Superelasticity Effect Research Articles

The role of texture on superelasticity and elastocaloric effect in severely rolled Ti-44Ni-5Cu-1Al (at%) shape memory alloy

The effects of crystallographic texture on the superelasticity and elastocaloric effect of nanograin Ti-44Ni-5Cu-1Al rolled sheet are investigated. Stress-strain curves with different orientation angles between tensile direction and rolling direction show that the tensile strain of the sheet is largest in rolling direction (RD) along <110> and smallest in transverse direction (TD) parallel to <100>. This texture dependence is further studied by analyzing the evolution of each strain component. With the increase of the orientation angle, intergranular constraint effect reaches the maximum in TD. As a result, transformation strain and adiabatic temperature change have a similar monotonic decreasing trend. The material coefficient of performance of the sheet reaches 11.2 in RD. This value makes it possible for severely rolled Ti-44Ni-5Cu-1Al sheet to be a potential candidate for solid-state refrigeration application at room temperature.

Softening Effects in Biological Tissues and NiTi Knitwear during Cyclic Loading.

Samples of skin, tendons, muscles, and knitwear composed of NiTi wire are studied by uniaxial cyclic tension and stretching to rupture. The metal knitted mesh behaves similar to a superelastic material when stretched, similar to soft biological tissues. The superelasticity effect was found in NiTi wire, but not in the mesh composed of it. A softening effect similar to biological tissues is observed during the cyclic stretching of the mesh. The mechanical behavior of the NiTi mesh is similar to the biomechanical behavior of biological tissues. The discovered superelastic effects allow developing criteria for the selection and evaluation of mesh materials composed of titanium nickelide for soft tissue reconstructive surgery.

Mechanical properties and scaling laws of polycrystalline CuZr shape memory alloy

Thanks to their excellent properties such as superelasticity, high hardness, and shape memory effect, polycrystalline shape memory alloys (SMAs) have extensive applications in various engineering fields including automobile, functional materials, and aerospace. Using molecular dynamics simulations, the present paper aims to a systematic study of the fundamental tensile behavior in the nanoscale of polycrystalline B2-CuZr SMAs with mean grain sizes in the range of 6–25 nm. Effects of mean grain size, temperature, and tensile rate on mechanical properties are considered. Our results show that along with the increase in mean grain size came increases in Young's modulus, yield strength, flow stress, and ultimate tensile strength. The development of amorphous regions in the grain cores is the major deformation mode in polycrystalline CuZr SMAs with larger grain sizes, while the grain boundary sliding and grain rotation for smaller grain sizes. Besides, an increased temperature results in mechanical performance degradation and the temperature sensitivity of mechanical properties does not depend on the mean grain size. Our work would lay the groundwork for the optimization of the mechanical properties of polycrystalline SMAs as well as serving as a useful theoretical guideline for their practical engineering applications.

Evolutions of superelasticity and elastocaloric effect of Ti50Ni48Fe2 and aged-hardened Ni-rich Ti49.2Ni49.3Fe1.5 shape memory alloys under cyclic compressive deformation

The transformation and superelasticity characteristics of solution-treated Ti50Ni48Fe2 and aged-hardened Ti49.2Ni49.3Fe1.5 shape memory alloys during cyclic compressive deformation were investigated. The Ti50Ni48Fe2 alloy could not be precipitation hardened, while the Ti49.2Ni49.3Fe1.5 alloy, aged at 400 °C, was hardened by Ti3Ni4 precipitates. During the cyclic deformation, the B2⇆R⇆B19′ transformation peaks broadened and spread to a large temperature span. At the same time, the superelasticity behavior became linear, and the associated elastocaloric cooling capacity decreased to a stable value. Among these samples, Ti49.2Ni49.3Fe1.5 alloy aged at 400 °C for 150 h exhibited the largest recoverable strain in superelasticity and retained the largest cooling effect after 1000 deformation cycles. Furthermore, it showed elastocaloric cooling of −4.1 °C to −7.0 °C at operating temperatures of −40–80 °C. Experimental results revealed that B19′ transformation was suppressed significantly by cyclic deformation, and thus the transformation occurred in a wide temperature range of −160 to −50 °C. Additionally, the linear superelasticity exhibited a low slope of the Clausius–Clapeyron relation of about 0.5 MPa/°C. These features allow the alloys to exhibit superelasticiy and the elastocaloric effect over a wider temperature range.

