Ni Shape Memory Alloy Research Articles

Effect of Sn Addition on Transformation Temperature and Thermal Properties for Cu-Al-Si Shape Memory Alloy

Sn was added to Cu-14%Al-4.5%Ni shape memory alloy in three Percentages (0.5,1,3)%to study the effect of the addition on microstructure, Transformation temperature, thermal properties and activation energythermal properties. SEM-EDS, XRD tests were performed on the specimens; DSC Measurement was performed on the alloys. A computer model was built via MATLAB to calculate the thermal properties by means of graphical integration for the DSC data. Results showed an increase in the transformation temperature and Equilibrium temperature outside the domain, also an increase in hysterics and spread with the increase of Sn Percentage, also results shown an increase in thermal properties (enthalpy and entropy and free energy), results showed also a decrease in activation energy more than the base alloy the 3% Sn Addition gave the best results in both transformation temperature and activation energy.

Cross-sectional analysis of the graded microstructure and residual stress distribution in a TiNi alloy treated with low energy high-current pulsed electron beam

A Ti-(55.08wt.%)Ni shape memory alloy (SMA) having a grain size of 30 μm, was subjected to low-energy high-current pulsed electron beam (HCPEB) irradiation with parameters: pulse duration τ = 2−2.5 μs, maximum electron energy 25 keV, energy density ES = 3.8 ± 0.7 J/cm2; beam diameter of ∼ 60 mm, number of pulses n = 32. Microstructure modifications, a value and distribution of residual stress induced by HCPEB treatment were investigated in detail. XRD and cross-sectional TEM/EDS/SAED analysis were used for microstructural characterization of the TiNi samples before and after HCPEB treatment. As a result, the HCPEB-modified TiNi surface layer consists of four successive sublayers differing in phase composition, type of texture and defect substructure. In total, the thickness of the HCPEB-modified TiNi surface layer is, at least, 10 μm. Based on the XRD and nanoindentation data, the dependences of residual stress values on the depth from the irradiated surface in the HCPEB-modified TiNi surface layer were estimated and plotted. The values and sings of the stress components in perpendicular (σI⊥) and parallel (σI||) directions to the TiNi sample surface were calculated: σI⊥ <0, σI||>0. The gradient of residual stress values is preserved in the HCPEB-modified TiNi surface layer: from ∼ 800 MPa (in absolute value) near the irradiation surface to ∼ 220 MPa at a depth of about ∼ 10 μm. The residual stress fields are localized in the near-surface layer I and sublayer III with different type of B2-structure. Their relaxation occurs in the sublayer II by means of the stress-induced В2 → R martensitic transformation.

Effect of Substrate Roughness on Adhesion and Structural Properties of Ti-Ni Shape Memory Alloy Thin Film.

Ti-Ni shape memory alloy (SMA) thin films are very attractive material for industrial and medical applications such as micro-actuator, micro-sensors, and stents for blood vessels. An important property besides shape memory effect in the application of SMA thin films is the adhesion between the film and the substrate. When using thin films as micro-actuators or micro-sensors in MEMS, the film must be strongly adhered to the substrate. On the other hand, when using SMA thin films in medical devices such as stents, the deposited alloy thin film must be easily separable from the substrate for efficient processing. In this study, we investigated the effect of substrate roughness on the adhesion of Ti-Ni SMA thin films, as well as the structural properties and phase-transformation behavior of the fabricated films. Ti-Ni SMA thin films were deposited onto etched glass substrates with magnetron sputtering. Radio frequency plasma was used for etching the substrate. The adhesion properties were investigated through progressive scratch test. Structural properties of the films were determined via Feld emission scanning electron microscopy, X-ray diffraction measurements (XRD) and Energy-dispersive X-ray spectroscopy analysis. Phase transformation behaviors were observed with differential scanning calorimetry and low temperature-XRD. Ti-Ni SMA thin film deposited onto rough substrate provides higher adhesive strength than smooth substrate. However the roughness of the substrate has no influence on the growth and crystallization of the Ti-Ni SMA thin films.

