Segregation Of Cu Research Articles

The Impact of Vibrational Entropy on the Segregation of Cu to Antiphase Boundaries in Fe3Al

We performed a quantum mechanical study of segregation of Cu atoms toward antiphase boundaries (APBs) in Fe3Al. The computed concentration of Cu atoms was 3.125 at %. The APBs have been characterized by a shift of the lattice along the ⟨001⟩ crystallographic direction. The APB energy turns out to be lower for Cu atoms located directly at the APB interfaces and we found that it is equal to 84 mJ/m2. Both Cu atoms (as point defects) and APBs (as extended defects) have their specific impact on local magnetic moments of Fe atoms (mostly reduction of the magnitude). Their combined impact was found to be not just a simple sum of the effects of each of the defect types. The Cu atoms are predicted to segregate toward the studied APBs, but the related energy gain is very small and amounts to only 4 meV per Cu atom. We have also performed phonon calculations and found all studied states with different atomic configurations mechanically stable without any soft phonon modes. The band gap in phonon frequencies of Fe3Al is barely affected by Cu substituents but reduced by APBs. The phonon contributions to segregation-related energy changes are significant, ranging from a decrease by 16% at T = 0 K to an increase by 17% at T = 400 K (changes with respect to the segregation-related energy difference between static lattices). Importantly, we have also examined the differences in the phonon entropy and phonon energy induced by the Cu segregation and showed their strongly nonlinear trends.

Realization of synergistic enhancement for fracture strength and ductility by adding TiC particles in wire and arc additive manufacturing 2219 aluminium alloy

TiC reinforced Al-matrix composites were fabricated by wire and arc additive manufacturing (WAAM) method. The effects of TiC content on the evolution of grain boundary structure, phase transformation, grains distribution, interface mismatch, and mechanical properties of the WAAM-deposited 2219 Al–Cu alloys were investigated. The columnar grains in the inner-layer zone were transformed to equiaxed grains by the addition of TiC particles, which eventually induced the decrease of free energy for the Al-matrix, promoting an opportunity for nuclei to grow on the TiC substrate. TiC particles played an important role in generating the nucleation supercooling (ΔTns, 3.8 °C), multi-site heterogeneous nucleation with a lower value of ΔTns inhibited the constitutional supercooling (ΔTcs) caused by segregation of Cu. The degree of grain boundary segregation was greatly weakened, and the α-Al+θ-CuAl2 phase was semi-coherent with the matrix at the grain boundary, i.e. [1–31]Al2Cu//[0–11]Al, (211)Al2Cu//(100)Al. The fine spot-like phase possessed a strong interfacial bonding with the Al-matrix. The Al2Cu and TiC possessed a coherent interface with crystal orientation relations, i.e. [00–1]TiC//[01-1]Al2Cu, (110)TiC//(100)Al2Cu. Besides that, the fine spot-like phases and the well-dispersed TiC particles within the grains promoted the formation of dislocations. Therefore, the strength and toughness of the deposited 2219 alloy were improved synergistically. Eventually, the deposited sample exhibited a tensile strength around 384 MPa, and the elongation was up to 18.3%.

Precipitation in reactor pressure vessel steels under ion and neutron irradiation: On the role of segregated network dislocations

The ultrahigh density of Mn-Ni-Si-Cu precipitates that form in irradiated reactor pressure vessels (RPV) result in hardening and embrittlement, which may limit the service life of aging nuclear reactors. Here, we quantitatively analyze solute segregation to, and precipitation on, network dislocations in irradiated low alloy RPV steels. The analysis is based on a broad thermodynamic framework, which allows proper identification of possible non-equilibrium perturbative effects of irradiation, like radiation induced segregation (RIS). For the first time, we quantify the segregation of Cu, Mn, Ni and Si to ≈ 5–10 nm network dislocation segments, typically separated by a string-of-pearl type array of MnNiSi precipitates (MNSPs); the MNSPs are appended to Cu rich co-precipitates (CRPs) in steels bearing this element. Detailed atom probe tomography (APT) data are reported for 16 RPV steels, with a wide matrix of tailored compositions, irradiated by both neutrons and 6.4 MeV Fe3+ ions at 320 and 290 °C, respectively. A key aspect of this study is that the very high displacement per atom (dpa) doses and radiation enhanced diffusion (RED) result in nearly full phase separation, allowing isolation of thermodynamic (equilibrium or non-equilibrium) effects. We characterize segregation and precipitates with a comprehensive set of descriptors under both ion and neutron irradiation, including: a) solute enrichment factors (EFs) at dislocations, as a function of alloy composition; and, b) matrix versus dislocation precipitates and their respective characteristics. Formation of these dislocation features can be due to RIS, or thermodynamic in origin, or both. Coupled with simple models, we show that the nucleation MNSP features in low Cu steels is enhanced by segregation. However, in typical supersaturated RPV steels, rapid growth of the precipitates is thermodynamically driven to a quantitatively predictable, nearly full phase separation mole fraction.