Numerical investigation on cyclic behaviour of superelastic shape memory alloy (SMA) dampers

In recent decades, researchers have developed many technologies like energy dissipating dampers to improve the response of structures in seismic events but still limitations persist in earthquake-resistant design. Residual drift is still a significant problem encountered while using dampers which results in a reduction in their performance. Many types of dampers have been introduced to localize the damages in a defined section of a structure to prevent structural failure and decrease the repairing cost. However, in general, rehabilitation of a structure using a damper is not an economical option because residual deformation occurs due to limitations of constituent materials of the damper. Therefore, in this paper, a shape memory alloys (SMAs) damper is proposed to mitigate the performance degradation problem caused by residual deformation of a structure and to reduce maintenance and repairing costs. The shape memory alloys can reduce residual deformation at room temperature due to the superelastic effect. In addition, a pretension force was applied to prevent damage by reducing the fastening force of the shape memory alloy bar and to improve the load performance. Finite element analysis was performed to verify the performance of the damper to which the pretension was applied. Furthermore, recentering performance and energy dissipation capacity of the damper were analyzed. The analysis results show that the proposed damper can reduce the residual strain by recentering, as well as improve energy dissipation and ultimate capacity.

Twin boundary structure and mobility

Twinning is an important mechanism of deformation in various crystalline materials, and in particular in shape memory alloys, where it is inherent to the shape memory and super-elasticity effects. This paper presents a generalized methodological approach for analyzing and modeling twin boundary dynamics with particular relevance for shape memory alloys. This approach combines the topological model description of the interface structure at the atomistic/lattice scale with analytical analysis of energy barriers and mechanisms of motion that provide macro-scale kinetic laws for the twin boundary motion. We emphasize the main differences between the topological structures of different types of twin interfaces and their implications for the mobilities of the different twin types. In particular, we elaborate on the relaxed topological structure of type II twin boundaries that contains a coherently facetted structure, where the facets are rational planes that accommodate misfit strain. Then, we clarify the lattice barriers’ role in determining the different regimes of the kinetics of twin boundary motion. Further, we develop models leading to analytical expressions for the activation energies of various nucleation processes that dictate the overall kinetics of twin boundary motion, and identify of the rate-limiting process for the different twin types. In the case of compound and type I twins, the analysis leads to an explicit expression for the magnitude of the twinning stress, revealing a strong dependency on the shear modulus and the twinning shear, which is in excellent quantitative agreement with experimental values reported for BaTiO3, Ni-Ti, Cu-Al-Ni, and 10M and NM Ni-Mn-Ga. Moreover, our analysis reasons the different temperature dependencies of the twinning stress exhibited by the different twin types, and in particular the very low temperature sensitivity of type II twins.

Is Gutta-Percha Still the “Gold Standard” among Filling Materials in Endodontic Treatment?

The paper is an extensive monographic review of the literature, and also uses the results of the authors’ own experimental research illustrating the noticed developmental tendencies of the filling material based on gutta-percha. The whole body of literature proves the correctness of the research thesis that this material is the best currently that can be used in endodontics. Caries is one of the most common global infectious diseases. Since the dawn of humankind, the consequence of the disease has been the loss of dentition over time through dental extractions. Both tooth caries and tooth loss cause numerous complications and systemic diseases, which have a serious impact on insurance systems and on the well-being, quality, and length of human life. Endodontic treatment, which has been developing since 1836, is an alternative to tooth extraction. Based on an extensive literature review, the methodology of qualifying patients for endodontic treatment was analyzed. The importance of selecting filling material and techniques for the development and obturation of the root canal during endodontic treatment was described. Particular attention was paid to the materials science aspects and the sequence of phase transformations and precipitation processes, as well as the need to ensure the stoichiometric chemical composition of Ni–Ti alloys, and the vacuum metallurgical processes and material processing technologies for the effects of shape memory and superelasticity, which determine the suitability of tools made of this alloy for endodontic purposes. The phenomena accompanying the sterilization of such tools, limiting the relatively small number of times of their use, play an important role. The methods of root canal preparation and obturation methods through cold side condensation and thermoplastic methods, including the most modern of them, the thermo-hydraulic condensation (THC) technique, were analyzed. An important element of the research hypothesis was to prove the assumption that to optimize the technology of development and obturation of root canals, tests of filling effectiveness are identified by the density and size of the gaps between the root canal wall, and the filling methods used and devices appropriate for material research, using mainly microscopy such as light stereoscopic (LSM) and scanning electron (SEM). The most beneficial preparations were obtained by making a longitudinal breakthrough of 48 natural human teeth, extracted for medical reasons, different from caries, with compliance with all ethical principles in this field. The teeth were prepared using various methods and filled with multiple obturation techniques, using a virtual selection of experimental variants. The breakthroughs were made in liquid nitrogen after a one-sided incision with a narrow gap created by a diamond disc using a materialographic cutter. The best effectiveness of the root canal filling was ensured by the technology of preparing the root canals with K3 rotary nitinol tools and filling the teeth with the THC thermoplastic method using the System B and Obtura III devices with studs and pellets of filling material based on gutta-percha after covering the root canal walls with a thin layer of AH Plus sealant. In this way, the research thesis was confirmed.

