Cu-based Shape Memory Alloys Research Articles

Investigation into micro slotting of Cu-based shape memory alloy via µ-ECM using ethylene glycol mixed aqueous NaCl electrolyte

ABSTRACT Micro-Electrochemical Machining (µECM) presents significant promise as a future micromachining process offering higher machining rates, improved precision and the ability to work with a wide range of materials. Cu-based shape memory alloys (SMAs) have exceptional properties that make them quite difficult to machine using traditional techniques. In this investigation a new electrolyte solution consisting of ethylene glycol (EG) and NaCl has been explored while attempting µECM of Cu-SMA. The Cu-based shape memory alloy used consists primarily of Cu-53.19%, Zn-41.50%, and 5.2% other elements. Four different parameter combinations selected based on pilot experiments were used for the main experimentation conducted in four sub-sets. The influence of micromachining parameters including machining voltage, electrolyte concentration and micro-tool feed rate on µECM characteristics such as material removal rate (MRR) and surface roughness (SR) during micro-slot formation has been investigated. With the identified optimum parameters, a high-quality micro-slot was successfully machined on Cu-based shape memory alloys achieving a material removal rate of 0.323 mg/min and surface roughness of 0.384 μm. The investigation demonstrated that an ethylene glycol electrolyte containing NaCl is more suitable for µECM of micro-slots offering superior surface integrity and shape accuracy compared to a water-based electrolyte.

Shape memory effect enhancement via aging treatment of the Cu-Al-Mn-Si alloy manufactured using laser powder bed fusion

This study investigated the effects of aging treatments (200–500℃, 1 h) on the Cu-11.1Al-8.15Mn-0.37Si shape memory alloy manufactured using laser powder bed fusion (LPBF). As the aging temperature increased, the residual stress of the alloy decreased, and the microstructure transitioned from an austenite-martensite dual-phase structure to an austenite single-phase structure. A phenomenon of martensite stabilization induced by low-temperature aging at 200–300℃ was observed, leading to increased phase transformation temperatures and decreased mechanical properties. After aging at 400℃, the plasticity was improved and the shape memory effect (SME) recovery strain experienced a significant 48 % enhancement and reached a maximum value of 3.10 %. This enhancement was due to the improved ordering and texture homogenization of the austenite phase, confirmed by EBSD results. Meanwhile, EPMA analyses revealed the pinning effect of Mn5Si3 precipitations migrated from the grain interior to the grain boundaries which no longer obstructed the movement of martensitic habit planes during the recovery process. Thus, the SME improved. Additionally, after aging at 500℃, a large amount of α phase precipitated along grain boundaries leading to a decrease in mechanical properties. These findings underscore the importance of tailored aging treatments for optimizing shape memory properties in LPBF-manufactured Cu-based shape memory alloys.

Hysteresis gap-shrinking and structural effects of minor Al and Ti modifications on binary CuAl-based high-temperature shape memory alloys

Cu-based shape memory alloys (SMAs), except for exhibiting shape recovery, superelasticity, and high damping, are desirable because these smart materials have higher electrical and thermal conductivity and much lower prices than NiTi SMAs. However, they also have some downsides in mechanical strength and brittleness (mostly stemming from their coarse grain structure) and thermal instability. Therefore, adding some grain refining elements to these SMAs to improve their shape memory effect (SME), and thermal, structural, and mechanical properties is a widespread and simple way that significantly affects their martensitic phase transitions, structure, and mechanical properties. One of these grain-refining elements is titanium. Its thermal conductivity is lower than those of Cu and Al elements and has a low solubility in Cu-matrix. Besides the effects of small Al variations, the use of minor amounts of titanium in binary CuAl-base alloys can show impressive effects on all characteristics of these shape memory alloys, such as shape memory effect properties, martensitic transformation kinetics parameters, and microstructural features. In this research work, CuAlTi ternary high-temperature shape memory alloys (HTSMAs) with new compositions were produced by the arc melting method without a complicating use of Mn or Ni components in usual ternary CuAlMn and CuAlNi shape memory alloys. Thermal analyses of the prepared samples of the alloys were investigated by using differential scanning calorimetry (DSC) and differential thermal analysis (DTA) measurements. In contrast, x-ray diffraction (XRD) test results and optical micrographs were used for analyzing the structure of the alloy samples. The effect of different amounts of low soluble and grain refining Ti element on the binary CuAl alloy system was investigated.

