Fe Shape Memory Alloys Research Articles

The efficiency assessment of Ni(40)Ti(50)Cu(x)Fe(10−x) shape memory alloy produced by combustion synthesis through thermal analysis

The efficiency assessment of Ni(40)Ti(50)Cu(x)Fe(10−x) shape memory alloy produced by combustion synthesis through thermal analysis

Perspectives on Adhesive–Bolted Hybrid Connection between Fe Shape Memory Alloys and Concrete Structures for Active Reinforcements

The prestressed active reinforcement of concrete structures using iron-based shape memory alloys (Fe-SMAs) is investigated in this experimental study through three connecting methods: adhesive–bolted hybrid connection, bolted connection, and adhesively bonded connection by activating at elevated temperatures (heating and cooling) and constraining deformation to generate prestress inside Fe-SMAs, through which compressive stress is generated in the parent concrete structures. In tests, the Fe-SMA is activated at 250 °C using a hot air gun, generating a prestress of 184.6–246 MPa. The experimental results show that local stress concentration in the concrete specimen and Fe-SMA plate around the hole is caused by the bolted connection. The adhesively bonded connection is prone to softening and slip of the structural adhesive during the activation process, thereby reducing the overall recovery force of Fe-SMAs. The adhesive–bolted hybrid connection effectively mitigates the local stress concentration problem of concrete and Fe-SMAs at anchor holes, while avoiding the prestress loss caused by the softening and slip of structural adhesive during elevated-temperature activation, achieving good reinforcement effect. This study on the connection methods of an Fe-SMA for reinforcing concrete structures provides both experimental support and practical guidance for its engineering application, offering new perspectives for future research.

Shear strengthening and damage control effects of CFRP and self-prestressing iron-based SMA for concrete columns

Although prestressed shape memory alloy (SMA) has shown a great performance in flexural retrofitting of slender RC columns, its shear strengthening effect for squat RC columns has been barely studied. This study explores the shear strengthening and damage control effects of iron-based SMA (Fe SMA) for squat RC columns. The heat-activated prestressing of Fe SMA was evaluated first at material level, then applied to component level structural testing of RC columns. The four circular RC columns with different retrofitting schemes were tested under quasi-static lateral cyclic loading. The specimens strengthened with carbon fiber-reinforced polymer (CFRP) sheet and Fe SMA strip exhibited satisfactory global responses without showing significant shear failure. From the visual inspection and non-destructive damage assessment, the prestressed Fe SMA was found to be superior in delaying damage accumulation in concrete compared to CFRP.

Effect of Al content on thermal stability, shape memory effect and mechanical properties of Cu–Al–Fe shape memory alloys

Effect of Al content on thermal stability, shape memory effect and mechanical properties of Cu–Al–Fe shape memory alloys

Development of boron-microalloyed Co–V–Al–Fe shape memory alloys

Development of boron-microalloyed Co–V–Al–Fe shape memory alloys

Enhanced barocaloric effect for Pd–In–Fe shape memory alloys with hydrostatic-pressure training

The influence of hydrostatic-pressure training on barocaloric effects (BCEs) has been investigated for the Pd59.3In23.2Fe17.5 shape memory alloy. We demonstrate that the shift of the martensitic transformation temperature by the applied pressure (dTm/dp) could be significantly improved from 11 K to 21 K GPa−1 by hydrostatic-pressure training. By using an indirect method of the magnetic measurement under an external pressure to determine the barocaloric effect, the entropy change for the Pd59.3In23.2Fe17.5 alloy increases from 15 to 16 J kg−1 K−1 after hydrostatic-pressure training. The alloy also exhibits a wider working window and a larger refrigeration capacity (from 113 to 171 J kg−1) after pressure training. Moreover, the maximum reversible entropy change ΔSrev increases from 3 J kg−1 K−1 to 8 J kg−1 K−1 and the reversible RC increases from 11 J kg−1 to 50 J kg−1 by hydrostatic-pressure training. The hydrostatic-pressure training is a feasible approach to obtain an improved realistic BCE by a lower pressure.

