Cu-rich Alloy Research Articles

Corrosion resistant high entropy conventional alloy (HECA) with superior work hardenability

Cu-based alloys are known for their high corrosion resistance but with a lack of processing ability and vice versa. Here we present a novel alloy design concept realizing Cu-rich high entropy conventional alloy (HECA) having exceptional corrosion resistance (Ecorr = - 0.27 V, icorr = 2.83 × 10−6 A/cm2) and work hardenability (strength = 413 MPa, total elongation = 28 %) synergy simultaneously in as-fabricated state. This cocktailing effect in HECA (Cu-12Fe-8Mn-7.5Co-2.5Cr, all in at%) is attributed to the formation of Fe-Mn-Co-Cr containing high entropy phase (HEP) in the Cu-rich matrix. A pronounced two-phase hardening by hetero-deformation induced (HDI) strengthening effect at the HEP/Cu matrix resulted in excellent work hardenability whereas, exceptional corrosion resistance was attributed to delayed corrosion kinetics owing to the preferential corrosion of the Cu-rich phase over HEP in HECA. Thus, Cu-rich HECA overcomes the corrosion-strength ductility dilemma in Cu-rich alloys when compared with classical binary Cu-Fe alloys in an as-fabricated state.

Effect of 5.31Ti (at.%) content used as ternary in quaternary Cu-rich high-temperature shape memory alloy cast via arc melting

Effect of 5.31Ti (at.%) content used as ternary in quaternary Cu-rich high-temperature shape memory alloy cast via arc melting

Relationship of the atomic dynamics and excess volume of a copper rich Cu76Ti24 alloy melt

We investigate the atomic dynamics of a Cu-rich Cu76Ti24 alloy between 1223 K and 1453 K using the quasi-elastic neutron scattering technique. The obtained mean Cu/Ti self-diffusion coefficient D exhibits an Arrhenius-like temperature dependence with an activation energy of 0.46�0.02 eV per atom. Compared with those of the pure elements at a given temperature, D is slower than that for pure Cu, but similar to pure Ti. This slowing down of the liquid dynamics upon alloying has been observed for most binary alloy systems. However, in this study, the packing fraction of the Cu-Ti alloy is lower than that of the pure elements, which can be explained by the positive excess volume of the Cu-Ti system. Therefore, the compositional dependence of the atomic dynamics cannot be linked to a macroscopic packing argument. Only, the atomic dynamics is not correlated with an increase of the average packing fraction of the melt.

Bimetallic Au-Cu gradient alloy for electrochemical CO2 reduction into C2H4 at low overpotential

Electrocatalytic reduction of CO2 (CO2RR) represents a promising approach to reduce CO2 emission and generate value-added chemicals. Herein, we developed bimetallic Au-Cu gradient alloy nanostructures (AuCu-g) comprising of ultrathin Cu-rich alloy surface and Au-rich alloy core as electrocatalyst via a facial solvothermal method. Impressively, the AuCu-g can stably generate a considerable amount of C2H4 with faradaic efficiency (FE) ∼20 % at a low limiting potential of −0.4 V versus reversible hydrogen electrode (RHE) due to its unique gradient structure and multi-component tandem effect. The potential-dependent in situ Raman spectrum indicated an enhanced *CO adsorption strength and a remarkable CO intermediate generation over Au-Cu gradient alloy at low overpotentials during CO2 reduction process. This work shines a light for developing mutilmetallics toward efficient CO2 RR.