Relationship between Chemical Composition and Ms Temperature in High-Entropy Shape Memory Alloys

Five high entropy alloys with shape memory effect or superelastic effect were prepared by cold crucible melting to understand the effect of their chemical composition on the transformation temperatures. The microstructure and phases of the alloys at room temperature were investigated by optical and scanning electron microscopy. The calorimetric study of these alloys is employed to analyze the reversible transformation from austenite to martensite and to determine the transformation temperatures of the five alloys. The paper presents the results of several published works relating the transformation temperatures of high entropy shape memory alloys (HE-SMA). An experimental database has been built up to understand the influence of the different alloying elements and their related concentrations on the transformation temperature Ms (Martensite Start) of the HE-SMAs. An equation is identified using the database to predict the transformation temperature Ms of a high entropy shape memory alloy as a function of its weighted chemical composition, which exhibits a metallurgical solutioned treatment (ST) state and a specific mixing entropy (ΔSmix/R) range.

Research Status and Prospect of Additive Manufactured Nickel-Titanium Shape Memory Alloys.

Nickel-titanium alloys have been widely used in biomedical, aerospace and other fields due to their shape memory effect, superelastic effect, as well as biocompatible and elasto-thermal properties. Additive manufacturing (AM) technology can form complex and fine structures, which greatly expands the application range of Ni-Ti alloy. In this study, the development trend of additive manufactured Ni-Ti alloy was analyzed. Subsequently, the most widely used selective laser melting (SLM) process for forming Ni-Ti alloy was summarized. Especially, the relationship between Ni-Ti alloy materials, SLM processing parameters, microstructure and properties of Ni-Ti alloy formed by SLM was revealed. The research status of Ni-Ti alloy formed by wire arc additive manufacturing (WAAM), electron beam melting (EBM), directional energy dedication (DED), selective laser sintering (SLS) and other AM processes was briefly described, and its mechanical properties were emphatically expounded. Finally, several suggestions concerning Ni-Ti alloy material preparation, structure design, forming technology and forming equipment in the future were put forward in order to accelerate the engineering application process of additive manufactured Ni-Ti alloy. This study provides a useful reference for scientific research and engineering application of additive manufactured Ni-Ti alloys.

Assessing the biomechanical properties of nitinol staples in normal, osteopenic and osteoporotic bone models: A finite element analysis

ObjectiveBone staples are internal fixation devices that are frequently used in the foot, ankle, and hand to provide stabilization. Fixation stability is vital after fusion or fracture surgeries to ensure proper bone healing. Patients undergoing surgeries that require fixation to keep bones aligned and stable may present with diminishing bone mechanical properties, and this may compromise the ability of the fixation hardware to maintain a stable construct. The purpose of this study was to investigate the mechanical performance of shape memory and superelastic nitinol bone staples with different bridge geometries in normal, osteopenic, and osteoporotic bone models. Contact forces and maximum principal stress and strain in the bone were recorded. MethodsFinite element simulations of a bone staple fixation procedure were performed to examine the initial and post-surgery contact force, as well as the maximum principal stress and strain of 15 mm bridge and 20 mm bridge staple-bone constructs. ResultsShape memory nitinol staples exhibited higher contact forces compared to superelastic nitinol staples. Nitinol bone staples with 20 mm bridge lengths displayed higher contact forces and lower stresses in all bone types, as well as lower strains in osteoporotic bone models compared to nitinol staples with a 15 mm bridge length. ConclusionNitinol bone staple constructs with 20 mm bridge length staples provide higher contact forces and display lower stresses in the bone than 15 mm bridge staple-bone constructs, which may be beneficial in bone with diminishing mechanical properties. Both superelastic and shape memory effect nitinol staples provide adequate compression and stress relief. However, if osteopenia is present, shape memory effect nitinol staples with a 20 mm bridge length may provide more stress relief and compression, if the bone anatomy allows.

