Cu-based Alloys Research Articles

Rational design of low fatigue phase-transforming Cu-based alloys

Rational design of low fatigue phase-transforming Cu-based alloys

Electronic structure, mechanical properties and possible martensitic transformation in Ni<sub>2</sub>Cu-based Heusler alloys：A theoretical study

Ni<sub>2</sub>-based Heusler alloys have attracted increasing attention for the shape memory effects in them and the related application properties. It can be interesting to explore new Ni<sub>2</sub>-based shape memory alloys with novel properties. In this paper, the site preference, electronic structure, elastic parameters and martensitic transformation of new Ni<sub>2</sub>Cu-based Heusler alloys Ni<sub>2</sub>CuZ (Z = Al, Ga, In, Si, Ge, Sn and Sb) were investigated theoretically. Between the two highly-ordered structures of Heusler alloys, Ni<sub>2</sub>CuZ alloys tend to crystallize in the L2<sub>1</sub> structure with Cu atom entering the B site in the cubic lattice. In contrast, the XA structure is higher in energy and less stable. This is different from the usual rule that transition metal atoms with more valence electrons tend to occupy the A, C sites at first and can be related to the strong covalent hybridization between Ni and main group element Z in L2<sub>1</sub> type Ni<sub>2</sub>CuZ.<br>Ni<sub>2</sub>CuZ martensites are all lower in energy compared with the corresponding austenites, which makes them candidates as shape memory alloys. This can be explained by the Jahn‒Teller effect characterized by the reduced states near <i>E<sub>F</sub></i> in the DOS structure and the mechanical instability of the cubic austenite lattice. The martensite-austenite energy difference <i>ΔE<sub>M</sub></i> are strongly influenced by main group elements Z. When Z are in the same group, the <i>ΔE<sub>M</sub></i> increases with the increase of their atomic number, but when Z are in the same period, an opposite trend is observed. The <i>ΔE<sub>M</sub></i> can be looked on as the driving force for the martensitic transformation, a larger <i>ΔE<sub>M</sub></i> corresponds to a higher martensitic transformation <i>T<sub>M</sub></i>. InHeusler alloys, electron concentration <i>e/a</i> and electron density <i>n</i> are usually used to discuss the variation of <i>T<sub>M</sub></i>. An increase of<i> e/a</i> or n tends to leads to the increase of <i>T<sub>M</sub></i>. However, this is contrary to the results in Ni<sub>2</sub>CuZ. New factors, the negative shear modulus<i> C’</i> and softening of the elastic constant <i>C<sub>44</sub></i> and their variations with Z elements can be used to explain this. These results reveal the close relation between the martensitic transformation and mechanical parameters and suggest that they are important factors to predict new shape memory alloys and analyse their properties in Heusler alloys. It is also found that the Young’s modulus, shear modulus increase and Poisson’s ratio decreases after the martensitic transformation. Thus, the Ni<sub>2</sub>CuZ martensite has higher stiffness and rigidity but lower ductility compared with the austenite.

Collaborative improvement of mechanical and electrical properties of Cu–Ni–Co–P alloys via regulation of nanophase precipitation behavior

Owing to their excellent strength and electrical conductivity, Cu–Ni–Co–P alloys present strong potential as next-generation materials for integrated circuits in electronic information systems. However, these outstanding properties are closely tied to the precise control of nanophase precipitation behavior within Cu-based alloy systems. Herein, the design of alloy composition was combined with aging treatment to regulate the nanoprecipitation process. Furthermore, the effects of P content and aging treatment conditions, including temperature and duration, on the microstructure and the mechanical, and electrical properties of Cu–Ni–Co–P alloys were systematically investigated. The findings reveal that Cu–0.3Ni–0.3Co–0.16P alloys, when aged at 500 °C for 4 h, primarily consist of a Cu-rich matrix interspersed with numerous nanoprecipitates. These nanoprecipitates were identified as the hexagonal CoNiP phase, precipitating in Guinier–Preston (GP) zones and maintaining a coherent relationship with the Cu matrix. The as-annealed Cu–0.3Ni–0.3Co–0.16P alloys demonstrated a tensile strength of 652.9 MPa, a yield strength of 631.2 MPa, a Vickers hardness of 203.2 HV, and an electrical conductivity of 66.4 %IACS. Aberration-corrected scanning transmission electron microscopy revealed that G.P. zones suppressed the coarsening of the CoNiP phase, thereby enhancing the mechanical strength of the Cu–Ni–Co–P alloys. The strength analysis calculations suggest that fine-grain and precipitation strengthening mechanisms are the predominant factors in improving the mechanical strength of these alloys. This study provides valuable insights into the development and manufacturing of high-performance Cu-based alloys for advanced applications in the electronics industry.

