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Nickel titanium

Nickel titanium, commonly known as Nitinol, is a nearly equiatomic intermetallic alloy composed of approximately 55 weight percent nickel and 45 weight percent titanium, renowned for its unique shape memory effect and superelasticity arising from a reversible martensitic phase transformation.^[1] This alloy demonstrates the ability to return to a predefined shape after deformation when subjected to specific temperatures or stresses, making it distinct from conventional metals.^[2] Discovered in 1962 by metallurgist William J. Buehler at the U.S. Naval Ordnance Laboratory—where the name Nitinol derives from "Nickel," "Titanium," and "Naval Ordnance Laboratory"—the material was initially developed for potential use in missile components due to its high elasticity and fatigue resistance.^[1]^[3] Buehler's serendipitous observation occurred during experiments with nickel-titanium compositions, revealing the shape memory behavior when a deformed sample spontaneously recovered upon heating.^[4] Key physical properties include a density of about 6.5 g/cm³, a melting range of 1240–1310°C, and transformation temperatures tunable from −100°C to over 100°C through compositional adjustments or heat treatments.^[1] Additionally, Nitinol offers excellent corrosion resistance, biocompatibility, and a Young's modulus ranging from 28–83 GPa depending on phase (martensite to austenite), generally lower than traditional titanium (~110 GPa) or stainless steel (~200 GPa) alloys, reducing stress shielding in load-bearing applications.^[2]^[5] The alloy's defining characteristics—shape memory effect (SME), where it deforms in a low-temperature martensitic phase and recovers upon heating to the austenitic phase, and superelasticity (pseudoelasticity), enabling large recoverable strains up to 10% at body temperature—have driven its widespread adoption.^[1]^[2] In biomedical fields, Nitinol is extensively used for self-expanding stents, orthodontic archwires, and orthopedic implants like scoliosis correction rods, leveraging its biocompatibility and ability to mimic soft tissue mechanics.^[2] Beyond medicine, applications span aerospace actuators, naval couplings, vibration dampers, and consumer products such as eyeglass frames and flexible antennas, capitalizing on its durability, non-magnetic nature, and energy absorption capabilities.^[1] Ongoing advancements in additive manufacturing further enhance its customization for complex structures in tissue engineering and minimally invasive devices.^[2]

Properties

Composition and Crystal Structure

Nickel-titanium (NiTi) alloys are primarily composed of nearly equiatomic mixtures of nickel and titanium, with the stoichiometric NiTi intermetallic compound forming at approximately 50 at% Ni, equivalent to about 55 wt% Ni due to the atomic mass difference between the elements. The binary Ni-Ti phase diagram reveals a complex system with multiple intermetallic phases, including the congruent-melting Ni₃Ti (on the Ni-rich side) and NiTi, as well as the NiTi₂ compound (on the Ti-rich side), which contribute to the alloy's microstructural stability by delineating regions of solid solution and eutectic reactions. These phases emerge from peritectic and eutectoid transformations during solidification, ensuring that near-equiatomic compositions yield predominantly the NiTi matrix essential for functional properties like the shape memory effect.^[6]^[7] The crystal structure of NiTi undergoes a reversible martensitic transformation central to its behavior. At elevated temperatures (above the austenite finish temperature, typically around 100–200°C depending on composition), the alloy exists in the B2 austenite phase, an ordered body-centered cubic structure akin to the CsCl prototype, characterized by alternating Ni and Ti atoms at the corners and body center of the cubic unit cell. Upon cooling below the martensite start temperature, this transforms to the low-temperature B19' martensite phase, which adopts a monoclinic crystal structure (space group P2₁/m) with distorted orthorhombic-like features, enabling the twinned variants responsible for shape recovery. This structural shift from cubic symmetry to lower monoclinic symmetry accommodates the shear deformation without permanent distortion.^[8]^[9]^[10] Deviations from the equiatomic composition significantly influence the phase transformation temperatures and overall stability. Ni-rich variants (e.g., 50.5–51 at% Ni) promote the formation of Ni₄Ti₃ precipitates during aging, depleting matrix Ni and thereby elevating transformation temperatures, which is leveraged to tune the austenite-martensite transition for specific applications. Conversely, Ti-rich compositions (e.g., below 50 at% Ni) stabilize higher transformation temperatures and incorporate Ti₂Ni precipitates, enhancing thermal stability but potentially reducing ductility. For instance, a mere 0.4 at% increase in Ni content from 49.8 at% to 50.2 at% can depress martensite start temperatures by approximately 40°C, underscoring the sensitivity of these alloys to stoichiometry. The intermetallic compounds Ni₃Ti and NiTi₂ play crucial roles in off-stoichiometric alloys by acting as secondary phases that pin grain boundaries and control precipitate distribution, thereby improving resistance to grain growth and maintaining phase purity in the NiTi matrix.^[8]^[11]^[6]

Mechanical and Thermal Characteristics

Nickel-titanium alloys, known as Nitinol, have a density of approximately 6.45 g/cm³ and a melting point of 1310 °C. These physical attributes contribute to their lightweight nature and high-temperature processability. Nitinol exhibits excellent corrosion resistance, primarily due to the spontaneous formation of a thin, stable titanium dioxide passive layer that protects against environmental degradation in physiological and aqueous environments. Furthermore, Nitinol demonstrates strong biocompatibility, with low cytotoxicity and minimal nickel ion release when surfaces are properly passivated, enabling safe implantation in the human body. The thermal properties of Nitinol are governed by its reversible martensitic phase transformation, which involves key temperatures: martensite start (Ms), martensite finish (Mf), austenite start (As), and austenite finish (Af). These transformation temperatures are highly tunable through precise control of nickel content (typically 49-51 at.%) and heat treatment, allowing ranges from -100 °C to 100 °C to suit specific functional requirements. For instance, superelastic grades often have Af temperatures between -65 °C and 45 °C, while shape memory variants may extend higher. Mechanically, Nitinol displays remarkable strength and ductility. Superelastic forms exhibit yield strengths (critical stress for phase transformation) ranging from 200 to 600 MPa, ultimate tensile strengths up to 1200 MPa, and elongations greater than 10%, far surpassing many conventional alloys in recoverable deformation. The stress-strain response features a characteristic hysteresis loop, where the area represents energy dissipation during austenite-to-martensite detwinning and reverse transformation.