Effect of bias voltage on the structure and properties of CuNiTiNbCr dual-phase high entropy alloy films

The dual-phase structure has been proved to overcome the effect of strength-ductility trade-off of high-entropy alloys. However, most of the high entropy alloy films with larger atomic size difference tend to form a single amorphous structure under non-equilibrium deposition conditions such as magnetron sputtering. In this study, the dual-phase CuNiTiNbCr high entropy alloy film containing the Cu-rich FCC alloy phase and amorphous phase were synthesized by high-power pulsed magnetron sputtering at different bias voltages. The poor affinity of copper with other elements led to the segregation and enrichment of copper to form a Cu-rich FCC phase. The effects of substrate bias voltage on the microstructure, mechanical and corrosion properties of the films were investigated. With the increase of bias voltage, the content of copper in the film decreased, the stress state of the film changed significantly, and the compactness of the structure was improved. The hardness of all films was higher than that of most other high entropy alloy film systems. The films deposited under low bias voltage have better toughness. The film deposited at －50 V showed the best wear resistance due to a combination of high hardness and good toughness. The film deposited at －150 V showed the best corrosion resistance since it had the lowest self-corrosion current density (6.1 ×10−8 A/cm2), which was due to its compact structure and lower impurity content.

Carbon induced segregation of Ni atoms in Cu-Ni alloy

We reported a novel driving force for surface segregation of CuNi alloy by using first-principles theoretical calculation. It is found that carbon atoms dissolved in the CuNi alloy are segregated to the surface with Ni atoms, leading to the formation of Ni-rich skin alloy, which is completely different from the previously reported Cu-rich skin alloy. Moreover, the well-known Van der Waals interaction between graphene and the CuNi surface does not reverse the segregation tendency of Cu-rich surface. Our study provides a novel approach to tune the surface composition of alloy catalyst and thus the catalytic activity of the bimetallic catalysts.

Structure and Magnetic Properties of Thermodynamically Predicted Rapidly Quenched Fe85-xCuxB15 Alloys.

In this work, based on the thermodynamic prediction, the comprehensive studies of the influence of Cu for Fe substitution on the crystal structure and magnetic properties of the rapidly quenched Fe85B15 alloy in the ribbon form are performed. Using thermodynamic calculations, the parabolic shape dependence of the ΔGamoprh with a minimum value at 0.6% of Cu was predicted. The ΔGamoprh from the Cu content dependence shape is also asymmetric, and, for Cu = 0% and Cu = 1.5%, the same ΔGamoprh value is observed. The heat treatment optimization process of all alloys showed that the least lossy (with a minimum value of core power losses) is the nanocomposite state of nanocrystals immersed in an amorphous matrix obtained by annealing in the temperature range of 300–330 °C for 20 min. The minimum value of core power losses P10/50 (core power losses at 1T@50Hz) of optimally annealed Fe85-xCuxB15 x = 0,0.6,1.2% alloys come from completely different crystallization states of nanocomposite materials, but it strongly correlates with Cu content and, thus, a number of nucleation sites. The TEM observations showed that, for the Cu-free alloy, the least lossy crystal structure is related to 2–3 nm short-ordered clusters; for the Cu = 0.6% alloy, only the limited value of several α-Fe nanograins are found, while for the Cu-rich alloy with Cu = 1.2%, the average diameter of nanograins is about 26 nm, and they are randomly distributed in the amorphous matrix. The only high number of nucleation sites in the Cu = 1.2% alloy allows for a sufficient level of grains’ coarsening of the α-Fe phase that strongly enhances the ferromagnetic exchange between the α-Fe nanocrystals, which is clearly seen with the increasing value of saturation induction up to 1.7T. The air-annealing process tested on studied alloys for optimal annealing conditions proves the possibility of its use for this type of material.

Platinum and gold placer from Tugidak Island, Alaska: Platinum-group minerals and their inclusions, gold, and chromite mineralogy