Strain glass by aging in Ti–Pd–Fe shape memory alloys

Up to now, most of strain glasses are achieved by doping point defects into martensitic alloys. Here we report a strain glass in a Ti54Pd36Fe10 shape memory alloy achieved by low-temperature aging. Aging at 523 K generates Ti2Pd-like nanoprecipitates, which are responsible for the formation of strain glass. By continuously increasing the aging time, we studied how the strain glass transition gradually evolves from a martensitic transformation. A short aging time (12 min) is enough to generate strain glass, while the martensite still persists as the aging time increases to 300 min. A temperature–aging time phase diagram is established accordingly.

A Study of the Damping Capacity of Mechanically Processed Cu – 9.2Al – 5.3Mn – 0.6Fe Shape Memory Alloys

The effect of deformation on the damping capacity of a copper-base shape memory alloy produced by standard methods is studied. The metallographic analysis is performed with the help of scanning electron microscopy. The internal friction is measured at different temperatures. The damping capacity of the alloy is analyzed and its relation to the mechanical and physical properties is determined.

Micromechanism of Cu and Fe alloying process on the martensitic phase transformation of NiTi-based alloys: First-principles calculation

Using first-principles pseudo-potential plane wave method, the formation enthalpy ΔH, binding energy ΔE, elastic constants, and electronic structure were calculated and analyzed carefully for NiTiX (X = Cu, Fe) shape memory alloy. The results show that the Cu or Fe element prefers to occupy the Ni site in the NiTi matrix phase respectively. Compared with the NiTi matrix phase, the ΔH, ΔE, c44 and c′ of NiTi (Cu) are similar to each other. However, the structural stability of the NiTi phase is improved obviously by the Fe alloying process. Simultaneously, the shear modulus c44 and c′ of NiTi (Fe) are larger than those of the NiTi matrix phase. Furthermore, Milliken population results indicate that QCu–Ti is smaller than QNi–Ti after the Cu alloying process, but QFe–Ti is larger than QNi–Ti. The electron density difference shows that some covalent bonding exists between Fe and Ti elements. Based on the upward analysis, the difference in the phase stability and elastic constants of NiTiX (X = Cu, Fe) is the substantial mechanism for the different Ms of NiTiX (X = Cu, Fe) although Cu or Fe substitutes for the same atom Ni elements in the NiTi matrix phase.

Role of microstructure on phase transformation behavior in Ni–Ti–Fe shape memory alloys during thermal cycling

Two different microstructures of Ni–Ti–Fe shape memory alloys processed through different thermo-mechanical treatments with nearly similar grain size and in-grain misorientation but different crystallographic textures were subjected to series of thermal cycles without external loading. The microstructures and the phase transformation behavior of the samples were examined after every seventy cycles. The experiment involved treating the samples with liquid nitrogen (LN2) for complete martensitic (B19′) transformation and then heating it back to parent austenite (B2) condition. Thermal cycling introduced significant differences in microstructural parameters especially the grain boundary nature, stored elastic energy and the misorientation or defect densities. These microstructural alterations during thermal cycling were related to changes in transformation temperatures and enthalpy. Thermal cycling also brought out changes in crystallographic orientations of austenite grains. The present study aims to address the role of microstructure on the thermal fatigue behavior in Ni–Ti based shape memory alloys during cyclic transformations.

Oxidation of high-temperature Cu–Al–Fe shape memory alloy

Isothermal oxidation behavior of the high-temperature Cu–13Al–5Fe (in mass, %) SMA on temperature range of 500–900 °C was studied using thermo-gravimetric method. TG curve showed that the alloy has linear oxidation characteristics. From thermo-gravimetric measurements, it was determined that the alloy shows abnormal oxidation characteristics at 600 °C. As K P values of the alloy at oxidation temperatures of 700 and 800 °C were calculated as 0.00166 mg cm−2 s−1 and 0.0022 mg cm−2 s−1, respectively, K P value at 600 °C was found as 0.0029 mg cm−2 s−1. DTA curve exhibited that reason of the abnormal oxidation behavior at 600 °C is the endothermic reaction which causes dissolution of Fe(Al,Cu) precipitates within matrix at 568.13 °C. XRD patterns of the oxidized samples were found to be compatible with the results obtained from thermo-gravimetric measurements.

