Al Ni Shape Memory Alloys Research Articles

Experimental and theoretical evaluation of Cu–Al–Ni shape memory alloys shielding properties at the 511–1333 keV gamma energy range

Experimental and theoretical evaluation of Cu–Al–Ni shape memory alloys shielding properties at the 511–1333 keV gamma energy range

Identification and Characterization of Elusive α Precipitates in Cu–Al–Ni Shape Memory Alloys with Combined Electron Microscopy Techniques

Identification and Characterization of Elusive α Precipitates in Cu–Al–Ni Shape Memory Alloys with Combined Electron Microscopy Techniques

Effect of short heat treatment on mechanical properties and shape memory properties of Cu–Al–Ni shape memory alloy

Abstract The transformation of shape-memory alloys to high-temperature shape-memory alloys can be achieved through either the addition of alloying elements or heat treatment. However, heat treatment is more effective in improving the properties of the alloys. This research paper explores the impact of annealing on the mechanical and shape memory properties of Cu–Al–Ni shape memory alloys. The alloys were first cast, homogenized, and then machined before being aged at temperatures of 250, 300, and 350°C, and finally air-cooled. The results showed an increase in transformation temperature and recovery strain, as well as shape memory effect, and a decrease in hardness. Moreover, there was an increase in yield stress and strain. In conclusion, aging was found to improve the shape memory properties and mechanical properties better than thermomechanical treatment and some alloying elements.

Martensitic transformation characteristics, mechanical properties and damping behavior of Cu–Al–Ni shape memory alloys: A review of their modifications and improvements

Copper-based shape memory alloys (SMAs) have recently been introduced as a viable alternative to Ni–Ti SMAs. This is attributed to the fact that Cu-based SMAs are cheaper than Ni–Ti SMAs and exhibit satisfactory shape memory properties. Of these materials, Cu–Al–Ni SMAs have been widely used as they possess high thermal resistance and good mechanical properties. The concentration of Al and Ni is the most important factor determining the martensite type and transformation temperatures of these SMAs. Furthermore, thermal treatment, including quenching and aging, significantly affects the microstructural evolution and martensitic transformation (MT) temperatures of Cu–Al–Ni SMAs. Modifying the formed martensite phases and MT temperatures is possible by controlling the quenching rate and ageing temperature. Damping ability is one of the distinct advantages of these Cu-based SMAs, which has been modified and improved by many researchers. Plastic deformation is an effective method of evolving the microstructure of Cu–Al–Ni SMAs and improving their mechanical properties. Therefore, this present study examines the effect of alloy composition and thermal treatment on the MT temperatures and the microstructural evolution of Cu–Al–Ni SMAs. It also discusses the solutions to control the damping behavior of Cu-based SMAs, as well as the role of plastic deformation in improving the different properties Cu–Al–Ni SMAs. Lastly, additive manufacturing (AM) is proposed as a modern method of producing porous Cu–Al–Ni SMAs since it grants the possibility of controlling the porosities more efficiently.

Effects of carbon nanotube addition on the microstructures, martensitic transformation, and internal friction of Cu–Al–Ni shape-memory alloys

In this study, we analyze the influences of carbon nanotube (CNT) addition on the martensite transformation and internal friction of Cu–Al–Ni shape-memory alloys (SMAs). X-ray diffraction and differential scanning calorimetry results demonstrate that Cu–13.5Al–4Ni–xCNT (x = 0, 0.2, 0.4, 0.6, and 0.8 wt%) SMA/CNT composites exhibit a β1(DO3)⇄β1′(18R)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\upbeta }_{1}({\\mathrm{DO}}_{3})\\rightleftarrows {\\upbeta }_{1}^{\\mathrm{^{\\prime}}}(18\\mathrm{R})$$\\end{document} martensitic transformation. The martensitic transformation temperatures and transformation enthalpies of the martensitic transformation peaks for the Cu–13.5Al–4Ni–xCNT (x = 0–0.8 wt%) composites gradually decrease with the increase in the amount of CNT addition. Compared to the Cu–13.5Al–4Ni SMA, the Cu–13.5Al–4Ni–xCNT (x = 0.2–0.8 wt%) SMA/CNT composites exhibit significant improvements in the amount of dissipation of energy (storage modulus (E′))\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${E}^{\\prime}))$$\\end{document} and mechanical strength. However, the tan δ of the internal friction peak gradually decreases with the increase in the CNT content above 0.6 wt%. The reduction in tan δ is attributed to the decrease in the magnitude of the austenite-to-martensite transformation and precipitation of γ2 (Cu9Al4) phase particles, which impede the interface motion in between the parent/martensitic phase and martensitic phase.

