Copper-based Shape Memory Alloys Research Articles

Experimental and theoretical results of gamma shielding features for copper based shape memory alloys

In this study, the gamma ray attenuation characteristics for CuAlNi shape memory alloys with different proportions of Sn doping was investigated. We determined the mass attenuation coefficient (μ/ρ) of CuAlNiSn alloys both experimentally and theoretically within an energy range of 59.5–1332.5 keV. The experimental measurements were made using a high purity Germanium detector (HPGe) and theoretical calculations were made using WinXCOM program. To evaluate the gamma radiation shielding abilities of the alloy samples, the obtained (μ/ρ) values were used to determine the gamma protection parameters μ, HVL, TVL, MFP, and Zeff. In addition, the radiation protection efficiency (RPE) parameter was determined using gamma ray intensities in the absence and presence of the attenuator. Further analysis of the samples was conducted using a Rigaku Miniflex 600 model computer-controlled X-ray diffractometer (CuKα & λ = 1.5405 A0). The crystallographic structure of the alloys before and after irradiation was investigated. Other analysis which include EDX analysis (to investigate the chemical content) and SEM analysis (to investigate the microstructure) were conducted. According to result outcomes, gamma ray radiation did not affect the shape memory properties of structure. Another interesting observation is that, the radiation attenuation properties increase with increasing Sn concentration. Finally, we discovered that the CuAlNiSn4 alloy (which has the highest doping rate) provides good protection especially at low energy levels.

Effect of pulse time (Ton), pause time (Toff), peak current (Ip) on MRR and surface roughness of Cu–Al–Mn ternary shape memory alloy using wire EDM

Shape memory and super elasticity are two outstanding properties of Cu–Al–Mn SMAs together with additional copper-based shape memory alloys that make them superior to NiTi alloys. It's quite hard to machine Cu–Al–Mn SMA. The machinability properties of Cu–Al–Mn SMAs during Wire Electrical Discharge Machining (WEDM) were experimentally investigated using molybdenum wire as the electrode material. Material Removal Rate (MRR) and Surface Roughness (SR) are two machining qualities that are studied in relation to the combinational values of pulse time (Ton), pause time (Toff), and peak current (Ip), which are selected as the changeable input process factors. From the experimental investigation, it was found that both MRR and Ra values were increased with an increase in pulse on time(Ton), pulse off time(Toff), and peak current (IP)values. Because the wire electrode contains maximum current under these conditions, it is easy to remove more material at the tool and work material interface, resulting in moderate surface finish. Surface quality was higher on samples machined at low energy input than it was on samples machined at high energy input. This SEM micrograph clearly shows that a lower pulse on time produces a superior surface quality.SEM images and the analysis of the machined surface morphology on the surface of the CAM7 alloy clearly showed that the machined surface of the alloy had a lower surface roughness value at a lower Ip-2A and was associated with a higher surface roughness value at a higher Ip-6A, as well as a lot of uncleared debris and blow holes.

A review on CuAlNi shape memory alloys: Production methods, applications and current trends

Shape Memory Alloys (SMAs) are one sort of shape memory material (SMM) that “remembers” the initial shape when subjected to stimuli like magnetic or thermomechanical changes. Cu-based SMAs in the past decade have emerged successfully as potential materials in various applications such as Sensors, actuators, and high-damping materials. Cu-Al-Ni SMAs have received attention because they are more thermally stable than other Copper-based SMAs. Cu-Al-Ni SMA is an excellent candidate with excellent SME and super-elastic behaviour in the narrow temperature range of 373–473 K. Nickel is added in the binary system of Cu-Al to lower the high transformation temperature and stabilise the austenite phase. This Paper reviews Production Methods, Applications and Current Trends of CuAlNi SMA.

Compositional influence of CuAlMn SMA coated optical fiber towards sensing low temperature

