Ti Shape Memory Alloy Research Articles

Experimental and theoretical analyses of transformation temperatures of Cu-based shape memory alloys

Binary-shape memory alloys that are based on copper, mainly copper–aluminium, copper–zinc and copper–tin alloys, either with or without ternary elemental additions, are of special interest to the industry and academia because of their good shape recovery, ease of processing, larger recovery strain and lower cost. However, unlike Ni–Ti shape memory alloys, their uses are moderately limited due to shortcomings, such as stabilization of martensite due to ageing, brittleness and low mechanical strength. Therefore, efforts have been made over the years to overcome these limitations using appropriate ternary and quaternary elemental additions. This work takes into account the data obtained from the experimental work carried out by the authors of this paper as well as the data obtained from the experimental and theoretical works carried out by earlier researchers in this area that have been published in the literature over the years. It is observed in quaternary shape memory alloys based on copper that with an increase in the atomic radius of the quaternary element, the hysteresis width is found to increase. With the addition of ternary elements to binary Cu-based alloys (Cu–Al and Cu–Zn), and quaternary elements to ternary Cu-based alloys (Cu–Al–Fe, Cu–Al–Ni, Cu–Al–Mn, Cu–Zn–Al, Cu–Zn–Ni and Cu–Zn–Si), the $$M_{\mathrm{s}}$$ temperature either increases or decreases. This influence is directly correlated with the $$e_{\mathrm{v}}/a$$ ratio and $$c_{\mathrm{v}}$$ values. It is also observed that as the concentration of electrons decreases, the $$M_{\mathrm{s}}$$ temperature decreases too. In addition, in this paper, we have tried to obtain relationships between the $$M_{\mathrm{s}}$$ temperature and the mass or atomic% of different elements through multiple regressions to generalize the interpretations.

Influence of Ni–Ti shape memory alloy short fibers on the flexural response of glass fiber reinforced polymeric composites

Polymeric composites are structures reinforced with particles, fiber and whiskers. In this study, as a unique attempt GFRP composites are selectively reinforced with Ni–Ti shape memory alloy (positioned at a section below the neutral axis) for enhancing the flexure resistance. Under static loading condition, up to 4 wt% of shape memory alloy reinforcement, the GFRP exhibit enhanced flexure resistance. However, under dynamic loading, the shape memory alloy reinforced composite exhibit a mixed mode of response. It is observed that combination of wt% with loading frequency such as 2 wt% with 60 Hz and 4 wt% with 120 Hz facilitates better possible performance.

Series Ni–Ti shape memory alloy wires with different martensitic–austenitic phase transformation temperatures as an actuator for input shaping control

This study presents series shape memory alloy (SMA) wire actuators featuring different martensitic–austenitic phase transformation temperatures for input shaping control of flexible structures, such as compliant robot manipulators. Similar to conventional electric motors, the proposed actuator can generate stair-wise input shaping commands by simply applying a step current input. A practical input shaping control of flexible structures (e.g. beam manipulator) actuated by a series SMA wire actuator with different martensitic–austenitic phase transformation temperatures was proposed, and its ability to suppress residual vibration was successfully validated through simulation and laboratory experiments.

Structure and Mechanical Properties of Multi-Functional Layer Deposited on Surface of Ni–Ti Shape Memory Alloy

Structure and Mechanical Properties of Multi-Functional Layer Deposited on Surface of Ni–Ti Shape Memory Alloy

Symmetry and pathway analyses of the twinning modes in Ni–Ti shape memory alloys

The complex interplay of multiple deformation modes in Ni–Ti systems play a critical role in determining the mechanical properties of the shape memory alloys, e.g., superelasticity, shape memory effect and functional fatigue resistance. In particular, several different twinning modes have been observed in experiments, which include both transformation twins (generated by a phase transformation between two phases) and mechanical twins (generated in a single phase). In spite of well-established theories to treat transformation twins and mechanical twins independently, a general framework capturing the intrinsic coupling between them is still unavailable. Here we systematically analyze all the twinning modes in Ni–Ti alloys, by employing a phase transition graph approach. We show that transformation twins and mechanical twins are intrinsically coupled in symmetry-breaking processes, which results in multiple interconnected deformation pathways. By investigating those deformation pathways, we demonstrate additional characteristic twinning modes arising from the coupling, which includes both symmetric and asymmetric twins. Our work provides a theoretical foundation to investigate the coupling between transformation twins and mechanical twins from a symmetry point of view.

