Shape Memory Alloy Research Articles

The effect of heat treatment on crystal structure and thermodynamic properties of Cu–Al–Ni shape memory alloy

The effect of heat treatment on crystal structure and thermodynamic properties of Cu–Al–Ni shape memory alloy

Shape Memory Alloys for Reversible Restoration of Ancient Monuments

Abstract The preservation of ancient structures through anastylosis requires methods that are both effective and reversible, while also preserving architectural integrity. Recent research into shape memory alloys (SMAs) offers a promising solution for reversible restoration, thanks to their ability to return to a predefined shape when exposed to thermal or mechanical triggers. However, challenges, such as cost, feasibility, and repeatability persist. This study focuses on characterizing the thermomechanical behavior of Nitinol SMAs under various conditions, with the aim of developing functional SMA devices for restoring monumental elements at the Valle dei Templi archeological site in Agrigento, Italy. The prototype’s superelastic properties and shape memory effects will be assessed to determine its effectiveness and applicability in different operational scenarios. This evaluation is grounded in a comprehensive analysis of the site's environmental conditions and an assessment of the alloy’s thermomechanical properties. By integrating SMAs into restoration efforts, the research aims to establish a methodology for creating reversible, replicable solutions that adhere to the principles of structural conservation.

The THE EFFECT OF ZIRCONIUM ADDITIVES ON PROPERTIES OF (Cu22%Zn4%Al) SHAPE MEMORY ALLOY

Shape memory alloys (SMAs) are one of the most important types of smart materials. It define as the materials that can undergo large pseudo elastic deformations while having the ability to recover to their original shape once subjected to a memory stimuli such as a specific temperature ,stress ,or strain. This study examines the effects of varying Zirconium (Zr) additive amounts on the microstructure, mechanical, and shape memory effect for all specimens of Cu-Zn-Al SMAs. Powder metallurgy was used to create Cu–22%Zn–4%Al SMAs, both base and with the inclusion of 0.2 and 0.4 weight percent Zr. 650MPa compact pressure was used to create the alloys after the particles had been mixed for five hours. The alloys underwent a three-step sintering procedure in a vacuum tube furnace for one hour at 350 ˚C, then for one hour at 550 ˚C, and for two hours at 850 ˚C. To characterise the microstructural and phase characteristics of alloys, both with and without Zr additions, XRD diffraction analyses, optical microscopy (OM), and scanning electron microscopy (SEM) were performed. With differential scanning calorimetry, the transition temperatures of all alloys were determined (DSC).As well as the shape memory effect test (SME) was measured. Results confirmed that all alloys compositions were found to include the predominant (Cu5Zn8) phase, as proven by XRD and microstructural investigation. The Zr addition dramatically lowered the transition temperatures, according to the transformation temperature data. Hardness experiments reveal that alloys' hardness and volume losses were enhanced by adding up to 0.4% weight percent of Zr reached to (64.8%) and (0.3909)mm3 respectively compared to base alloy.

Impact of NiTi Shape Memory Alloy Substrate Phase Transitions Induced by Extreme Temperature Variations on the Tribological Properties of TiN Thin Films

NiTi alloys and thin film/NiTi composites are extensively utilized in frictional environments, particularly those experiencing extreme temperature fluctuations. Current studies mainly focus on preparing wear-resistant films on NiTi alloy surfaces but neglect the potential impact of temperature-induced phase transitions in the NiTi substrate on thin films’ performance. This study examines the effect of NiTi alloy phase transitions, induced by extreme temperature variations, on the tribological properties of TiN thin films on NiTi substrates. TiN films (1 μm thick) were deposited on NiTi alloy surfaces using magnetron sputtering technology. The transition of the main phase in the NiTi substrate between the R phase and the B19′ phase was achieved via liquid nitrogen cooling (−196 °C) and water bath heating (90 °C). XRD, EDS, SEM, and tribological tests analyzed the phase structure, elemental composition, micromorphology, and tribological behavior. Fatigue wear was identified as the predominant wear mechanism for the TiN films, with minor contributions from oxidative and abrasive wear. Phase transition from the R phase to the B19′ phase in the NiTi substrate induced by temperature change couls reduce the wear rate of the TiN film by up to 41.97% and decrease the friction coefficient from about 0.45 to about 0.25. Furthermore, the shape memory effect of the NiTi alloy substrate, caused by B19′ → B2 phase transition, resulted in the recovery of the TiN thin film wear track depth from 920 nm to 550 nm, manifesting a “self-healing” phenomenon. The results in this study are important and necessary for the provision of thin film/NiTi composites in frictional environments.