Fabrication and Damping Property of Porous Cu–Al–Ni Shape Memory Alloys Fabricated using Different Raw Materials

Porous Cu–Al–Ni shape memory alloys (SMAs) are fabricated via powder metallurgy method using Cu, Al, Ni powders and Cu–Al–Ni alloy powder as raw materials, respectively. It is found that the two kinds of specimens have similar macroscopic morphologies: connected pores are uniformly distributed in the Cu–Al–Ni matrix, forming a 3D network structure. By comparison, the specimen fabricated using alloy powder has much finer microstructures than the specimens fabricated using Cu, Al, Ni powders. After adding Ce element to the latter, the microstructure of the Cu–Al–Ni matrix is significantly refined because of the formation of Ce‐rich particles. Damping tests show that the latter has superior damping capacity than the former. With the increase of Ce content, the damping of the latter increases first and then decreases. When the Ce content reaches 0.05 wt%, the highest damping can be achieved. Correlated mechanisms are discussed based on the microstructural observations.

Consolidation and properties of porous Cu–Al–Ni shape memory alloys manufactured by powder metallurgy

ABSTRACT A method to manufacture a porous Cu–Al–Ni shape memory alloy by powder metallurgy using space holders is presented. Two aluminium powders with different particle morphologies were employed to investigate their influence on phase formation, microstructure and mechanical properties. The variation of the relative amount of space holders in the mixture allows to obtain different porosities. Samples prepared with irregular-shaped aluminium powder include both 18R and 2H martensitic phases and exhibit the shape memory effect and pseudoelastic behaviour under uniaxial compression tests. In contrast, the samples made with aluminium flakes present the α phase accompanying the 18R martensitic phase, and do not exhibit the shape memory effect. Both the aluminium flakes flat shape and the higher proportion of aluminium oxide associated with its larger surface area to volume ratio hindered the interdiffusion of the metals, resulting in an aluminium-depleted martensitic phase surrounded by an aluminium oxide-rich layered structure.

Effects of V addition on microstructure and pseudoelastic response in Fe–Mn–Al–Ni alloys

Avoiding quench cracks and controlling the formation process of NiAl precipitates are essential to regulate the microstructure and pseudoelastic properties of Fe–Mn–Al–Ni shape memory alloys (SMAs). In this study, we investigated the effect of 1.5 at.%V addition on the quench sensitivity of Fe–Mn–Al–Ni SMAs and the precipitation behavior of NiAl precipitates in air-cooled Fe–Mn–Al–Ni–V SMAs. It is found that the V addition significantly inhibits the precipitation process of non-transforming γ-phase. Polycrystalline sample of bamboo structure was prepared by abnormal grain growth and tested by incremental strain cycling tensile test at room temperature. The polycrystalline Fe–Mn–Al–Ni–V SMAs obtain fully reversible thermoelastic martensitic transformation without quenching, which also prevents the formation of quenching cracks. Single crystal samples were further prepared by directional recrystallization. High number-density and relatively large-size coherent β-NiAl precipitates were obtained to strengthen the matrix in the single crystal without aging, resulting in large stress hysteresis and irrecoverable strain. After aging Fe–Mn–Al–Ni–V single crystal for 3 h at 200 °C, both the stress hysteresis and irrecoverable strain decreased, thereby achieving good pseudoelasticity in Fe–Mn–Al–Ni–V SMAs.

Stress-induced pseudoelasticity in freestanding Cu–Al–Ni thin film by AFM-assisted nanoindentation

Freestanding thin films of Cu–Al–Ni shape memory alloys (SMAs) have attracted interests in recent years for the development of next generation micro-scaled sensors and actuators in MEMS. Thin films’ capacity to recover stress-induced strain is critical to assess their potential for applications in these technologies. In this work, we report for the first time a quantitative study of this capacity in a freestanding Cu–Al–Ni thin film by Atomic Force Microscopy (AFM)-assisted nanoindentation. Stress-induced pseudoelastic (or superelastic) effects were successfully observed by this technique for relatively high strains up to a relative indentation depth of 30% concerning the film thickness. This effect highlights a clear shape memory effect, suggesting a sample's high mechanical performance for potential applications in the design of micro actuators for MEMS technologies. Results enable to set new perspectives of the use of this technique as an efficient methodology for future study of pseudoelasticity in micro/nanostructured SMAs.

