Nickel-titanium Shape Memory Alloy Research Articles

Cyclic and uniaxial tensile properties of superelastic niti shape memory alloy cables

This study investigates the impact of various factors, including annealing duration, strain amplitude, cyclic loading, loading rate, and pre-training, on the mechanical properties of Nickel–Titanium shape memory alloy (SMA) cable. The primary focus is on evaluating their recovery ability and energy dissipation capabilities. The tested SMA cable has an outer diameter of 9 mm and a 7 × 7 configuration. The variation of strength, stiffness, residual strain, hysteretic energy, and equivalent viscous damping ratio of SMA cable with the loading cycle is analyzed. Furthermore, the impact of various annealing durations on the tensile strength and elongation of both SMA cables and wires was examined through monotonic tensile tests. The results indicate that the annealing duration considerably affects the superelastic behavior of SMA cables by shifting the stress-strain loops down and widening them. The recovery ability of SMA cable degrades more progressively with increasing loading amplitude and the number of loading cycles. The mechanical properties gradually stabilized after 20 times of constant strain amplitude loading and unloading training. The strain selection for cyclic training should not make the SMA cable in the martensite hardening stage. The recovery ability and peak stress of SMA cable can be significantly improved by pre-training. With the increase of annealing duration, the tensile strength of the SMA cable decreases gradually. Compared with SMA wire, SMA cable has better ductility and robustness and provides sufficient restoring force under large deformation.

Phase transformation behavior and shape memory effect of nickel-titanium shape memory alloy using the magnetic field assisted wire electrical discharge machining

Nickel-titanium shape memory alloy (NiTi-SMA) can restore its original shape after deformation, making it show great application in the fields of biomedicine, aerospace, etc. The wire electrical discharge machining (WEDM) has the advantage of machining micro and complex structures, which can greatly promote the application of NiTi-SMA. However, there are issues such as heat affected layer (HAL) on the surface of WEDM, which can affect the functionality of NiTi-SMA. Therefore, when using WEDM to NiTi-SMA, more attention should be paid to the functional changes after machining. This article primarily examine is the impact of peak current and pulse on time on the phase transformation behavior, shape memory effect, and mechanical properties of NiTi-SMA during WEDM, and introduces into the magnetic field assisted (MFA) process to improve the machining performance of NiTi-SMA. The results indicate that the HAL formed on the surface of NiTi-SMA is primarily composed of the irreversible phase transformation of B2 austenite. This layer induces a hardening effect, resulting in an increase in the phase transition temperature and a decrease in the phase transition energy (∆HM-A), as a result, the martensitic phase transformation behavior is suppressed. When the peak current and pulse on time increase, the surface quality of the NiTi-SMA processed decreases. The thickness of the HAL and microhardness increase, causing an increase in the phase transition temperature of the NiTi-SMA processed samples. Additionally, the transformation energy ∆HM-A, shape recovery rate, and mechanical properties decrease, and after recovery, more surface cracks appear and show larger extensions. MFA-WEDM can improve the surface quality of NiTi-SMA processing, reduce the thickness of the HAL, and effectively enhance the phase transformation temperature and energy ∆HM-A of the NiTi-SMA processed samples. With a magnetic field strength of 0.45T, the tensile shape recovery rates of 98%, 94.4%, and 91.0% were achieved at 2%, 5%, and 8% strain, respectively. This represents an improvement of 8.9% compared to the maximum shape recovery rate with conventional WEDM. At the same time, it also inhibits the generation and propagation of surface cracks after deformation recovery. Additionally, MFA-WEDM improves the mechanical properties of NiTi-SMA, and reduces the thickness of the brittle fracture region by 49.7% compared to conventional WEDM. Therefore, MFA-WEDM can effectively enhance the shape memory effect of NiTi-SMA. However, it is important to avoid excessive peak currents and pulse on time to achieve optimal shape memory functionality.