A Microstructural Study of Cu-10Al-7Ag Shape Memory Alloy in As-Cast and Quenched Conditions

Shape memory alloys (SMAs) represent an exceptional class of smart materials as they are able to recover their shape after mechanical deformation, making them suitable for use in actuators, sensors and smart devices. These unique properties are due to the thermoelastic martensitic transformation that can occur during both thermal and mechanical deformation. Cu-based SMAs, especially those incorporating Al and Ag, are attracting much attention due to their facile production and cost-effectiveness. Among them, Cu-Al-Ag SMAs stand out due to their notably high temperature range for martensitic transformation. In this study, a Cu-based SMA with a new ternary composition of Cu-10Al-7Ag wt.% was prepared by arc melting and the samples cut from this casting alloy were quenched in water. Subsequently, the phase composition and the development of the microstructure were investigated. In addition, the morphology of the martensite was studied using advanced techniques such as electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The analyzes confirmed the presence of martensitic structures in both samples; mainly 18R (β1′) martensite was present but a small volume fraction of (γ1′) martensite also was noticed in the as-quenched sample. The observation of fine, twinned martensite plates in the SMA alloy with symmetrically occurring basal plane traces between the twin variants underlines the inherent correlation between microstructural symmetry and the properties of the material and provides valuable insights into its behavior. The hardness of the quenched sample was found to be lower than the as-cast counterpart, which can be linked to the solutioning of Ag particles during the heat treatment.

Revealing the impact of Hot Isostatic Pressing temperature on the microstructure and mechanical characteristics of Selective Laser Melted CuAlNiMn shape memory alloy

The present research examines the impact of temperature during Hot Isostatic Pressing (HIP) on the mechanical, microstructure, and density characteristics of Cu-based shape memory alloys (SMAs) made by Selective Laser Melting (SLM). HIP improved the density of the built components by 11.5 %, with a reduction in density with an increase in HIP temperature. Pore aspect ratio analysis revealed non-spherical pores at higher temperatures, while spherical and small pores were observed at 950 °C. SEM analysis demonstrated the disappearance of shrinkage porosity and an increase in grain size with higher HIP temperatures. XRD analysis confirmed phase transformation and variation in crystallite size with an increase in HIP temperature. After HIP treatment, microhardness and tensile strength significantly improved, with the 950 °C sample showing the highest values.

Machine learning-assisted efficient design of Cu-based shape memory alloy with specific phase transition temperature

Machine learning-assisted efficient design of Cu-based shape memory alloy with specific phase transition temperature

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.

Simultaneous enhancement of mechanical and functional properties by heat-treatment in CuAlNi shape memory alloys fabricated by laser powder bed fusion

Laser powder bed fusion (LPBF) is a promising manufacturing method for fabricating Cu-based shape memory alloys (SMAs), but further performance improvement is needed to ensure service stability and broaden the engineering applications. To achieve simultaneous enhancement of mechanical and functional properties of CuAlNi ternary SMAs fabricated via the LPBF process, this study conducts isochronous and isothermal quenching treatments to tailor the microstructure. The heat-treated specimens with a high quenching temperature and long soaking time exhibited high ultimate tensile strength of 696 ± 10 MPa, large ductility of 8.9 ± 0.2%, and excellent recoverable strain under 2% pre-strain with a shape recovery rate of 100%, which were considerably superior than those of as-built specimens (ultimate tensile strength of 612 ± 10 MPa, elongation of 2.6 ± 0.1%, and 1.26% recoverable strain). This is attributed to the element homogenization during heat treatment, release of residual stress, and coordinated martensite network boundary. However, no significant strain platform of martensite reorientation or detwinning was found in the tensile deformation of the as-built and heat-treated samples, due to localized strain concentration in the parent grain. The microstructural evolution under different quenching treatments and the underlying mechanisms for the improvement of mechanical and functional properties are discussed in detail. This work not only reveals the unique functional response of LPBF fabricated Cu-based SMAs, but also provides a simple and effective method to improve their performance.