Low temperature sensing with currently available sensors is a challenging task due to the several limitations in usage under harsh environmental conditions. Hence, optical fiber-based sensors could be a better alternative for sensing and monitoring applications due to their immunity at extreme temperatures (both Cryogenic and high temperature), pressure, electromagnetic interference, and power fluctuations. Moreover, the sensing properties are further improved by applying metal coating on optical fiber. In this respect, Shape Memory Alloy (SMA) coating on optical fiber shows enhanced sensitivity due to its unique property of shape memory effect. Particularly, copper-based SMAs are investigated in this regard because of their solid-state actuation characteristics at extreme temperature conditions. Hence, we have coated the optical fiber with CuAlMn SMA by thermal evaporation technique. We have varied the composition of SMA to control the transformation temperature (TT) at low-temperature regions. In the CuAlMn system, TTs are highly dependent on the concentrations of Al and Mn content. We have varied the weight percentages of Al and Mn present in CuAlMn SMA, to achieve the actuation at sub-zero temperature. We have used 2 different wire compositions (Cu-9Al-12.6Mn, and Cu-8.8Al-12.2Mn) for the preparation of the CuAlMn SMA thin films. The film obtained using the Cu-9Al-12.6Mn wires, has shown the lowest transformation temperature and maximum actuation/ displacement (∼10 mm) at low temperature (liquid N2) region. Such actuation of SMA-coated fiber results in significant optical signal attenuation (∼ 8 V peak-to-peak voltage difference under liquid N2 exposure) at the detector end. Thus, we can claim that the CuAlMn-coated optical fiber can be used as a cryogenic sensor due to its significant optical signal attenuation.

Experimental Investigation on Fracture Toughness Of Hydrogen Embrittled Cu-Al-Be Shape Memory Alloy

Copper based Shape Memory Alloys (SMAs) possess good Shape Memory Effect (SME) and Superelasticity and the alloys are prone to corrosion due to atmospheric conditions. The SMAs absorb hydrogen which results in hydrogen embrittlement which affects the SMAs characteristics. The fracture toughness of the hydrogen embrittled alloys were estimated for compositions of ternary Alloy-Beryllium (0.47 by weight %) under uniaxial tensile testing (Mode –I type). Strain energy release rate and Stress Intensity factors were determined. 0.47 wt. % of Be in the SMA has the higher fracture toughness and the stress Intensity factor is directly proportional and strain energy release rate is inversely proportional with the increase in Crack length.

Unravelling the use of silica recovered from waste foundry sand in sustainable water jet machining of a copper-based ternary shape memory alloy

The progressive growth of manufacturing industries has resulted in a consequential increase in waste generation, posing significant challenges to environmental sustainability. Within the realm of manufacturing, waste emerges as an inevitable byproduct, accumulating at an unprecedented rate and exerting a profound strain on ecological equilibrium. By harnessing the transformative potential of recycling, manufacturing facilities embrace a paradigm shift, transcending the mundane constraints of waste disposal. Thus, recycling fosters building nations’ capabilities by incorporating an array of exquisite and comprehensible linguistic prowess. One such change can be brought by reusing the foundry sand after the casting process to power the abrasive water jet machining (AWJM) to carry out the machining process. Therefore, in this research work, the aim was to promote sustainable development and indulge in the simultaneous cutting of a copper-based shape memory alloy. Shape memory alloys are perceived to be the most potential product in the aerospace and biomedical industries. There are only fewer indagations that analyze and investigate the effects of AWJM on the CuAlFe shape memory alloys. The effects of the cutting process on the surface and shape memory characteristics of the CuAlFe shape memory alloy were analyzed by performing tests like scanning electron microscopy, differential scanning calorimetry, and finally X-ray diffraction. The shape reverting temperature of the alloy before and after machining was 416.57 °C and 415.43 °C indicating the loss of shape memory effect even after AWJM is very less. Apart from this, optimal machining parameters were also deduced using Taguchi-Grey relational analysis of the L27 orthogonal design matrix. Of the chosen 3 parameters, the selected combination from this method was A1B1C2. From this analysis, the optimal material removal rate and surface roughness was found to be 1.873 (cm3/min) and 2.965 (μm) which are far good values in the industry. The outcomes proved to be effective in examining the optimal parameters and the surface properties of the CuAlFe Shape memory alloy thus ensuring sustainable development.

Laser powder bed fusion of full martensite Cu-Al-Mn-Ti alloy with good superelasticity and shape memory effect