Low temperature effect on cyclic behavior of shape memory alloy U-shaped dampers

Although Nickel-Titanium (NiTi) shape memory alloys (SMAs) have been widely studied as seismic response mitigation devices in civil structures, their temperature sensitivity due to the coupled thermo-mechanical behavior prevents their practical implementation in cold temperature environments. This paper investigated the effects of varying ambient temperatures (particularly low ambient temperature) on the hysteretic behavior and self-centering (SC) ability of shape memory alloy U-shaped dampers (SMAUDs) that were made of NiTi showing superelasticity (SE) at room temperature. Thermo-mechanical properties of SMAUDs were identified through differential scanning calorimetry (DSC) tests. Cyclic loading experiments on SMAUDs were conducted at a wide ambient temperature range from −40°C to 20°C. The variations in the hysteretic characteristics of the SMAUD, including partial superelasticity (SE), strength, stiffness, SC, and energy dissipation capabilities, at different ambient temperatures were investigated. In general, the decreasing ambient temperature leads to the degradation of the SC ability. At ambient temperatures below the phase transformation temperature, the SMAUDs lose the SE but still maintain certain levels of strength and energy dissipation, which is different from common axial-type SMA elements. Meanwhile, the SMAUDs can restore their SC ability and strength after the recovery from low temperatures to room temperature, making them suitable for use in a cold environment.

Experimental investigation during nano powder added µ-ED milling on nickel-titanium shape memory alloy

Nickel-titanium (NiTi) shape memory alloy (SMA) is one of the smart materials which has a vast application in the aerospace and biomedical industry due to its shape memory effect (SME), strong corrosion and wear resistance. Thus, the present study investigates the influence of process variables like gap voltage (V), powder concentration (PC) and pulse on time (ton) towards the material removal rate (MRR), surface roughness (SR) and micro-hardness (MH) amid graphene nano powder added micro-electrical discharge milling (µ-ED milling) of NiTi SMA. ANOVA analysis has been carried out to determine the % distribution of individual machining parameters towards all responses. The addition of graphene nano particles to the dielectric oil considerably enhanced the MRR, MH, and decreased the SR of the milled micro-channel. Taguchi’s grey relational analysis (GRA) and grey-desirability approach have been applied for multi-response optimisation to find the maximum MRR, MH, and minimum SR. It is discovered that the grey-desirability method improves all the responses. The Field emission scanning electron microscopy (FESEM) micro-graphs confirm defect-free mirror-like surface finish at the optimal grey-desirability setting. The X-ray diffraction (XRD) analysis discovered the formation of oxides and hardened phases in the machined surface. The application of graphene enhanced the recast layer thickness and reduced the indentation depth at subsurface region. The nano indentation test validates the rise in nano hardness and elastic modulus at the grey desirability optimal setting compared to the initial machining condition.

Investigation into microdefects and corrosion resistance of nickel-titanium shape memory alloy using electrical discharge coating process

Investigation into microdefects and corrosion resistance of nickel-titanium shape memory alloy using electrical discharge coating process

Relationship between ceramic additives and improved biodegradability, osseointegration, and surface roughness of Ni–Ti shape memory alloy for use in load-bearing bone site applications

To make metallic biomaterial implants acceptable for use in bone replacement applications, this research aimed to identify a potential means of improving the poor wear resistance of implants as well as their limited osseointegration capability and rapid biodegradation. In this regard, mechanical alloying was used to make a nickel-titanium (Ni–Ti) shape memory alloy with increasing amounts of hardystonite (HT) and niobium carbide (NbC). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to examine the phase composition and microstructure of the sintered samples. To test osseointegration and biodegradation, samples were immersed in simulated body fluid (SBF). They were then analyzed using SEM, weight loss measurements, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The SEM pictures indicated that increasing HT and NbC helped build apatite layers on their surfaces, anticipating successful osseointegration if utilized as bone implants. ICP findings showed that HT and NbC significantly reduced Ni2+ ion release, preventing tissue damage. In contrast to electrical conductivity, these ceramics improved the compressive strength and microhardness of the examined samples. The improvement in their strength was 10.81, 27.02, 21.62, and 31.89 %. SEM results confirmed the role of ceramic materials to enhance the wear resistance of the tested samples. Based on these findings, the prepared nanocomposites achieved the main goal of this study.

Commentary: Evaluation of the mechanical properties and clinical application of nickel-titanium shape memory alloy anal fistula clip.

Commentary: Evaluation of the mechanical properties and clinical application of nickel-titanium shape memory alloy anal fistula clip.

Unstable Vancouver B1 periprosthetic femoral fracture fixation: A biomechanical comparison between a novel C-shaped memory alloy implant and cerclage wiring.