Understanding structure–property relation in nano-crystalline Ni–Ti shape memory alloy thin film micro-actuator

The present investigations is based on annealing heat treatment of co-sputtered Ni–Ti thin films and its effect on structure, morphology, composition, phase formations, intermetallic precipitate formation, and nano-mechanical properties. Ni–Ti thins films were co-sputtered using individual targets and subsequently annealed in vacuum at different temperatures ranging from 400 to 700 °C. The influence of annealing temperature on transformation temperatures and hardness is discussed. Efforts are made to understand the influence of heat treatment temperature on the novel characteristics of Ni–Ti shape memory alloy thin films for their prospective deployment in MEMS-based microactuators.

On wire spark erosion machining induced surface integrity of Ni55.8Ti shape memory alloys

Ni55.8Ti shape memory alloys (SMAs) find applications in different fields of medical and engineering. In every field, surface integrity greatly affects the functional performance of shape memory alloy parts. In the present work, wire spark erosion machining of Ni55.8Ti shape memory alloys has been conducted and surface integrity parameters of the machined specimens have been evaluated. Experiments are designed using Taguchi L16 robust design of experiment technique. Effect of important process parameters, i.e. voltage, pulse-on time and pulse-off time on maximum surface roughness has been studied. Deterioration in surface integrity at various combinations of pulse-on and pulse-of time which produced high discharge energy has been observed. Scanned electron microscopic investigation, energy dispersive spectroscopy and XRD analyses, roughness measurement, and micro-hardness testing results are presented, analyzed and discussed. Optimization of process parameters resulted in surface integrity enhancement with low roughness (Rt – 7.78μm and Ra – 1.45μm) and very thin recast layer (4–6μm) along with minimum subsurface defects.

The Influence of High-Energy Krypton Ion Implantation Temperature on Structure and Properties of Ni–Ti Alloy

The influence of the temperature of implantation of Ni–Ti shape memory alloy with 84Kr15+ions at the energy E = 147 MeV on its structural-phase state is investigated. At the implantation temperatures 250 and 300°С, within the projective range Rp and out-range area the following processes and phenomena are observed: new formation of the martensitic В19'-phase, formation of nano-sized particles of the R-phase, increase in resistivity due to the formation of radiation-defect structures, strengthening of the alloy in the austenitic structural-phase state, and longer phase-transition temperature intervals.

Uncertainty quantification of the parameters and predictions of a phenomenological constitutive model for thermally induced phase transformation in Ni–Ti shape memory alloys

In this work, a probabilistic calibration approach has been adopted to quantify the uncertainties of the parameters and predictions of a phenomenological shape memory alloys (SMAs) constitutive model which has been used to predict the thermally induced phase transformation of Ni–Ti SMAs. Furthermore, the impact of the adopted calibration method, which enables the determination of the uncertainty bounds of the model predictions, on the design of robust engineering applications has been discussed. To this end prior to the probabilistic model calibration, a design of experiments has been performed in order to identify the most influential parameters on the response of the system and thus reduce the dimensionality of the problem. Subsequently, uncertainty quantification (UQ) of the influential parameters has been carried out through Bayesian Markov Chain Monte Carlo (MCMC). The assessed uncertainties in the model parameters has been then propagated to the model predictions using an approximate approach based on the variance–covariance matrix of the MCMC-calibrated model parameters and then an explicit propagation of uncertainty through MCMC-based sampling. The determined 95% Bayesian confidence intervals of the model predictions, by the latter methods, have been demonstrated and compared. Additionally, good agreement between the experimentally measured and model predicted SMA hysteresis loops has been observed where the experimental data are situated within the predicted 95% Bayesian confidence intervals. Finally, the application of the MCMC-based UQ/UP approach in decision making for experimental design has also been shown by comparing the information that can be gained by performing multiple repetitive experiments under identical thermo-mechanical conditions versus experiments under different conditions.

