1. What shape memory alloys are (the short version)

• An alloy that moves between two crystal structures: nitinol is an alloy of nickel and titanium in nearly equal atomic proportions, and it undergoes a reversible transformation between a high-temperature phase (austenite) and a low-temperature phase (martensite). Driven by temperature it gives the shape memory effect; driven by stress it gives superelasticity (pseudoelasticity) Sourced [Ref. 1]
• The transformation temperatures move with composition, processing, heat treatment and cycling: the introduction of a review states that in shape memory alloys in general a composition change of 1 at.% can shift the transformation temperature by about 100 K. In Ni–Ti too, aging and thermal cycling move the values Sourced [Ref. 8, 6, 9]
• Evaluation standards are mainly JIS H 7xxx and the ASTM F series; ISO, IEC and IEEE standards could not be confirmed: even for the transformation temperature alone, thermal analysis and bend-and-free-recovery need not give the same value Sourced [Ref. 1, 32]

2. Mechanism — a reversible transformation between two crystal structures

Nitinol is a nearly equiatomic Ni–Ti alloy. The FDA guidance explains that its properties come from reversible transformations between austenite and martensite, which can be induced by temperature (shape memory) or by stress (pseudoelasticity) Sourced [Ref. 1]. As for crystal structures, the review by Wang et al. says that, depending on thermal or mechanical conditions, the alloy can be B2 austenite, B19′ martensite (monoclinic) or the rhombohedral R-phase Sourced [Ref. 10]. Shamimi et al. likewise treat transformations in which the R-phase appears between the B2 parent phase and B19′ martensite [Ref. 6].

The transformation temperatures are defined separately for cooling and heating. On cooling, the temperature at which the high-temperature phase starts to turn into martensite is Ms and the temperature at which it finishes is Mf. On heating, the temperature at which martensite starts to revert is As and the temperature at which it finishes is Af. For two-stage transformations with an R-phase in between, the definitions are given in terms of the R-phase (the FDA guidance reproduces the definitions) Sourced [Ref. 1].

View the original SVG schematic and exact annotations

Superelasticity is the phenomenon in which, above Af, applying a force triggers the transformation and a large deformation, and removing the force makes the reverse transformation return the original shape. In the stress-strain curve a “plateau”, over which the stress is nearly constant, appears while the transformation proceeds, and the plateau on unloading is lower than on loading (Fig. 3). The FDA guidance also notes that the region of near-constant stress is why mechanical testing is commonly done under displacement control Sourced [Ref. 1].

The strain that can be recovered depends strongly on conditions. The review by Wang et al. cites recovery from deformations of up to about 10% in Ni-Ti [Ref. 10]. Tanaka et al. describe a superelastic strain of more than 13% in an iron-based alloy as “almost twice the maximum superelastic strain obtained in the Ni-Ti alloys” [Ref. 13]. A review of actuators, on the other hand, says that straight wires give predictable cyclic durability at moderate strain levels of 3–4% or less [Ref. 23]. Even the same “recovery strain” means different things for a single recovery or repeated recovery, and with or without load Sourced.

3. What moves the transformation temperatures — composition, processing, aging, cycling, measurement

The transformation temperature is not a constant of an alloy. Fig. 4 shows six factors that the sources confirm.

(1) Composition: a small difference in Ni content makes a large difference

In their introduction, Beke and Azim state the known fact that in shape memory alloys a composition change of 1 at.% can shift the transformation temperature by about 100 K. They also note that in Ti–Pd-based alloys this slope varies by about a factor of four, between −15 K/at.% and −60 K/at.%, depending on the third alloying element Sourced [Ref. 8]. This is a statement about shape memory alloys in general, not a value for NiTi alone. In a NiTi-20 at.% Zr high-temperature shape memory alloy, varying Ni by just ±0.2 at.% (49.8, 50.0 and 50.2 at.%) gave very different transformation temperatures, and different responses to aging at 550 °C and 600 °C. In the solutionized state the Ni-lean alloy had the highest transformation temperatures; with aging, those of the Ni-lean alloy kept falling while those of the Ni-rich alloy rose Sourced [Ref. 9].

