Ni Shape Memory Alloy 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

Decomposition features and mechanical properties of aging Ti49Ni51 alloy with shape memory effects subjected to heat treatment

The features of the microstructure of the Ti–51 at.%Ni shape memory alloy have been studied after aging at various temperatures. In combination with studies using optical and electron microscopy and X-ray analysis, mechanical properties were tested for tensile strength at room temperature. It has been established that the aged alloy is distinguished by a high level of mechanical properties (tensile strength up to 1200 MPa with a relative elongation of up to 35 %) due to highly dispersed homogeneous decomposition and the effect of simultaneous hardening and increased plasticity as a result of deformation-induced martensitic transformation.

Functional Characteristics of Ultrasonic Shot-peened Ti–Ni Shape Memory Alloy with Functionally Graded Property

Functional Characteristics of Ultrasonic Shot-peened Ti–Ni Shape Memory Alloy with Functionally Graded Property

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

Transformation Behaviors and Microstructure Modifications in Hydrogen-Charged Ti–Ni Shape Memory Alloy

AbstractThe effect of hydrogen charging duration on the transformation behavior, microstructural evolution, and dynamic microstructural changes associated with thermoelastic martensitic transformation in Ti–Ni shape memory alloy was investigated. Compared with the uncharged specimen, the martensitic transformation start (Ms) and reverse transformation finish (Af) temperatures increased with charging time, whereas the martensitic transformation finish and reverse transformation start temperatures remained almost unchanged. In situ SEM results were consistent with these behaviors. Upon cooling, the transformation progressed from the center to the surface in charged specimens, indicating a higher transformation temperature in the center than the surface. The latent heat of transformation decreased with increasing charging time, quantitatively attributed to an untransformed region consisting of hydrogen-induced martensite and a hydrogen-affected layer. The hydrostatic effect from those layers on the interior B2 phase was proposed as the origin of the increased Ms and Af temperatures.

Microstructure Evolution, Hardness, and Tribological Behaviors of Ti-50.8Ni SMA Alloy with Ultrasonic Surface Shot Peening Treatment.

To explore a new method to improve the wear resistance of TiNi shape memory alloy (SMA), Ti-50.8Ni alloy was treated by the method of ultrasonic surface shot peening. The microstructure evolution, hardness, and tribological behaviors have been further investigated to evaluate the effect of ultrasonic surface shot peening (USSP). The surface microstructure can be refined to some extent while the basic phase composition has little change. USSP can facilitate the martensitic transformation in the surface layer, which benefits improving the surface hardness. Additionally, the hardness of Ti-50.8Ni alloy increases first and then decreases with the increase of applied load, but the USSP-treated alloy tends to be more sensitive to load. USSP treatment can improve the wear resistance and reduce the coefficient of friction (COF) in case of a low sliding wear speed of 5 mm/s. However, the tribological properties of USSP-treated alloy are reversely worse in the case of 10 mm/s. This is mainly attributed to the combined effect of stress-induced martensite transformation and degeneration resulting from the frictional heating during the dry sliding wear process.

Effect of niobium addition on the microstructure and wear properties of mechanical alloyed Cu–Al–Ni shape memory alloy

Abstract In this study, the influence of the addition of Nb in varying amounts (0.5, 1, 1.5, and 2 wt.%) to Cu–14Al–4Ni shape memory alloy on the microstructure and wear behavior of the alloy was investigated. Cu–Al–Ni-xNb alloys were produced from elemental powders using the mechanical alloying (MA) method. The microstructures of the produced samples were examined using SEM + EDS and XRD, and density and hardness measurements were performed. For the wear tests of Cu–14Al–4Ni and alloys containing different amounts of Nb, a pin-on-disk type wear testing device was used with three different loads (10 N, 20 N, and 30 N) and five different sliding distances (400 m, 800 m, 1,200 m, 1,600 m, and 2000 m). As a result of the conducted research, it was determined that an increase in the Nb content resulted in a decrease in the average grain size and a more homogeneous grain size distribution. The highest hardness and density values were measured in the alloy with 2 wt.% Nb addition. In the wear tests, it was observed that the friction coefficients decreased with increasing load, and the lowest wear rate was achieved in the alloy with 2 wt.% Nb addition.

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

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

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.

Unveiling the microstructure evolution and mechanical properties in a gas tungsten arc-welded Fe–Mn–Si–Cr–Ni shape memory alloy

Fe–Mn–Si–Cr–Ni shape memory alloys (SMAs) are unique low-cost materials with shape memory properties that grant them the ability to be used in both functional and structural applications. Such SMAs are especially sought in the construction sector for the creation of new components and/or the reinforcement of damaged ones. In this study, a Fe–17Mn–5Si–10Cr–4Ni–1(V, C) wt% SMA was gas tungsten arc welded, with the objective to investigate the microstructure and mechanical performance changes occurring after welding. A comprehensive assessment of processing, microstructure and properties relationships was established combining microscopy (optical and electron), synchrotron X-ray diffraction, microhardness mapping and tensile testing including cycling assessment of the joint’s functional performance. It is shown that the present SMA has good weldability, with the joints reaching nearly 883 MPa at fracture strain of 23.6 ± 2.1%. Alongside this, several microstructure differences were encountered between the as-received and as-welded condition, including the formation of ferrite and Fe5Ni3Si2 P213 cubic precipitates amidst the fusion zone in the latter region.Graphical abstract