ABSTRACT Black sand beach placers from Kodiak, Sitkinak, and Tugidak Islands, Alaska, have been mined intermittently for gold and minor platinum-group alloys for more than 100 years. High-grade platinum-rich magnetic separate and accompanying black sand from the southern beach placer of Tugidak Island were studied using electron microprobe WDS and scanning electron microscope EDS; mineral classification and identification were based on these techniques. The major platinum mineral is isoferroplatinum, followed by minor tetraferroplatinum and tulameenite, and rare ferronickelplatinum. Two types of alteration were identified in about 3–4% of the alloy grains: rim formation involving Pt loss and increased Fe, Ni, and/or Cu, and fracturing and vein filling by Cu-rich alloy. Ruthenium-Ir-Os-Pt alloys occur as inclusions and veins as well as form part of composite grains. Ten percent of the alloy grains contain a large variety of platinum-group minerals (PGM). Inclusions of cuprorhodsite, malanite, cuproiridsite, laurite, erlichmanite, cooperite, braggite, bowieite, kashinite, miassite, hollingworthite, irarsite, sperrylite, stillwaterite, genkinite, stibiopalladinite, keithconnite, zvyagintsevite, and probable palladodymite and vincentite were identified. Two unidentified inclusion phases also occur. Most of the PGM inclusions are primary and were trapped by a growing crystal from a melt; some inclusions exhibit textures that suggest trapping of an As,Te,S-rich immiscible melt. Secondary inclusions and evidence of deformation were observed in a few alloy grains. Associated with PGM inclusions or as separate inclusions are various base-metal sulfides. Two silicate-melt inclusions in one isoferroplatinum grain have an andesite–shoshonite composition. Minor gold and Ag-rich gold in the high-grade magnetic separate contain magnetite, pyrrhotite, and chromite inclusions. The gold composition suggests that their sources are the numerous quartz veins and apophyses related to granitoids on Kodiak Island. The composition of the placer chromite is similar to chromite from the Border Ranges mélange fault system and suggests that the Uyak Complex ultramafic and mafic rocks are part of a supra-subduction-zone ophiolite and are the source of the platinum-group minerals.

Calculations of Hydrogen Associative Desorption on Mono- and Bimetallic Catalysts

Transition-metal-based materials can activate C–H and O–H bonds in industrially significant reactions such as hydrocarbon and alcohol reforming. Recently, bimetallic alloys based on Au, Ag, and Cu have shown unique chemistry including coke-resistance, promising reaction activity, and interesting product selectivity. However, the mechanism of their key reaction step, the hydrogen associative desorption process, is not well-understood. In this work, density functional theory calculations were used to study the kinetics and thermodynamics of hydrogen associative desorption on 8 monometallic and 70 bimetallic Au–, Ag–, and Cu–X (X = Ir, Ni, Pd, Pt, and Rh) close-packed surfaces. We identified two different mechanisms for hydrogen associative desorption on these surfaces, which are selected by the density of states overlap between a gas-phase H2 molecule and the d-band of the surface metal. We show that specific bimetallic atomic ensembles have significantly lower kinetic barriers for hydrogen associative desorption. A linear correlation between the hydrogen desorption barriers and the reaction energies was found for most of the surfaces studied. More importantly, we show that a Au-/Ag-/Cu-rich ensemble alloy with a small portion of a strong-binding metal can effectively lower the hydrogen associative desorption barrier. This finding is significant for the design of highly active and selective catalysts for H2 production through the activation of organic molecules.

High-temperature behaviour of HVOF (Co,Ni)O coated Cu-Ni-Fe anodes

Cu-Ni-Fe alloys are promising inert anodes for green Al production but their corrosion resistance must be improved. Here, protective (Co,Ni)O coatings are deposited by high velocity oxygen fuel (HVOF) process on Cu-Ni-Fe alloys. The influence of the coating and substrate compositions on their behavior is studied at 1000 °C under argon and air. On Cu-rich alloy, CoxNi1−xO coatings with higher nickel content slow down oxygen diffusion to the substrate, as well as copper diffusion to the sample surface. On Ni-rich alloy, the formation of a NiFe2O4 scale is observed, whose thickness decreases as the Ni content of the CoxNi1−xO coatings increases.

The geometric and electronic structures of a Ag13Cu10(SAdm)12X3 nanocluster.