Strain glass state in Ni-rich Ni-Ti-Zr shape memory alloys

This work reports the existence of the strain glass state in Ni-rich Ni-Ti-Zr shape memory alloys induced by the precursor stages of the H-phase precipitation, typical of this alloy system. The strain glass is detected from dynamic mechanical testing and microstructural observations by electron diffraction and Transmission Electron Microscopy (TEM). The elastic modulus measurements also suggest the elinvar effect in these alloys. The strain glass state of this material exhibits superelastic effect in compression with recoverable strain levels over 4% and very little temperature dependence of the stress-strain curves over a temperature range of 230 to 300 K.

Phase field study on the microscopic mechanism of grain size dependent cyclic degradation of super-elasticity and shape memory effect in nano-polycrystalline NiTi alloys

A non-isothermal and crystal plasticity based phase field model was established by incorporating various inelastic deformation mechanisms, i.e., martensite transformation, martensite reorientation, the austenitic plasticity caused by dislocation slipping, and the martensitic plasticity caused by dislocation slipping and deformation twinning, in which the deformation twinning mechanism was newly considered. The grain size (GS) effect of martensite transformation and reorientation was characterized by introducing a grain boundary energy, and the GS dependent resistances of dislocation slipping and deformation twinning were considered in the phase field simulation for the first time to describe the GS dependence of plastic deformation. Through a series of phase field simulations on the inelastic cyclic deformation of two-dimensional nano-polycrystalline NiTi shape memory alloy (SMA) systems, the microscopic mechanism of the GS dependent cyclic degradation of the super-elasticity (SE), one-way shape memory effect (OWSME) and stress-assisted two-way shape memory effect (SATWSME) of such alloy systems was newly clarified. The simulated results show that with decreasing the GS, the cyclic degradations of the SE and SATWSME are both mitigated gradually, while that of OWSME is aggravated first and then mitigated; when reducing the GS to 10 nm, almost no functional degradation occurs. Further analysis shows that the GS dependence of the cyclic degradations of SE and SATWSME can be attributed to that: as reducing the GS, the plastic deformation resistances gradually increase due to the Hall-Patch effect, and the GS effect of martensite transformation and reorientation reduces the deformation mismatch introduced in the polycrystalline system and leads to the decrease of local internal stress level (i.e., the driving force of plastic deformation decreases) (Factor I) during the cyclic deformation, therefore, the generation and accumulation of plastic deformation are inhibited. However, for the cyclic degradation of OWSME, besides Factor I, since the reorientation-induced plasticity is mainly concentrated on the grain boundaries and their nearby grain interiors, the increase of grain boundary proportion results in the concentration and accumulation of plastic deformation at more locations during the cyclic deformation (Factor II). The competition between Factors I and II makes the cyclic degradation of OWSME show a non-monotonic variation with the decrease of the GS .

Achieving excellent superelasticity and extraordinary elastocaloric effect in a directionally solidified Co-V-Ga alloy

We demonstrate excellent superelasticity and giant elastocaloric effect in a directionally solidified Co50.7V33.3Ga16 alloy. Owing to the formation of [001]A preferentially oriented columnar grains, the as-grown alloy displays nearly perfect superelastic behaviors with fully reversible compressive strain of up to 5.4%, narrow stress hysteresis of about 40 MPa and a wide operating temperature window from 258 to 373 K. Simultaneously, a giant adiabatic temperature change ΔTad of -18.7 K is obtained on removing a uniaxial stress of 400 MPa at room temperature, which is in good agreement with the theoretical values based on Maxwell relation (-19.0 K) and calorimetric measurements (-19.9 K). A large |ΔTad| of greater than 12.5 K is obtained over a wide temperature span of at least 115 K. Moreover, both superelasticity and elastocaloric effect remain good functional stability without any evident degradation for 100 cycles.