Abnormal Grain Growth and Pseudoelasticity of Industrially Processed Fe–Mn–Al–Ni Shape Memory Alloy Joined by Metal Inert Gas Welding

The effect of metal inert gas welding on the microstructure, abnormal grain growth and the pseudoelastic properties of industrially processed Fe–Mn–Al–Ni shape memory alloy sheets were studied. Square-butt welds were manufactured using similar filler material. The influence of alternating mean arc linear energy on the microstructure of the individual zones is shown. A correlation between the process parameters, the associated heat input, the grain morphology and the α/γ-ratio could be deduced. As the mean arc linear energy increases, the α/γ-ratio in the fusion zone and the heat-affected zone increases. To evaluate the influence of the welding process on abnormal grain growth, a post-weld cyclic heat-treatment was carried out. Although no loss of major alloying elements in the fusion zone was observed after welding, metal inert gas welding has a significant effect on grain growth upon cyclic heat treatment. While abnormal grain growth occurred in the base material, a polycrystalline microstructure characterized by significantly smaller grain sizes was visible in the former fusion zone. Incremental strain tests revealed severe plastic deformation near the grain boundaries in the former fusion zone. However, the grain boundaries of the bamboo-like grown grains in the base material turned out to be more critical for structural failure.

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.

Inverse gradient nanostructure through gradient cold rolling demonstrated with superelasticity improvement in Ti-50.3Ni shape memory alloy

Gradient nanostructured (GNS) metallic materials are commonly achieved by gradient severe plastic deformation with a gradient of nano- to micro-sized structural units from the surface/boundaries to the center. Certainly, such GNS can be inversely positioned, which however has not yet been reported.The present work reports a facile method in deformation gradient control to attain inverse gradient nanostructured (iGNS), i.e., tailoring the cross-section shape, successfully demonstrated in Ti-50.3Ni shape memory alloy (SMA) wire through cold rolling. The microstructure of the rolled wire is characterized by a macroscopic inverse gradient from boundaries to the center—the average sizes of grain and martensite domain evolve from micrometer to nanometer scale. The iGNS leads to a gradient martensitic transformation upon stress, which has been proved to be effectively reversible via in-situ bending scanning electron microscopy (SEM) observations. The iGNS Ti-50.3Ni SMA exhibits quasi-linear superelasticity (SE) in a wide temperature range from 173 to 423 K. Compared to uniform cold rolling, the gradient cold rolling with less overall plasticity further improves SE strain (up to 4.8 %) and SE efficiency. In-situ tensiling synchrotron X-ray diffraction (SXRD) analysis reveals the underlying mechanisms of the unique SE in the iGNS SMAs. It provides a new design strategy to realize excellent SE in SMAs and sheds light on the advanced GNS metallic materials.

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.

Effect of caliber rolling on microstructures and properties of an inoculated Cu–Al–Ni shape memory alloy

With the aim of property enhancement, the grains in a Cu–Al–Ni shape memory alloy (SMA) were successfully refined by adding Al–La–B inoculant. In order to further optimize the microstructure, the inoculated Cu–Al–Ni SMA was then subjected to caliber rolling. It was found that the grains were further significantly refined after caliber rolling, but there was α phase precipitation. After quenching treatment, the α phase disappeared, whereas the grain size slightly increased. The changes of properties with the increase of rolling reduction were investigated. It was found that the tensile strength increased, whereas the elongation increased first and then decreased. After quenching treatment, the tensile strength and elongation increased monotonously. The internal friction (IF) peak arising from the reverse martensitic transformation (MT) decreased, and the peak position shifted towards the high temperature side. After quenching treatment, the IF peak increased monotonously, whereas the peak position remained nearly unchanged. Correlated mechanisms were discussed.

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.

Structural and superelastic properties of Fe–Mn–Al–Ni shape memory alloy sheets produced on industrial process routes by hot rolling

In the present study the structural and functional properties of Fe–Mn–Al–Ni shape memory alloy sheets produced on an industrial process route focusing on hot rolling were investigated. The as-processed condition is characterized by a high fraction of the non-transforming γ-phase, which ensures good workability, but is associated with poor superelasticity. The alloy shows good structural properties with a yield strength of about 600 MPa, which is well above the usual transformation stress related to the martensitic phase transformation for the investigated alloy composition. After solution annealing, a microstructure showing no preferred orientation being characterized by distinctly larger grains is present. The results obtained reveal that the previous thermo-mechanical processing had no impact on the subsequent texture, however, provided a sufficient amount of driving force for abnormal grain growth. Imposed by a cyclic heat treatment, oligocrystalline structures with grain sizes above 10 mm can be achieved in the industrially processed material, which show superelastic properties similar to material processed in small batches in the laboratory.

Investigation of the Thermal Properties of Cu-based Shape Memory Alloy

This study aims to investigate the thermal properties of the phase transformation that may occur with the effect of temperature in Cu-14.70wt.%Al-4.72wt.%Ni shape memory alloy. The sample was annealed at 1203 K for 30 min in an argon atmosphere and then cooled rapidly in salt-ice water. By using Differential Scanning Calorimetry (DSC), the martensitic phase transformation parameters of the sample were found. The activation energy required for these transformations was calculated using the Kissinger, Augis-Bennett, and Takhor methods. Thermogravimetric Analysis (TGA) measurements investigated the mass changes that may occur with the effect of temperature. Surface morphology was analyzed using an optical micrograph.