Effect of thermomechanical treatment on deformational behavior of ferromagnetic Fe–Ni–Co–Ti alloy under uniaxial tension

To improve the functional properties of a ferromagnetic shape memory alloy, a thermomechanical treatment that includes drawing followed by quenching and high-temperature annealing was proposed, as a result of which a nanostructured state is formed. Thermomechanical treatment (TMT) increases the alloy thermoelasticity, although it is accompanied by a large temperature hysteresis of martensitic transformation and results in a significant hardening of the matrix, which, in its turn, enlarges the effects of shape memory and superelasticity (or pseudoelasticity). It has been established that TMT of Fe–Ni–Co–Ti shape memory alloy contributes to an increase in reversible superelastic deformation up to ~ 3%. In a superelastic cycle with wide mechanical hysteresis, a large dissipation energy per loading–unloading cycle was gained, that favors the use of this alloy as a damper of mechanical oscillations.

Solution effect on improved structural compatibility of NiTi-based alloys by systematic first-principles calculations

The functional stability of a shape memory alloy (SMA) may be related to its structural compatibility between the parent-phase and the martensitic-phase structures. In this study, we perform systematic first-principles calculations for 276 Ni–Ti-based ternary alloys to investigate their energetic stability as well as their structural compatibility between the parent- and the martensitic-phase structures. We analyze in detail the dependences of the energetics and structural properties on the additional element X, on X concentration, and on the replaced chemical element. Some X are found to energetically stabilize the B19 structures more than the B19′ structures at X concentrations above 6.25 at. %. It is also found that the B19–B2 martensitic transformation shows better structural compatibility than the B19′–B2 transformation for most of the investigated ternary Ni–Ti–X alloys. These alloys also tend to have better structural compatibility than binary equiatomic NiTi. Moreover, we screen the investigated alloys on the basis of their energetic stability and structural compatibility, and we identify 26 Ni–Ti–X alloys as possible SMAs with good functional stability. In this study, we reveal a strong potential of the computational design for improving the functional stability of Ni–Ti SMAs by alloying additional elements.

Influence of Cobalt on the Hot Deformation Characteristics of an NiTi Shape Memory Alloy

Among shape memory alloys (SMAs), Ni–Ti alloys are more widely used in multifarious sectors because of their functional properties of shape memory effect and superelastic effect. With an emphasis on miniaturization and higher performance of actuators and biomedical devices these days, there is a necessity to develop SMAs with high stiffness, i.e., high upper/lower plateau stress, and high modulus. In recent times, there have been attempts to improve their shape memory characteristics, mechanical properties and corrosion resistance through alloying, thermal treatment, etc. In this context, addition of Co has been made to binary Ni–Ti alloys. But till date, there has been a dearth of literature on hot deformation characteristics of NiTiCo SMAs. This work therefore investigates the role of cobalt on hot deformation characteristics of an Ni–Ti SMA. The addition of cobalt results in raising the yield strength and reducing the Ms temperature of the alloys. In this study, elemental forms of high-purity nickel, titanium and cobalt were melted together in a vacuum induction melting furnace to produce cylindrical rods. These rods were homogenized at 900 °C for 3 h and quenched to room temperature in water and subsequently machined so as to obtain a length-to-diameter ratio of 1.5, which was ideal to carry out hot deformation studies on a Gleeble thermomechanical simulator. The samples were deformed at different strain rates (0.01, 0.1, 1 and 10 s−1) at temperatures of 800, 900, 1000 and 1100 °C, respectively. Elaborate results on the deformation characteristics of an NiTiCo SMA have been discussed in this paper.