Effect of B2 austenite grain size and aging time on microstructure and transformation behavior of thermomechanically treated titanium nickelide

The size and morphology of Ti3Ni4 precipitates, as well as their transformation behavior after isothermal aging, were studied in a Ti-50.7 аt.%Ni shape memory alloy with various B2 austenite grain sizes. A 0.3 mm thick band with an accumulated strain of ε = 44% (e = 0.6) obtained by cold rolling was used. The samples were then solution-treated at 600–800°С for 0.3–1 h with subsequent quenching in water to obtain the structure with different grain size (GS) from 5 to 15 μm. The samples were then subjected to isothermal annealing at 430 °C for 1, 3 and 10 h. The SEM observations were carried out using a JSM-6460LV. The microstructure was studied using a JEOL 2100 TEM. Characteristic temperatures were measured using a “Mettler Toledo” DSC. The results of the microstructure study prove that the GS strongly affects Ti3Ni4 particle size and morphology, as well as the degree of microscale microstructure heterogeneity, transformation kinetics and transformation sequences. This influence is non-unique and depends on the duration of isothermal annealing. After 1 h of aging, the particle thickness and diameter maintain the nanometer range in the whole GS range of 5–15 μm. The increase of aging time to 3 and 10 h leads to localization of nanosized precipitates in the grain-boundary region, with the width of these regions decreasing with increasing GS. After aging for 1 h, the samples with the GS of 5 μm show the B2→R transformation. The increase in the GS to 15 μm and aging duration to 10 h is accompanied by multiplication of martensitic transformations to four stages. The study explains the influence of GS on the precipitated particle size and morphology, transformation kinetics and staging.

Investigation of Fe content in Cu–Al–Ni Shape Memory Alloys

Polycrystalline Cu–Al–Ni–Fe-based shape memory alloys with different chemical composition were produced in an arc-melting furnace under an argon atmosphere. Homogenized and aged specimens were prepared for multiple analyses. The temperatures of reversible martensitic transformations, namely As, Af, Ms, Mf, Amax and ΔH enthalpy values were determined by a DSC device. The phase transition analysis from the room temperature to 850°C was undertaken by DTA. To characterize the lattice structure, an XRD analysis was conducted, the results of which were confirmed by microstructure images obtained from optical microscope observations.

Effect of the Thermomechanical Treatment on Structural and Phase Transformations in Cu–14Al–3Ni Shape Memory Alloy Subjected to High-Pressure Torsion

The possibilities of controlling the structure and properties of a Cu–Al–Ni shape memory alloy due to the use of different schemes of the thermomechanical treatment, including forging, homogenizing in the austenitic state and subsequent quenching, and high-pressure torsion have been found. For the first time, an ultrafine-grain structure has been produced in this alloy via severe plastic deformation using high-pressure torsion. It has been detected that high-pressure torsion using ten revolutions of the anvils leads to the formation of a nanocrystalline structure with a grain size of less than 100 nm. The subsequent short-term heating of the alloy to 800°С (10 s) in the temperature region of the existence of the homogeneous β phase made it possible to form an ultrafine-grain structure with predominant sizes of recrystallized grains of 1 and 8 μm. The quenching after heating prevented the decomposition of the solid solution. The refinement of the grain structure changed the deformation behavior of the alloy, having provided the possibility of the significant plastic deformation upon mechanical tensile tests. The coarse-grained hot-forged quenched alloy was brittle, and fracture occurred along the boundaries of former austenite grains and martensite packets. The highstrength ultrafine-grained alloy also experienced mainly the intercrystalline fracture along the high-angle boundaries of elements of the structure, the grain size of which was less by two orders than that in the initial alloy. This determined an increase in its relative elongation upon mechanical tests.