Designing for Shape Memory in Additive Manufacturing of Cu-Al-Ni Shape Memory Alloy Processed by Laser Powder Bed Fusion.

Shape memory alloys (SMAs) are functional materials that are being applied in practically all industries, from aerospace to biomedical sectors, and at present the scientific and technologic communities are looking to gain the advantages offered by the new processing technologies of additive manufacturing (AM). However, the use of AM to produce functional materials, like SMAs, constitutes a real challenge due to the particularly well controlled microstructure required to exhibit the functional property of shape memory. In the present work, the design of the complete AM processing route, from powder atomization to laser powder bed fusion for AM and hot isostatic pressing (HIP), is approached for Cu–Al–Ni SMAs. The microstructure of the different processing states is characterized in relationship with the processing parameters. The thermal martensitic transformation, responsible for the functional properties, is analyzed in a comparative way for each one of the different processed samples. The present results demonstrate that a final post–processing thermal treatment to control the microstructure is crucial to obtain the expected functional properties. Finally, it is demonstrated that using the designed processing route of laser powder bed fusion followed by a post–processing HIP and a final specific thermal treatment, a satisfactory shape memory behavior can be obtained in Cu–Al–Ni SMAs, paving the road for further applications.

Deformation twinning with different twin-boundary mobility in 2H martensite in Cu–Ni–Al shape memory alloy

Three possible twinning modes, Type I, Type II, and compound, as well as corresponding twin boundaries in 2H martensite of Cu69.4Ni3.4Al27.2 single crystal, were studied by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The results are discussed with regard to the sharply different twinning stress or twin-boundary mobility. In self-accommodated martensite, all three modes not only coexist but are crystallographically coupled. The compound twin boundary is a coherent coplanar mirror plane with the smallest twinning shear. The Type II twin boundary is also a coherent strain-free interface. The high index rational approximation of Type II twin boundary was determined by trace analysis with the help of stereographic projection. The approximation is in good agreement with irrational indices calculated from elastic continuum. The Type I boundary is the most complex interface associated with high stress and high density of stacking faults inside the twin bands. Using HRTEM, two different stressed boundaries of Type I were confirmed. The intrinsic twinning mode in Cu-Ni-Al alloy is the compound twinning. In compression, the Type II twinning is the major deformation twinning mode. During deformation the Type I twins are eliminated, leaving Type II twinning bands with compound twins. The observed differences between the atomic structure of different twin boundaries can contribute significantly to the sharp differences in twinning stress.

Enhancing the shape memory effect of Cu–Al–Ni alloys via partial reinforcement by alumina through selective laser melting

Cu–Al–Ni shape memory alloys (SMAs) have high thermal stability and various potential applications. The most significant factors limiting their application are their relatively low elastic strain and poor shape memory effect known as recoverable strain. In addition, the incorporation of new elements for reinforcement usually results in a polycrystalline structure with a larger grain size, which is not suitable for shape memory applications. To overcome these drawbacks, a new method is introduced in this study to increase the shape memory effect and its stability in Cu–Al–Ni SMAs through partial reinforcement with alumina (Al2O3) by selective laser melting. In this approach, the reinforcing lines are deposited in-plane at the mid-height of the printed part, i.e., in the neutral plane. To characterize the effect of partial reinforcement, partially reinforced parts with 0.3 wt% and 0.9 wt% Al2O3 are compared to fully reinforced parts. The results show that the accumulation of localized residual compressive stresses above the reinforcing lines in the neutral plane, induced during selective laser melting, increases the shape memory effect as a result of the increase in mechanical anisotropy in the building direction. Moreover, a new phenomenon named the “waistband effect” is observed in cyclic compressive operation, which results in incremental penetration of the reinforcing particles into the neutral plane during compression. This facilitates a higher strain recovery in the partially reinforced part. These results clearly confirm that partial reinforcement with Al2O3 significantly enhances the shape memory effect of Cu–Al–Ni SMAs.