Effects of Ni Content on Particle Size of Secondary Phase in Cu-Based Alloys with Liquid Immiscibility by Laser-Melting

Effects of Ni Content on Particle Size of Secondary Phase in Cu-Based Alloys with Liquid Immiscibility by Laser-Melting

Machine-learning-accelerated density functional theory screening of Cu-based high-entropy alloys for carbon dioxide reduction to ethylene

Computational screening of high-entropy alloy (HEA) catalysts as alternatives to the typical Cu electrocatalyst for CO2 reduction reaction (CO2RR) has been extensively focused on C1 products, but C2+ products have received significantly less attention. This work optimized CuZnPdAgAu HEA catalyst composition for CO2RR to ethylene via density functional theory and supervised machine learning regression techniques. Candidates were identified from 106,045 HEA data for enthalpy of adsorption of *CO2, *H, *HOCCOH, and *C2H4 species, and the Gibbs free energy of *H. The electrocatalytic properties during the reaction were examined on the surface of the optimized HEA candidate – Cu0.36Zn0.18Pd0.10Ag0.18Au0.18 benchmarked to Cu (111). The Pd site of such a candidate functions as the active site for the CO2 activation step. In terms of catalytic activity, it showed lower Gibbs free energy for the potential determining step – the *OCCOH formation step compared to that on the Cu (111). Insight into electronic properties demonstrated that the candidate reduces the uphill reaction energy for *HOCCOH production pathway due to increased electron density in the C–C bond, donated from two Cu sites. It is shown that the HEA catalyst candidate has the potential for CO2RR targeting ethylene, an alternative to a common Cu catalyst.

Tunable Selectivity on Cu-Sb Bimetallic Alloy via Electrodeposition for Electrochemical CO2 Reduction