Effects of Cu on the Morphology and Growth Mode of Graphite in Compacted Graphite Iron

In this article, Cu is found to have a great influence on the graphite morphology and growth mode in compacted graphite iron (CGI). Metallographic pictures show that the number of vermicular graphite of the surface of CGI casting is significantly higher than that of the core, and there is more spheroidal graphite in the core of casting. In addition, a special form of graphite, which is defined as distorted graphite appears in the matrix. From the EPMA results, it can be concluded that the segregation of Cu promotes the distortion of graphite, and part of distorted graphite is transformed into vermicular graphite under the action of vermicular elements (Mg, La, and Ce). The increase in the number of spheroidal graphite improves the strength of casting, but it reduces the thermal conductivity.

Microstructure evolution and corrosion mechanism of laser cladded Zr-Cu-Ni-Al in-situ metallic glass matrix composite coatings

Laser cladding provides a widely applicable method for the preparation of metallic glass matrix composite (MGMC) coatings, where the mechanical property and the corrosion resistance can be tailored by the in-suit precipitated crystalline phases. Thus, the investigation on the microstructure evolution and corrosion mechanism of MGMC coating to achieve superior performance is of great importance. In the presented work, Zr50.7Cu28Ni9Al12.3 MGMC coatings, which are constituted by Zr&Cu enriched dendrites and Ni&Al enriched metallic glass (MG) matrix, were prepared by laser cladding. The effect of the laser power on the microstructure and the corrosion property of the MGMC coatings was investigated. It has been found that the MG content increases and the size of the dendrites decreases with decreasing laser power. Increasing MG content in the coating can decrease the self-etching current density due to the rapid surface oxidation, and decrease the open-circuit-potential due to the higher chemical activity of MG. Besides that, a probable corrosion mechanism of the Zr-Cu-Ni-Al MGMC coating in the NaCl solution was proposed. The segregation of Cu could be the main inducement for pitting. The increasing MG phase content can suppress the segregation of Cu and therefore increase the pitting corrosion resistance of the coating.

Characterization of Nanostructures in the High Pressure Die Cast A383 Alloys

Several interesting nanostructures of high pressure die cast A383 alloys were characterized via transmission electron microscopy (TEM) and atom probe tomography (APT). The refinement of the eutectic Si, which was caused by Sr addition, was found to be associated with the formation of nano-Al particles (~5 nm), with Cu partitioning (up to 5 at. %) at the Al/Si interface, within the eutectic Si. Direct observation of Sr segregation (0.4 at. %) was achieved at the interface between the eutectic Al and refined eutectic Si using APT. It is proposed that Sr refines the eutectic Si by restricting the growth of Si. Interestingly, the segregation of Mg (10.2 at. %) and Cu (0.9 at. %) is also present at the interface between the eutectic Al and the refined eutectic Si. Moreover, the presence of nano-Si particles (~20 nm) in the primary Al was characterized in the primary Al via APT. Segregations of Mg (2.9 at. %) and Cu (2.8 at. %) were also found at the interface between the primary Al and the nano-Si particles. Density functional theory (DFT) was used to assess the driving force for the segregation behavior of Cu and Mg at the Al/Si interface. DFT results also suggest that the segregation of Cu and Mg slightly decreases the cohesive energy of Al/Si interface but is a function of the length scale of the interface.

Особенности упрочнения структурированного интенсивной пластической деформацией сплава Al-Cu-Zr

The effect of small additions of copper on the microstructure and physic-mechanical properties of an ultrafine-grained Al-1.47Cu-0.34Zr (wt%) alloy structured by high pressure torsion after preliminary annealing at 375 °C for 140 h has been studied. As a result of processing, high values of strength characteristics (conditional yield strength 430 MPa, ultimate tensile strength 574 MPa) with an acceptable level of electrical conductivity (46.1% IACS) and ductility (elongation to fracture ~ 5%) have been achieved. On the basis of the microstructural parameters determined by X-ray diffraction analysis and transmission electron microscopy, hardening mechanisms responsible for such high strength have been analyzed. It was shown that Cu plays the key role in strengthening. The addition of copper significantly contributes to grain refinement and, consequently, to grain-boundary hardening. Alloying with copper leads to significant additional hardening (~ 130 MPa) in the ultrafine-grained alloy, which is not typical for coarse-grained state. Segregation of Cu at grain boundaries and the formation of Cu nanoclusters are the most probable reasons for this hardening.