Property	Typical Value/Range	Notes/Source Context
Density	6.45 g/cm³	Bulk alloy value; enables lightweight designs.^[12]
Melting Point	1310 °C	High thermal stability for processing.^[13]
Yield Strength (Superelastic)	200–600 MPa	Plateau stress at ~3% strain; varies with processing.^[14]
Ultimate Tensile Strength	Up to 1200 MPa	Post-transformation fracture strength.^[14]
Elongation	>10%	High ductility in tension.^[14]
Transformation Temperatures (Ms to Af)	-100 °C to 100 °C	Tunable via composition and annealing.^[15]

Nitinol's fatigue resistance is exceptional, with superelastic variants sustaining over 10^6 cycles at strain amplitudes up to 8% under optimized conditions, attributed to the stress-induced martensite reorientation. Cyclic stability is enhanced by microstructural refinements such as precipitation hardening, which minimize defect accumulation and preserve superelastic recovery over thousands of load cycles.

History

Discovery and Early Research

The shape memory effect in alloys was first observed in the 1930s by Swedish researcher Arne Ölander, who noted the phenomenon in a gold-cadmium (Au-Cd) alloy during studies of phase transitions, marking an early precursor to later developments in shape memory materials.^[16] However, these early alloys were impractical for widespread use due to their toxicity and high cost, prompting searches for more viable alternatives. In the late 1950s, at the U.S. Naval Ordnance Laboratory (NOL) in White Oak, Maryland, metallurgist William J. Buehler initiated research into intermetallic compounds for high-performance applications, such as durable missile nose cones that could withstand extreme temperatures and fatigue. During this work, Buehler and his team developed an equiatomic nickel-titanium (NiTi) alloy in 1959, initially valued for its acoustic damping properties rather than any memory effect.^[17] The alloy, later named Nitinol (derived from NIckel, TIanium, Naval Ordnance Lab), was part of broader efforts to develop corrosion-resistant materials for naval and aerospace uses.^[18] The unique shape memory property of Nitinol emerged serendipitously in 1962 when physicist Frederick E. Wang, who had joined Buehler's group in 1962 to investigate its crystal physics, conducted deformation tests on the alloy. In one notable experiment, a thin Nitinol strip was accidentally bent and folded into an accordion-like shape during handling, exhibiting rubbery behavior at room temperature; upon subsequent heating to around 100°C, it fully recovered its original straight form, revealing the "memory" effect tied to a reversible martensitic phase transformation.^[19] This observation, confirmed through repeated trials on equiatomic compositions, highlighted the alloy's potential beyond initial damping applications. Early dissemination of these findings occurred through key publications and patents from the NOL team. A seminal overview appeared in Buehler, J.V., Gilfrich, J.V., and Wiley, R.C.'s 1963 paper, which summarized Nitinol's properties and potential in ocean engineering contexts. Further structural analysis was detailed in Wang, F.E., Buehler, W.J., and Pickart, S.J.'s 1965 study, identifying the martensitic transition responsible for the memory effect.^[19] Buehler and Wiley secured U.S. Patent 3,174,851 in 1965 for the nickel-base alloys, establishing foundational intellectual property for NiTi compositions.^[17] These works laid the groundwork for understanding Nitinol's phase transformations, though commercial exploration remained limited at the time.

Commercialization and Key Milestones

The commercialization of nickel titanium, commonly known as Nitinol, began in the 1970s with Raychem Corporation leading the way in industrial applications. Raychem pioneered the first major commercial use in 1969, developing CryoFit couplings for aircraft hydraulic lines, which leveraged the shape memory effect to create reliable, leak-proof connections without tools or adhesives.^[20] This marked the transition from laboratory research to practical engineering solutions, particularly in aerospace, where actuators based on Nitinol's thermal recovery were also introduced for mission-critical components.^[21] By the mid-1970s, these products demonstrated the alloy's potential for scalable production, though challenges in consistent material properties initially limited broader adoption. In the 1980s, the discovery and refinement of Nitinol's superelasticity at body temperature spurred consumer and medical applications. Eyeglass frames emerged as a key milestone, with superelastic Nitinol temples allowing frames to bend significantly without permanent deformation, enhancing durability and comfort; these products gained popularity by the late 1980s as manufacturers optimized the alloy for room-temperature performance.^[22] This period also saw initial medical device explorations, building on orthodontic archwires introduced in the late 1970s, which utilized Nitinol's unique elasticity for gentler tooth alignment. The 1990s represented a pivotal era for medical commercialization, driven by regulatory advancements. In 1989, the U.S. Food and Drug Administration (FDA) approved Nitinol for medical applications, enabling its use in implants and devices.^[23] Self-expanding Nitinol stents followed in the mid-to-late 1990s, with early approvals for peripheral vascular use, such as the Intracoil stent in 2000—though foundational trials and humanitarian exemptions began in the prior decade—revolutionizing minimally invasive treatments for arterial blockages by allowing deployment through small catheters.^[24] The 2010s brought significant manufacturing innovations, particularly in additive techniques, expanding Nitinol's design flexibility for complex geometries. Selective laser melting (SLM) emerged as a key method, enabling the production of intricate components like vascular scaffolds with precise control over phase transformation properties, reducing post-processing needs and improving customization for biomedical uses.^[25] Standardization efforts solidified Nitinol's reliability for medical applications, with ASTM F2063 established as the primary specification for wrought nickel-titanium shape memory alloys in surgical implants and devices, defining composition, mechanical properties, and biocompatibility requirements to ensure consistency across global supply chains.^[26] In the 2020s, developments in porous Nitinol structures advanced orthopedic implants, where additive manufacturing produced scaffolds with tailored porosity (up to 70%) to promote bone ingrowth and osseointegration while maintaining superelasticity. These innovations, often combining SLM with surface modifications, have shown enhanced biocompatibility in vivo, supporting load-bearing applications like spinal fusion devices.^[27] Intellectual property in Nitinol has evolved extensively, with over 10,000 patents filed or granted worldwide by 2025, covering alloys, processing methods, and device integrations, reflecting its high-impact status in materials science and biomedicine.

Shape Memory Mechanism

Phase Transformations

The phase transformations in nickel-titanium (NiTi) alloys, known as Nitinol, are characterized by a reversible martensitic transformation between the high-temperature austenite (B2 cubic) phase and the low-temperature martensite (B19' monoclinic) phase. In many compositions, particularly near-equiatomic and Ni-rich alloys, an intermediate rhombohedral R-phase forms prior to the B19' martensite, resulting in a two-step transformation sequence (austenite → R-phase → martensite). The R-phase transformation occurs over a narrow temperature range (typically 20–40°C) and contributes to reduced hysteresis, improved fatigue resistance, and smoother superelastic behavior.^[28]^[29] This process is diffusionless and shear-dominated, involving a coordinated, displacive rearrangement of atoms across the lattice without atomic diffusion, which enables rapid transformation kinetics and reversibility essential for the shape memory effect.^[30]^[31] The forward transformation upon cooling begins at the martensite start temperature (Ms), the point where the first martensite plates nucleate, and completes at the martensite finish temperature (Mf), beyond which the structure is entirely martensitic. The reverse transformation upon heating initiates at the austenite start temperature (As), where martensite begins reverting to austenite, and concludes at the austenite finish temperature (Af), above which the material is fully austenitic. These temperatures form a hysteresis loop, with the heating path offset above the cooling path by typically 20–50°C, reflecting the energy barrier for nucleation and growth.^[30]^[32] The influence of applied stress on these transformation temperatures follows the Clausius-Clapeyron relation, which quantifies the shift in equilibrium temperature with stress:

\frac{dT}{d\sigma} = \frac{T \epsilon_{tr}}{\Delta H}

Here, T is the absolute temperature, \epsilon_{tr} is the transformation strain (approximately 6–8%), and \Delta H is the latent heat of transformation (around 20 J/g). This relation predicts that increasing stress elevates the transformation temperatures, with a typical slope d\sigma/dT of 5–9 MPa/K for NiTi, enabling stress-assisted transformations.^[30]^[33]^[34] In the martensite phase, the structure accommodates the transformation strain through twinning, forming multiple self-accommodating variants with twin boundaries that preserve the overall macroscopic shape. Under applied stress below the austenite range, detwinning occurs as the stress favors certain variants, causing twin boundary motion and variant reorientation, which produces large, recoverable strains up to 6–8% aligned with the loading direction.^[30]^[35]^[36] Superelasticity, also known as pseudoelasticity, in nickel-titanium alloys arises from the stress-induced formation of martensite above the austenite finish temperature (Af), enabling the material to exhibit large recoverable strains of up to 8–10% without permanent deformation upon unloading. This behavior stems from the reversible martensitic phase transformation, where applied tensile stress orients twinned martensite variants to accommodate deformation, distinct from the elastic response of conventional metals. For equiatomic or near-equiatomic compositions, the critical stress for initiating this transformation typically ranges from 400 to 600 MPa at room temperature, allowing applications requiring high flexibility and fatigue resistance.^[35] The characteristic stress-strain curve during superelastic loading displays a hysteresis loop, featuring upper and lower plateaus that correspond to the forward (austenite to martensite) and reverse (martensite to austenite) transformations, respectively. The flatness of these plateaus indicates near-constant stress during phase change, while the enclosed area of the loop quantifies energy dissipation through frictional work and heat generation, often amounting to 10–20 J/cm³ per cycle. This dissipation mechanism contributes to the alloy's damping capabilities but also limits efficiency in high-cycle applications.^[35] Related phenomena include variations in shape memory effects tied to these phase transformations. The one-way shape memory effect recovers a single programmed shape upon heating through the transformation temperatures, relying on detwinning of thermal martensite below Af. In contrast, the two-way shape memory effect enables reversible deformation between two shapes during temperature cycling without external stress, achieved through thermomechanical training that preferentially orients martensite variants and introduces internal stresses. Certain Ni-rich compositions exhibit rubber-like behavior under superelastic conditions, with elastic moduli approaching those of elastomers (around 20–50 GPa during transformation) and recoverable strains exceeding 6%, mimicking the compliance of natural rubber while maintaining metallic strength.^[37]^[38] The Tanaka model provides a foundational mathematical framework for describing transformation kinetics in these phenomena, expressing the martensite fraction ξ as a function of stress σ and temperature T via thermodynamic driving forces. For isothermal stress-induced transformation above Af, the forward kinetics are given by

\xi = \frac{1}{2} \left[ 1 - \cos \left( \pi \frac{\sigma - \sigma_s^{cr}(T)}{\sigma_f^{cr}(T) - \sigma_s^{cr}(T)} \right) \right],

where σscr(T) and σfcr(T) are the critical stresses for the start and finish of martensite formation, linearly dependent on T per the Clausius-Clapeyron relation. The reverse transformation follows a similar cosine form, enabling simulation of the hysteresis and strain recovery in superelastic cycles. This one-dimensional model has been widely adopted for its simplicity in capturing the nonlinear thermomechanical coupling.

Manufacturing

Alloy Production Techniques

The production of nickel-titanium (NiTi) alloys, commonly known as Nitinol, requires high-purity starting materials to minimize inclusions and ensure the desired phase transformations, such as the targeted B2 austenite phase. High-purity nickel ingots and titanium in forms like sponge or crystal bar are typically used, as titanium's extreme reactivity with oxygen, nitrogen, and carbon necessitates careful handling to prevent contamination during melting.^[39]^[40]^[41] Vacuum induction melting (VIM) serves as a primary method for initial alloy synthesis, where high-frequency induction coils heat the raw materials in a vacuum chamber to achieve a homogeneous melt without direct contact crucibles that could introduce impurities. In VIM, the materials are loaded into a graphite or ceramic-lined crucible under vacuum pressures below 10^{-3} torr, and the process allows for precise temperature control up to 1600°C to fully liquefy the reactive titanium. This technique is favored for its ability to produce initial ingots with low oxygen content, typically under 100 ppm, which is critical for maintaining the alloy's shape memory properties.^[42]^[39]^[43] Vacuum arc remelting (VAR) is commonly employed as a subsequent refining step to further homogenize the alloy and reduce inhomogeneities from the initial VIM melt. In VAR, an electric arc is struck between a consumable electrode of the pre-melted ingot and a water-cooled copper base plate in a vacuum environment, progressively melting the electrode drop-by-drop to form a refined ingot with directional solidification. This double-melting approach—VIM followed by VAR—enhances purity by segregating impurities like carbon or oxides to the ingot's extremities, achieving carbon levels below 100 ppm and uniform microstructure essential for industrial applications.^[39]^[44]^[45] For binary NiTi alloys, precise compositional control is paramount, with the nickel content targeted at 50 at% (approximately 55 wt%) for standard grades and adjusted to 50.5–51 at% Ni for medical applications to fine-tune transformation temperatures while adhering to standards like ASTM F2063, which specifies 54.5–57 wt% Ni. Deviations as small as 0.1 at% can shift phase transition temperatures by over 10°C, so analytical techniques like inductively coupled plasma spectroscopy are used post-melting to verify the ratio and enable adjustments in subsequent melts.^[46]^[47]^[48] Production has scaled from laboratory methods, such as small-scale non-consumable vacuum arc or electromagnetic levitation melting for research batches under 1 kg, to industrial processes yielding up to 1 ton per batch via large-scale VAR furnaces by the 2020s. This scale-up supports high-volume demands in sectors like biomedical devices, with facilities optimizing yield through automated vacuum systems and multiple remelts to achieve over 95% material recovery.^[49]^[50]^[51]