For decades, global warming has posed a significant environmental challenge worldwide, CO2 generated by human activities is considered to be a major cause of its escalation. Among the methods to convert CO2 into high value-added chemicals, like carbon monoxide (CO), methane (CH4), ethylene (C2H4) and ethanol(C2H5OH), electrochemical CO2 reduction reaction (CO2RR) at a low temperature has gained considerable attention. Nevertheless, given the high reaction barrier, sluggish kinetics, and diverse pathways involved in CO2RR, well-designed electrocatalysts are crucial for facilitating reactions and adjusting selectivity for specific products. Copper (Cu) has garnered the most attention in recent years due to its ability to generate hydrocarbons beyond CO owing to its moderate *CO adsorption energy. However, Cu exhibits a low selectivity for specific products with wide range of hydrocarbons and undergoes the hydrogen evolution reaction which competes with CO2RR.Incorporation of Cu-based bimetallic alloys can enhance selectivity by regulating the intrinsic active sites of the material to control the adsorption energy of reaction intermediates. Among many secondary metals, post-transition metals such as tin (Sn), indium (In), and bismuth (Bi) have been proven to be active in CO2RR alone, and studies have reported that combining them with Cu selectively produces CO and HCOO-. While antimony (Sb) possessed similar properties, it went unnoticed due to its lack of CO2RR activity alone. However, recent studies have revealed that the addition of a small amount of Sb to Cu results in high CO activity.Electrocatalytic assessments are typically performed using a standard three-electrode H-type cell. Due to the limited accessibility of CO2 by the catalyst, constrained by the solubility of CO2 (approximately ~34 mM at ambient conditions), the highest achievable operating current density is capped at around ~20 mA cm−2. In a gas diffusion electrode system, gaseous CO2 is fed directly to the catalyst, enabling rapid mass transport of CO2. Among these methods, membrane electrode assembly (MEA) electrolyzer offers enhanced efficiencies owing to the reduced ohmic resistance inherent in their zero-gap design. In a MEA electrolyzer, the membrane is sandwiched between the cathode and anode catalyst layers on each side. During operation, the cathodic side receives humidified CO2 but no flowing electrolyte. The anode is typically fed an alkaline electrolyte and commonly consists of a carbon gas diffusion layer with deposited IrOx nanoparticles to facilitate the oxygen evolution reaction.Here in, a series of bimetallic CuXSb10-X (X = 0, 2, 5, 8, 10) catalysts with adjustable compositions for CO2RR was prepared. CuXSb10-X catalysts were synthesized via direct co-electrodeposition onto a gas diffusion layer (MPL/CP) under the room temperature. Characterization reveals that CuXSb10-X catalysts have a typical morphology consisting of nano-sized particles with well-dispersed Cu and Sb. CO2RR tests were performed in a gas flow MEA single cell using humidified gaseous CO2 and anion exchange membrane (AEM). Unlike Pristine Cu, Cu5Sb5 and Cu8Sb2, which have major composition of Cu, show CO (72.4%) as a main product at 3.0 Vcell. Meanwhile, Cu2Sb8 exhibits enhanced selectivity for CH4 (49.7%) with a partial current density of 152.1 mA cm-2, at 3.6 Vcell despite pristine Sb having an inability to produce any CO2RR product. We assume that Cu serves as the main active site in this catalyst. At the same time, the CO2RR selectivity shifts towards CH4 when the site of Cu decreases and becomes isolated near Sb. Later, in situ Raman spectroscopy will be used to reason that the Cu-Sb interface in Cu weakens the binding energy of *CO. Also, Sb surrounding isolated Cu in Cu2Sb8 promotes the CO2RR to CH4 through enhancing the binding energy of *CHO which is key intermediate of CH4 reaction pathway.

Effect of in-situ submicron Al3Ti particles on grain refinement and strengthening of Al–Zn–Mg–Cu-based alloy

Extensive research has been conducted to improve the efficiency for grain refinement of aluminum cast alloys. Herein, we propose a novel strategy to significantly reduce the cast grain size using in-situ submicron Al3Ti particles. The ZnO nanoparticles with enhanced wettability via mechanical stirring process provide finely dispersed α-Al2O3 particles, which serve as heterogeneous nucleation sites for primary Al3Ti particles. A large number of primary Al3Ti nuclei are formed from the α-Al2O3 particles without coarsening even under a relatively slow cooling rate. As a consequence, the size of Al3Ti particles was reduced to approximately 600 nm, resulting in the fine cast grain size of approximately 20 μm. Furthermore, a sheet made of the refined cast alloy has reduced recrystallized grain size and simultaneously improved strength and ductility.

Cu Based Dilute Alloys for Tuning the C2+ Selectivity of Electrochemical CO2 Reduction.

Electrochemical CO2 reduction is a promising technology for replacing fossil fuel feedstocks in the chemical industry but further improvements in catalyst selectivity need to be made. So far, only copper-based catalysts have shown efficient conversion of CO2 into the desired multi-carbon (C2+) products. This work explores Cu-based dilute alloys to systematically tune the energy landscape of CO2 electrolysis toward C2+ products. Selection of the dilute alloy components is guided by grand canonical density functional theory simulations using the calculated binding energies of the reaction intermediates CO*, CHO*, and OCCO* dimer as descriptors for the selectivity toward C2+ products. A physical vapor deposition catalyst testing platform is employed to isolate the effect of alloy composition on the C2+/C1 product branching ratio without interference from catalyst morphology or catalyst integration. Six dilute alloy catalysts are prepared and tested with respect to their C2+/C1 product ratio using different electrolyzer environments including selected tests in a 100-cm2 electrolyzer. Consistent with theory, CuAl, CuB, CuGa and especially CuSc show increased selectivity toward C2+ products by making CO dimerization energetically more favorable on the dominant Cu facets, demonstrating the power of using the dilute alloy approach to tune the selectivity of CO2 electrolysis.