Herein, we report the synthesis and total structure of a Cu-rich alloy nanocluster protected by twelve adamantanethiolate ligands, i.e., [Ag13Cu10(SAdm)12]X3 (-SAdm = SC10H15, X = counterion), which was confirmed by single-crystal X-ray structure determination and electrospray ionization mass spectrometry (ESI-MS). X-ray crystallographic analysis indicated that [Ag13Cu10(SAdm)12]X3 consisted of an icosahedral Ag13 core, covered by a cage-like shell of Cu10(SAdm)12. Furthermore, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations on the geometric and electronic structures and KS orbitals and UV-vis spectroscopy were performed on the model [Ag13Cu10(SMe)12]3+ and its monometallic analog [Ag23(SMe)12]3+. This work will deepen the understanding of core-shell Ag-Cu alloy nanoclusters.

Hollow PtCu octahedral nanoalloys: Efficient bifunctional electrocatalysts towards oxygen reduction reaction and methanol oxidation reaction by regulating near-surface composition

In response to the scarcity of precious metals, the development of precious-metal-saving electrocatalysts exhibiting high mass activity (MA) and durability towards oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) for both proton-exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) has aroused increasing attention. In this study, octahedral Cu-rich PtCu alloy is seeded to fabricate near-surface composition-tunable PtCu hollow octahedral nanoparticles (HONs) with the wall thickness of ~2.1 nm. Due to both the alloying effects of near surface and the special hollow octahedral structure, the PtCu/C HONs exhibit significantly higher MA and durability than commercial Pt/C towards both ORR in alkaline medium and MOR in sulfuric acid electrolyte. The ORR MA of Pt44.1Cu55.9/C HONs are up to 2.60 A mgPt−1 that is 18.5-fold enhancement compared with that of Pt/C. Besides, after 10,000 voltage cycles, the MA of Pt44.1Cu55.9/C HONs remains to be 1.61 A mgPt−1, a datum 53.7 times that of Pt/C. The in situ CO polarization curves exhibit that the Pt44.1Cu55.9 HONs/C own high resistance to CO poisoning. For MOR in sulfuric acid electrolyte, the optimum SA/MA of PtCu/C HONs is 5.33 mA cm−2/1.94 A mgPt−1, which is 10.25/5.87 times higher than that of Pt/C. This study provides effective bifunctional cathode and anode electrocatalysts for both PEMFCs and DMFCs.

Wafer-scale few-layer graphene growth on Cu/Ni films for gas sensing applications

Pristine, few-layer graphene (FLG)/Si nanopillar assemblies are introduced as gas sensitive chemiresistors showing unprecedented sensitivity towards NO2 when operated at room temperature (25 °C) and in humid air. To achieve this, we first developed wafer-scale (∼50 cm2) FLG growth using sub-micrometer thick films of thermally evaporated Cu/Ni on a SiO2/Si substrate. The Ni film was deposited and annealed to induce the formation of a Cu-rich binary alloy. This alloy formation limited the inter-diffusion of Cu and SiO2, a phenomenon known to take place during the CVD growth of graphene on Cu/SiO2/Si. The as-grown high structural quality FLG was transferred, using a conventional wet chemical method, to lithographically patterned arrays of Si nanopillars (non-flat substrate). Testing of the FLG/Si assembly revealed a NO2 sensitivity that outperforms what is reported in the literature for pristine graphene. Overall, our growth and device fabrication work-flow demonstrate a way to design graphene-based gas sensing systems without incurring inconvenient processing steps such as metal foil etching, surface functionalization or particle loading.

Composition-driven shape evolution to Cu-rich PtCu octahedral alloy nanocrystals as superior bifunctional catalysts for methanol oxidation and oxygen reduction reaction.