Modeling and optimization of Wire-EDM parameters for machining of Ni55.8Ti shape memory alloy using hybrid approach of Taguchi and NSGA-II

In the present research, Ni55.8Ti shape memory alloy has been machined by wire electric discharge machining (wire-EDM) process. The effects of input parameters such as spark gap voltage, pulse on-time, pulse off-time, and wire feed on productivity, i.e., metal removal rate (MRR) and surface quality, i.e., mean roughness depth (Rz), have been investigated. Empirical modeling and ANOVA study have been done after conducting 16 experiments based on Taguchi’s L16 design of experiment technique. Ranking and crowding distance–based non-dominated sorting algorithm-II (NSGA-II) is used for process optimization. The error percentage varies within ± 6% between experimental results and the predicted results developed by NSGA-II. It has been observed that the wire-EDM machining of Ni55.8Ti alloy at optimum parameters resulted in improved MRR —0.021 g/min—and surface quality with good surface finish (Rz—6.2 μm) and integrity as significant reduction in the formation of cracks, lumps, and deposited layers.

Wire Spark Erosion Machining of Ni rich NiTi Shape Memory Alloy for Bio-Medical Applications

The application of NiTi shape memory alloys are growing day by day in biomedical industry. These materials present inherent problems when undergoing conventional machining processes during manufacture of bioimplants. Conventional machining processes require high consumption of energy and resources, and assistance of post processing operations to make high quality implants of shape memory alloys. Unlike conventional methods, nonconventional methods are capable to eliminate the need for post processing amongst other advantages and thus prove to be the most economic means of producing biomedical implants. Wire spark erosion machining (also known as Wire Electro Discharge machining i.e. Wire-EDM) is one such nonconventional machining process that has been explored for the machining of biomedical implants by Ni rich NiTi. The present study aims to analyze and optimize the machinability of Ni55.8Ti shape memory alloy during wire electric discharge machining for biomedical applications. The L16 Orthogonal array using Taguchi design of experiments has been employed for this experimental study. The variable input parameters are namely pulse on time, pulse off time, servo voltage and wire feed rate. Machining at optimum parameters produced good surface finish, high material removal rate and excellent surface integrity. In this paper, specifically, the effect of the aforementioned Wire-EDM parameters on cutting rate, process optimization for the highest cutting rate, and surface roughness obtained at optimum parameters are reported. The outcomes encourage exploring wire spark erosion machining of other shape memory alloys for different scientific and industrial applications.

Cyclic tensile of refurbish NiTi reinforcement bar for seismic mitigation

This research highlighting the novel properties of pseudo-elastic Ni-Ti bar owing to their ability to reverse macroscopically inelastic deformation during earthquake known as recentering capability and large elastic strain capacity which originated from the reversible austenite to martensite phase transformation. Hence, this paper presented and evaluates the cyclic properties of pseudo elastic Ni–Ti shape memory alloys to assess their prospective use for seismic applications to be exploited as seismic resistant design and retrofit. In addition, the correlation of hysteretic behavior of Ni-Ti alloy in terms of cyclic loading number and history, mechanical properties at ambient temperature, equivalent damping, energy dissipation and recovery stress were evaluate. The NiTi bar with weight percentage of Ti-43.98 at. % Ni 56.02 and diameter of 8 mm. The tensile cyclic test obtained demonstrated a rounded loading curve based on a 0.2% offset. The as received bar exhibited superior pseudo-elastic behaviour and recentering through repeated cycling without significant degradation or permanent deformation but low energy dissipation due to narrow hysteresis while the steel rebar shows vice versa. Experimental results show potential for the use of SMAs in seismic applications and provide areas for continued research. It was conclude that the as-received pseudo elastic Ni-Ti bar is suitable use for seismic mitigation despite of their ability to undergo cyclical strains is 6% which is greater than 5%, with minimal residual strain, 0.15% which is less than 1%.

Initiation of the shape memory effect by temperature variation or ultrasonic vibrations in the NiTi shape memory alloy after different preliminary deformation

The strain variations induced by conventional heating or ultrasonic vibrations in the Ni – 49.8 at.% Ti shape memory alloy after different preliminary deformation (from 5 to 30%) in the martensite state were studied. It was found that if the residual strain was 16% or less, then the shape memory effect value did not depend on the initiation method. The strain recovery was induced by ultrasonic vibrations during 20 s and occurred at lower temperatures than during conventional heating, due to partially suppression of the martensite stabilisation effect. The ultrasonic vibrations did not influence the plastic strain but they decreased the value of the two-way shape memory effect due to the dislocation rearrangement. The results of the study showed that the USVs might be successfully used for the initiation of the shape memory effect in actuators without heat sources.