Forming and Heat Treatment Processes

Nickel titanium (NiTi), commonly known as Nitinol, is typically processed through a combination of hot and cold working techniques to achieve desired forms such as wires, sheets, and tubes. Hot working, performed at temperatures between 600°C and 1050°C, involves processes like extrusion, forging, and rolling to refine the microstructure and improve grain structure while the material is in a more ductile state.^[52] Cold working follows, utilizing drawing and rolling to further shape the alloy, where Nitinol exhibits rapid work hardening that necessitates intermediate annealing steps to restore ductility.^[47] These cold working operations can achieve total area reduction ratios of up to 90% across multiple passes, enabling the production of fine wires down to diameters of 0.025 mm or thin sheets.^[53] Shape-setting heat treatments are essential to impart the one-way shape memory effect by fixing the austenite phase structure. The formed Nitinol components are constrained in the desired shape using fixtures and aged at temperatures typically ranging from 400°C to 500°C for durations of 30 to 120 minutes, allowing atomic diffusion to stabilize the high-temperature austenite configuration.^[54] This aging process enhances shape recovery, with optimal results observed at 500°C where recovery strains exceed 8% upon heating.^[55] Following aging, rapid quenching in water or air prevents unwanted phase changes and locks in the set shape, adjusting transformation temperatures to suit specific applications.^[56] To enable two-way shape memory, where the alloy recovers both the high- and low-temperature shapes without external constraints, training via cyclic thermomechanical loading is employed. This involves repeated cycles of deformation in the martensitic phase at low temperatures (e.g., below 0°C), followed by heating to the austenitic phase under constant stress, typically 50-200 MPa, for 50-100 cycles to imprint preferential variant orientations.^[57] The process induces internal stresses that guide the reverse transformation path, achieving reversible strains up to 3-4% without fixtures.^[58] Such training is particularly useful for actuators requiring bidirectional motion. Emerging additive manufacturing techniques, such as selective laser melting (SLM), allow fabrication of complex Nitinol geometries unattainable by traditional methods, using laser powder bed fusion to melt NiTi powders layer by layer at energy densities of 50-150 J/mm³.^[59] However, SLM introduces significant residual stresses from rapid thermal gradients, which can distort parts and degrade superelasticity; post-processing via solution annealing at 800-1000°C followed by aging at 400-500°C, or stress relief through hot isostatic pressing, is required to mitigate these stresses and homogenize the microstructure.^[60] This approach has enabled intricate biomedical implants with functional properties comparable to wrought Nitinol.^[61]

Applications

Biomedical and Biocompatible Uses

Nickel-titanium (NiTi), commonly known as Nitinol, has become a cornerstone material in biomedical applications due to its superelasticity, shape memory effect, and biocompatibility, enabling the development of minimally invasive implants and devices that conform to physiological movements.^[62] These properties allow Nitinol devices to be compressed for delivery and then expand or recover shape within the body, reducing surgical trauma and improving patient outcomes.^[63] One of the most prominent uses is in self-expanding stents for cardiovascular applications, where Nitinol's superelasticity facilitates deployment in arteries to maintain patency. The first Nitinol stent received FDA approval in 1989, marking the beginning of widespread clinical use in the 1990s for treating conditions like peripheral artery disease and coronary blockages.^[23] By 2025, the global market for Nitinol-based medical devices, including stents, is projected to reach $5 billion, driven by the increasing prevalence of cardiovascular diseases and the material's durability in dynamic environments.^[64] Clinical studies report implantation success rates of approximately 92.5% and secondary patency rates of 77% at 10 years for bare-Nitinol stents in superficial femoral artery lesions.^[65]^[66] In orthodontics and dentistry, Nitinol archwires provide continuous, low-level forces for tooth alignment and leveling, minimizing patient discomfort and reducing the need for frequent adjustments compared to traditional stainless steel wires.^[67] Introduced in the late 1970s, these superelastic wires exploit the austenite-martensite phase transition to deliver consistent force over a wide range of deformations, making them ideal for initial treatment stages.^[68] Orthopedic implants such as spinal rods and bone staples utilize Nitinol's shape memory to apply compressive forces that promote bone healing and stability. Spinal rods reduce adjacent segment disease risk by accommodating natural spinal motion, while bone staples enable precise fixation in procedures like foot and ankle fusions.^[69]^[70] For minimally invasive surgeries, Nitinol guidewires offer kink resistance and flexibility, facilitating navigation through tortuous vessels during catheter-based interventions.^[63] Nitinol's biocompatibility is evaluated under ISO 10993 standards, which assess cytotoxicity, sensitization, and implantation effects to ensure safety for long-term body contact.^[71] Concerns over nickel ion release, which can cause allergic reactions, are addressed through passivation layers like titanium oxide (TiO₂), reducing leaching to less than 0.1 μg/cm²/week and enhancing corrosion resistance.^[72]^[73] These treatments result in long-term implant success rates exceeding 90% in orthopedic and cardiovascular applications, with low complication rates (0.5-7% at 1 year for certain devices).^[65]^[74]

Actuators and Damping Systems

Nickel-titanium (NiTi), commonly known as Nitinol, is widely utilized in thermal actuators due to its shape memory effect, which enables reversible deformation in response to temperature changes. Wire-based linear actuators made from Nitinol are particularly effective in robotics and valve systems, where they provide compact, lightweight motion control. These actuators can achieve strains of up to 5-7% under typical operating conditions, generating significant forces relative to their mass—often reaching blocking forces of several hundred newtons for wires with diameters around 0.5 mm.^[75]^[76] The activation of these thermal actuators commonly involves electrical current through Joule heating, which rapidly raises the wire temperature to induce the austenite phase transformation and subsequent contraction. This method allows for integration with sensors, such as thermocouples or resistance monitors, to create closed-loop smart systems that precisely control positioning and force output in dynamic environments like robotic grippers or fluid control valves. Response times for such actuators are typically on the order of 1 second for heating, though cooling can extend the cycle to several seconds depending on ambient conditions and wire diameter; thinner wires (e.g., 0.1-0.25 mm) facilitate faster recovery due to higher surface-to-volume ratios.^[77]^[78]^[79] In damping systems, Nitinol's superelastic properties and hysteretic behavior enable effective vibration absorption and energy dissipation in civil engineering applications, such as bridge cables and seismic isolators. These devices leverage the material's ability to undergo large reversible strains (up to 6-8%) while dissipating seismic or wind-induced energy through phase transformation hysteresis, with equivalent viscous damping ratios reaching 10-15% of the input energy in superelastic configurations. For instance, Nitinol-reinforced bridge cables have demonstrated enhanced fatigue resistance and self-centering capabilities under cyclic loading, reducing structural damage during earthquakes by absorbing and redistributing vibrational energy.^[80]^[81] Aerospace applications further exploit Nitinol's actuation and damping traits in morphing wings and deployable structures for satellites. Morphing wing technologies use Nitinol wires or strips to enable adaptive airfoil shapes that optimize lift and drag during flight, actuated via thermal cycles that align with the shape memory mechanism's phase transformations. In satellites, Nitinol-based actuators facilitate the deployment of antennas and solar arrays, providing reliable, low-power release mechanisms that operate in vacuum and extreme temperatures, with strains enabling precise positioning over multiple cycles. These systems benefit from the alloy's high work density—up to 10^7 J/m³—making them ideal for mass-constrained space missions.^[82]^[83]^[84]