(2) Cold work and aging: setting the shape, strengthening, and tuning the temperature

According to Shamimi et al., the medical device industry uses a combination of cold work and aging on Ni-rich Ni–Ti to shape-set, strengthen and adjust the transformation temperatures. These three aims conflict. Accurate shape setting is promoted by longer times at higher temperatures, whereas maximum strength requires keeping the cold work, hence low temperatures and short times. Controlling the transformation temperatures requires precise control of the heat-treatment temperature, which sets the amount of Ni₄Ti₃ precipitation and the Ni/Ti ratio of the matrix. The commonly used aging and shape-setting range is 350–575 °C Sourced [Ref. 6].

The effect of heat treatment is also shown in a separate study of a similar composition. When a rapidly solidified Ti49Ni51 alloy was heat-treated at 723, 773 and 823 K, the microstructure (B2 phase, Ti₃Ni₄, Ti₂Ni and so on) and the transformation path (such as the number of stages A→R→M) changed, and at 773 K the thermal hysteresis became small Sourced [Ref. 11]. A NASA report found that for nitinol ribbon the room-temperature tensile behavior depends strongly on the thermomechanical history before the test, and that the amount and stress state (twinned or detwinned) of the R-phase decide the critical stress of the first plateau Sourced [Ref. 18].

Even low-temperature aging changes the values. Shamimi et al. aged Ni 50.8 at.% Ni–Ti, after solution treatment and after ordinary cold work plus aging, at a further 25–250 °C for 1 hour to 1 month (720 hours). Even at 100 °C they saw nickel clustering and nanometre-scale Ni₄Ti₃ precipitation, and the transformation temperatures moved (in a solution-treated sample aged at 100 °C for 105 hours, precipitates of about 5 nm were seen by transmission electron microscopy). The paper points out that many medical devices specify transformation temperature ranges as tight as ±3 °C, and that temperatures in this range occur in processing steps such as co-extrusion and the application and curing of coatings Sourced [Ref. 6].

(3) Repeated thermal cycling: values move until they settle

For their NiTi-20Zr alloys, Carl et al. followed Af and Ms over ten thermal cycles and defined a transformation as “stable” when it dropped by less than 0.5 °C between consecutive cycles. The Ni-lean and equiatomic alloys were nearly stable after three heating cycles in the solutionized state, but the Ni-rich alloy needed eight, and the difference in Af between the first and tenth cycles was 39.5 °C in the solutionized state and about 25 °C after heat treatment Sourced [Ref. 9]. A value measured on the first cycle differs from the value after the alloy has settled in use.

(4) How it is measured: the same sample gives different values by method

The FDA guidance recommends giving the transformation temperatures for the final finished form (after all manufacturing steps, including sterilization), and where possible from samples of at least three production lots, because the transformation temperatures are sensitive to small variations in temperature or heating time. As methods it names thermal analysis (ASTM F2004), bend and free recovery (ASTM F2082) or an equivalent method, and notes that these test methods do not necessarily measure the same Af temperature for a given material or device Sourced [Ref. 1].

NASA researchers tested 55NiTi on specimens from the same heat and the same batch, changing only the test procedure. Under constant stress and thermal cycling, the test procedure changed the transformation strain by 0.005–0.01 mm/mm, which translates to a difference in work output of about 2 J/cm³. The transformation temperatures were less affected than the transformation and irreversible strains, and differed only with respect to the applied external stress. The authors also state that, although shape memory alloys have been around for almost five decades, apart from some standards for transformation temperatures no real standards exist for the mechanical and thermomechanical properties (a statement from 2008) Sourced [Ref. 17].

4. How superelastic stress changes with temperature

Superelastic stress is tightly linked to temperature. Shamimi et al. express the height of the plateau (the stress at which the transformation starts) as the difference between the test temperature T and Ms, multiplied by the slope of stress against temperature (the Clausius–Clapeyron coefficient) dσ/dT.

σ = ( T − M_s ) × dσ/dT

In systems without an R-phase, dσ/dT is about 6–7 MPa/°C, a value for wire or tube measured in tension (the paper notes that it depends on the deformation mode and the texture). When an R-phase is involved and the A/R/M triple point lies above room temperature, it is the 3.5–4.0 MPa/°C of R→M Sourced [Ref. 6]. For the iron-based Fe–Mn–Al–Ni alloys, Omori et al. report a superelastic stress that varies by only 0.53 MPa/°C (from −196 to 240 °C) for one composition, which they explain by a small transformation entropy change brought about by a magnetic contribution Sourced [Ref. 12].