Nanoscale short-range ordering induced cellular structure and microchemistry evolution in Sm2Co17-type magnets

Sm2Co17-type permanent magnets have important application value due to their advanced magnetic properties, which can be ascribed to their unique cellular structure and element segregation in various phases developed after isothermal aging treatment. In this study, the evolution of the microstructure combined with the microchemistry of Sm2Co17-type magnets from solid solution precursor to the cellular structure is investigated, and a new insight into the formation of the cellular structure is provided. We report for the first time that a large number of strip-like nanoscale short-range ordered micro-domains are distributed in the disordered matrix of the solution precursor, which serve as the nucleation centers in the formation of the embryos of the cellular structure. Based on atomic scale structural analyses, a new mechanism concerning the ordering transformation from short-range 2:17R microtwins to long-range 2:17R phase is proposed, involving collective glide of three partial dislocations on successive basal planes with the net Burgers vector to be zero. Furthermore, microchemistry analysis reveals that the segregation of Cu and Fe in the early stage of isothermal aging is accelerated substantially during the ordering transformation, indicating that the ordering transformation can act as a new driving force for element segregation in Sm2Co17-type magnets. These findings provide new considerations for the development of high performance Sm2Co17-type magnets.

Dehydrogenation of Cyclohexanol to Cyclohexanone Over Nitrogen-doped Graphene supported Cu catalyst

In this study, the dehydrogenation of cyclohexanol to cyclohexanone over nitrogen-doped reduced graphene oxide (N-rGO) Cu catalyst has been reported. The N-rGO support was synthesized by chemical reduction of graphite oxide (GO). The synthesized N-rGO was used as a support to prepare the Cu/N-rGO catalyst via an incipient wet impregnation method. The as-prepared support and the Cu/N-rGO catalyst were characterized by FESEM, EDX, XRD, TEM, TGA, and Raman spectroscopy. The various characterization analysis revealed the suitability of the Cu/N-rGO as a heterogeneous catalyst that can be employed for the dehydrogenation of cyclohexanol to cyclohexanone. The catalytic activity of the Cu/N-rGO catalyst was tested in non-oxidative dehydrogenation of cyclohexanol to cyclohexanone using a stainless-steel fixed bed reactor. The effects of temperature, reactant flow rate, and time-on-stream on the activity of the Cu/N-rGO catalyst were examined. The Cu/N-rGO nanosheets show excellent catalytic activity and selectivity to cyclohexanone. The formation of stable Cu nanoparticles on N-rGO support interaction and segregation of Cu were crucial factors for the catalytic activity. The highest cyclohexanol conversion and selectivity of 93.3% and 82.7%, respectively, were obtained at a reaction temperature of 270 °C and cyclohexanol feed rate of 0.1 ml/min. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Reactive wafer bonding with nanoscale Ag/Cu multilayers

Reactive bonding using nanoscale multilayers based on the high specific surface/interface energy is a promising low-temperature and low-pressure wafer-bonding process. Herein, Si wafers were bonded using nanoscale Ag/Cu multilayers in N2 or the ambient atmosphere. A flawless joint composed of Ag-rich and Cu-rich face-centered cubic (fcc) phases was achieved in N2 with 22.2 MPa shear strength. However, a peculiar “fcc-(Ag)+voids/Cu2O/fcc-(Ag)+voids” three-layer sandwich structure with 11.1 MPa shear strength was formed due to significant out segregation of Cu toward the bonding-interface in the ambient atmosphere. The bonding mechanism and the role of oxygen were unveiled based on CALPHAD (CALculation-of-PHAse-Diagram) thermodynamic modeling.

Effect of fiber laser welding on solute segregation and proprieties of CoCrCuFeNi high entropy alloy

The effect of fiber laser welding on solute segregation and proprieties of CoCrCuFeNi high entropy alloy was investigated. The microstructure and mechanical properties of the parent metal and the fusion zone were comparably studied. The parent metal was dendrite, with elemental Cu segregated to interdendrites owing to small bonding energies with Fe, Co, Ni, and Cr atoms. After laser welding, the microstructure in the center of the fusion zone was predominantly equiaxial grains, whereas that in the edge region was mainly columnar crystals oriented perpendicular to the fusion line. The segregation of Cu in the fusion zone is alleviated by grain refinement and molten pool agitation. Because of the fine-grain strengthening and precipitation hardening effect, the hardness and yield stress of the fusion zone are 12.84% and 26.87% greater than those of the parent metal, respectively.