Influence of applied stress on shape memory characteristics of Ni50Ti45Cu5 (at.%) alloy subjected to thermomechanical cycling

Shape memory alloys have made rapid progress in many domains, primarily biomedical (endovascular stents, orthodontic archwires), and engineering (smart actuators, robotics, hydraulic couplings). The selection of a shape memory alloy for the indented application is based on its characteristic phase transformation temperatures. These characteristic temperatures are influenced by myriad parameters, such as composition, microstructure of the alloy, defect density, etc. When an shape memory alloy under an external load is subjected to cyclic operations to perform useful work, for example, actuators, these characteristic temperatures are modified. This study, therefore, aims to understand the influence of external loading on the shape memory characteristics of a Ni50Ti45Cu5 (at.%) alloy. A wire of 1.43 mm diameter and length of 100 mm was subjected to heating and cooling between its phase transformation temperatures in a cyclic manner under constant stress (of up to 60 MPa). The maximum recovery strain, actuation/retraction rate, and the stress influence coefficient were determined and compared with those of the other Ni-Ti and Cu-based shape memory alloys. The results show that raising the load level causes an increase in the transition temperatures, especially the Ms (martensite start temperature) rather than the other phase transformation temperatures (martensite finish (Mf), austenite start (As), austenite finish (Af)). It also significantly affects the recovery strain and the rate of retraction during forward transformation and the symmetry of operation.

The effect of Hf on the microstructure, transformation temperature, and the shape memory properties of Zr–Cu-based high-entropy shape memory alloys

The microstructures, phase transformation temperatures, and shape memory properties of Hf-modified Zr50−xHfxCu25Ni7.5Co17.5 and Zr50−xHfxCu25Ni10Co15 high-entropy shape memory alloys (SMAs) were investigated. Hf additions can alter the valence electron concentration, strengthen the alloy matrix, and introduce more secondary phase particles, which significantly influence the properties of the alloys. The results reveal that high austenitic transformation temperature (over 600 K) with very small thermal hysteresis (70–80 K) can be achieved by tailoring the Hf contents, and the best shape memory recovery strain (up to 2.44%) compared with other Zr–Cu-based SMAs could be obtained in Zr42Hf8Cu25Ni10Co15 alloy. This study demonstrated that high-performance Zr–Cu-based high-entropy SMAs can be realized by incorporating Hf additions.

A Review on Comparison between NiTi-Based and Cu-Based Shape Memory Alloys

One of the best types of smart materials is Shape Memory Alloys (SMAs), which have more applications in modern technology such as aerospace, automotive, biomedical, civil engineering, robotics, and so on. Among all parts of them NiTi-based, and Cu–based are more focused on because they have some interesting properties that have made them more widely used in modern technology. In this work, the classifications and applications of SMAs according to the different application fields like biomedical, automotive, and aerospace have been reviewed. Besides the characteristic of (NiTi-based, Cu – based) and the comparison between them in many areas such as: In terms of cost, creation, corrosion resistivity, density, and electrical and thermal conductivity were represented. Each of NiTi and Cu-based SMAs has many useful applications and strengths, but they have some limitations.

Effect of Silver Addition on Cu-based Shape Memory Alloys

Effect of Silver Addition on Cu-based Shape Memory Alloys

Effect of the Tempering Heat Treatment on the Cu-Based Shape Memory Alloy Exposed to a Commonly used Corrosive Medium