The shape of the superelastic plateau also needs care. Shamimi et al. say that strain localization such as the “Lüders bands” seen in uniaxial tension (the transformation spreading in bands) shows up as a drop in stress on unloading (a reverse yield drop) and a flat plateau, and that the unloading plateau can be higher than predicted from the transformation temperatures of a stress-free thermal test [Ref. 6]. The transformation temperature from thermal analysis and the plateau stress from tensile tests must be measured separately and then related to each other.

5. Fatigue — read it with strain amplitude and number of cycles

Fatigue of shape memory alloys has two meanings. “Structural fatigue” is failure by cracks that start and grow under repeated loading. “Functional fatigue” is the gradual change, before failure, of functions such as the transformation temperatures, the plateau stress and the residual strain. The title of the review by Eggeler et al., “Structural and functional fatigue of NiTi shape memory alloys”, reflects this distinction [Ref. 26]. The fall in Af during thermal cycling in Carl et al. (Section 3) is an example of a change in function [Ref. 9].

On structural fatigue, an FDA regulatory science tool explains that several studies have associated low-cycle fatigue (less than approximately 10 million cycles) with cyclic phase transformation in nitinol, that load levels without cyclic phase transformation would be expected to survive to approximately 10 million cycles, and that fatigue fractures beyond 10 million cycles may still occur. It applies only to pseudoelastic nitinol Sourced [Ref. 2]. The FDA guidance recommends fatigue testing in a liquid close to the service environment rather than in air, because tests in air are sensitive to test frequency through heating effects. It says that a constant-life diagram of mean versus alternating strain, rather than stress, has been found to model fatigue life well, that fatigue life is sensitive to composition and processing, and that the effect of pre-strain (such as crimping a stent) should be considered Sourced [Ref. 1].

A recent study shows a large extension of bending-fatigue life by surface treatment. With a surface treatment called pre-strain warm laser shock peening (a method that works the surface layer by the impact of laser pulses), the bending fatigue life exceeded 5 million cycles at a maximum surface tensile strain of 1.94%, more than 3000 times that of untreated nanocrystalline NiTi (the authors’ claim, for a specific NiTi and specific conditions) Sourced [Ref. 25]. For temperature, Lin et al. found in dynamic mechanical analysis tests that above Af the fatigue life becomes shorter as temperature rises and the energy dissipation decreases [Ref. 24].

6. Cu-based, Fe-based and high-temperature shape memory alloys

Ni–Ti is at the centre of practical use, but other alloy systems have their own features. Tanaka et al. state that, as of 2010, the Ni-Ti-based alloy, which exhibits some ductility and excellent superelastic strain, was the only superelastic material available for practical applications Sourced [Ref. 13]. The table summarizes what we could confirm, including later systems.

All Sourced (statements in the abstracts and introductions of the papers). The arrangement of the table is our commentary. Values for different systems come from different test conditions and sample forms, so they are not ranked against each other.

The NASA report by Noebe et al. shows that “having a high transformation temperature” and “being able to do work” are different things. Ni₃₀Pt₂₀Ti₅₀ (20Pt) has transformation temperatures above 230 °C and Ni₂₀Pt₃₀Ti₅₀ (30Pt) above 530 °C. Both, deformed at room temperature, showed 100% no-load strain recovery for strain levels up to their fracture limit (3–4%). Under constant load and thermal cycling, however, the 20Pt alloy behaved like conventional binary NiTi, with a maximum work output of nearly 9 J/cm³ limited by its tensile ductility. The 30Pt alloy, in contrast, had an austenite yield strength similar to or lower than that of martensite, so its transformation strain under load was essentially zero and its work output was zero Sourced [Ref. 16].

7. Applications and how they are evaluated — medical devices, aerospace, actuators

(1) Medical devices: what regulatory documents ask of the material

The FDA guidance says that nitinol is used in cardiovascular devices such as stents, heart valves, guidewires and vena cava filters, and in a growing number of products for minimally invasive procedures. It adds that nitinol’s thermomechanical behavior and processing sensitivity raise special considerations compared with conventional metals such as stainless steel, titanium or cobalt-chrome, and it sets out technical considerations for non-clinical assessment. The guidance contains nonbinding recommendations; the version issued on 9 July 2021 is the current one Sourced [Ref. 1].

From the materials side, the guidance’s items correspond to the earlier sections of this article (our commentary).