Evolution of the Second-Phase Particles and Their Effect on Tensile Fracture Behavior of 2219 Al-xCu Alloys

In this study, the continuous evolution of the second-phase particles across as-cast, homogenization, multi-directional forging (MDF), and solution-aging treatment and their effect on tensile fracture behavior of 2219 aluminum alloys with different Cu contents was examined by optical microscopy (OM), scanning electron microscopy (SEM), and tensile tests. The results showed that the microstructure of as-cast 2219 aluminum alloy consisted of the α-Al matrix, Al2Cu coarse phase, and Fe-rich impurity phase. Severe segregation of Cu existed, and eutectic networks can be observed in the ingot. With an increase in Cu content, the eutectic networks became coarsen and thicker. During the complex improved process, the refinement mechanisms were fragmentation, dissolution, and diffusion of Al2Cu particles. Most fine Al2Cu particles were fully dissolved into the matrix and partial coarse particles were still retained after solution-aging treatment. Thus, the elongations of all the samples, undergoing solution treatment followed by water quenching, increased evidently. Then, the elongations decreased slightly due to the increase of precipitates. The fractography analysis of peak aged condition samples indicated that the fracture mode was diverted from a typical inter-granular fracture to a mainly trans-granular fracture with increase in Cu content from 5.56% to 6.52%. Fracture initiation mainly occurred by original microcrack propagation and microvoid nucleation at the coarse constituents.

Durability screening of Pt ternary alloy (111) surfaces for oxygen reduction reaction using Density Functional Theory

Degradation of Oxygen Reduction Reaction (ORR) catalytic activity in acidic environments is one of the biggest challenges in developing cost-effective Proton Exchange Membrane Fuel Cells (PEMFCs). In this work, we screened the durability of 138 Pt ternary alloy (111) surfaces by calculating the surface Pt vacancy formation energy, and surface segregation energy using a Density Functional Theory (DFT). Specifically, we investigated Pt ternary systems showing improved durability over corresponding Pt binary systems. Our results identify Pt-Cu-Pd as the most promising candidate. We analyzed the reason for the improved durability using a Density Derived Electrostatic and Chemical (DDEC) method. The improved durability is attributed to the strong resistance to oxygen-induced surface segregation of Cu and Pd, attractive interactions between corresponding bonds (Pt-Cu, Pt-Pd, Cu-Pd). We also show that the ORR activity of the Pt-Cu-Pd(111) is higher than that of Pt(111). We studied the effect of Pd on the ORR activity, and we found that the subsurface Pd slightly strengthen the bonding between surface Pt and adsorbates but its effect is negligible when the overall Pt content is 75 at%, while the effect is noticeable when Pt content is ~50 at%. Although Pt-Cu-Pd catalysts were previously synthesized and tested, our comprehensive screening of Pt ternary alloy (111) surfaces provides an explanation of why Pt-Cu-Pd is the most durable ORR catalysts in an acidic environment.

Phase evolution and mechanical properties of novel FeCoNiCuMox high entropy alloys

In this work, the effect of Mo addition on phase evolution and mechanical properties of as-cast FeCoNiCuMox (molar ratio X = 0.2, 0.4, 0.6, 0.8, 1) high entropy alloy systems (HEAs) have been investigated. It has been found that with increasing Mo concentration, atomic size difference (δ), geometrical parameter (∧) and enthalpy of mixing (ΔHmix) of this multi-component alloy systems decrease. However, the mixing entropy (ΔSmix), electronegativity difference (ΔX), d-orbital energy level parameter (Md‾), root mean square residual strain (RMS) and critical parameter (Ω) increases which clearly indicates the formation of the solid solution with no intermetallic compounds. X-ray diffraction and scanning electron microscope analysis also confirm that FCC solid solution phases are formed at X = 0.2 to 0.6. Further, on increasing the Mo concentration beyond 13 at % (X > 0.6), FCC1 and FCC2 phase were detected due to large positive enthalpy of mixing between Cu and others (Fe, Co, Ni, and Mo) elements. Moreover, the segregation of Cu in the FeCoNiCuMox (X = 0.8 and 1) alloy can be well predicted via φ and λ parameters. The Compressive strength and hardness were found to increase with Mo concentration in FeCoNiCuMox HEAs due to solid solution strengthening.