Enhancement of the glass forming ability of superelastic Ni-Ti-Cu-Zr-Si alloy

In this study, the use of (Ni0.35Ti0.30Cu0.15Zr0.20)100−xSix (x = 0, 0.5, 1.0, 2.0 at%) alloy as a metallic glass precursor for a superelastic alloy, following thermoplastic forming, is investigated. The addition of Si improved the glass forming ability such that a fully amorphous sample with a thickness of ~450 µm was obtained with the x = 2.0 at% alloy. The addition of Si effectively stabilises the supercooled liquid by significantly increasing the activation energy of glass transition. The incubation time, τ, increased from 89 s for the x = 0 alloy to 346 s for the x = 2.0 at% alloy. The parameters relevant to superelastic effects, such as the maximum indentation depth (Dmax) and remnant indentation depth (Drem), remained almost constant. However, the remnant depth ratio increased slightly with the addition of Si. The fabrication of millimetre-scale Ni-Ti-Cu-Zr-Si metallic glass was achieved via the hot pressing of overlapped as-cast plates.

Enhanced working stability of elastocaloric effects in polycrystalline Ni-Fe-Ga dual phase alloy

Stable elastocaloric effect (eCE) over multiple stress cycles is an indispensable aspect for the commercialization of elastocaloric refrigeration. Here, we addressed the enhanced functional stability in polycrystalline Ni53.2±0.4Fe19.4±0.2Ga27.4±0.6 dual-phase alloy, where interstitial γ-phase was incorporated via aging precipitation. The intergranular γ-precipitates confirmed the reversible superelastic effects at room temperature (296 K), which is greatly conducive to multiple interphase movement. As a consequence, notable adiabatic temperature change (ΔTad) 6.2 K with a large coefficient of performance (COPmat) 14.5 was achieved under maximum stress 300 MPa. A stable eCE cooling performance (ΔTad~2.6 K) over 500 superelastic cycles with insignificant degradation was found under nominal stress 250 MPa. Consequently, the current work demonstrates that manipulating the microstructure by incorporating the interstitial secondary phase is a promising approach to enhance the mechanical and functional properties of ferromagnetic shape memory alloys (FMSMAs) for solid-state cooling technology.

Production and Mechanical Properties of Cu-Al-Ni-Be Shape Memory Alloy Thin Ribbons Using a Cold Co-Rolled Process

The use of shape memory alloys for micro-actuators constitutes a field of application in which copper–aluminum-based alloys find their usefulness because they can reach higher activation temperatures and are easier to produce than titanium-based alloys, particularly by the method proposed in this work. SMA tapes are a two-dimensional structure that offers many design options such as stamping, punching, and deep drawing, but they are also suitable for laser cutting, engraving, stamping, and EDM machining. This work has been made to study the manufacture of copper-based shape memory alloys (SMAs) using the cold co-rolling process also called the cold-roll bonding (CRB) process. In this process, a thin metal sandwich can be produced with a rolling machine. This sandwich consists of layers of CuNiBe master alloy and Al. During the rolling phase, the sandwich has no shape memory effect (SME) or superelastic effect (SE), so thin strips can be easily produced. After the rolling phase, the sandwich is subjected to a complex heat treatment to gain the SME. To validate this process to produce Cu-based SMAs, several alloys with different CuAlNiBe compositions have been tested. The SMAs obtained were characterized by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The martensitic transformation was studied by Differential Scanning Calorimetry (DSC) and SME and SE were studied by three-point bending tests. This work shows that the CRB is a good process for making a wide variety of Cu-based SMA ribbons.

Orientation dependence of elastocaloric effect in Ni50Mn30Ga20 single crystals

In this study, the orientation dependence of the elastocaloric effect and superelasticity in Ni50Mn30Ga20 single crystals undergoing L21–10M/14M–L10 martensitic transformations was investigated. The maximum value of the adiabatic temperature change ΔTad at reverse stress-induced martensitic transformations was shown to weakly depends on the orientation and equals 10.8 and 12.3 K in compression along the [001] and [011] directions, respectively. The superelasticity and elastocaloric effect temperature intervals were determined from the crystal orientation and were 80 K from 373 to 453 K for [001]-oriented crystals and 30 K from 373 to 403 K for [011]-oriented crystals. The strong orientation dependence of stress hysteresis Δσ (Δσ = 50–60 MPa for [001]-oriented crystals and Δσ = 110–142 MPa for [011]-oriented crystals) did not significantly affect the ΔTad, but determined the efficiency of the material for practical use as a solid state cooling device. The factors influencing the ΔTad(T) dependence were analyzed.