All Sourced (a summary of the items of the FDA guidance [Ref. 1]). The guidance ties the details of each item to the conditions of each product. This article does not assess any particular product and gives no medical advice.

(2) Aerospace: actuation, weight saving and high temperature

The review by Hartl and Lagoudas covers aerospace applications of shape memory alloys, for both atmospheric flight and space flight, including past and present examples and design challenges [Ref. 22]. NASA technical reports give concrete examples.

• Variable geometry chevron: chevrons, the serrated trailing edges of a jet engine’s exhaust nozzle, reduce noise at takeoff. Cabell et al. tested a full-scale variable geometry chevron (VGC) fan nozzle incorporating shape memory alloy actuators under representative flow conditions in Boeing’s Nozzle Test Facility. A proportional-integral control system that regulates the heating of the actuators controlled the chevron’s tip immersion, and controllable immersion was demonstrated Sourced [Ref. 19].
• For hot exhaust: a 2011 NASA Tech Brief explains that high-temperature shape memory alloy technology enables adaptive chevron devices to operate in both the low-temperature fan flow and the high-temperature core flow Sourced [Ref. 20].
• Superelastic spring tire: NASA Glenn Research Center and Goodyear developed a compliant, non-pneumatic tire made of woven coil springs for Martian and Lunar rover vehicles. The version with superelastic shape memory alloy springs is described as able to undergo approximately 30 times more reversible deformation than a steel spring, and large-scale finite element analysis that includes the complex interaction of the springs is used in its design Sourced [Ref. 21].

(3) Actuators: response is set by cooling more than by heating

A 2026 review by Romančík et al. says that shape memory alloy actuators are most commonly cooled by heat dissipation to the room-temperature surroundings, and that faster operation needs forced cooling such as forced air convection, heat sinks, cooling liquids or Peltier elements. The response time is governed by the heating and, in particular, the cooling rate, and one motion cycle usually takes several seconds; this is among the most significant limitations. Straight wires give high recovery stress and predictable cyclic durability at moderate strain (3–4% or less), but their usable stroke is limited. Coils amplify displacement at the expense of mechanical bandwidth and fatigue life, and multi-wire bundles accumulate heat, which reduces the achievable cycle frequency Sourced [Ref. 23]. The same review states that the energy density of SMA actuators is reported at 5000–25,000 kJ/m³, far above the 40–70 kJ/m³ of human skeletal muscle Sourced [Ref. 23].

(4) Fabrication and processing

Wang et al. say that NiTi has poor workability, which makes complex-shaped components difficult, and that additive manufacturing such as selective laser melting (SLM) offers freedom to build complex structures. Their review summarizes the distinctive microstructure that SLM produces and the transformation behavior and mechanical properties reported for various build conditions Sourced [Ref. 10]. The transformation temperatures and function of built parts are likely to depend on build conditions and heat treatment (our commentary), but a quantitative comparison is outside the scope of our research.

8. Limits, and what we could not confirm

(1) The quantitative link between composition and transformation temperature

We could not show, from the primary sources we confirmed, how much the transformation temperature of NiTi changes per at.% of Ni. The “about 100 K per at.%” in Section 3 is a statement about shape memory alloys in general.

(2) How the papers were read

We read the full texts of Shamimi et al., the FDA guidance, the FDA regulatory science tool page, the introduction and results of Carl et al., the introduction of Beke et al. and the introduction of Wang et al. For Tanaka et al., Omori et al., Ma et al. and Sutou et al. we checked the publisher abstracts only, and for the NASA reports the abstracts on the NASA Technical Reports Server only. For the reviews of Eggeler et al. and of Otsuka and Ren, we confirmed only existence and bibliographic details. The Elsevier (ScienceDirect) pages state that AI and similar uses are prohibited, so we did not retrieve their contents.

(3) The text of the standards

We have not read the text of JIS H 7001 to 7107 or of ASTM F2004, F2063, F2082, F2516, F2005, F2633, F3211, E2948 and F2129. We confirmed only numbers, titles, years, FDA recognition status and the dates of establishment and revision of the JIS. The ASTM International website states that AI use is prohibited, so we did not open any ASTM site.

(4) International standards (ISO, IEC, IEEE)

A search of the ISO catalogue (10 October 2026) found no standards for “shape memory alloy” or “nitinol”. We could not confirm any applicable IEC or IEEE standard either. Application-specific standards, such as those for orthodontic wires, may cover NiTi, but we did not check this.