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.

Boosted direct electrochemical reduction of As(III) from arsenic wastewater via Cu(II)-assisted codeposition on a CuIn alloy electrode

Arsenic contamination is a severe environmental problem. A promising strategy for addressing this issue is the direct conversion of highly toxic As(III) to less toxic elemental arsenic (As(0)) using electrochemical reduction technology. In this study, a novel CuIn alloy nanoparticles-modified copper foam (CuIn NPs/CF) was prepared as an efficient cathode for the electrocatalytic reduction of highly mobile As(III) to solid As(0). Density functional theory (DFT) results revealed that the Cu-In bimetallic system exhibited weaker H atom bonding, and the Cu-ln surface was more favorable for the adsorption of *AsO₃ species than the Cu surface. Compared to the pristine CF electrode, CuIn NPs/CF was demonstrated to effectively suppressed the hydrogen evolution reaction with an enlarged hydrogen evolution potential of 1.45 V, and displayed a superior As(0) recovery yield. The conversion of As(III) to As(0) was further enhanced by adding Cu²⁺ to the electrolyte, facilitating a Cu-As co-deposition process. Notably, the CuIn NPs/CF electrode achieved an As(0) recovery yield of 5.38 mg cm⁻² after eight successive recycling tests. This work not only presents a green and sustainable strategy for As(III) removal, but also provides valuable insights into the rational design of Cu-based alloy cathodes for electrocatalytic reduction.

Effect of current on the tribological behavior of Cu-Fe-P immiscible alloy produced by laser powder bed fusion

Cu-based immiscible alloys have significant potential application value in the field of electrical contacts. This study investigated the tribological behavior of Cu-Fe-P immiscible alloys produced via laser powder bed fusion (LPBF) under current-carrying conditions. The alloys consist of softer ε-Cu phase and harder Fe-rich phases. The Fe-rich phase acts as a protective reinforcement during current-carrying friction and wear tests, improving the wear resistance of the alloy. With the increasing current, the coefficient of friction initially rose and then decreased, whereas the wear rate showed a gradual increase. At low currents (0, 2, 3 and 5 A), mechanical wear predominantly governs the wear mechanism. As the current increases, the mechanical wear gradually transitions from adhesive wear to abrasive wear, accompanied by weak oxidative wear. At higher currents (7 A and 10 A), the wear mechanism is dominated by arc erosion wear and oxidative wear. Notably, when the current exceeded 2 A, an oxide film consisting of CuO, Fe2O3, and Fe3O4 formed, enhancing the frictional properties of the alloy. Once the current surpassed 5 A, the arc discharge occurred at high currents, forming molten phases and arc erosion pits on the worn surface of the Cu-Fe-P immiscible alloy.

Self-Inhibition Phenomena in Cu3Pt Oxidation by CO2.

This study investigates the oxidation behavior of Cu3Pt(100) in CO2 using a combination of ambient-pressure X-ray photoelectron spectroscopy, mass spectroscopy, and density functional theory modeling. Our in situ measurements reveal the simultaneous oxidation and reduction of Cu2O due to the opposing effects of atomic oxygen and CO generated from dissociative CO2 adsorption, leading to a dynamic equilibrium state of simultaneously occurring redox reactions. Complementary atomistic calculations elucidate the inhibitory effects of subsurface Pt enrichment and the counteracting roles of CO2 and CO in surface oxidation and reduction. These results provide mechanistic insights into the dissociative pathway of CO2 molecules and dynamic evolution of surface composition and reactivity of Cu-based alloy catalysts in CO2-rich environments, with broader implications for tuning gas-surface reactions by manipulating gas reactants or solid surface composition.