A copper-based shape memory alloy Cu-11.85Al-3.2Mn-0.1Ti with desirable superelasticity and shape memory effect was printed by laser powder bed fusion (LPBF), which demonstrated the feasibility of engineering applications through the deformation and recovery of complex corrugated structural components. The microstructure of LPBF-printed Cu-11.85Al-3.2Mn-0.1Ti was composed of full β1' martensite with a high density of stacking faults and twin crystals. The abnormal phase constitution of full martensite in the printed Cu-11.85Al-3.2Mn-0.1Ti is correlated to substrate preheating and thermal cycling during LPBF. The start and finish transformation temperatures of martensite (Ms and Mf) and austenite (As and Af) were 172.5 °C, 144.4 °C, 180.2 °C and 209.2 °C, respectively. The printed samples exhibited compressive strength of 1319 MPa with a compressive fracture strain of 16.1%. The printed alloy displayed remarkable superelasticity and shape memory effect. The superelastic recovery rate reached a maximum value of 87% at 6% pre-strain, corresponding to a superelastic recovery strain of 5.22%. The mechanism of superelasticity is attributed to the rubber-like deformation behavior. Moreover, the pre-strained samples demonstrated a desirable shape memory effect under the temperature stimulation, where the shape memory recovery rate of up to 100% at a pre-strain of 6%, corresponding to a shape memory recovery strain of 0.78%. The reasons for the favorable shape memory effect were: (i) the thermoelastic inversion of martensitic transformation and (ii) the precipitation of γ2(Cu9Al4) phase along the grain boundaries. As a result, these findings suggest that the LPBF technique can produce Cu-Al-Mn-Ti parts with superelasticity and good shape memory properties, which provided valuable references for printed copper-based shape memory alloys with full martensitic structures.

Deformation mechanism of Cu-Al-Ni shape memory alloys fabricated via laser powder bed fusion: Tension-compression asymmetry

Introducing the unique advantage of additive manufacturing technology into copper-based shape memory alloys (SMAs) to fabricate high-performance alloys has garnered great attention in recent years, but the intrinsic relationships between microstructure and mechanical properties need to be further clarified. In this paper, the microstructural evolution of ternary CuAlNi SMAs fabricated by laser powder bed fusion (LPBF) under the tensile-compressive loading was investigated to determine the underlying mechanism of tension-compression asymmetry, that is, excellent compressive but poor tensile properties. Multiscale characterization of the different deformation stages revealed the numerous activated deformation mechanism on the 18R martensite matrix. A twin-related transformation dominated the main plastic deformation process due to lower stacking faults energy and high-density pre-existing planer defects in the CuAlNi SMAs. Deformation twinning nucleated at prior austenite boundaries and developed into parallel and network structures inside the parent grain of different sizes. In addition, the preferred orientation in different stages, the stress-induced γ phase transformation, and the interaction between dislocations and stacking faults are discussed. These results not only provide significant insights to understand the detwinning and deformation twinning process of SMAs but also establish the essential framework of microstructure and mechanical properties of Cu-based SMAs fabricated by LPBF.

Superelastic pendulum isolator with multi-stage variable curvature for seismic resilience enhancement of cold-regional bridges

This study develops a novel superelastic pendulum isolator with multi-stage variable curvature (SPIVC) to enhance the seismic resilience of the cold-regional bridges. The SPIVC comprises the improved conical friction pendulum bearing (CFPB) with flat surface, spherical surface and inclined surface connected in series and re-centering devices fabricated by copper-based shape memory alloy (CuSMA). The novel SPIVC features the deformation accommodation under service loadings and seismic isolation under seismic shaking. The numerical model of the SPIVC is developed within OpenSees using the experimentally observed parameters. A typical continuous bridge is selected as benchmark bridge to investigate the seismic performance of the SPIVC system in cold regions. To achieve optimum parameters of the SPIVC, a cost-effective design method is developed based on the hysteretic characteristics of the re-centering device. The seismic performance of cold-regional bridge with SPIVCs under near-fault earthquakes is investigated and assessed by case study. Results show that the proposed method is effective to capture the isolator parameters. Case studies demonstrate the re-centering and seismic isolation performance of the SPIVC system employing the optimum parameters for bridges in cold regions, i.e., the novel SPIVC system can perform the dual control of the girder displacement, permanent isolator displacement and the seismic shear of the piers for each ambient temperature. The achieved findings can be employed to guide the resilience enhancement of the cold-regional structures and potential seismic applications.