(5) Regulation and markets

The FDA guidance is a US document. We have not checked how Japanese or EU medical device regulation treats nitinol, nor prices and supply in any country. We do not rank any company’s products.

(6) Differences between sources

The role of Af differs between sources (Shamimi et al. argue that it can be an unsuitable indicator of superelasticity, whereas the FDA asks for Af, R′f or mechanical data). This article shows both and does not unify them.

9. How to read the evaluation standards

The evaluation of shape memory alloys divides into (a) transformation temperatures (As, Af, Ms, Mf and the R-phase temperatures), (b) tensile properties (plateau stress, recovery strain, residual strain), (c) behavior under repetition (changes of transformation temperature in thermal cycling, mechanical fatigue), (d) composition and specification, and (e) corrosion and release. Japan has a dedicated group of JIS H 7xxx standards for shape memory alloys, and the US has the ASTM F series (a group of nitinol standards for medical devices and surgical implants). We could not confirm international standards (ISO, IEC, IEEE) within the scope of our research.

Table of corresponding standards

JIS titles are our translations from the Japanese.

Numbers, titles and editions were confirmed as follows: ISO on the ISO catalogue pages; JIS in the JISC database; ASTM in the FDA database of recognized consensus standards (last updated 28 September 2026); we did not open any ASTM site [Ref. 29, 28, 32, 33, 3, 4, 5]. The arrangement of the table is our commentary. The ASTM editions (-24, -23, -18 and so on) are those listed in the FDA database and are not necessarily the latest.

The number, title, edition and date of each standard are Sourced (confirmed on the official pages of the standards bodies, the Japanese Industrial Standards Committee and the FDA). Which standard goes in which cell is our own arrangement (Our calculation). We found no revision or draft in progress, so no row falls under Not yet confirmed.

Cautions when reading standards

1. Many of the JIS standards for shape memory alloys were last revised long ago. H 7101 and H 7106 were revised in 2002, H 7001 and H 7107 in 2009, and H 7103 and H 7105 in 2012, and all have been confirmed in recent years (2021 to 2024) [Ref. 33, 32]. The ASTM F series, on the other hand, has had its editions updated in recent years for medical devices (FDA recognition status) [Ref. 3]. JIS and ASTM assume different objects of measurement (laboratory evaluation of a raw material versus a component of a medical device), so their numbers cannot be compared directly.
2. Standards for transformation temperature can give different values depending on the method. The FDA notes that F2004 and F2082 need not give the same Af [Ref. 1]. Read a reported value together with the method, the state of the sample (raw material or final form) and the heating rate.
3. We found no standard that directly specifies fatigue of superelastic alloys. Fatigue is planned by combining F3211 (a guide to fatigue-to-fracture methodology for cardiovascular devices), E2948 (rotating-bending fatigue of fine wire) and others, following the approach of the FDA regulatory science tool [Ref. 2, 5, 4]. A standard is a method, not a guarantee of life.
4. NASA researchers stated in 2008 that standards for the mechanical and thermomechanical properties were not in place. That F2516 and others have since been put in place can be seen from FDA recognition [Ref. 3], but we could not confirm an international standard that directly specifies actuator use (thermal cycling under load, work output) [Ref. 17].