Synergetic effects between Pt and a cheap metal, downshift of the d-band center of Pt and the shape can boost the catalytic performance of Pt-based nanocrystals. Therefore, tailoring the shape and composition within the nanoscale is the key to designing a robust electrocatalyst in electrochemical energy conversion. Here, Cu-rich PtCu octahedral alloys achieved by a composition-driven shape evolution route have been used as outstanding bifunctional electrocatalysts for both methanol oxidation (MOR) and oxygen reduction reaction (ORR) in an acid medium. When benchmarked against commercial Pt black or Pt/C, for MOR, the specific activity/mass activity on Pt34.5Cu65.5 octahedra is 4.74/7.53 times higher than that on commercial Pt black; for ORR, the specific activity/mass activity on Pt34.5Cu65.5 octahedra is 7.7/4.2 times higher than that on commercial Pt/C. After a current-time test for 3600 s, the remaining mass activity on Pt34.5Cu65.5 octahedra is 35.5 times higher than that on commercial Pt black for MOR. After undergoing 5000 cycles for ORR, the remaining mass activity on Pt34.5Cu65.5 octahedra is 4.2 times higher than that on commercial Pt/C.

Anti-Corrosion Properties of a TCP Pretreatment Conversion Coating on Aluminum Alloy 2024-T3 during Moist SO2 Atmospheric Testing: Effects of Galvanic Coupling

The anti-corrosion properties of a trivalent chromium process (TCP) conversion coating on Cu-rich aluminum alloy 2024-T3 were studied when galvanically coupled to an uncoated Ti-6Al-4V fastener. Coated and uncoated test specimens were exposed to a 14-day moist SO2 exposure (40 ± 3°C, 360 ppm SO2, 336 h). The TCP coating (Bonderite T5900, Henkel) provided corrosion resistance to this alloy in this acidic environment both stand-alone and when galvanically coupled. The results revealed that the stand-alone corrosion protection of the coating is excellent during the exposure. Roughness, pit density, pit depth and pit diameter are all significantly reduced as compared to the uncoated control. The coating also provided excellent resistance against galvanic corrosion. Corrosion damage and corrosion product formation were confined to the region under the contacting fastener head. Regions away from the through-hole were largely free of discoloration and pitting. Electrochemical parameters, Rp and icorr, were good predictors of the trends observed during the SO2 testing. Corrosion of the alloy initiates at sites where the conversion coating and or the native oxide does not cover and passivate the surface. Corrosion leads to the formation of a Alx(OH)y(SO4)z product layer that undercuts the TCP coating. The corrosion product eventually passivates the surface. By and large, the TCP coating remains intact and passivating after the 14-day exposure.

Effect of Nonmagnetic Cap Layers for Nd–Fe–B Thin Films With Small Addition of Rare-Earth Element

Nd-Fe-B sintered magnets [1] exhibit a highest maximum energy products (BH) max among all permanent magnets, so they have been used for wide variety of applications. Particularly, their usage to traction motors for hybrid and electric vehicles (HEV's) have been increased recently and also will be increased in the future due to the consideration for the environmental issues. Since the Nd-Fe-B sintered magnets show a relatively low curie temperature of 315 0C, the substitution of heavy rare earth elements (HRE) such as Dy and Tb for Nd is essential for realizing a high thermal stability [2]. However, due to the scarce and localized natural resources of the HRE elements, Dy-free or less permanent magnet is strongly required. It is well known that the structure and the chemistry of the grain boundary phase between Nd 2 Fe 14 B phases play an important role to understand coercivity mechanism. Recent studies revealed that the magnetic coupling between the Nd 2 Fe 14 B main phases is thought to reduce by the grain boundary phase with Nd-rich and Cu-rich alloy phases after post-sinter annealing [3-4]. Furthermore, a lot of studies using a thin film fabrication technique have been done to control a structure and chemistry of the grain boundary phase [5]. However, coercivity mechanism has not yet been understood completely. Then, the elucidation of the coercivity mechanism is essential for reducing the amount of heavy rare earth elements from the Nd-Fe-B magnets. In this study, in order to see the effect of non-magnetic cap layers for Nd-Fe-B thin films, Nd-Fe-B/ Nd-Cu multilayer thin films with small addition of rare earth element have been prepared and their structure and magnetic properties have been investigated.