Effect of Processing Parameters on the Phase Transformation of a High Temperature Copper-Based Shape Memory Alloy

Effect of Processing Parameters on the Phase Transformation of a High Temperature Copper-Based Shape Memory Alloy

RSM-based optimization and predictive modelling of the gravimetric corrosion behaviour of solution-treated copper-based shape memory alloy in HCl solution

RSM-based optimization and predictive modelling of the gravimetric corrosion behaviour of solution-treated copper-based shape memory alloy in HCl solution

Seismic performance upgrading of bridges using superelastic pendulum isolators with variable stiffness considering temperature effects

To enhance the seismic resilience of bridges, this study proposes a novel superelastic pendulum isolator with variable stiffness (SPIVS) equipped with copper-based shape memory alloy (CuSMA) against near-fault earthquakes. The sensitivity of the novel SPIVS to outside temperature effects is considered. A three-span bridge equipped with the proposed SPIVSs incorporating the CuSMA devices is modeled in OpenSees software. A fractional factor based design method is proposed to optimize the parameters of the SPIVS system. The seismic performance of the novel SPIVSs for bridges is assessed considering outside temperature effects by conducting case studies. Results show that the optimum parameters of the novel SPIVS system for various cases are obtained by the proposed method. The novel SPIVS using CuSMA devices can dually control the girder peak displacement and isolator residual deformation for various ambient temperatures. The base force increment of piers is also controlled within 10% to limit the seismic demand. The feasibility and effectiveness of the novel SPIVS system using CuSMA devices, in terms of re-centering and damping capacities for bridge response control at different outside temperatures, are discussed and demonstrated by various cases.

Design and Development of High-Strength and Ductile Ternary and Multicomponent Eutectoid Cu-Based Shape Memory Alloys: Problems and Perspectives

An overview is presented on the structural and phase transformations and physical and mechanical properties of those multicomponent copper-based shape memory alloys which demonstrate attractive commercial potential due to their low cost, good shape memory characteristics, ease of fabrication, and excellent heat and electrical conductivity. However, their applications are very limited due to brittleness, reduced thermal stability, and mechanical strength—properties which are closely related to the microstructural features of these alloys. The efforts of the authors of this article were aimed at obtaining a favorable microstructure of alloys using new alternative methods of thermal and thermomechanical treatments. For the first time, the cyclic martensitic transformations during repeated quenching, methods of uniaxial megaplastic compression, or torsion under high pressure were successfully applied for radical size refinement of the grain structure of polycrystalline Cu-Al-Ni-based alloys with shape memory. The design of the ultra- and fine-grained structure by different methods determined (i) an unusual combination of strength and plasticity of these initially brittle alloys, both under controlled heat or hot compression or stretching, and during subsequent tensile tests at room temperature, and, as a consequence, (ii) highly reversible shape memory effects.

Effect of alloying constituents on thermal, microstructural, mechanical and shape memory properties of Cu-Al-Ag shape memory alloys

PurposeThe purpose of this study is to assess the influence of Al and Ag addition on thermal, mechanical and shape memory properties of Cu-Al-Ag alloy.Design/methodology/approachThe material is synthesized in a controlled atmosphere to minimize the reaction of alloying elements with the atmosphere. Cast samples were homogenized, then subjected to hot rolling and further betatized, followed by step quenching. Eight samples were chosen for study among which first four samples varied in Al content, and the next set of four samples varied in Ag composition.FindingsThe testing yielded a result that the increase in binary alloying element decreased transformation temperature range but increased entropy and elastic energy values. It also improved the shape memory effect and mechanical properties (UTS and hardness). An increase in ternary alloying element increased transformation temperature range, entropy and elastic energy values. The shape memory effect and mechanical properties are enhanced by the increase in ternary alloying element. The study revealed that compositional variation of Al should be limited to a range of 8 to 14 Wt.% and Ag from 2 to 8 Wt.%. Microstructural and diffraction studies identified the ß’1 martensite as a desirable phase for enhancing shape memory properties.Originality/valueNumerous studies have been made in exploring the transformation temperature and phase formation for similar Cu-Al-Ag shape memory alloys, but their influence on shape memory effect was not extensively studied. In the present work, the influence of Al and Ag content on shape memory characteristics is carried out to increase the design choice for engineering applications of shape memory alloy. These materials exhibit mechanical and shape memory properties within operating ranges similar to other copper-based shape memory alloys.

Effect of hydrogen embrittlement on the characteristics of copper-based shape memory alloy

Because of the good shape memory effect and superelasticity, copper-based shape memory alloys (SMAs) with aluminum and beryllium as binary and ternary elements are widely used in many applications (Cu-Al-Be SMAs). However, they are prone to corrosion in atmospheric conditions. This alloy is susceptible to corrosion due to hydrogen. This affects the characterization of the SMAs by absorbing the hydrogen and results in hydrogen embrittlement, makes changes in SME and SE effect. The process of hydrogen absorption was carried out under electrolytic charging under constant current density and the charged specimens were aged in the air at room temperature. The results show the decrement in SME from 99.8 % to 62%, and the tensile test revealed an increment in the transformation stress level from 200MPa- 290MPa in the case of the charged specimen.