Challenges and Future Directions

Material Limitations and Solutions

One significant limitation of nickel-titanium (NiTi) alloys, commonly known as Nitinol, is their fatigue and fracture behavior, where the cycle life is typically restricted to 10^4 to 10^6 cycles under superelastic loading conditions due to the initiation and propagation of microcracks from surface defects or inclusions.^[85] These microcracks often arise during manufacturing or under cyclic strain amplitudes of 4-8%, leading to functional degradation and eventual fracture.^[86] To mitigate this, surface treatments such as electropolishing have been widely adopted, as they remove microscopic imperfections and inclusions, thereby enhancing fatigue resistance by up to several orders of magnitude in some cases; for instance, electropolished Nitinol wires exhibit improved crack initiation thresholds compared to mechanically polished counterparts.^[87] Magnetoelectropolishing further refines this approach by promoting a smoother, defect-free surface that delays crack propagation.^[88] Corrosion represents another key drawback for NiTi in harsh environments, particularly pitting in chloride-containing solutions like physiological fluids or seawater, where localized breakdown of the passive oxide layer occurs at potentials above 0.5 V versus saturated calomel electrode.^[89] This pitting is exacerbated by nickel-rich phases that undermine the protective titanium dioxide film, potentially leading to ion release and biocompatibility issues in biomedical applications. Improvements have been achieved through Ti-rich compositions, which favor the formation of a more stable, thicker TiO2-dominated surface oxide layer, significantly raising the pitting potential and reducing corrosion rates in chloride media by promoting selective dissolution of nickel during processing.^[90] Electropolishing also contributes here by enriching the surface in titanium, enhancing overall pitting resistance without altering the bulk composition.^[91] NiTi alloys exhibit temperature sensitivity, with operating windows tunable from -100°C to over 100°C depending on the austenite finish temperature (Af), though sensitivity to exact Af can restrict applications in varying thermal environments without compositional adjustments or heat treatments. Alloying with elements like niobium (Nb) or copper (Cu) addresses this by tuning phase transformation temperatures and hysteresis; for example, Nb additions lower critical transformation temperatures while widening hysteresis to over 50°C, enabling operation across broader ranges such as -100°C to 50°C. Cu alloying, on the other hand, increases Af and reduces hysteresis to 10-15°C, facilitating precise control for applications requiring minimal thermal lag, such as in actuators operating near room temperature.^[92]^[93] Recent advancements in the 2020s have focused on nanostructuring and coatings to bolster durability, with studies demonstrating substantial fatigue life enhancements; severe plastic deformation techniques, such as high-pressure torsion, refine grain sizes to the nanoscale, inducing compressive residual stresses that double the fatigue life under cyclic bending compared to coarse-grained NiTi. Thin-film coatings like alumina (Al2O3) applied via atomic layer deposition have similarly shown to extend cycle life by factors of 1.5 to 2 in thin wires, by shielding against environmental corrosion and crack initiation while preserving superelasticity. These approaches, validated in high-cycle fatigue tests up to 10^8 cycles, underscore ongoing efforts to overcome inherent limitations through microstructural engineering. As of 2025, fatigue studies have extended to one billion cycles for medical-grade Nitinol, informing designs for ultra-high durability applications.^[94]^[95]^[86]

Environmental and Economic Considerations

The production of nickel-titanium (NiTi) alloys, commonly known as Nitinol, involves significant environmental challenges stemming from the extraction and processing of its constituent metals. Nickel mining is associated with substantial pollution, including heavy metal contamination of waterways that harms aquatic ecosystems and air pollution linked to health impacts in processing regions like Indonesia. Titanium extraction, primarily via the energy-intensive Kroll process, consumes approximately 100-250 MJ/kg and contributes to habitat destruction, soil erosion, and waste generation from mining activities.^[96]^[97] These processes underscore the need for improved sustainability in Nitinol manufacturing, where efforts like renewable energy adoption in production facilities aim to mitigate emissions and pollutants. Recycling of NiTi alloys remains limited, with challenges arising from the material's complex composition and processing requirements, though emerging hydrometallurgical methods show promise for higher recovery. Traditional recycling rates for titanium alloys are low, often below 1% relative to primary production volumes, exacerbating resource depletion. Hydrometallurgical approaches, such as acid leaching treatments, enable recovery of NiTi from medical waste like endodontic files, achieving high leaching efficiencies through processes like acid baking, though specific recovery percentages for Ni and Ti vary by method and require further optimization for industrial scale. In medical applications, potential toxicity from nickel leaching poses concerns, as Nitinol devices can release nickel ions under physiological conditions, potentially causing allergic reactions or cytotoxicity, particularly with certain surface finishes. This is regulated under the European REACH framework, which restricts nickel release in consumer and medical products to minimize environmental and health risks. As of 2025, predictive toxicokinetic models aid in assessing long-term nickel release risks from implants like vascular stents.^[98] Eco-friendly alternatives, such as iron-based shape memory alloys (Fe-SMAs), are gaining attention for their lower cost, easier processing, and reduced reliance on nickel, offering sustainable substitutes in structural and biomedical uses. Economically, NiTi's high production costs, ranging from $200 to $400 per kg due to vacuum melting and precise compositional control, limit broader adoption despite its unique properties. The global Nitinol market was valued at approximately USD 7.7 billion in 2024 and is projected to grow at a 7.1% CAGR to USD 13.3 billion by 2032, reflecting increasing demand in minimally invasive procedures.^[99] Future directions emphasize sustainable sourcing to address supply chain vulnerabilities in nickel and titanium, alongside additive manufacturing techniques like selective laser melting, which reduce material waste by minimizing secondary machining and enabling near-net-shape production. Ongoing research explores variants with enhanced recyclability, though biodegradable NiTi options remain in early development stages focused on alloy modifications for controlled degradation in biomedical contexts.

