudoelasticity and shape memory effect, the material is flexible enough to serve different purposes. 

Looking for where to buy the nitinol wire? Give us a call at Tuolian Metal. We are the best nitinol wire suppliers in the market, and we’ll be able to get you what you need.  

Frequently Asked Questions 

How much is nitinol wire.

Generally, you should be able to get nitinol wire for about $427 per kilogram. However, note that the price you pay will also vary based on the manufacturer and supplier. 

The nitinol wire price is one of the most significant factors to be considered when making a purchase. However, you should also remember that a cheaper wire doesn’t necessarily mean it’s the best for you. We recommend getting in touch with us at Tuolian Metal to discuss the best nitinol wire option for you while considering all factors. 

Is nitinol wire used in surgery?

Among the many uses of nitinol wire in the medical field, the material can also be used for surgery. It works for vascular surgeries, as well as in manufacturing medical prostheses and other tools. 

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How to shape set nitinol.

Why Aren’t Detailed Shape Setting Instructions Posted Online?

This is one of the most common questions we get from customers who are building prototypes.  Obviously, it would be greatly helpful if specific instructions could be published and followed precisely because, then more people would be using nitinol and nitinol would rapidly be adopted by just about everyone.

Unfortunately, there isn’t a detailed, standardized process to follow.  This is largely due to the fact that nitinol is extremely sensitive to the heat profile.  Changing the heat treatment profile by a few degrees can have rather dramatic changes in the mechanical properties of the nitinol.  This means that seemingly unrelated things, like changing the fixture, can have significant changes in the properties of the part unless the heat treatment profile is customized for that part.

So, even though specific heat treatment profiles cannot be published, some guidelines can be published:

• Basic shape setting: To set the memory shape, you want the nitinol to reach a temperature of 500-550℃ (930-1020℉).  If the temperature exceeds 600℃ (1,100℉), you start to lose the microstructure.
• At Kellogg’s Research Labs, we use temperatures ranging 250-750℃ (480-1,380℉).
• Short heat treatment times result in smaller grains, yielding better fatigue properties and higher stiffness.
• At Kellogg’s Research Labs, we use heat treatment times ranging from 30 seconds to 72 hours.
• Multi-step heat treatment profiles are common.  At Kellogg’s Research Labs, we use up to 8 stage heat treatment profiles with quenches and ramps between each stage.
• Optimum properties are going to be tightly distributed around a particular heat treatment profile, so the profile must be closely adhered to.

While this may come as a bit of a let-down, I hope it provides some clarity about why specific heat treatment profiles are not posted online. Read our book Nitinol in Plain Language to learn more about the shape setting process. https://www.kelloggsresearchlabs.com/product/nitinol-in-plain-language/

Alina Baron

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Vibration control of composite laminate via nitinol-steel wire ropes: modeling, analysis, and experiment, establishment of the model, establish the dynamic equation, experimental design, conclusions, declaration of competing interest, acknowledgments, recent progress of reinforcement materials: a comprehensive overview of composite materials, j. mater. res. technol., some experimental investigations in the drilling of carbon fiber-reinforced plastic (cfrp) composite laminates, int. j. mach. tool manuf., in-flight and wireless damage detection in a uav composite wing using fiber optic sensors and strain field pattern recognition, mech. syst. sig. process., functionalized composite structures for new generation airframes: a review, compos. sci. technol., recent advances of interphases in carbon fiber-reinforced polymer composites: a review, compos. b eng., recent advances in nonlinear passive vibration isolators, j. sound vib., an investigation into the performance of macro-fiber composites for sensing and structural vibration applications, multi-disciplinary design optimization of composite structures: a review, compos. struct., new b-value parameter for quantitatively monitoring the structural health of carbon fiber-reinforced composites, identification of temperature-dependent elastic and damping parameters of carbon–epoxy composite plates based on experimental modal data, synergetic enhancement of interfacial properties and impact resistant of uhmwpe fiber reinforced composites by oxygen plasma modification, lamb wave-based damage assessment for cfrp composite structures using a chmm-based damage localization algorithm and a damage quantitative expression, nonlinear vibrations and dynamic snap-through behaviors of four-corner simply supported bistable asymmetric laminated composite square shell, a review of composite lattice structures, novel designable strategy and multi-scale analysis of 3d printed thermoplastic fabric composites, multi-directional compression behaviors and failure mechanisms of 3d orthogonal woven composites: parametric modeling and strength prediction, mater. design., vibration characteristics of novel multilayer sandwich beams: modelling, analysis and experimental validations, an experimental method to estimate the electro-mechanical coupling for active vibration control of a non-collocated free-edge sandwich plate, analysis and design of a semi-active x-structured vibration isolator with magnetorheological elastomers, passive and active vibration isolation systems using inerter, nonlinear energy pumping under transient forcing with strongly nonlinear coupling: theoretical and experimental results, an inertial nonlinear energy sink, nonlinear energy sink with inerter, a device capable of customizing nonlinear forces for vibration energy harvesting, vibration isolation, and nonlinear energy sink, a lever-type nonlinear energy sink, nonlinear dynamic analysis and vibration reduction of two sandwich beams connected by a joint with clearance, dynamic characteristics and vibration control of composite laminate wall panels in electric aircraft using niti shape memory alloys, nonlinear broadband vibration reduction of nitinol-steel wire rope: mechanical parameters determination and theoretical-experimental validation, dynamics control of l-shaped composite structure in electric aircraft: theoretical analysis and experimental validation, vibration control of interconnected composite beams: dynamical analysis and experimental validations, a generalized bouc–wen model for simulating the quasi-static and dynamic shear responses of helical wire rope isolators.