Microstructure and superelastic properties of free forged Ti–Ni shape-memory alloy

Abstract Elemental titanium (Ti) and nickel (Ni) powders were consolidated by spark plasma sintering (SPS) to fabricate Ti–51%Ni (mole fraction) shape-memory alloys (SMAs). The objective of this study is to enhance the superelasticity of SPS produced Ti–Ni alloy using free forging as a secondary process. Products from two processes (with and without free forging) were compared in terms of microstructure, transformation temperature and superelasticity. The results showed that, free forging effectively improved the tensile and shape-memory properties. Ductility increased from 6.8% to 9.2% after forging. The maximum strain during superelasticity increased from 5% to 7.5% and the strain recovery rate increased from 72% to 92%. The microstructure of produced Ti–51%Ni SMA consists of the cubic austenite (B2) matrix, monoclinic martensite (B19′), secondary phases (Ti3Ni4, Ti2Ni and TiNi3) and oxides (Ti4Ni2O and Ti3O5). There was a shift towards higher temperatures in the martensitic transformation of free forged specimen (aged at 500 °C) due to the decrease in Ni content of B2 matrix. This is related to the presence of Ti3Ni4 precipitates, which were observed using transmission electron microscope (TEM). In conclusion, free forging could improve superelasticity and mechanical properties of Ti–51%Ni SMA.

Functional Properties of Porous Ti-48.0 at.% Ni Shape Memory Alloy Produced by Self-Propagating High-Temperature Synthesis

The functional behavior of the porous shape memory alloy produced by self-propagating high-temperature synthesis from the Ti-48.0 at.% Ni powder mixture was studied. It was found that a large unelastic strain recovered on unloading and it was not attributed to the pseudoelasticity effect. A decrease in deformation temperatures did not influence the value of strain that recovered on unloading, while the effective modulus decreased from 1.9 to 1.44 GPa. It was found that the porous Ti-48.0 at.% Ni alloy revealed the one-way shape memory effect, where the maximum recoverable strain was 5%. The porous Ti-48.0 at.% Ni alloy demonstrated the transformation plasticity and the shape memory effects on cooling and heating under a stress. An increase in stress did not influence the shape memory effect value, which was equal to 1%. It was shown that the functional properties of the porous alloy were determined by the TiNi phase consisted of the two volumes Ti49.3Ni50.7 and Ti50Ni50 where the martensitic transformation occurred at different temperatures. The results of the study showed that the existence of the Ti49.3Ni50.7 volumes in the porous Ti-48.0 at.% Ni alloy improved the functional properties of the alloy.

Computer Approach of Effect of 0.3 % of Ge, Te and Ce Additions on Thermodynamic Properties and Shape Memory Effect of Cu-14%Al-4.5%Ni Shape Memory Alloys

This paper aims to study the effect of 0.3% addition of Ge, Te and Ce on Cu-14%Al-4.5%Ni Shape memory alloys by building a computer model via MATLAB of two direction strain temperature with the calculation of enthalpy(ΔH) and entropy (ΔS) results showed the Ge addition gave the best results in the thermodynamic properties and also in strain ring ,also the use of a mathematical model via MATLAB to calculate the shape memory strain with compared with the actual results , it showed a close ratio with the actual results of the thermo-mechanical testing also results shown an increase in enthalpy entropy and heat flow for all alloy the Ge addition gave the best results as for the hysteresis loops the Ce and Ge Addition gave the best results in general the computer model results and the thermo mechanical showed about 2.7%deffernece in results.

Selective Leaching and Surface Properties of Cu–Al–Ni Shape Memory Alloys

Selective Leaching and Surface Properties of Cu–Al–Ni Shape Memory Alloys

Heat-Conduction-Type and Keyhole-Type Laser Welding of Ti–Ni Shape-Memory Alloys Processed by Spark-Plasma Sintering

Heat-Conduction-Type and Keyhole-Type Laser Welding of Ti–Ni Shape-Memory Alloys Processed by Spark-Plasma Sintering

Interfacial Stresses and the Anomalous Character of Thermoelastic-Deformation Curves of a Cu–Al–Ni Shape-Memory Alloy

Thermoelastic-deformation curves of a single-crystalline Cu–13.5 wt % Al–4.0 wt % Ni shapememory (SM) alloy have been studied. Cyclic temperature variation in a 300–450 K interval revealed an anomalous character of thermoelastic hysteresis loops with regions of accelerated straining at both heating and cooling stages. The observed phenomenon can be used for increasing the response speed of SM-alloy based drive and sensor devices. Analysis of this phenomenon in the framework of the theory of diffuse martensitic transformations showed that the anomalous character of thermoelastic hysteresis loops may be related to the influence of interfacial stresses on the dynamics of martensitic transformations in these SM alloys.