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[PDF] Thermodynamic Description of Ni Based Binary Phase Diagrams
The binary Ni–Ti system was evaluated by Murray [26]. Three intermetallic compounds were formed: Ni3Ti, NiTi and NiTi2. Ni3Ti and NiTi are melted congruently, ...
[5]
Binary Ni-Ti phase diagram [8]. - ResearchGate
The NiTiNb alloy fabricated using the SLM in-situ alloying featured the microstructure consisting of the NiTi matrix, fine NiTi+β-Nb eutectics, as well as ...
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Physical metallurgy of Ti–Ni-based shape memory alloys
This paper presents a brief review on the current progress in stimuli-responsive SMMs, from recent development in traditional shape memory alloys (SMAs) and ...
[7]
Microstructure and Phase Transition Characteristics of NiTi Shape ...
Crystal structure of the B2 austenite. In NiTi binary alloy, austenite phase (parent phase) is body centered cubic (bcc) B2 structure. B2 phase is a typical ...
[8]
A novel B19′ martensite in nickel titanium shape memory alloys
In Ni–Ti shape memory alloys, the high temperature ordered cubic parent phase, B2, transforms to the monoclinic B19′ (distorted B19) structure by the martensite ...
[9]
Effect of Ni-Content on the Transformation Temperatures in NiTi-20 ...
Nov 21, 2017 · Small changes in Ni-content cause a dramatic drop in transformation temperatures, with a 110°C change from 49.8% to 50.2% Ni.
[10]
Nitinol Rod Properties and Applications - XOT Metals
Mar 25, 2019 · Appearance:this is a bright silvery metal. Density:The density of this alloy is 6.45 gm/ cm3. Melting Point:Its melting point is around 1310 °C.Missing: g/ yield 200-600 MPa
[11]
Porous NiTi for bone implants: A review - PMC - NIH
2. Fabrication methods. Since NiTi has a high melting point (1310 °C), production methods for porous NiTi have been limited to date to powder-metallurgy ...
[12]
[PDF] MATERIAL DATA SHEET Superelastic Nitinol Alloys*
The mechanical and superelastic properties shown here are typical for standard superelastic straight Nitinol at room temperature tested in uniaxial tension.Missing: 6.45 200-600
[13]
Transition temperature range of thermally activated nickel-titanium ...
All thermally activated NiTi archwires analyzed presented stage transformation during thermal scanning in the range between -100°C and 150°C (Figures 2 to 8).
[14]
shape memory alloys | Total Materia
Shape memory alloys (SMAs) are specialized metals exhibiting two unique properties: pseudo-elasticity and the shape memory effect. Arne Olander first observed ...Missing: precursor | Show results with:precursor
[15]
US3174851A - Nickel-base alloys - Google Patents
This invention relates to a series of novel structural alloys of the intermetallic compound type which are characterized by unusual mechanical and physical ...Missing: 1960s | Show results with:1960s
[16]
The Metal With A Memory | Invention & Technology Magazine
The work that resulted in the discovery of nitinol began in early 1958. Buehler was testing intermetallic compounds for the nose cone of the Navy's below-the- ...Missing: 1962 | Show results with:1962
[17]
Crystal Structure and a Unique ``Martensitic'' Transition of TiNi
Buehler and R. E. Wiley, Naval Ordnance Laboratory Rept. 61‐75 (August 1961) ... 1965. This content is only available via PDF. Open the PDF for in ...
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[PDF] A New Wide Hysteresis NiTi Based Shape Memory Alloy and its ...
One of the first major commercial uses of shape memory alloys was pioneered by Raychem Corporation in 1969. The application waa as couplings for aircraft ...Missing: history | Show results with:history
[19]
Shape Memory History - Intrinsic Devices
After pioneering the commercialization of NiTi shape memory alloys for more than 20 years, in the early 1990's Raychem decides to divest its shape memory metals ...
[20]
[PDF] An Overview of Nitinol Medical Applications Duerig, Pelton, Stoeckel ...
Nitinol arch wires were introduced in the late. 1970's. We estimate that over 30% of the archwires used today are nitinol. Superelastic eyeglass frames provide ...
[21]
Nitinol Stents in the Femoropopliteal Artery: A Mechanical ... - NIH
... Nitinol had excellent fatigue resistance and other unique properties. While presenting a long strip of the alloy to colleagues, an accidental discovery of ...
[22]
[PDF] IntraCoil® Self-Expanding Peripheral Stent - accessdata.fda.gov
Jan 10, 2001 · Date of Notice of Approval to the Applicant: GMP/QSR Inspection: January 10, 2001. 2. Indications for Use. The IntraCoil® Self-expanding ...
[23]
A Review on Additive Manufacturing Methods for NiTi Shape ... - NIH
Mar 8, 2024 · Indeed, by changing the Ni content by 0.1 at.%, the Ms temperature varies by 10–15 °C [5]. The shape memory and superelasticity are strongly ...
[24]
What is ASTM F2063 Super Elastic Nickel Titanium - GEE SMA
Jan 6, 2025 · ASTM F2063 is a standard specification established by ASTM International, aimed specifically at the characteristics of Nitinol used in medical devices.
[25]
Nickel–titanium alloy porous scaffolds based on a dominant cellular ...
These scaffolds demonstrate excellent biocompatibility, support in vitro osteogenesis, and possess significant in vivo bone ingrowth capabilities.
[26]
Physical metallurgy of Ti–Ni-based shape memory alloys
This review is intended to give a self-consistent and logical account of key issues on Ti–Ni based alloys from physical metallurgy viewpoint on an up-to-date ...
[27]
Martensitic phase transformation in TiNi | Scientific Reports - Nature
Sep 18, 2019 · It was found that in doped alloy, MT can takes place through the B2-B19-B19′. In this case, the B19 is an orthorhombic phase (space group Pmmb).
[28]
[PDF] The Measurement and Interpretation of Transformation ...
Nov 6, 2017 · Transformation temperatures in Nitinol, like Austenite finish (Af), are measured using Differential Scanning Calorimetry and Bend Free Recovery ...
[29]
Strain dependence of the Clausius Clapeyron relation for ...
Aug 7, 2025 · Considering the Clausius-Clapeyron relationship dσ c /dT = ρ ∆H M-A /(∆ε·T 0 ) where ∆ε is the strain resulting from the transformation in the ...
[30]
Mechanocaloric effects in shape memory alloys - Journals
Aug 13, 2016 · The shift in the transition temperature with stress is given by the Clausius–Clapeyron ... alloys results in a larger dT/dσ. With regard to the ...
[31]
[PDF] Mechanical fatigue and fracture of Nitinol
Several authors emphasised the importance of combining cold work and aging treatments to optimise the microstructure of Nitinol for cyclic stability.3,16,17 ...
[32]
On the Detwinning Mechanism in Shape Memory Alloys
When a martensitic NiTi is stressed beyond its yield limit, a “detwinning” process is responsible for the observed inelastic deformations.
[33]
One-way and two-way shape memory effect in thermomechanically ...