10. Glossary

11. References (primary sources)

1. U.S. Food and Drug Administration (FDA) “Technical Considerations for Non-Clinical Assessment of Medical Devices Containing Nitinol — Guidance for Industry and FDA Staff” (issued 9 July 2021; first issued 15 October 2020; draft 19 April 2019; docket FDA-2019-D-1261; states that it contains nonbinding recommendations) — www.fda.gov/regulatory-information/search-fda-guidance-documents/te…
2. U.S. FDA, Center for Devices and Radiological Health (CDRH) “Strategy to Estimate Low to High Cycle Fatigue Transition of Nitinol for Fatigue to Fracture Test Planning” (Catalog of Regulatory Science Tools) — cdrh-rst.fda.gov/strategy-estimate-low-high-cycle-fatigue-transitio…
3. U.S. Food and Drug Administration (FDA) “Recognized Consensus Standards: Medical Devices” database, search results for titles containing nickel-titanium (database page last updated 28 September 2026) — www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfStandards/results.cfm?…
4. U.S. Food and Drug Administration (FDA) “Recognized Consensus Standards: Medical Devices” database, search results for titles containing nitinol (page last updated 28 September 2026) — www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfStandards/results.cfm?…
5. U.S. Food and Drug Administration (FDA) “Recognized Consensus Standards: Medical Devices” database, search results for reference number F3211 — www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfStandards/results.cfm?…
6. Shamimi A. et al. “The Effect of Low Temperature Aging and the Evolution of R-Phase in Ni-Rich NiTi”, Shap. Mem. Superelasticity 4, 417–427 (2018), DOI 10.1007/s40830-018-0193-9 (full text hosted on a Confluent Medical Technologies page) — doi.org/10.1007/s40830-018-0193-9
7. Confluent Medical Technologies Full-text PDF of the paper by Shamimi et al. above (company document page; we read this full text) — confluentmedical.com/wp-content/uploads/2023/05/5851cb2c40d9a5258e0…
8. Beke D. L., Azim A. A. “On the Strong Composition Dependence of the Martensitic Transformation Temperature and Heat in Shape Memory Alloys”, Materials 17, 4116 (2024), DOI 10.3390/ma17164116 (open access) — doi.org/10.3390/ma17164116
9. Carl M. et al. “Effect of Ni-Content on the Transformation Temperatures in NiTi-20 at. % Zr High Temperature Shape Memory Alloys”, Metals 7, 511 (2017), DOI 10.3390/met7110511 (open access) — doi.org/10.3390/met7110511
10. Wang X. et al. “A Short Review on the Microstructure, Transformation Behavior and Functional Properties of NiTi Shape Memory Alloys Fabricated by Selective Laser Melting”, Materials 11, 1683 (2018), DOI 10.3390/ma11091683 (open access) — doi.org/10.3390/ma11091683
11. Li S. et al. “Effect of Heat Treatment Temperature on Martensitic Transformation and Superelasticity of the Ti49Ni51 Shape Memory Alloy”, Materials 12, 2539 (2019), DOI 10.3390/ma12162539 (open access) — doi.org/10.3390/ma12162539
12. Omori T. et al. “Superelastic Effect in Polycrystalline Ferrous Alloys”, Science 333, 68–71 (2011), DOI 10.1126/science.1202232 — doi.org/10.1126/science.1202232
13. Tanaka Y. et al. “Ferrous Polycrystalline Shape-Memory Alloy Showing Huge Superelasticity”, Science 327, 1488–1490 (2010), DOI 10.1126/science.1183169 — doi.org/10.1126/science.1183169
14. Ma J., Karaman I., Noebe R. D. “High temperature shape memory alloys”, Int. Mater. Rev. 55, 257–315 (2010), DOI 10.1179/095066010X12646898728363 — doi.org/10.1179/095066010X12646898728363
15. Sutou Y. et al. “Ductile Cu–Al–Mn based shape memory alloys: General properties and applications”, Mater. Sci. Technol. 24, 896–901 (2008), DOI 10.1179/174328408X302567 — doi.org/10.1179/174328408X302567
16. Noebe R. et al. (NASA) “Properties and Potential of Two (Ni,Pt)Ti Alloys for Use as High-Temperature Actuator Materials”, Proc. SPIE (16 May 2005), NASA Technical Reports Server 20050185200 — ntrs.nasa.gov/citations/20050185200
17. Padula S. A. II et al. (NASA) “Influence of Test Procedures on the Thermomechanical Properties of a 55NiTi Shape Memory Alloy” (conference paper, March 2008), NASA Technical Reports Server 20080047419 — ntrs.nasa.gov/citations/20080047419
18. Lach C. L. et al. (NASA) “Effects of Thermomechanical History on the Tensile Behavior of Nitinol Ribbon” (2002), NASA Technical Reports Server 20030014802 — ntrs.nasa.gov/citations/20030014802