Stress- and Magnetic Field-Induced Martensitic Transformation at Cryogenic Temperatures in Fe–Mn–Al–Ni Shape Memory Alloys

Stress-induced and magnetic-field-induced martensitic transformation behaviors at low temperatures were investigated for Fe–Mn–Al–Ni alloys. The magnetic-field-induced reverse martensitic transformation was directly observed by in situ optical microscopy. Magnetization measurements under pulsed magnetic fields up to 50 T were carried out at temperatures between 4.2 and 125 K on a single-crystal sample; full magnetic-field-induced reverse martensitic transformation was confirmed at all tested temperatures. Compression tests from 10 to 100 K were conducted on a single-crystal sample; full shape recovery was obtained at all tested temperatures. It was found that the temperature dependence of both the critical stress and critical magnetic field is small and that the transformation hysteresis is less sensitive to temperature even at cryogenic temperatures. The temperature dependence of entropy change during martensitic transformation up to 100 K was then derived using the Clausius–Clapeyron relation with critical stresses and magnetic fields.

Transformation entropy change and precursor phenomena in Ni-rich Ti–Ni shape memory alloys

Abstract

High temperature deformation behavior and processing map for a nickel-titanium shape memory alloy

The hot deformation behavior of 49.2Ti-50.8Ni shape memory alloy was studied using hot compressive deformation testing in the temperature range of 1023-1323 K and at strain rates of 0.01-10 s-1. The work-hardening rate was induced to analyze the stress-strain curves, and the critical stress σc and the dynamic recovery saturation stress σsat were measured which can be specified approximately by the expressions: σsat-1.12σp and σc-0.86σp. An Arrhenius model was calculated to describe the relationship between peak stress and the Z parameter. The relationship between deformation activation energy, the deformation conditions and the effect of Ni component in a binary TiNi alloy on the activation energy were discussed in this work. With the help of electron backscattering diffraction, a connected mode dynamic recrystallization microstructure was confirmed in peak efficiency regimes (850 °C & 0.01 s-1 and 1050 °C & 10 s-1) of the processing map.

Analysis of Compositional Modification of Commercial Aluminum Bronzes to Obtain Functional Shape Memory Properties

In copper-based shape memory alloys (SMAs), some exceptional phenomena, such as the shape memory effect (SME) or superelasticity (SE), are observable. However, commercial aluminum bronzes, Cu3Al-based alloys, do not present these functional properties (SME and/or SE) in their original state. Thus, since one of the main copper-based SMA systems is the Cu-Al-Ni alloy, this paper aims to analyze the modification of these commercial aluminum bronzes to SMA by the addition small amounts of Cu, Al and/or Ni. These modified bronzes were reprocessed by induction melting and injected by centrifugation into a ceramic coating mold. The modifications were made to determine the nominal composition for a Cu-13,0Al-4,0Ni (%wt) SMA. The effectiveness of the modifications was verified by differential scanning calorimetry (DSC) thermal analysis. All modified Cu-Al-Ni bronzes presented DSC peaks of the thermoelastic martensitic phase transformation, showing that SMA behavior was achieved, while the non-modified bronzes revealed no transformation. These results were supported by Vickers hardness (HV), X-ray diffraction (XRD), semi quantitative composition by EDS analysis and optical microscopy.

Electron beam welding of Fe–Mn–Al–Ni shape memory alloy: Microstructure evolution and shape memory response

The present study reports on the impact of abnormal grain growth (AGG) on the microstructural evolution following electron beam (EB) welding of Fe–Mn–Al–Ni shape memory alloy (SMA). Polycrystalline sheet-like material was EB-welded and a cyclic heat treatment, studied in previous work, was conducted for inducing AGG and a bamboo-like microstructure, respectively. Optical and electron microscopy were carried out to characterize the prevailing microstructure upon cyclic heat treatment. For characterization of the functional properties following AGG, a load increase test was conducted. The current results clearly show that good shape memory response can be obtained in Fe–Mn–Al–Ni SMA upon EB welding and subsequent post-heat treatment. These results further substantiate the potential use of conventional processing routes for Fe–Mn–Al–Ni SMA.