The Evolution of Microscopic Damage Mechanisms During Actuation Fatigue Cycling in High Temperature Shape Memory Alloys

The Evolution of Microscopic Damage Mechanisms During Actuation Fatigue Cycling in High Temperature Shape Memory Alloys

Axial stress-strain behavior of shape memory alloy strips constrained concrete columns

Axial stress-strain behavior of shape memory alloy strips constrained concrete columns

Cyclic pseudoelastic behavior of friction stir processed NiTi shape memory alloy: Microstructure and W-alloying

Cyclic pseudoelastic behavior of friction stir processed NiTi shape memory alloy: Microstructure and W-alloying

Influence of shape memory alloy in seismic response of coupled shear wall of concrete structures

Influence of shape memory alloy in seismic response of coupled shear wall of concrete structures

Research on variable stiffness robotic joint actuator based on shape memory alloy

Research on variable stiffness robotic joint actuator based on shape memory alloy

Stochastic response of a shape memory alloy laminated beam with viscoelastic matrix

Stochastic response of a shape memory alloy laminated beam with viscoelastic matrix

Modeling and adaptive NN control for SMA flexible actuating systems with modified GPI hysteresis model

In this study, a shape memory alloy (SMA) actuating system is constructed to achieve flexible actuation ability. To improve the actuating performance, an effective control scheme needs to be developed to address the negative effects caused by the nonlinear nature of the internal SMA material and accommodate complex operating conditions. A modified generalised Prandtl-Ishlinskii (MGPI) hysteresis model is proposed to accurately characterise the strong saturated asymmetric hysteresis nonlinearity in the SMA wires. The modification of the input shape function allows for greater flexibility in controller design. Using this hysteresis modelling approach, an adaptive neural network (NN) control with a command filter is designed to achieve superior control performance. Experimental results validate the effectiveness of the proposed controller strategy.

Microchannel fabrication on bio-grade Nitinol SMA by μ-ED milling process using sustainable oil for improving the machining performance and biocompatibility

The process of micromachining has garnered attention for its ability to create three-dimensional tiny features, particularly in ultra-hard and exotic materials. The present work investigates the effect of different parameters of theμ-ED milling, such as pulse on time (Ton), pulse off time (Toff), voltage (V), and tool rotation (TR) on the dimensional deviation (DD), material removal rate (MRR), surface roughness (Ra), and machined surface characteristics (analyzed by EDS and FESEM). The sesame oil as dielectric and tungsten-copper as tool electrodes were used to maintain the accuracy and improve the machinability of bio-grade Nitinol shape memory alloy (SMA). Response surface methodology (RSM) and genetic algorithms (GAs) were used to optimize the various input parameters of theμ-ED milling process. Artificial neural network was combined with GA to find the best parametric combination for microchannel fabrication. The cytotoxicity test was also performed on the machined surface to analyze the biocompatibility of the machined surface. It was found that the cell viability of Nitinol SMA was improved by 85.11% after machining at the optimum condition. The highest MRR was found to be 0.076 gm min-1, and the lowest DD and Ra were found to be 16.47μm and Ra 0.387μm, respectively.

Influence of Recast Layer Formation of Nitinol Shape Memory Alloy according to Manufacturing Methods

Influence of Recast Layer Formation of Nitinol Shape Memory Alloy according to Manufacturing Methods

Molecular Dynamics Investigation on Grain Size-Dependent Superelastic Behavior of CuZr Shape Memory Alloys

The superelasticity of CuZr shape memory alloys (SMAs) originates from stress-induced transformations between the B2 (austenite) and B19’ (martensite) phases. Grain size is a key parameter affecting the superelasticity of shape memory alloys. Previous studies on NiTi, Fe-based, and Cu-based SMAs confirm that altering grain size effectively regulates superelasticity. Current research on the influence of grain size on the superelasticity of CuZr shape memory alloys (SMAs) is relatively sparse. This study employs molecular dynamics simulations to evaluate the effect of grain size on the superelasticity of CuZr SMAs through uniaxial loading–unloading tests. Polycrystalline samples with grain sizes of 6.59 nm, 5 nm, and 4 nm were analyzed. The results indicate that reducing grain size can decrease the irrecoverable strain, thereby enhancing superelasticity. The improvement in superelasticity is attributed to a higher recovery rate of the martensite-to-austenite transformation, allowing more plastic deformation within the grain interior to recover during unloading, and thereby reducing the irrecoverable strain. The recovery rate of the martensite-to-austenite transformation is closely related to the elastic strain energy accumulated within the grain interior during loading.

Advancements in Surface Modification of NiTi Alloys for Orthopedic Implants: Focus on Low-Temperature Glow Discharge Plasma Oxidation Techniques