To compare the biomechanical stability of a novel, C-shaped nickel-titanium shape memory alloy (SMA) implant (C-clip) with traditional cerclage wiring in the fixation of a Vancouver B1 (VB1) periprosthetic femoral fracture (PFF). In total, 18 synthetic femoral fracture models were constructed to obtain unstable VB1 fracture with an oblique fracture line 8 cm below the lesser trochanter. For each model, the distal portion was repaired using a 10-hole locking plate and four distal bi-cortical screws. The proximal portion was repaired using either three, threaded cerclage wirings or three, novel C-shaped implants. Specimens underwent biomechanical testing using axial compression, torsional and four-point bending tests. Each test was performed on three specimens. The C-clip was statistically significantly stronger (i.e., stiffer) than cerclage wiring in the three biomechanical tests. For axial compression, medians (ranges) were 39 (39-41) and 35 (35-35) N/mm, for the C-clip and cerclage wiring, respectively. For torsion, medians (ranges) were, 0.44 (0.44-0.45) and 0.30 (0.30-0.33) N/mm for the C-clip and cerclage wiring, respectively. For the four-point bending test, medians (ranges) were 39 (39-41) and 28 (28-31) N/mm; for the C-clip and cerclage wiring, respectively. Results from this small study show that the novel, C-shaped SMA appears to be biomechanically superior to traditional cerclage wiring in terms of stiffness, axial compression, torsion and four-point bending, and may be a valuable alternative in the repair of VB1 PFF. Further research is necessary to support these results.

Residual height of surface topography in milling nickel-titanium shape memory alloy using a small-diameter cutter

The milled surface topography of nickel-titanium shape memory alloy plays a crucial role in determining both frictional behavior and biocompatibility. Through a combination of simulation and experimentation, this study delves into the influence of radial depth of cut on the formation of surface topography during the milling of nickel-titanium shape memory alloy. The inhibitory effects of work hardening and plastic deformation on material rebound are considered, providing an explanation for the mechanism of topography changes. The results show that the degree of work hardening increases with increasing radial depth of cut, and the residual height increases from 1.31 μm to 11.47 μm, with the error varying from 5.9 % to 2 %. The research aims to inform the improvement of machined surface quality of tiny components in the medical and microelectronics industries.

A study on Analysing the Selection of Materials for Knee Implant Femoral Components using the TOPSIS method

Specialists are creating more sophisticated and useful materials daily as technology advances. For orthopaedic implants such as "knee replacements, hip replacements, and orthopaedic accessories", biomaterials are employed to produce prosthetic organs. In patients with severe osteoarthritis (OA) of the knee, "total knee replacement (TKR)" is one of the most successful surgical procedures for pain management and functioning rehabilitation. Humans continue to experience issues with the kneecap, such as aseptic dislocation brought on by excessive wear across articular surfaces, stress-shielding of the bone by prostheses, and soft tissue formation at the junction of implanted bone. due to improper “TKR material selection”. Since selecting the best materials for the femoral component of TKR requires careful consideration, the "technique for order of preference by similarity to ideal solution (TOPSIS)" is used in this research paper. This technique uses an order of preference based on how closely the preferred option is to the ideal solution. The "equal weights method (EWM)" assigns various criteria distinct weights of importance. The rank of alternatives using the TOPSIS method for “Co-Cr-Mo is fourth, Co-Ni-Cr-Mo is third, NiTi SMA is first, Porous NiTi SMA is second, pure Ti is sixth and Ti-5Al-2.5Fe is fifth”. The result indicated that FC material using TKR Nickel Titanium Shape Memory Alloy (NiTi SMA) is at rank 1 with properties such as Tensile Strength 960 MPa, Density 6.45 g/cc, extremely high Corrosion resistance, and exceptionally high Wear resistance.

3D in-situ characterization of dislocation density in nickel-titanium shape memory alloys using high-energy diffraction microscopy

3D in-situ characterization of dislocation density in nickel-titanium shape memory alloys using high-energy diffraction microscopy

EBSD study of variant reorientation, texture, and twin formation in a martensitic NiTi alloy deformed in compression

Martensitic crystallography plays a vital role in the texture evolution and mechanical properties in Nickel-Titanium (NiTi) shape memory alloys when subjected to deformation. However, their microstructural changes during deformation are not well known and understood. In this study, we systematically investigate the stress-induced change of the microstructure of NiTi shape memory alloy under compression using the electron backscattered diffraction (EBSD) technique, and more specifically the variant reorientation, the evolution of textures, and the formation of twins. The EBSD maps reveal that upon strain the martensite morphologies shift from needle to block and their orientations are strongly reinforced along the loading axis. To quantify these microstructural changes, we used the Interaction Work (IW) associated with the lattice distortion of single variant, which provides a good fit with the experimental observation. A strong dependence of reorientation on the pre-textures of the parent B2 grains was also put in evidence. Other plasticity sources were confirmed such as dislocations and deformation twins. The calculations indicate that, for some specific orientations of parent grains, the active deformation twins could be easier for {011}M twin than that of (201¯)M deformation twin, whereas other orientations only favor the (201¯)M deformation twin.