Effect of Crystallographic Orientation and Grain Boundaries on Martensitic Transformation and Superelastic Response of Oligocrystalline Fe\u2013Mn\u2013Al\u2013Ni Shape Memory Alloys

In situ tensile tests employing digital image correlation were conducted to study the martensitic transformation of oligocrystalline Fe–Mn–Al–Ni shape memory alloys in depth. The influence of different grain orientations, i.e., near-〈001〉 and near-〈101〉, as well as the influence of different grain boundary misorientations are in focus of the present work. The results reveal that the reversibility of the martensite strongly depends on the type of martensitic evolving, i.e., twinned or detwinned. Furthermore, it is shown that grain boundaries lead to stress concentrations and, thus, to formation of unfavored martensite variants. Moreover, some martensite plates seem to penetrate the grain boundaries resulting in a high degree of irreversibility in this area. However, after a stable microstructural configuration is established in direct vicinity of the grain boundary, the transformation begins inside the neighboring grains eventually leading to a sequential transformation of all grains involved.

Superelastic damping at nanoscale in ternary and quaternary Cu-based shape memory alloys

Superelasticity is a characteristic thermomechanical property in shape memory alloys (SMA), which is due to a reversible stress-induced martensitic transformation. Nano-compression experiments made possible the study of this property in Cu–Al–Ni SMA micropillars, showing an outstanding ultra-high mechanical damping capacity reproducible for thousands of cycles and reliable over the years. This scenario motivated the present work, where a comparative study of the damping capacity on four copper-based SMA: Cu–Al–Ni, Cu–Al–Be, Cu–Al–Ni–Be and Cu–Al–Ni–Ga is approached. For this purpose, [001] oriented single-crystal micropillars of comparable dimensions (around 1 µm in diameter) were milled by focused ion beam technique. All micropillars were cycled up to two hundred superelastic cycles, exhibiting a remarkable reproducibility. The damping capacity was evaluated through the dimensionless loss factor η, calculated for each superelastic cycle, representing the dissipated energy per cycle and unit of volume. The calculated loss factor was averaged between three micro-pillars of each alloy, obtaining the following results: Cu–Al–Ni η = 0.20 ± 0.01; Cu–Al–Be η = 0.100 ± 0.006; Cu–Al–Ni–Be η = 0.072 ± 0.004 and Cu–Al–Ni–Ga η = 0.042 ± 0.002. These four alloys exhibit an intrinsic superelastic damping capacity and offer a wide loss factor band, which constitutes a reference for engineering, since this kind of micro/nano structures can potentially be integrated not only as sensors and actuators but also as dampers in the design of MEMS to improve their reliability. In addition, the study of the dependence of the superelastic loss factor on the diameter of the pillar was approached in the Cu–Al–Ni–Ga alloy, and here we demonstrate that there is a size effect on damping at the nanoscale.

Influence of thermo-mechanical treatment on mechanical properties and shape memory effect of CuAlNiMnTi shape memory alloys

Shape memory alloys (SMAs) are vital in many advanced applications, such as micro-electro-mechanical systems (MEMS). Therefore, this work aimed at studying the effect of thermo-mechanical treatment in conjunction with alloying elements modification on improving the mechanical properties and shape memory effect (SME) of Cu–Al–Ni SMAs. In this study, the samples were divided into two groups: the first group was solution treated at 900 °C for 30 min. (S.T), and the other group was hot-rolled at 900 °C followed by solution treatment at 900 °C for 30 min. (H.R.S.T). The results showed that the hardness of the samples decreased with increasing the percent of Ni. In addition, the DSC investigations revealed that the martensite start temperature (Ms) decreased by 50–60 °C compared to the predicted Ms reported in the literature. Surprisingly, the alloying additions as well as thermo-mechanical treatment achieved a tensile elongation up to 22%, and a tensile fracture stress up to 600 MPa. Moreover, the shape recovery ratio exceeded 97%.

Influence of Titanium Additions on the Corrosion Behavior of Cu-Al-Ni Shape Memory Alloys

The Cu- Al-Ni shape memory alloys have numerous industrial applications such as actuators, Cryofit hydraulic couplings, fire safety valves ,etc. while the parts that soaked in the sea water suffer severe corrosion that lead to worsening in the properties of the alloys. In the current research, the effect of adding titanium on corrosion behavior of the shape memory alloys (Cu-13wt. %Al-4wt. %Ni) were studied. Titanium was added in different weight ratios (0.4, 0.8, and 1.2 wt.%) to the base alloy. The alloys were prepared using powder metallurgy, whereby the alloys were sintered with two stages of heating under Argon atmosphere, at 550°C for (120 min.) and 950°C for (180 min.)respectively. All the sintered samples are solution treated by heating the samples at 900 °C for (60 min.) followed by rapid quenching in ice water at ( 3 ~ 6) °C. After that aging heat treatment has been done for quenched samples at 200 °C for (30 hrs.) followed by rapid quenching in iced water. Several tests such as microstructures observation and phase analysis using scanning electron microscope, energy dispersive spectrometer, and X-ray diffraction analysis have been done. Further , Corrosion behavior for all samples in aged conditions in 3.5%NaCl solution have been performed. Corrosion test results have showed that the highest corrosion resistance was found in the addition of (1.2 wt.% Ti) which give the lowest corrosion rate (0.003 mpy) in 3.5% NaCl solution . Noted that the corrosion rate of base alloy was (9.021)mpy. EDS analysis showed chemical composition of the aged surface and also mapping images for the distribution of Cu, Al, Ni, and Ti elements on the surface. Phases formed on aged samples conditions are α-Cu and AlCu3.