19. Cabell R. H. et al. (NASA) “Feedback Control of a Morphing Chevron for Takeoff and Cruise Noise Reduction” (2004), NASA Technical Reports Server 20040139184 — ntrs.nasa.gov/citations/20040139184
20. Quackenbush T. R., McKillip R. M. Jr. (NASA) “High-Temperature Smart Structures for Engine Noise Reduction and Performance Enhancement” (NASA Tech Briefs, February 2011), NASA Technical Reports Server 20110012201 — ntrs.nasa.gov/citations/20110012201
21. Naghipour P. et al. (NASA) “Development of the Shape Memory Alloy Spring Tire for Martian Temperatures” (NASA Technical Reports Server 20260008869, released September 2026) — ntrs.nasa.gov/citations/20260008869
22. Hartl D. J., Lagoudas D. C. “Aerospace applications of shape memory alloys”, Proc. Inst. Mech. Eng. G 221, 535–552 (2007), DOI 10.1243/09544100JAERO211 — doi.org/10.1243/09544100JAERO211
23. Romančík J. et al. “Shape Memory Alloy Actuators in Robotics”, Actuators 15, 162 (2026), DOI 10.3390/act15030162 (open access) — doi.org/10.3390/act15030162
24. Lin Y. et al. “Experimental Study on Temperature Effects on NiTi Shape Memory Alloys under Fatigue Loading”, Materials 13, 573 (2020), DOI 10.3390/ma13030573 (open access) — doi.org/10.3390/ma13030573
25. Yan et al. “Bending-fatigue-resistant hierarchical NiTi shape memory alloy”, Nat. Commun. 17, 6376 (2026), DOI 10.1038/s41467-026-72857-z (open access) — doi.org/10.1038/s41467-026-72857-z
26. Eggeler G. et al. “Structural and functional fatigue of NiTi shape memory alloys”, Mater. Sci. Eng. A 378, 24–33 (2004), DOI 10.1016/j.msea.2003.10.327 — doi.org/10.1016/j.msea.2003.10.327
27. Otsuka K., Ren X. “Physical metallurgy of Ti–Ni-based shape memory alloys”, Prog. Mater. Sci. 50, 511–678 (2005), DOI 10.1016/j.pmatsci.2004.10.001 — doi.org/10.1016/j.pmatsci.2004.10.001
28. ISO “ISO 10993-15:2019 Biological evaluation of medical devices — Part 15: Identification and quantification of degradation products from metals and alloys” (ISO catalogue page) — www.iso.org/standard/68937.html
29. ISO “ISO 6892-1:2019 Metallic materials — Tensile testing — Part 1: Method of test at room temperature” (ISO catalogue page) — www.iso.org/standard/78322.html
30. Japanese Industrial Standards Committee (JISC) JISC database entry for “JIS Z 2241” (tensile testing method for metallic materials; established 22 July 1952, latest revision 21 August 2023 [Amendment 1]) — www.jisc.go.jp/app/jis/general/GnrJISNumberNameSearchList?show&jisS…
31. Japanese Standards Association (JSA) Preview pages of JIS Z 2241:2022 (the foreword names ISO 6892-1:2019 as the corresponding international standard, degree of correspondence MOD) — webdesk.jsa.or.jp/preview/pre_jis_z_02241_000_000_2022_j_ed10_ch.pdf
32. Japanese Industrial Standards Committee (JISC) JISC JIS search, list of JIS numbers starting with H 7 (including the JIS for shape memory alloys) — www.jisc.go.jp/app/jis/general/GnrJISNumberNameSearchList?show&jisS…
33. Japanese Industrial Standards Committee (JISC) JIS search (by number or title). JIS Z 2255, C 2501, K 7121, K 7122, R 1611, H 7801, R 3257, R 1703-1, H 7101 and others were confirmed (number, title, dates of establishment and revision) on the JIS list and detail pages — www.jisc.go.jp/app/jis/general/GnrJISSearch.html

12. Claim-to-source audit

Last updated: 10 October 2026. Sources are limited to primary material (peer-reviewed papers, the FDA guidance and regulatory science tool, NASA technical reports, and the databases of the Japanese Industrial Standards Committee, ISO and the FDA). We have not read the text of the standards. Because the article includes organization of structure and readings of materials design, these are marked as “commentary” and kept apart from sourced facts. We could not confirm, and therefore do not state, the change of NiTi’s transformation temperature per at.% of Ni, dedicated ISO, IEC or IEEE standards for shape memory alloys, the text of the standards and the test conditions of ASTM standards, the treatment of nitinol in Japanese and EU medical device regulation, prices and supply in any country, or a quantitative comparison of additively built parts. The values of transformation temperature, stress, strain and life are results for specific alloys, heat treatments and test conditions, and cannot be generalized to other alloys or products. We give no medical advice and no ranking of any product or company. Figs. 2 to 6 are vector drawings and Figs. 1 and 7 are AI-generated images; none of them shows an actual micrograph or a real product.