May 25, 2008 · A brief review of shape memory effects and fabrication processes of NiTi shape memory ... two-way shape memory effect in a Ni-rich NiTi alloy.
[34]
[PDF] FUNDAMENTAL CHARACTERISTICS AND DESIGN METHOD FOR ...
In the early 1960s, BUEHLER and his co-workers at the U.S. Naval Ordnance Laboratory discovered the shape memory effect in an equiatomic alloy of nickel and ...<|control11|><|separator|>
[35]
Nitinol melting: How raw NiTi is manufactured for medical devices
Jul 28, 2023 · The two main melting options for making nitinol are vacuum induction melting (VIM) and vacuum arc remelting (VAR). Double-melting is a process ...
[36]
Nitinol Manufacturing and Metalworking - Kellogg's Research Labs
Jan 4, 2019 · Metals can be melted in a furnace and cast into an ingot but Nitinol needs to be prepared in a vacuum because few oxygen atoms reduces its ...Missing: levitation | Show results with:levitation
[37]
Experimental Continuous Casting of Nitinol - MDPI
Apr 14, 2020 · Nitinol describes a group of nearly equiatomic alloys composed of nickel and titanium. The alloy was developed in the 1970s. The alloy belongs ...
[38]
Ni-Ti Shape Memory Alloy - an overview | ScienceDirect Topics
The most common method for producing Ti-Ni ingots is vacuum melting such as vacuum induction melting (VIM) and vacuum arc remelting (VAR) because of the high ...<|control11|><|separator|>
[39]
(PDF) Vacuum induction melting of NiTi shape memory alloys in ...
Aug 9, 2025 · During melting, carbon reacts with Ti and forms TiC. This alters the Ni/Ti ratio in the alloy and thereby changes the transformation ...
[40]
Recent observations of particulates in Nitinol - ScienceDirect.com
Particulates in Nitinol are commonly associated with the reactivity of titanium and melting practices for alloy production: vacuum arc and induction melting.
[41]
[PDF] Vacuum Arc Melting Processes for Biomedical Ni-Ti Shape Memory ...
Vacuum arc remelting (VAR) uses a water-cooled crucible to purify nickel and titanium, then melts them into nitinol alloy. VAR also explores purification and ...Missing: 50-51 grades
[42]
[PDF] Forming Nitinol - Confluent Medical Technologies
Less energy is needed to stress-induce and deform martensite than to deform the austenite by conventional mechanisms. Up to 10% strain can be accommodated by ...
[43]
An Overview of Nitinol: Superelastic and Shape Memory
Oct 1, 2015 · Nitinol is popular due to its biocompatibility and superelasticity. Nitinol is used to manufacture stents, guide wires, stone retrieval baskets, filters, ...
[44]
Nitinol manufacturing and micromachining: A review of processes ...
The Ni–Ti ratio is key to manufacturing nitinol as it varies the number of electrons available for bonding [32] and therefore has a great influence on the ...
[45]
Vacuum Melting - Kellogg's Research Labs
Production Scale: 60 pound VIM; 325 pound VIM; 550 pound VIM; 1 ton VAR. If you are interested in custom melted nitinol, please feel ...Missing: batch | Show results with:batch
[46]
Vacuum induction melting of NiTi shape memory alloys in graphite ...
Out of the various melting methods, vacuum induction melting (VIM) and vacuum arc remelting (VAR) are widely used for commercial production of NiTi alloys. In ...
[47]
Scale up of NiTi shape memory alloy production by EBM - NASA/ADS
An alternative process to produce NiTi alloys is by electron beam melting (EBM) using a water-cooled copper crucible that eliminates carbon contamination, and ...
[48]
What Makes Nitinol Tubing Unique? The Role of Manufacturing ...
Aug 6, 2025 · This step uses high heat, from 600°C to 1050°C, to shape the metal. Hot working like extrusion, forging, or rolling makes the grains better.
[49]
[PDF] Evaluation of a production route for cold-drawn Nitinol wires
Sep 7, 2016 · This master thesis has summarized articles and patents found that have been evaluating and optimizing cold-drawing of nitinol wire.
[50]
(PDF) Effect of Heat Treatment Time and Temperature on the ...
Oct 12, 2025 · Nitinol wires were heat treated at different temperatures, 400–500 °C, and times, 30–120 min, to study the effects of these heat treatment parameters.
[51]
Effect of Heat Treatment Time and Temperature on the ...
Sep 29, 2023 · Nitinol wires were heat treated at different temperatures, 400–500 °C, and times, 30–120 min, to study the effects of these heat treatment ...
[52]
[PDF] Nitinol Post-Shape-Setting Time Temperature Transformation (TTT ...
Mar 31, 2025 · All wires were quenched in water immediately following the straightening heat treatment. In the second arm of the study, a single alloy formula-.
[53]
(PDF) Experimental study on two way shape memory effect training ...
Apr 29, 2025 · This research describes training procedures for shape memory alloys (SMAs). SMAs are considered as a unique class of metal alloys that can recover apparent ...
[54]
Constant-torque thermal cycling and two-way shape memory effect ...
Cycling to lesser UCTs of 250 °C (vs. 300 °C) resulted in the highest two-way shape memory effect (TWSME), measuring over 3.25%. This was attributed to the ...
[55]
Advances in Selective Laser Melting of Nitinol Shape Memory Alloy ...
Mar 8, 2019 · In this paper, the most recent publications related to the SLM processing of Nitinol are reviewed to identify the various influential factors involved and ...
[56]
Investigation of Post-Processing of Additively Manufactured Nitinol ...
This transformation extends to −22.4 °C and thus over a temperature range of 73 °C, of which only the first 29 °C were reached at RT. Thus, the springs are ...
[57]
Evaluating residual stress in additively manufactured nitinol shape ...
Apr 30, 2025 · This study provides a comprehensive analysis of residual stress characteristics in nitinol parts fabricated via laser powder bed fusion (PBF-LB).
[58]
Manufacturing, Processing, and Characterization of Self-Expanding ...
... FDA approval for the Innova vascular self-expanding stent made from nitinol. This stent was equipped with an advanced delivery system designed to treat ...
[59]
Nitinol for Medical Applications: A Brief Introduction to the Properties ...
Aug 6, 2025 · Nickel-titanium alloys are used to manufacture coronary and ureteral stents, surgical instruments, flexible micro-needles, endoscopic catheters, ...
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Nitinol-Based Medical Device Market Size and Forecast 2025 to 2034
Apr 10, 2025 · The global nitinol-based medical device market size is calculated at USD 5.00 billion in 2025 and is forecasted to reach around USD 9.37 billion by 2034.Missing: history 1990s
[61]
[PDF] Nitinol: Medical Device Material Safety Summary - FDA
Mar 10, 2022 · 5 patients required a 2nd stent placement, and 3 patients required a 3rd stent placement after 30 days of 1st stent placement. Response ...
[62]
Ten-Year Clinical Follow-Up Following Bare-Nitinol Stent ...
Freedom from reintervention was 59% at 10 years, and freedom from occlusion (secondary patency) was 77% at 10 years. As these results are almost on par with ...Missing: success | Show results with:success