Structure and thermal decomposition of a nanocrystalline mechanically alloyed supersaturated Cu–Ta solid solution

Abstract

Arsenic Adsorption on Copper–Palladium Alloy Films

The adsorption of arsine by copper–palladium alloys was studied using a high-throughput composition spread alloy film (CSAF) sample library. A CuxPd1–x CSAF coupon that spanned the complete alloy composition space (x = 0–1) was prepared by an evaporative deposition technique. The coupon was exposed to AsH3 in a N2 background at 288 °C in a small flow reactor. Arsenic uptake was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy (SEM-EDX), and micro X-ray diffraction (μ-XRD). Pd- and Cu-rich alloy compositions exhibited large surface concentrations of As after exposure to AsH3. In the Cu-rich alloy, composition and structure measurements suggest the formation of a Cu3As phase. Arsenic uptake at Pd-rich alloy compositions is consistent with Pd2As or Pd8As3 phases; structural results suggest Pd2As with a hexagonal structure. In contrast, over a wide range of intermediate compositions (xCu ≈ 0.20–0.75), little As uptake was observed. These results contribute to a basis for rat...

The significance of copper concentrations in natural gold alloy for reconnaissance exploration and understanding gold-depositing hydrothermal systems

Analytical studies of placer (detrital) gold grains, intended to track bedrock sources and styles of mineralization, mainly consider alloy Ag content and inclusion mineralogy to generate ‘microchemical signatures’. Occasionally Hg and Pd help discriminate gold from different sources; Cu infrequently because electron microprobes seldom detect the low concentrations. Reporting of Cu has been largely confined to gold from porphyry–epithermal environments, and this has biased subsequent interpretations of observed Cu-bearing gold alloys. This study focuses on placer gold in the Mourne Mountains, Northern Ireland, where auriferous bedrock remains undiscovered and the complex geology is consistent with either orogenic or intrusion-related mineralization. Over 500 gold grains analysed average 0.17% Cu ranging to >1% Cu and show a wide variation in Ag content. Inclusion mineralogy mainly matches that of orogenic gold elsewhere in the host terrane; however, some signatures are suggestive of zonation within an orogenic hydrothermal mineralizing system, or possibly metamorphic-hydrothermal remobilized gold associated with subsequent intrusive activity. One locality in the study area has placer gold of a distinctive Cu-rich alloy composition containing Cu sulphide inclusions, an association noted elsewhere in gold derived from alkali Cu-Au porphyries. Consideration of Cu-bearing gold alloys worldwide indicates that previously proposed compositional correlations with deposit type are of limited value. We show that Cu contents to at least 0.8% are permissible within orogenic gold – the first time that such compositions have been clearly ascribed to orogenic mineralization. The result is particularly important considering on-going exploration in northern Canada which employs gold grain analysis to help define exploration targets.

Melt separation phenomena in CoNiCuAlCr high entropy alloy containing silver

The effects of Ag additions to AlCoCrCuNi or AlCoCrCuFeNi high entropy (HE) alloys are described. It is shown that Ag additions to these HE alloys results in liquid phase separation (LPS) into two melts, namely, an AlCoCr(Fe) rich liquid (L1) and a second liquid enriched in Ag and Cu (L2). Further, since the L2 has a higher density and a lower melting temperature, it tends to flow to the bottom of the arc melted buttons due to liquid flow (a) along the outer surface of the unmelted L1 and (b) through the interdendritic channels. In addition to the primary macroscopic LPS, secondary (within the different primary liquids) melt separation was observed in the two melts: the upper L1 layer contained L2 spheres which tended to sink to the fusion line while the L2 melt layer found at the bottom of the buttons contained L1 spheres which tended to float to the top of the L2 layer. The L1 microstructure and microhardness resembles that of an Ag-free AlCoCrCuFeNi HE alloy. In spite of the melt separation, relatively simple microstructures were obtained from the two different liquids; these are described in light of the current understanding of this class of alloys. Finally, the possibility of metastable LPS in a Cu-rich HE alloy using electron beam surface melting, which is known to produce significant dynamic undercoolings on the order of 150°C, was investigated but was not observed.