Study of effect of Fe, Cr and Ti on the martensite phase formation in Cu-12.5 wt% Al-5wt % Mn SMA

Copper based shape memory alloys are studied throughout the world for their high transition temperatures and high thermal stability. Among Copper based shape memory alloys(SMAs), Cu-Al-Mn SMAs have shown good ductility and high transition temperature. Only those alloy systems that can show the formation of β phase are capable to demonstrate the shape memory properties. In this paper the effects of the alloying elements on the formation of martensite phase have been studied exclusively. Addition of 1 wt% of Fe, Cr and Ti to the Cu-12.5Al-5Mn shape memory alloy has been investigated in detail. Therefore, four alloys have been synthesized through liquid metallurgy route using pure metals of 99.9% purity in a melting furnace weighing 1kg each. Samples were heat treated at the temperature of 920˚C for 2 hours and then quenched in ice water. The optical micrographs show the formation of the martensite structures in all the samples except in the samples in which 1 wt% Fe was added. X-Ray diffractions also revealed the same facts as obtained in the optical microscopy. Vickers Hardness of all four samples were carried out. The result shows no sign of martensite formation in sample containing Fe; therefore, this alloy should not be used for further study in the direction of understanding shape memory behaviors of the copper based shape memory alloys. Moreover, it was also observed that the addition of Cr yielded good martensitic formation as compared to the alloy containing Ti. Copyright © 2016 VBRI Press.

THERMAL PARAMETERS AND STRUCTURAL INVESTIGATIONS OF Cu-BASED SHAPE MEMORY ALLOYS IRRADIATED WITH Co-60

Gamma radiation is a type of radiation that can change the structural properties of materials. Many physical and structural properties of metals and alloys change due to defects in their crystal structures in response to irradiation. Shape memory alloys (SMAs) are functional materials and are used in mechanical devices for monitoring nuclear facilities. In this study, copper-based SMAs were used. Copper-based SMAs are very sensitive to alloying elements and small changes in element percentages. Cu-11.6Al-0.42Be, Cu-11.8Al-0.47Be, Cu-13Al-4Ni, and Cu-13.5Al-4Ni (wt%) SMA samples were irradiated with a fixed radiation dose of 50 kGy. The effect of irradiation on the thermodynamic parameters and structural properties of copper-based SMAs was investigated. The effects of irradiation on thermodynamic parameters were determined by differential scanning calorimetry (DSC). Structural examinations were made by X-ray diffraction (XRD) and optical microscope observations. Microhardness measurements were taken. The results obtained for Cu-based SMAs were evaluated both as homogeneous and irradiated samples and according to alloying elements.

Biocompatibility of copper-based shape memory alloy

To represent biocompatibility of CuAlNi shape memory alloy manufactured by continuous casting. Test samples were cut by electro erosion into discs shape. After polishing and cleaning, samples were UV sterilized for 1h. For the indirect test, discs were incubated in DMEM for 24h at 37°C in humidified 5% CO2 atmosphere (0.2 g/ml), and supernatant was collected the next day. Human gingival cells (HGCs) were isolated by outgrowth method from gingival tissues of healthy donors. HGCs were seeded in 96 well plates, and the next day undiluted material extract was added in corresponding wells. For the assessment of mitochondrial activity of HGCs after 24 and 168h from exposure to material supernatant, medium was discarded, and medium containing 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide was added to each well and incubated. After 4h supernatant was discarded, and dimethyl sulfoxide was added to each well and optical density was measured. Cells cultured in growth medium alone were used as control. After 24h mitochondrial activity was increased in test group (HGCs exposed to material supernatant) in comparison to control group (untreated HGCs). After 168h of exposure to extracts mitochondrial activity was still higher in test group in comparison to control. T-test of paired samples showed that there was not statistically significant decrease in mitochondrial activity during time (p=0.642). Although Cu-based alloys are controversial in terms of their biocompatibility, our study justified that biocompatibility depends on the manufacturing process and surface modification but not directly from the content of Cu.

Correction to: Investigation of Damping Characteristics on Copper-Based Shape Memory Alloy Frictional Damper in Boring Process

Correction to: Investigation of Damping Characteristics on Copper-Based Shape Memory Alloy Frictional Damper in Boring Process

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.