Nanoporous Cu-based amorphous alloys prepared by selective dissolution in acidic media

Abstract Functional nanoporous materials are considered a significant category of nanostructured materials that exhibit distinct characteristics like high surface area, porosity, and improved mass transport properties. These qualities render them suitable for a wide range of applications including catalysis, energy storage, biomedical fields, and electrochemical sensors. Dealloying or laser-induced technologies are the primary methods employed to fabricate such nanoporous materials. Dealloying is a dependable top-down approach used to produce hierarchical, disordered nanoporous materials with customizable pore sizes in the range of a few nanometers. The process of dealloying involves the selective elimination or dissolution of one or more elements from an alloy through a corrosion mechanism, using various dealloying techniques, such as chemical, electrochemical, liquid metal, or vapor phase dealloying. In the present study, copper-based amorphous metallic ribbons (Cu75Ni6Sn5P10Ga4) were initially manufactured using the melt-spinning method. The Cu-based amorphous ribbons were structurally investigated by X-ray diffraction and thermal analysis. Subsequently, the ribbons were subjected to a dealloying treatment, using an acidic solution to selectively dissolve the nickel from their composition and to obtain a nanoporous structure. The microstructure and chemical composition of the ribbons before and after the dealloying process were investigated using scanning electron microscopy (SEM), combined with energy-dispersive X-ray spectroscopy. The dealloying process performed in 1 M H2SO4 solution at 25 °C for 60 minutes leads to a large number of nanopores, uniformly distributed onto the surface of the Cu-based ribbons.

Assessment of imaging performance for metal alloys of the first Italian neutron imaging beamline NICHE (Pavia, Italy)

In this paper, the imaging capabilities and performance of the new neutron imaging beamline developed at the LENA facility of Pavia (Italy) in the framework of the NICHE project (Neutron Imaging in Cultural HEritage) are presented. For this purpose, the estimation of bronze and brass alloys attenuation coefficient has been obtained through imaging analysis of a set of Cu-based alloy reference samples produced ad-hoc with chemical composition similar to ancient artefacts. In addition, some samples were realised using a different cooling ramp in order to test the influence of the alloy production procedures in neutron attenuation. Moreover, the tomographic capabilities of the beamline were tested for different metallic and plastic materials.

Ti6Al4V alloy with diamond particle-reinforced Cu-based coatings: Microstructure and tribological performance

To enhance the surface wear resistance of the Ti6Al4V alloy, diamond particles-reinforced Cu-based composite coatings (D500/D1000/D2000 coating: 500/1000/2000 mesh diamond: Cu-based alloy powder = 1:30 (wt%)) were fabricated by vacuum cladding. Cu-based alloys with liquid phase temperatures lower than the phase transition temperature of Ti6Al4V alloys were employed as cladding materials to avoid performance deterioration of Ti6Al4V substrates. The microstructure, mechanical properties, and dry-sliding tribological properties of the Cu-based composite coatings have been investigated systematically. The Cu-based composite coatings are composed of the ductile intermetallic compounds Ti3Sn and SnTi2 as the metal matrix, the hard and brittle intermetallic compounds CuTi, CuTi2, Ti(Cu, Al)2 and CuSn3Ti5, in situ generated TiC and the directly introduced diamond particle as the reinforced phases. In addition, a TiC hard phase protective layer was formed around the diamond particles, which retained the original properties of the diamond. The hardness of diamond particles-reinforced Cu-based composite coatings is much higher than that of the Ti6Al4V. Among them, the D2000 coating possesses the highest microhardness. The average Vickers hardness (HV0.5) on the coating surface and nanoindentation hardness (H) on the coating cross-section (the middle part without diamond particles) of the D2000 coating are 1329.8 HV0.5 and 16.87 GPa), which are 4–5 times higher than that of the Ti6Al4V substrate (333 HV0.5 and 3.37 GPa). Nevertheless, the D2000 coating (wear rate of 50.75 ×10−5 mm3/Nm) demonstrates slightly inferior tribological performance compared to the D500 coating. The wear rate of the latter is approximately 13.37 × 10−5 mm3/Nm, which is only 1/5.6 of the substrate (75.67 ×10−5 mm3/Nm). The larger the diamond particle size, the more the diamond serves as a bearing capacity support point to prevent the hard WC ball from further ploughing into the composite coating, and the better the wear resistance of the coating. Notably, D500 coating with excellent wear resistance has the potential for application in various fields of the machinery industry, marine engineering, and aerospace.