A systematic investigation on the role of microstructure on phase transformation behavior in Ni–Ti–Fe shape memory alloys

A systematic study on the phase transformation behavior in a polycrystalline Ni–Ti–Fe shape memory alloy is reported. The investigation was carried out through series of differential scanning calorimetry (DSC) tests on three different samples with distinctly different microstructures of the alloy processed through different thermo-mechanical routes. The applied procedures involved cold rolling and marforming (rolling in liquid nitrogen) followed by short annealing treatments to recover the cold worked microstructure. These treatments altered the microstructure in terms of grain size, misorientation (defects) and texture. Three different microstructures were generated through adopted deformation processes (i) lower degree of texture, (ii) textured and (iii) refined grains with texture. The influence of the microstructural parameters on the phase transformations in terms of transformation temperature (TT) and associated energy of absorption/release was investigated. Temperature of transformation (TT) between different samples was affected predominantly by the grain size difference while enthalpy of transformation (austenite↔martensite) was mainly due to differences in texture, stored energy and in-grain misorientation. Though the differences in TT and enthalpy were not very significant, these results form a guideline for microstructure tailoring of bulk scale manufacturing of these alloys.

Dynamic recrystallization in a Ni–Ti–Fe shape memory alloy: Effects on austenite–martensite phase transformation

Signatures of hot deformed Ni–Ti–Fe microstructures ranged from strain localizations and grain boundary serrations to presence of relatively fine nearly equiaxed grains. The latter was shown, through estimates of in-grain misorientations, as dynamically recrystallized. Their presence was more at higher working temperatures and at higher strain rates. Increased presence of such dynamically recrystallized grains led to clear suppression of austenite↔martensite phase transformations.

Investigation of the Enthalpy/Entropy Variation and Structure of Cu–Al–Mn–Fe Shape Memory Alloys

Cu-based Cu–Al–Mn–Fe shape memory alloys were produced in an arc melter under vacuum. The crystal structure of the fabricated alloys were determined by means of X-ray diffraction (XRD). The XRD analysis results indicated that the martensitic phase of the samples have an M18R structure. The characteristic transformation temperatures, thermodynamic parameters, and the activation energy values of the samples according to Kissinger and Ozawa methods were determined by differential scanning calorimetry measurements. The austenite transformation temperatures \((A_{\mathrm{s}})\) of the samples were found as \(149.52\,^{\circ }\hbox {C}, 128.52\,^{\circ }\hbox {C},\hbox { and }103.86\,^{\circ }\hbox {C}\), respectively. Also, the calculated activation energy values of the samples according to Kissinger and Ozawa methods are compared with each other. The effect of the presence of Al and Fe in the samples on the thermodynamic parameters is studied in this work.

Cobalt addition effects on martensitic transformation and microstructural properties of high-temperature Cu–Al–Fe shape-memory alloys

The effects of the addition of Co on the martensitic transformation and microstructural properties of high-temperature Cu–Al–Fe shape-memory alloy systems were studied by means of DSC, XRD, optical microscopy and Vickers microhardness measurements. DSC analyses indicated that the Cu–Al–Fe alloy displayed high-temperature shape-memory characteristics and that the Co additions dramatically influenced the martensitic transformation of the alloys. Structural and morphological investigations showed that the alloys had 18R martensite structure and contained different precipitates. With increasing amounts of Co, it was seen that elemental compositions of precipitates changed and their volume fractions increased and, therefore, both thermal stability and microhardness values of the alloys were affected. As a result, whereas microhardness values of the alloys were increased by 313 ± 7.76 to 365.75 ± 7.84 Hv, the alloys exhibited poor thermal stability and high volume fraction of precipitates following Co addition.