Effect of robotic weaving motion on mechanical and microstructural characteristics of wire arc additively manufactured NiTi shape memory alloy

Abstract The effect of robotic weaving motion on the crystallographic orientation, texture and mechanical properties of thin-walled nickel titanium shape memory alloy fabricated via wire arc additive manufacturing is studied. Crystallographic orientation analysis reveals that the weaving motion alters the epitaxial growth of grains, which reduces the fraction of (001) oriented grains but increased the fraction of (110) and (111) oriented grains. Moreover, the weaving motion increases the fraction of equiaxed grains and homogeneously distributes Ni4Ti3 phases. These changes improve the hardness and strength of the build and also introduce isotropy in mechanical properties. Results of the study reveal that arc weaving strategy has a great potential in achieving near isotropic tensile characteristics and is beneficial in terms of tailoring texture in building nickel titanium thin-walled smart material structures.

Analysis of Shape-Memory-Alloy Fiber Interface Strength for Optimization of Self-Healing Composites

Self-healing materials, possessing an innate ability to mend damage and restore structural strength, have tremendous potential to improve safety and reliability, especially in space applications where recovery or manual performance of repairs may be prohibitive, dangerous, or impossible. Self-healing metallic materials developed with Nickel Titanium (NiTi) Shape Memory Alloy (SMA) reinforcement showed a promising prospect for recovering from larger scale damage. However, NiTi is known to form an inert oxide (TiO2) surface layer that is extremely hard to attach to. In this research, to promote better strength between the fiber and matrix, TiO2 surface layer has been removed by etching the NiTi wires in an inert environment and a pull test has been performed to evaluate the resulting change in adhesion strength between the fiber and metallic matrix. The experimental investigation of these interface fracture scenarios will enable the efficient design of composite materials.

On the Nature of Post‐Constrained Recovery Residual Stress of NiTi Shape Memory Alloys

In this article, the nature of the post‐constrained recovery residual stress (PCRRS) observed in nickel titanium (NiTi) shape memory alloys (SMAs) subjected to constrained recovery and returned to a low‐temperature state while remaining constrained is investigated. After performing the thermomechanical cycling to produce the PCRRS state, four experiments are performed with different deflection profiles applied from the PCRRS state, and the changes in the residual stress is observed. All tests produce a gradual decrease in stress after every load cycle, similar to cyclic softening. However, repetition of the process used to initially generate PCRRS restores the initial magnitude of the PCRRS, indicating that the decrease in residual stress is a stable, repeatable, and reversible phenomenon, and not true material degradation. To better understand the nature of PCRRS, an analysis is performed comparing the modulus relating stress and strain at different points along the thermomechanical loading path. In this analysis, it is shown that NiTi has a combination of twinned and detwinned martensite in the PCRRS state. Understanding the nature of PCRRS, properties and its stability have the potential for advanced engineering applications such as self‐healing and fatigue‐resistant materials by generating stresses without continuous actuation over a long period of time.

Evaluation of the mechanical properties and clinical application of nickel-titanium shape memory alloy anal fistula clip.

The study investigates the mechanical properties of a nickel-titanium shape memory alloy anal fistula clip (NiTi-AFC), studies the surgical method of treating anal fistula, and evaluates its clinical efficacy. The anal fistula clip was formed in nickel-titanium alloy with a titanium content of 50.0%-51.8%. The mechanical properties and chemical properties were tested. A total of 31 patients with anal fistula were enrolled between 1 January 2020 and 1 January 2023. All patients underwent internal orifice closure surgery using NiTi-AFC, and anorectal magnetic resonance or ultrasound was performed before surgery and 6 months after surgery for diagnosis and evaluation. Fistula cure rates, length of stay, perianal pain, and Wexner incontinence scores were retrospectively compared between patients treated with NiTi-AFC and patients treated with other surgical methods. NiTi-AFC has a density of 6.44-6.50 g·cm-3, with a shape-restoring force of 63.8 N. The corrosion rate of NiTi-AFC in 0.05% hydrochloric acid solution at atmospheric pressure and 20°C is approximately 6.8 × 10-5 g·(m·h)-1. A total of 31 patients (male/female: 19/12, age: 43.7 ± 17.8 years) were included. Among them, 22.6% (7) had multiple anal fistula, 16.1% (5) had high anal fistula, and 48.3% (15) had perianal fistula Crohn's disease. In total, 12.9% (4/31) did not achieve primary healing, underwent fistula resection, and eventually recovered. A retrospective analysis showed that the fistula healing rate, length of stay, and anal pain of NiTi-AFC treatment were similar to those of other traditional surgeries, but the Wexner incontinence score was significantly lower. NiTi-AFC has shape memory properties, corrosion resistance, superelastic effect, and surface cell adhesion. It is applied to internal orifice closure surgery of anal fistula, with good therapeutic effect, and can protect the anal function.