Pseudo Elastic and Self-healing Cyclic Properties of Smart NiTi Shape Memory Alloy for Seismic Mitigation

This research highlighting the novel properties of pseudo-elastic Ni-Ti bar owing to their ability to reverse macroscopically inelastic deformation during earthquake known as recentering capability and large elastic strain capacity which originated from the reversible austenite to martensite phase transformation. Hence, this paper presented and evaluates the cyclic properties of pseudo elastic Ni–Ti shape memory alloys to assess their prospective use for seismic applications to be exploited as seismic resistant design and retrofit. In addition, the correlation of hysteretic behavior of Ni-Ti alloy in terms of cyclic loading number and history, mechanical properties at ambient temperature, equivalent damping, energy dissipation and recovery stress were evaluated. The NiTi bar with weight percentage of Ti-43.98 at. % Ni 56.02 and diameter of 12mm. The tensile cyclic test obtained demonstrated a rounded loading curve based on a 0.2% offset. The NiTi bar exhibited superior pseudo-elastic behaviour and recentering through repeated cycling without significant degradation or permanent deformation but low energy dissipation due to narrow hysteresis while the steel rebar shows vice versa. Experimental results show potential for the use of SMAs in seismic applications and provide areas for continued research. It was concluded that the as-received pseudo elastic Ni-Ti bar is suitable use for seismic mitigation despite of their ability to undergo cyclical strains is 6% which is greater than 5%, with minimal residual strain, 0.01% which is less than 1%.

Microstructure, superelasticity and shape memory effect by stress-induced martensite stabilization in Cu–Al–Mn–Ti shape memory alloys

In this study, the microstructure, martensitic transformation, superelasticity, stabilization of stress-induce martensite and the corresponding shape memory effect of Ti-doped Cu–Al–Mn shape memory alloys were investigated. The results show that the present Cu–Al–Mn–Ti alloys consist of two types of L21 phases, including Cu2AlMn parent and Cu2TiAl precipitate. The dispersive L21–Cu2TiAl precipitates strengthen the stabilization of stress-induced 2H(γ′1) martensite from L21–Cu2AlMn parent. Thus, all studied alloys show not only superelasticity at deformation, but also shape memory effect after unloading by heating. Consequently, the Cu–12.9Al–8.3Mn–0.5Ti alloy (wt%) possesses the best superelastic strain up to 4.6% and a shape memory effect of 1.5% under a pre-deformation of 11%, while Cu–12.8Al–7.7Mn–2.6Ti alloy (wt%) shows the best shape memory effect up to 2.5% simultaneously showing 1.9% of superelastic strain with a pre-deformation of 10%.

Experimental Characterization and Control of a Force Actuator Based on Shape Memory Alloy Wire

This paper presents an experimental design of a force and position controller for a Ni–Ti shape memory alloy actuator. The focus of this work is a measurement device for the characterization of a SMA spring together with the fuzzy controller for position and force that can be quickly and easily implemented. This device makes it possible to develop a mechanism for robotic applications with slow actuation speed, e.g., to mimic a robotic finger. The contribution of our work to the scientific literature is an easy control of force and position, as well as weight reduction when compared to a similar actuator controlled by a traditional electric motor. Ni–Ti wire was winded up to form a coil; an electric current passing through the actuator changes its temperature, which leads to a phase transformation resulting in a length change of the wire. Thus, the actuator behaves as a spring, whose force exerted can be adjusted by an electric current. A closed-loop fuzzy logic controller was programmed in the LabVIEW environment, allowing the control of the force exerted by the actuator, as well as the position of an attached load. The actuator performance was evaluated experimentally before and after a training session.

High Strain Rate and Quasi-Static Compressive Behaviors of Ni–Ti Shape Memory Alloy

High Strain Rate and Quasi-Static Compressive Behaviors of Ni–Ti Shape Memory Alloy