Nanoscale twinning in Fe–Mn–Al–Ni martensite: a backscatter Kikuchi diffraction study

Iron-based Fe-Mn-Al-Ni shape-memory alloys are of rather low materials cost and show remarkable pseudoelastic properties. To further understand the martensitic transformation giving rise to the pseudoelastic properties, different Fe-Mn-Al-Ni alloys have been heat treated at 1473 K and quenched in ice water. The martensite, which is formed from a body-centred cubic austenite, is commonly described as face-centered cubic (f.c.c.), even though there are also more complex, polytypical descriptions of martensite. The presently studied backscatter Kikuchi diffraction (BKD) patterns have been evaluated, showing a structure more complex than simple f.c.c. This structure can be described by nanoscale twins, diffracting simultaneously in the exciting volume. The twinned structure shows a tetragonal distortion, not uncommon for martensite in spite of the lack of interstitial elements. These features are evaluated by comparing the measured BKD patterns with dynamically simulated ones.

Functionally graded structures realized based on Fe–Mn–Al–Ni shape memory alloys

In the present study a novel approach to obtain functionally graded properties in an Fe–Mn–Al–Ni shape memory alloy is introduced. A single crystalline sample showing superelastic properties was aged in a partially martensitic state. As a result, the area aged in austenite is characterized by a changed superelastic hysteresis with different critical stresses for forward and backward transformation, whereas the properties in the area aged in martensite remained almost unchanged. Transmission electron microscopy studies revealed that the mean average size of nanometric β precipitates, which strongly influence the transformation temperatures and eventually the transformation stresses, is about 9 nm in the area aged in martensite and about 12 nm in the area aged in austenite. Based on these results it seems to be feasible to tailor Fe–Mn–Al–Ni components in a way allowing them to show locally different functional properties.

On the Influence of Microstructure on the Corrosion Behavior of Fe–Mn–Al–Ni Shape Memory Alloy in 5.0 wt% NaCl Solution

Herein the corrosion behavior of Fe–Mn–Al–Ni shape memory alloys characterized by different microstructures in a 5.0 wt% NaCl solution is investigated. Open circuit potential and potentiodynamic polarisation tests are conducted. Generally, Fe–Mn–Al–Ni shows corrosion properties being similar to pure iron. However, the polarization curves of single crystals indicate the presence of an unstable passive system. The corrosion damage is analyzed by means of optical microscopy and electron microscopy. It is revealed that polycrystalline samples consisting of two different phases induced by heat treatment, i.e., α‐phase and γ‐phase or β‐Mn phase and γ‐phase, are suffering a selective corrosion attack of the α‐phase and β‐Mn–phase, respectively. On the contrary, the single crystal seems to form a protective layer on the surface. Upon presence of stress‐induced martensite, a selective corrosion attack of γ′–martensite is observed.

Thermodynamics of martensite formation in Fe–Mn–Al–Ni shape memory alloys

Fe−Mn−Al−Ni based shape memory alloys are regarded suitable for large scale applications due to relatively low materials costs and a good cold workability. The austenitic state consists of an A2 structured matrix with coherent B2 precipitates which are required to ensure thermoelasticity, supposedly due to a strengthening effect on the matrix. The martensitic state is based on the A1 structure. For a series of alloys, the martensite start temperatures were determined to be below ambient temperature, whereas for the same alloy compositions T0 temperatures of about 1000 °C are predicted for the transformation of the A2 matrix into A1 by means of CalPhaD-based calculations. It is shown by thermodynamic considerations that the undercooling of about 1000 K is caused by the resistance of the B2 precipitates (~NiAl with some content of Fe and Mn) to undergo the transformation to the L10 structure enforced by the martensitic transformation of the matrix.