Abstract. In the present work, the corrosion behavior of the as-cast Cu-9Al-3Ag alloy, with shape memory, SMA, and with tempering heat treatments at two temperatures, 400 and 600 °C, were studied. These treatments were selected due to the austenite-martensite phase transition or vice versa. For this investigation, a 0.5 M NaCl electrolyte was used. Micrographs using optical microscopy and scanning electron microscopy show the martensite phase in the Cu-9Al-3Ag alloy, likewise, in the tempered samples the austenite-martensite phases were also observed. For the evaluation of the corrosion behavior, the Tafel model was implemented, for whose curves a potential of ±200 mV was used from the Ecorr. It was observed that the sample with SMA presented a good resistance to corrosion, as well as the tempered samples, unlike the as-cast sample. Finally, impedance tests were carried out using a frequency range of 100 kHz to 10 mHz and an amplitude of 10 mV, in order to observe the resistances to the solution and to the charge transfer present in each one of the samples used. Resumen. En el presente trabajo se estudió el comportamiento de corrosión en la aleación Cu-9Al-3Ag en estado de colada, con memoria de forma en conjunto con tratamientos térmicos de revenido a temperaturas de 400 y 600 °C. Dichos tratamientos fueron seleccionados debido al cambio de transición de fase austenita-martensita o viceversa. Para esta investigación se utilizó un electrolito a 0.5 M NaCl. Las micrografías mediante microscopia óptica y microscopia electrónica de barrido muestran la fase martensita en la aleación Cu-9Al-3Ag, así mismo, en las muestras revenidas se puede observar las fases austenita-martensita. Para la evaluación del comportamiento de corrosión se implementaron las curvas de Tafel, en las cuales se utilizó un potencial de ±200 mV a partir del Ecorr. Se observó que la muestra con SMA presento una buena resistencia a la corrosión al igual que las muestras revenidas a diferencia de la muestra en estado de colada. Por último, se realizaron pruebas de impedancia utilizando un rango de frecuencia de 100 kHz a 10 mHz y una amplitud de 10 mV, con la finalidad de observar las resistencias a la solución y a la transferencia de carga presentes en cada una de las muestras utilizadas.

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.

Development of Cu-based shape memory alloy through selective laser melting from elemental powder mixture: Processing and characterization

The Cu-based shape-memory alloy 81Cu-11Al-3Ni-3Mn (wt%) was processed by selective laser melting (SLM) and the parameters were optimized to obtain samples with a high relative density of up to 99 %. The study used ball milling of elemental powders to obtain the feedstock material and the process was developed for building dense SMA structures. The process optimization is performed to obtain dense structures by varying laser power and scan speed. Further, the parameters yielding higher density is selected to study the influence of the different laser power on the overall density, defect distribution, mechanical properties, and grain sizes. Cu-based SMA fabricated at different laser powers were characterized using Scanning electron microscopy (SEM), Differential scanning calorimetry, X-ray diffraction (XRD), tensile test, and microhardness tests. It was observed that the processing technique has a strong influence on the degree of porosity and the distribution of the pores, the grain size as well as the grain morphology. Dense and uniform samples are formed with elemental powder which shows a maximum hardness of 380 HV, and tensile strength of 1550 MPa. The transformation peak became sharp with respect to laser power increment and the transformation temperature increased with an increase in laser power. The study provides a path toward the deployment of SLM for building dense Cu-based SMA from elemental powders.

Enhancing the Mechanical Properties of Cu-Al-Ni Shape Memory Alloys Locally Reinforced by Alumina through the Powder Bed Fusion Process.

A classical problem with Cu-based shape memory alloys (SMAs) is brittle fracture at triple junctions. This alloy possesses a martensite structure at room temperature and usually comprises elongated variants. Previous studies have shown that introducing reinforcement into the matrix can refine grains and break martensite variants. Grain refinement diminishes brittle fracture at triple junctions, whereas breaking the martensite variants can negatively affect the shape memory effect (SME), owing to martensite stabilization. Furthermore, the additive element may coarsen the grains under certain circumstances if the material has a lower thermal conductivity than the matrix, even when a small amount is distributed in the composite. Powder bed fusion is a favorable approach that allows the creation of intricate structures. In this study, Cu-Al-Ni SMA samples were locally reinforced with alumina (Al2O3), which has excellent biocompatibility and inherent hardness. The reinforcement layer was composed of 0.3 and 0.9 wt% Al2O3 mixed with a Cu-Al-Ni matrix, deposited around the neutral plane within the built parts. Two different thicknesses of the deposited layers were investigated, revealing that the failure mode during compression was strongly influenced by the thickness and reinforcement content. The optimized failure mode led to an increase in fracture strain, and therefore, a better SME of the sample, which was locally reinforced by 0.3 wt% alumina under a thicker reinforcement layer.