Oxidation parameters determination of Cu–Al–Ni–Fe shape-memory alloy at high temperatures

In this study, isothermal oxidation behavior of a Cu–Al–Ni–Fe shape-memory alloy between 500 and 900 °C was investigated. Alloy samples were exposed to oxygen by TG/DTA for 1 h at a constant temperature, allowing for calculation of the oxidation constant and activation energy values of the oxidation process. The oxidation constant value increased with temperature, reaching saturation at 800 °C. The effect of oxidation on crystal structure, surface morphology and chemical composition of the Cu–Al–Ni–Fe alloy was determined by X-ray diffractometer (XRD) and scanning electron microscope (SEM)–energy-dispersive X-ray (EDX) analyses. With increasing oxidation temperature, number and intensity of the characteristic 18R martensite phase peaks were reduced while Al2O3 phase peaks were increased. In parallel to the XRD results, the same variations were also detected by SEM–EDX measurements.

Characterization and process evaluation of Ni–Ti–Fe shape memory alloy macro-spheres directly fabricated via rotating electrode process

The present work demonstrates the manufacture of spherical millimeter sized macro-spheres of Ni–Ti–Fe shape memory alloy (SMA) for self-seizing bearing application through rotating electrode process (REP) through a set of optimized REP parameters and subsequent characterization. Image analysis has revealed that these macro-spheres follow a bimodal size distribution with larger mass fraction is about 1.5mm and that of smaller mass fraction has a mean value of 0.4mm. Differential scanning calorimetry (DSC) and compressive load–deformation behaviour confirm that both chemical and mechanical properties are consistent before and after REP. Microstructural characterization was carried out using high-resolution scanning electron microscope with electron backscattered diffraction (EBSD) technique. Process evaluation shows that there spheres form through the liquid ligament breakdown mechanism.

Crystallization behavior in severely cold-drawn Ti50Ni47Fe3 wire

The microstructures and crystallization behavior of Ti–47 at% Ni–3 at% Fe shape memory alloy wire under the condition of severe cold drawing at room temperature and different post-deformation annealing processes were intensively investigated using transmission electron microscope (TEM) and differential scanning calorimetry (DSC). It is indicated that the amorphous phase is dominant in the Ti50Ni47Fe3 wire after the cold drawing of 78 % areal reduction. The critical temperature for recrystalization is determined at about 300 °C. The average grain size grows from 7 up to 125 nm when annealing temperature rises from 300 to 500 °C. Post-deformation annealing process exerts significant influence on the crystallization temperature which climbs up with the increase of annealing temperature.

In vivo cytotoxic evaluation of Ti–Ni–Fe shape memory alloys

A series of Ti based shape memory alloys with composition of Ti50Ni48Fe2, Ti50Ni47Fe3 and Ti50Ni45Fe5 were developed by vacuum arc melting under a purified argon atmosphere. The study was designed to evaluate in vivo cytotoxicity of the Ti–Ni–Fe shape memory alloy system. The materials were implanted in rabbits, and blood examination and histology of various vital organs (liver, heart and kidney) were performed to determine cytotoxicity of these alloy systems, if any, after 4, 8 and 12 weeks. The results showed that Ti–Ni–Fe alloy neither was cytotoxic nor has any systemic reaction on living system in any of the test performed. Implantation shows good compatibility and a potential of being used directly in in vivo system.

Study of martensite transformation and microstructural evolution of Cu–Al–Ni–Fe shape memory alloys

In this study, variations in the transformation temperature, crystal structure, and microstructure of the arc melted alloy having nominal composition of Cu–13%Al–4%Ni–4%Fe (in mass%) were investigated for two different treatment conditions, homogenized and heat treated at 950 °C for 1 h. For both conditions, transformation temperature of the alloy was examined by DSC and it was determined as ~200 °C, similar to the value for Cu–Al–Ni alloys given in the literature. The crystal structure of the martensite Cu–13%Al–4%Ni–4%Fe (in mass%) alloy was identified as 18R using XRD. By heat treatment performed at 950 °C, diffraction peaks become more distinct. The microstructure of the alloy was studied with the help of optical microscope as a result of which parallel martensite plates and precipitates were detected. Microhardness value of the alloy was found as 361 and 375 Hv for homogenized and heat-treated conditions, respectively.