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The Technology behind SMA

Shape memory alloy as a technology - what's behind it?

Our products are used in many different areas. From household appliances and medical technology to aerospace. Behind all products is the same smart technology: the shape memory alloy. Shape memory alloys are functional materials that can assume key functions in modern technological applications thanks to their special effects. For example, they can advantageously substitute existing technologies or enable functions that cannot be implemented with conventional solutions under given boundary conditions. They are characterized by their ability to return to a defined shape after an apparently plastic deformation. A distinction is made based on the physical quantities that cause a shape memory effect:

• Mechanical: superelasticity / pseudoelasticity

• Thermal: two-way effect

• Thermomechanical: one-way effect

All shape memory effects are based on a solid state phase transformation, more precisely described, the martensitic phase transformation. A martensitic phase transformation proceeds diffusionless in a shear of the crystal lattice. Based on the nature of the phase transformation, the low-temperature phase in shape memory alloys, just as known in steels, is called martensite. The high-temperature phase is called austenite. The different effects that result from the solid state phase transformation enable it to be used for technical systems in an intelligent way that is adapted to the respective need. At Ingpuls, nickel-titanium-based shape memory alloys, also known as Nitinol, are primarily produced and used. NiTi-SMA are especially characterized by their high possible effect paths/forces, corrosion resistance and biocompatibility compared to other SMA.

 Pseudoelasticity / Superelasticity

Pseudoelasticity, or superelasticity, describes the ability of a metallic material to be subjected to elastic/reversible strains that are orders of magnitude above the elastic strains that a conventional steel can assume. In the case of pseudoelasticity, the material is in its high-temperature phase, austenite, at the application temperature. The component has thus already assumed its defined shape. If it is subjected to mechanical stresses, the material undergoes stress-induced transformation to martensite at a critical point. In the process, martensite variants are formed that are oriented favorably to the direction of stress. The formed "twinned martensite" provides the effect path, which macroscopically manifests itself in a large strain. When the material is unloaded, this converts back to austenite. Since austenite only permits lattice modification, the material reshapes itself into the original shape in the course of the unloading and associated transformation. The behavior is comparable to that of rubber. Pseudoelasticity is used primarily in medical technology. For example, stents made of pseudoelastic SMA can be guided through microcatheters due to their large elastic stretching capacity. When the stent reaches the vessel to be supported, the catheter is withdrawn and the stent can fully expand and support the vessel wall. Here, even after many years, it survives the cyclic stress of each heartbeat.

 One-way effect

In the one-way effect, a material is apparently plastically deformed in its low-temperature phase and then returns to its original shape in the course of heating. The low-temperature phase martensite is characterized in SMA by the presence of certain crystallographic regions within the martensite grains, so-called twins. If a stress is applied to a component as a martensitic phase, twin variants favorable to the stress direction grow at the expense of other variants above a critical stress. In this case, the material can be deformed at a low stress level. In the high-temperature austenite phase, there is only one way in which atoms can arrange themselves in the lattice. Thus, when heated above a critical temperature, the material reshapes into its original shape and remains in this shape after cooling to the low-temperature phase without the influence of a mechanical stress. Therefore, to take advantage of this effect in cyclic applications, an external mechanical stress is needed to deform the component into a different geometry when cold. This is known as the extrinsic two-way effect.

Two-way effect

The extrinsic two-way effect is used, for example, in thermostatic valves. Here, an SMA compression spring works against a spring made of a conventional steel. When cold, the steel spring applies a force high enough to compress the SMA compression spring. When warm, the SMA spring "remembers" its longer shape and thus applies a force that can compress the steel spring. Thus, with proper design, this effect can be applied for many 100,000 cycles. The temperatures that produce the effect are adjustable by alloy composition, microstructure and the design layout.

Subcategories

 From the discovery of SMA to your new possibilities

The shape memory effect was discovered by A. Ölander in a gold-cadmium alloy as early as 1932. In 1963, then, the Naval Ordnance Laboratory achieved a breakthrough with nickel-titanium in the USA. Since then, the research intensity has progressed in different waves. Thousands of patents were created, but in relation to this, only a few solutions proved to be feasible in the past.

With its peak competence in this field, Ingpuls GmbH stands out as a unique supplier worldwide. For the first time, solutions based on SMA are conquering the markets across industries - with a totally new maturity level - and are displacing established solutions: A new wave has been triggered which is finally leading to real products.

 Complexity down to the last atom. What are the challenges?

The breakthrough was lacking in the past due to several reasons. To begin with, there was a lack of a fully integrated supplier that represented the entire industrial value chain from the development to the installation in functional solutions. Many omissions and mistakes were made in the past especially at the interface between supplier and user. In addition, SMA requires absolute specialist knowledge in all areas concerned: With SMA, it is important to reconcile the extremely complex relationships between material composition (alloy) and processing (melting and heat treatment to the semi-finished product) with an understanding of the customer’s installation situation and operating conditions. Even the slightest deviation in any of these areas resulted in products that simply did not work anymore. So the customer would think: SMA works. But that is not true in most cases.

 How to make the most of your possibilities with SMA

Accordingly, only a fraction of SMA’s potential has been exhausted today. Used correctly, SMA offers you a blue ocean in your market. Its possibilities are diverse and almost unlimited, as SMA is a cross-sectional technology.

With Ingpuls as a fully integrated solution provider for functional materials made from SMA, you now have undreamt-of opportunities to innovate on the market. This is because Ingpuls masters the material-specific complexities like no other supplier before - and all from one source. All you need to do is tell us what you require. If you’d like to talk to us about your projects right away and simply see where your thoughts might lead - then simply contact us now.

 Your introduction to SMA

The more you understand the basic properties of SMA, the more likely you are to identify and filter out the best of your ideas and concepts. We offer you seminars and webinars in which you can learn the technical basics of SMA, at our office, at your premises as an in-house seminar or fully digitally without travel costs and CO2 emissions in the form of a webinar. Or would you like to get going straightaway? We cordially invite you to engage with the SMA topic and discover your new potentials. Should you have any further questions, we will be happy to assist you - just contact us!

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