Nickel–titanium (NiTi) shape memory alloys are promising materials for orthopedic implants due to their unique mechanical properties, including superelasticity and shape memory effect. However, the high nickel content in NiTi alloys raises concerns about biocompatibility and potential cytotoxic effects. This review focuses on the recent advancements in surface modification techniques aimed at enhancing the properties of NiTi alloys for biomedical applications, with particular emphasis on low-temperature glow discharge plasma oxidation methods. The review explores various surface engineering strategies, including oxidation, nitriding, ion implantation, laser treatments, and the deposition of protective coatings. Among these, low-temperature plasma oxidation stands out for its ability to produce uniform, nanocrystalline layers of titanium dioxide (TiO2), titanium nitride (TiN), and nitrogen-doped TiO2 layers, significantly enhancing corrosion resistance, reducing nickel ion release, and promoting osseointegration. Plasma-assisted oxynitriding processes enable the creation of multifunctional coatings with improved mechanical and biological properties. The applications of modified NiTi alloys in orthopedic implants, including spinal fixation devices, joint prostheses, and fracture fixation systems, are also discussed. Despite these promising advancements, challenges remain in achieving large-scale reproducibility, controlling process parameters, and reducing production costs. Future research directions include integrating bioactive and antibacterial coatings, enhancing surface structuring for controlled biological responses, and expanding clinical validation. Addressing these challenges can unlock the full potential of surface-modified NiTi alloys in advanced orthopedic applications for safer, longer-lasting, and more effective medical implants.

Additive Manufacturing of Ni–Ti SMA by the Sinter-Based MoldJet Method

Abstract Additive Manufacturing (AM) of Shape Memory Alloys (SMA), and specifically Ni–Ti alloys, is an evolving field with significant potential to applications in actuation, energy harvesting, and refrigeration. Sinter-based AM technologies show promise in tailoring and controlling the microstructure and properties of Ni–Ti, because the metal particles remain in the solid-state throughout the process. Here, we report on the manufacturing and characterization of Ni–Ti produced using a novel sinter-based MoldJet method: a wax-based mold is deposited layer-by-layer using jet-printing, and its cavities are simultaneously filled with metallic paste. This additive process produces a green body that is sintered to form a dense metal part. The low content of organic binder in the metallic paste results in reduced carbon and oxygen contamination compared to other sinter-based AM methods. Consequently, the reduced formation of carbides and oxides enhances the thermomechanical properties. Here, we show that Ni–Ti produced via MoldJet exhibits a superelastic response with a substantial recoverable strain of 5.6% in tension and 4.5% in compression, and irrecoverable plastic strain below 0.2%. The results indicate that MoldJet is a promising method for AM of Ni–Ti for advanced applications. Specifically, we show that the obtained material properties are adequate for elastocaloric cooling devices.

Microstructure and Mechanical Behavior of Various Solution Treated Biomedical Superelastic NiTi Shape Memory Alloy: An Experimental Investigation

Microstructure and Mechanical Behavior of Various Solution Treated Biomedical Superelastic NiTi Shape Memory Alloy: An Experimental Investigation

Study on axial compressive damage performance of SMA strips confined concrete columns by acoustic emission technology

Abstract The shape memory effect induced by thermally exciting shape memory alloy (SMA) provides an active constraint method for structural reinforcement. To investigate the axial compression performance and failure mechanism of SMA strips confined concrete columns, axial compression tests and real-time acoustic emission (AE) monitoring were performed on concrete columns with diverse pre-strain levels and constraint methods. The results reveal that the constraint of SMA strips improves the mechanical properties and inhibits the brittle failure. Based on the correlation between AE characteristic parameters and stress–time curves, the internal failure of confined specimens is classified into three stages: micro-crack initiation, crack stable development and macroscopic crack formation. The rise angle value grows and average frequency value reduces as the damage progresses, manifesting that the shear crack is in the stable propagation stage. The b-value generally diminishes as the load rises, illustrating that the cracking level inside the specimen is continuously increasing. Moreover, compared with the PC40-50-40 specimen, the AC40-50-40 specimen generates highly active AE signals. The distribution of AE damage events indicates that active constraint significantly accelerates the initiation and propagation of cracks in concrete columns during compression loading.

Mechanical property strengthening by post-heat treatments in NiTiCu shape memory alloys fabricated by twin-wire arc additive manufacturing

ABSTRACT To address the challenges of wide transformation hysteresis as well as the poor properties of NiTi-based alloys fabricated by twin-wire arc additive manufacturing, post-heat treatments were employed in as-deposited NiTiCu alloys. After aging at 450°C, 550°C, and 650°C, the alloys exhibited significant reduction in the precipitate sizes, narrow transformation hysteresis, uniform distribution of microhardness, and substantial improvement in mechanical properties. With the increase of the aging temperature, the matrix grain size and the precipitate size coarsened, which was detrimental to the resultant mechanical properties. The alloys aged at 450°C exhibited the narrowest transformation hysteresis of 11.7°C and optimal mechanical properties (tensile strength of 539 MPa and fracture strain of 6.9%). The enhancement of mechanical properties can be attributed to the smaller matrix grain size and precipitate size and the higher proportion of high-angle grain boundaries in this material condition. This work provides practical significance for the twin-wire arc additive manufacturing and performance optimisation of NiTi-based ternary alloys.

Effect of Radial Force and Radial Torque on Hole Quality Characteristics During Micro-Drilling of Nitinol Shape Memory Alloy

Effect of Radial Force and Radial Torque on Hole Quality Characteristics During Micro-Drilling of Nitinol Shape Memory Alloy