High-performance Cu-Al shape memory alloy in ternary combination with graphene fabricated by powder bed fusion process

The main characteristic feature of Cu-based high-temperature shape memory alloys (SMAs) such as Cu-Al-Ni alloys is their high transformation temperatures that enable their applications at high temperatures. The improvement of thermodynamic properties of SMAs with reinforcements is essential for more applications at high temperatures with fewer negative effects of exposure at high temperatures, such as alloy softening that can deteriorate the strength and shape memory effect (SME) simultaneously. To avoid the negative effects of micro-reinforcements such as stress localization, in this study, graphene (GN) was substituted with Ni, and a new alloy labeled Cu-Al-GN with 0.2 wt% graphene was formed. A graphene-reinforced alloy labeled Cu-Al-Ni-GN was also fabricated by a laser powder bed fusion process for comparison purposes. The results showed that the Cu-Al-GN alloy exhibited enhanced performance in terms of improved reinforcement distribution, finer grains, defect-free samples with the highest SME at subsequent cycles, and less time required to achieve a targeted SME during heating, despite the smaller SME in the initial recovery cycles. Thus, the results of this study confirm that the proposed Cu-Al-0.2GN alloy combination promises high performance for recovery cycles and is time and cost saving, rendering it a suitable candidate for rapid production.

Experimental investigation on fracture toughness of Cu-based shape memory alloys with silver addition

An attempt is made in the present work to determine the fracture toughness of shape memory alloys by the addition of Ag as a quaternary element. Cu-Al-Mn-Ag shape memory alloys are synthesized by using a bottom pouring type casting machine. Three samples are prepared by varying the Ag concentration by 2%, 4%, and 6% (wt.%) and keeping the Mn content constant (2 wt%). After preparing the samples, they are homogenized in a muffle furnace at 850 °C to achieve the required strength and homogeneity. Single-edged crack specimens are prepared and a three-point bend test was conducted on Universal Testing Machine (UTM) as per ASTM standards. The stress Intensity Factor (KIC) is calculated using an empirical formula. It is observed from the experimental results that Stress Intensity Factor increases with an increase in Ag concentration. Microstructural analysis is conducted using Image Analyzer Microscope. It is observed there is a decrease in grain size with an increase in Ag concentration. According to XRD data, a change in Ag concentration does not significantly alter the size of the crystallites.

New insights into the effects of solidification process on the thermodynamic parameters and mechanical properties of CuAlBeNbNi shape memory alloy

In this work, the influence of the processes of unidirectional solidification and squeeze casting in microstructure, thermodynamic parameters and mechanical properties of CuAlBeNbNi shape memory alloy (SMA) was investigated. The results show that the unidirectional solidification process causes an increase in phase transformation temperatures and ductility, improves fracture toughness and reduces stress-induced martensite, residual stress and dissipated energy after load-unload tensile test of the CuAlBeNbNi alloy. The squeeze casting process, on the other hand, causes an increase in the density of grain boundaries, increasing the stress-induced martensite and the elastic energy of the direct martensitic transformation, while decreasing the impact toughness, increasing the residual deformation, the residual stress and the dissipated energy after the tensile cycle tests. These results indicate that the processes of unidirectional solidification and squeeze casting offer an alternative method to modify the thermodynamic parameters, mechanical properties, and microstructural properties of the CuAlBeNbNi SMA while keeping the composition constant. This study aims to fill the knowledge gap regarding the impact of solidification processes on the properties of Cu-based SMAs, specifically investigating CuAlBeNbNi SMAs.

In Vitro Evaluation of the Potential Anticancer Properties of Cu-Based Shape Memory Alloys

Due to the unique functional properties of shape memory alloys (SMAs) and current scientific interest in Cu-containing biomaterials, a continuously cast Cu-Al-Ni alloy in the form of rods has been investigated as a potential candidate for biomedical application. Additionally, the fact that Cu- complexes have an antitumour effect served as a cornerstone to develop more efficient drugs based on trace element complexes. In line with that, our study aimed to analyse the basic properties of the Cu-Al-Ni alloy, along with its anticancer properties. The detailed chemical analysis of the Cu-Al-Ni alloy was performed using XRF and SEM/EDX analyses. Furthermore, a microstructural and structure investigation was carried out, combined with hardness measurements using the static Vickers method. Observations have shown that the Cu-Al-Ni microstructure is homogeneous, with the presence of typical martensitic laths. XRD analysis confirmed the presence of two phases, β' (monoclinic) and γ' (orthorhombic). The viability of osteosarcoma cells in contact with the Cu-Al-Ni alloy was evaluated using epifluorescence microscopy, while their morphology and attachment pattern were observed and analysed using a high-resolution SEM microscope. Biocompatibility testing showed that the Cu-Al-Ni alloy exerted a considerable antineoplastic effect.