Assessment of mechanical and biocompatible performance of ultra-large nitinol endovascular devices fabricated via a low-energy laser joining process.

Nitinol is an excellent candidate material for developing various self-expanding endovascular devices due to its unique properties such as superelasticity, biocompatibility and shape memory effect. A low-energy laser joining technique suggests a high potential to create various large diameter Nitinol endovascular devices that contain complex geometries. The primary purpose of the study is to investigate the effects of laser joining process parameters with regard to the mechanical and biocompatible performance of Nitinol stents. Both the chemical composition and the microstructure of the laser-welded joints were evaluated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). In vitro study results on cytotoxicity demonstrated that the joining condition of 8 Hz frequency and 1 kW laser power showed the highest degree of endothelial cell viability after thermal annealing in 500°C for 30 min. Also, in vitro study results showed the highest oxygen content at 0.9 kW laser power, 8 Hz frequency, and 0.3 mm spot size after the thermal annealing. Mechanical performance test results showed that the optimal condition for the highest disconnecting force was found at 1 Hz frequency and 1 kW power with 0.6 mm spot size. Two new endovascular devices have been fabricated using the optimized laser joining parameters, which have demonstrated successful device delivery and retrieval, as well as acute biocompatibility.

High-strength superelastic as-cast Ni50.9Ti49.1-TiB2 in-situ composites

In this study, as-cast Ni50.9Ti49.1−TiB2 in-situ composites were prepared by adding boron in the vacuum induction melting (VIM) process. With boron content of 1 at.%, TiB2 phases appear in the form of flakes at grain boundaries of the NiTi alloy matrix. These TiB2 flakes are two dimensional in geometry, featured with an ultrafine thickness less than 200 nm and two other dimensions up to ~20–60 μm. Increasing boron content to 2.4 at.% alters the morphology of TiB2 from discrete flakes to agglomerative clusters. This morphological dissimilarity has noticeable impact on resulting mechanical properties, superelasticity and shape memory effect. Overall, the NiTi-1at%B composite outperforms both the monolithic Ni50.9Ti49.1 alloy and the NiTi-2.4 at%B composite. More specifically, it exhibits complete superelasticity for pre-strains below 4% and up to 4.3% recoverable strain for 6% pre-strain, which is comparable to the pure as-cast Ni50.9Ti49.1 alloy. Meanwhile, the corresponding strength under 6% pre-strain reaches 1800 MPa, 20% higher than that of Ni50.9Ti49.1. In compression, the yield strength is 65% higher than that of pure Ni50.9Ti49.1. Moreover, a shape memory recovery ratio of 45.5%, slightly below 48.6% of the monolithic NiTi, was also achieved in NiTi-1at%B. This indicates that the addition of 1 at.% B can effectively improve the strength of NiTi while maintaining its superelasticity and shape memory effect.

Transformational, microstructural and superelasticity characteristics of Ti–V–Al high temperature shape memory alloys with Zr addition

This study analyzes the influences of Zr addition on the martensitic transformation behavior, microstructural evolution, mechanical properties and superelasticity effect of arc-melted Ti-12V-4Al-xZr (x = 0, 0.5, 1, 1.5 and 2 wt.%) high temperature shape memory alloys (HTSMA). The results revealed that the austenite transformation temperatures and activation energy values decreased linearly when the Zr addition was greater than 0.5 wt.%. The Ti-V-4Al (wt.%) and Ti12V-4Al-0.5Zr (wt.%) alloys were composed of α″ martensitic phase, while the others consisted of predominant α″ martensitic phase and a small amount of the β austenite phase. The thickness of martensitic plates in the alloys reduced with increased Zr addition. Hardness and reduced elastic modulus values calculated from load-depth curves of the alloys also decreased with increasing Zr addition. Along with the increase in the Zr addition, the alloys’ superelasticity behavior decreased at room temperature (24 °C), while this behavior increased at the high temperatures (450 °C).