[63]
Nickel titanium alloys as orthodontic archwires: A narrative review
Nickel-titanium (NiTi) archwires have been widely used in orthodontic treatments at the aligning and leveling step which is the initial stage of the treatment.
[64]
[PDF] Dental Arch Wire Straightening teeth is an arduous process ...
The key is a new type of arch wire material, called. Nitinol, with exceptional elasticity which helps reduce the required number of brace changes. An alloy of ...
[65]
Nitinol in Orthopedic Applications and Examples
From driving bone healing through continuous force in staples and clamps to reducing adjacent segment disease risk in spinal rods, Nitinol is revolutionizing ...
[66]
Top 6 Medical Applications of Nitinol - Stanford Advanced Materials
Jul 24, 2025 · Orthopedic applications of Nitinol include bone plates, staples, and intramedullary implants. Its shape memory property enables compression in ...
[67]
[PDF] Nitinol-Technical-Guidance July 9 2021 - FDA
Jul 9, 2021 · To assess the biocompatibility of your nitinol device, we recommend that you follow the guidance “Use of International Standard ISO 10993-1, ' ...
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Shape Memory Alloys in Biomedical Applications
Aug 14, 2025 · Upon cooling below the martensite start temperature (Ms), the high-temperature austenite phase (cubic lattice) undergoes diffusionless shear to ...
[69]
Advancements in Surface Modification of NiTi Alloys for Orthopedic ...
The biocompatibility of NiTi alloys is generally considered high, primarily due to the self-passivation effect, where a thin and stable oxide layer forms ...
[70]
Nitinol Compression Staples in Foot Orthopaedic Surgery
Nov 30, 2024 · This systematic review demonstrates that nitinol staples in foot surgery, whether alone or in combination with another construct, can achieve an acceptable ...
[71]
[PDF] Tailoring the Response Time of Shape Memory Alloy Wires through ...
Nov 5, 2009 · Response time of SMA wires can be improved by active cooling techniques, pre-stress, and fluid flow, which reduces the cooling cycle.Missing: Nitinol valves
[72]
Nitinol actuator technical information - Fort Wayne Metals
The actuator wire is held at a constant stress and subjected to a heating and cooling cycle. The amount of strain or "stroke" of the wire is monitored with a ...Missing: Joule | Show results with:Joule
[73]
Electro‐thermo‐mechanical characterization of shape memory alloy ...
Feb 18, 2024 · The experimental characterization of Joule heated NiTi wires concerning their actuator and sensor properties shows how to influence their ...<|control11|><|separator|>
[74]
[PDF] An Architecture for Fast and Accurate Control of Shape Memory ...
Abstract. This paper presents a new control architecture for fast, accurate force control of antagonistic pairs of shape memory alloy wires.
[75]
[PDF] Nitinol shape memory alloy spring
Nitinol (Ni-Ti) is a shape memory alloy with high power-to-weight ratio, shape memory effect, and high recoverable strain, used in springs.
[76]
Strain amplitude effects on the seismic performance of dampers ...
Oct 1, 2021 · The energy dissipation arises from the hysteretic phase transformation. Random vibration patterns, such as by earthquakes and wind, include not ...
[77]
Experimental study on the dynamic behavior of a small-scale cable ...
Jul 22, 2025 · These materials have gained popularity due to their ability to undergo large reversible deformations, coupled with their energy dissipation ...
[78]
Shape Memory Alloys for Aerospace, Recent Developments ... - NIH
Apr 15, 2020 · This paper presents a review of SMAs applications in the aerospace field with particular emphasis on morphing wings (experimental and modeling)
[79]
A space release/deployment system actuated by shape memory wires
The release and deployment mechanisms are actuated by a Shape Memory wire (Nitinol), which allows a complete symmetrical and synchronous release, in a very ...
[80]
New Alloys Improve Satellite Reliability
Nov 8, 2017 · Actuators made from shape-memory alloys have flown on several CubeSats built by Aerospace and are scheduled to fly on upcoming missions as well.<|control11|><|separator|>
[81]
Review on structural fatigue of NiTi shape memory alloys
In this paper, the latest progresses made in experimental and theoretical analyses for the structural fatigue features of NiTi shape memory alloys are reviewed.
[82]
Rotary Bend Fatigue of Nitinol to One Billion Cycles - PMC - NIH
Jan 18, 2023 · This work provides the first documented fatigue study of medical grade nitinol to 10 9 cycles, and the observations and insights described will be of value
[83]
U.S. Patent for Nitinol fatigue resistance using electropolishing ...
Oct 23, 2018 · The method for improvement of Nitinol fatigue fracture resistance may be accomplished by electropolishing or magnetoelectropolishing under ...Missing: limitations | Show results with:limitations
[84]
Mechanical fatigue and fracture of Nitinol - ResearchGate
Aug 9, 2025 · Here we review the existing knowledge base on the fatigue of Nitinol, both in terms of their stress or strain life (total life) and damage tolerant (crack ...
[85]
Susceptibility of nitinol to localized corrosion - Wiley Online Library
Jan 3, 2006 · The high resistance of EP nitinol to pitting corrosion is associated with the Ti-rich surface oxide and is consistent with titanium likewise ...
[86]
The corrosion resistance of Nitinol alloy in simulated physiological ...
As a biomedical material, Nitinol has to meet several requirements—high corrosion resistance in chloride-rich medium and biocompatibility combined with suitable ...
[87]
On the High Sensitivity of Corrosion Resistance of NiTi Stents with ...
Feb 10, 2020 · In this study, the influence of electropolishing on nitinol stents and its corrosion behavior were obsd. Electropolishing is an effective method ...<|separator|>
[88]
The thermo-mechanical behavior of NiTi-X shape memory alloys
Alloying NiTi with Nb decreases critical transformation temperatures, while Cu and Ta increase them. Nb causes the largest hysteresis, and Ta increases reverse ...Missing: sensitivity | Show results with:sensitivity
[89]
Thermal Hysteresis in Ni-Ti and Ni-Ti-X Alloys and Their Applications
Aug 6, 2025 · Generally, thermal hysteresis ranges from 1.5-2 K for R-phase transformations, 10-15 K for certain Ni-Ti-Cu alloys, 20-60 K for binary NiTi ...
[90]
Improving the fatigue strength of superelastic NiTi by using ...
Oct 3, 2023 · The fatigue life of supperelasticnitinol can be improved by using severe plastic deformation (SPD)induced compressive stressesand grain ...Missing: coatings | Show results with:coatings
[91]
Fatigue Resistance Improvement in Cold-Drawn NiTi Wires Treated ...
This study investigates the impact of Al 2 O 3 coating on the fatigue behavior of cold-drawn NiTi wires with a 0.125 mm diameter.