Characteristics of Transformation and Low-temperature Deformation of Ti-51.1Ni Shape Memory Alloy

Abstract Effects of annealing temperature on the phase transformation and the low temperature deformation characteristics in the deformed Ti-51.1Ni (at%) shape memory alloy (SMA) were investigated by differential scanning calorimetry (DSC), optical microscope (OM) and tensile test. The results show that the transformation types of Ti-51.1Ni alloy are changing from A→R/M→R→A to A→R→M/M→R→A to A→R→M/M→A (A-parent phase B2, R-R phase, M-martensite phase) upon cooling/heating along with increasing annealing temperature. The R transformation temperatures and martensite temperature hysteresis decrease, while the M transformation temperature increases and the R temperature hysteresis nearly keeps at about 6.5 °C. When deformation happen at 10 °C, the 400∼550 °C annealed Ti-51.1Ni SMA exhibits as the shape memory effect (SME) + superelasticity (SE), the 600∼700 °C annealed SMA shows SE, and the characteristics of alloy change from SME + SE to SE. In addition, the annealing recrystallization temperature of Ti-51.1Ni SMA is 590 °C, and the 590∼650 °C annealed alloy could obtain excellent capability of plastic deformation and 50.83 % values of fracture strain, so the forming processing temperature could be in the range of 590∼650 °C. When the Ti-51.1Ni alloy are used for energy consumption of damper and damping device, the suitable annealing temperature could be higher than 550 °C, and for making superelastic device, the suitable annealing temperature could be below 400 °C or above 600 °C.

Metal Forming Aspects of Cyclic Severe Plastic Deformation of Ti-Ni Shape Memory Alloys Using MaxStrain Device

The effect of severe plastic deformation using MaxStrain (MS) device which is a part of the Gleeble thermo-mechanical simulator of rolling and forging processes on the structure and functional properties of Ti–50.0 at.% Ni shape memory alloy has been studied. The use of the MS module allows performing SPD of the material under isothermal conditions with precise control of the deformation parameters. The deformation temperature was lowered from 370 to 330 °C. The accumulated true strain varied from e=4.6 to 9.5. Structure features were studied by the transmission electron microscopy. The maximum completely recoverable strain was determined by a thermomechanical method using a bending mode for strain inducing. A mixed submicrocrystalline and nanosubgrained structure with average grain/subgrain size below 100 nm was formed using SPD at 330 °C. A very high completely reсoverable strain (9.3%) was obtained against a reference treatment (2.5%).

Mechanical and superelastic properties of laser welded Ti–Ni shape-memory alloys produced by powder metallurgy

Tensile test showed that the strength of the welded joints of powder metallurgy Ti–51%atNi shape-memory alloys (SMAs) decreases after disk-laser welding due to the presence of pores and columnar structure in the fusion zone. There was a reduction in the superelastic behavior of the welded joints compared to the base metal. Superelastic properties of specimen LW1 (with welding speed of 6m/min and laser power input of 3kW) were close to the base metal after loading and unloading at room temperature. Welded specimens, which were subjected to solution treatment at 1000°C followed by aging at 500°C showed an increment in superelasticity properties. Superelasticity improved significantly after heat treatment in all the welded joints except LW2 (with welding speed of 7.5m/min and laser power input of 3kW), because it contained high amounts of porosity in the fusion zone. LW1 exhibited the best properties after heat treatment with superelasticity strain increasing up to 7%, which was higher than the base metal. Differential scanning calorimetry (DSC) investigations showed that heat-treated weld seams had similar phase transformation peaks of martensite, austenite, and R phases to the base metal, which may be due to the recovering of Ti3Ni4 precipitates.