Microstructure and Mechanical Properties of Low Stacking-Fault Energy Cu-Based Alloy Wires

Innovations in electronic devices and their capabilities have driven the demand for improved conductive materials relevant to device fabrication. To gain insights on developing solid solution-type Cu alloy thin wires with a superior balance of strength and conductivity, this study investigated variations in the microstructures and properties of pure Cu wires and Cu–5 at. pct Zn, Cu–5 at. pct Al, and Cu–5 at. pct In alloy wires during intense drawing and analyzed the effects of stacking-fault energy (SFE) of Cu alloys on their microstructural evolution. During the initial drawing stages, lower SFE Cu–5 at. pct Al and Cu–5 at. pct In alloys yielded more high-density deformation twins than pure Cu and Cu–5 at. pct Zn. Deformation twins promoted grain refinement during drawing. Effective grain refinement and dislocation accumulation during drawing in low-SFE Cu alloys substantially strengthened them without adversely impacting electrical conductivity. During intense drawing in the Cu–5 at. pct In alloy wires, ultrafine fibrous grains (diameter ~ 80 nm) and a high-dislocation density yielded excellent tensile strength and conductivity. These results indicate that adjusting the solute element content in Cu matrix to reduce SFE and optimizing deformation strain via wire drawing significantly improve alloy wire performance.

Achieving optimal comprehensive properties in heat resistant Cu-based alloys by regulating complex elemental interaction

Coherent γ′-phase precipitation strengthened heat-resistant Cu-based alloys exhibit promising application in the field of high-temperature. In the work, to further improve the comprehensive performance of the alloys, the elements Cr, Zr, Zn and Ti are introduced into the model alloy (Cu83.33Ni12.50Al4.17 at.%). The existence state of the adding elements and their influence on comprehensive properties, including the in-situ high-temperature hardness, tensile properties and stability, etc., was unveiled. Furthermore, the Cu83.33Ni11.11Al2.78Cr1.04Ti1.04Zr0.35Zn0.35 alloy with excellent comprehensive properties was designed and prepared, exhibiting a high-temperature tensile strength of 370 MPa and an elongation of 3.7 % and high temperature stability of up to 400 h at 873 K. The reasons for the improvement of comprehensive properties can be attributed to the following aspects: (1) The adding elements not only inhibit discontinuous precipitation but also refined the size of the γ' phase and improved its thermal stability; (2) Cr and Zr inhibit the precipitation of deleterious D024-Ni3Ti phase caused by Ti; (3) The BCC-Cr (precipitation strengthening phase) and Ni5Zr phases (grain boundary strengthening phase) are introduced. This study successfully demonstrates the advantages of addition of multiple-elements through regulating their interaction, thereby establishing a robust foundation for designing heat-resistant Cu-based alloys in future investigations.

Discovery of promising Cu-based catalysts for selective propane dehydrogenation to propylene assisted by high-throughput computations

The development of efficient catalysts with high selectivity is a major challenge for propane dehydrogenation (PDH), which is an on-purpose route to produce propylene. We have developed a high-throughput computational strategy to screen out the promising catalysts for propane dehydrogenation to propylene on Cu-based metal alloys. A total of 1500 candidates of Cu3M1 alloys are constructed, and four efficient descriptors are applied in our high-throughput screening to evaluate the activity and selectivity of catalysts. Four Cu-based alloys of Cu3Cr1, Cu3Pd1, Cu3Pt1, and Cu3Ag1 are identified as promising PDH catalysts, and their superior selectivity towards propylene could be explained by the synergistic effect of Cu and M atoms. Our theoretical screening method could assist the new catalyst design and accelerate the discovery of environment-friendly alloy catalysts for PDH.

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.