Investigation and optimization in electrochemical arc drilling of Ni55.7Ti nickel–titanium shape memory alloy with molybdenum electrode

Investigation and optimization in electrochemical arc drilling of Ni55.7Ti nickel–titanium shape memory alloy with molybdenum electrode

Study of ageing and size effects in Nickel–Titanium shape memory alloy using molecular dynamics simulations

ABSTRACT The effect of ageing process at 1073.15 K on the athermal phase transformation in different nanograins (4.5, 6 and 9 nm) of Nickel–Titanium shape memory alloy is studied using molecular dynamics simulations. The martensitic transformation start temperature and transformed martensite volume decrease with decreasing grain size. The two-stage phase transformation with intermediate phase formation is observed only in the smallest grain (4.5 nm) where a single martensite variant is formed. On the contrary, larger grains show a self-accommodated twinned martensite variants with one-stage transformation from austenite to martensite. The ageing process hardly influences the morphology of the martensite phase, however, it rises the martensite start temperature and reduces the austenite start temperature. The nano grain size models demonstrate the constrained transformation due to the transformation barrier and the accumulation of internal stress, while the ageing process shows the tendency for stress relaxation.

ELECTROCHEMICAL ARC DRILLING OF NICKEL–TITANIUM SHAPE MEMORY ALLOY USING MOLYBDENUM ELECTRODE: INVESTIGATION, MODELING AND OPTIMIZATION

In the present scenario, electrochemical arc machining (ECAM) (hybrid of electric discharge erosion and electrochemical dissolution) is an evolving procedure for difficulty in machining the materials due to constraints of existing processes. This research aims to investigate the machinability of Ni[Formula: see text]Ti alloy through electrochemical arc drilling using molybdenum electrode. Electrolyte concentration (ethanol with ethylene glycol and sodium chloride), supply voltage, and tool rotation are considered as the variable factors to evaluate the ECAM performance characteristics in drilling blind hole operation concerning overcut (OC), tool wear rate (TWR) and materials removal rate (MRR). Consequently, response surface methodology is implemented for predictive modeling of various performance characteristics. Finally, multi-objective optimization through desirability function approach (DFA) has produced a set of optimal parameters to improve the productivity along with the accuracy, which is the prime requirement for the industrial applicability of the ECAM process. Results demonstrated that supply voltage is the influential key factor for improvement of machining rate. Scanning electron microscope (SEM) photographs revealed the development of heat affected zone (HAZ), white layer, melted droplet, craters, re-solidified material, ridge-rich surface and voids as well as cavities around the end-boundary surfaces of a blind hole. Composition analysis through energy dispersive spectroscopy (EDS) indicated the oxygen content on the machined surface because electrolyte breakdown causes oxidation to take place at elevated temperatures across the machining zone. Moreover, carbide precipitation like TiC was found in the melting zone of the drilled hole, as revealed by X-ray diffraction (XRD) analyses, which has the affinity to reduce the SMA properties in HAZ.

Structural enhancement and repair of CFRP T-joint by the cross-embedded SMA wire

Owing to shape memory and super-elasticity, shape memory alloy (SMA) has been applied widely in many fields, such as aerospace, medical facility, civil engineering, and so on. In this paper, wires of nickel-titanium (NiTi) SMA are inserted into the carbon fiber-reinforced polymer (CFRP) T-shape structure. The enhancing laws are investigated via the comparison of the performance of the cases with or without SMA in tensile tests. According to the microscopic damage morphology and the damage degree in the simulative study, the reinforcement mechanism is further revealed. Then, the roles of the SMA in the adhesive repair of the T-joint with permanent damage, dominated by delamination, are analyzed by contrast experiments. Overall, both the advantage of SMA, super-elasticity and shape memory, are skillfully utilized to improve the mechanical property and subsequent adhesive repair of CFRP T-joints. Specifically, it raises by an average of 10% and 85% the value of ultimate force and elongation for T-joint cross-embedded with SMA compared with no SMA's, as well as increasing by 57.14% and 42.42% the number of ultimate force and healing efficiency by embedding SMA under thermal adhesion environment averagely.