Calculation of Grain Boundary Segregation in Cu–Based Alloys by CALPHAD Method

Calculation of Grain Boundary Segregation in Cu–Based Alloys by CALPHAD Method

Effect of pre-aging deformation on the intergranular corrosion resistance of 6000 series aluminium alloys

Aluminium alloys in the 6000 series may become susceptible to intergranular corrosion (IGC) by unfavourable thermomechanical processing in combination with presence of Cu and a low Mg/Si ratio. The IGC susceptibility has been related to the segregation of Cu during artificial ageing to form a nearly continuous Cu film along the grain boundaries with an anodic solute depleted zone adjacent to it. In this work, extruded alloys 6005 and C28 as well as two variants of 6016 automotive sheet were subjected to various degrees of deformation by rolling or stretching before artificial aging. Accelerated IGC testing showed that pre-deformation significantly improved the IGC resistance of the Cu containing extruded alloys, while no improvement was observed for the 6016 sheet materials containing < 0.01 wt% Cu. High resolution scanning transmission electron microscopy (STEM) of pre-deformed 6005 alloy showed precipitation of Cu-containing Q' phase on dislocations. As a result, the amount of Cu available for diffusion to the grain boundaries is reduced, which might explain why a beneficial effect of pre-deformation on the IGC resistance was observed only for the Cu-containing materials.

Giant dielectric permittivity with low loss tangent and excellent non−Ohmic properties of the (Na+, Sr2+, Y3+)Cu3Ti4O12 ceramic system

The (Na+, Sr2+, Y3+)Cu3Ti4O12 ceramic system was successfully synthesized using the solid-state reaction method; further, its crystal structure and microstructure were studied. The main phase associated with the CaCu3Ti4O12 like-structure was detected. A dense ceramic microstructure with segregation of Cu−rich phase at the grain boundaries (GBs) was observed in the sintered ceramics. A significantly high range of dielectric permittivity (1.63 × 103−2.34 × 104), and a low range of dielectric loss tangent (0.035–0.075) were observed for the sintered (Na1/2Y1/2)1-xSrxCu3Ti4O12 ceramics at x = 0.1 and 0.2. Further, a steep enhancement of non-Ohmic characteristics was achieved along with the high breakdown electric field of ~9.12 kV cm−1 and the nonlinear coefficient of ~84.7 for the (Na1/2Y1/2)0.90Sr0·10Cu3Ti4O12 ceramic sintered at 1060 °C for 18 h. The presence of heterogeneous microstructures, which are comprised of semiconducting grains and insulating GBs with, respectively, conduction activation energies of 0.05–0.09 eV and ~0.6 eV, was confirmed by impedance spectroscopy; the results displayed a large dielectric response and nonlinear electrical properties. The mixing of Cu+/Cu2+/Cu3+ and Ti3+/Ti4+ was confirmed by X−ray photoelectron spectroscopy, suggesting the presence of a semiconducting state inside the grains.

Investigation of the structure and properties of AlCrCuFeNiVx high-entropy alloys

Co-free AlCrCuFeNiVx (x = 0.2, 0.6, 1.0) high-entropy alloys were designed for the potential use as a friction material. The influence of the V content on the microstructure, component segregation, phases distribution, micro-hardness, and wear resistance of AlCrCuFeNiVx alloys was investigated in detail. The microstructure of the alloys with V contents lower than x = 0.6 was mainly comprised of simple body-centered cubic (Fe-Cr-V type BCC phase) and face-centered cubic (Ni-Cu-Al type FCC phase) duplex structures and a small amount of ordered intermetallic phases. When the V content in the alloys was x = 1.0, two kinds of BCC structures were dominant in the alloys, namely the AlFeV2 type metastable phase and the Fe-Cr-V type phase. The increase in the V content in the alloys altered the distribution of Cu, Ni, and Al, thereby promoting the segregation of Cu and weakening the segregation of Ni and Al. Heat treatment at 1000 °C for 2 h promoted the precipitation of the M3Al intermetallic phase and the decomposition of the metastable phases, increasing the component segregation. The microhardness of the alloys first increased with increasing V content and then decreased slightly after the V content reached x = 1.0. After the heat treatment, the microhardness was lower for the AlCrCuFeNiV0.2 and AlCrCuFeNiV0.6 alloys and higher for the AlCrCuFeNiV1.0 alloy due to precipitation strengthening and grain boundary strengthening. The delamination wear mechanism changed from adhesion to abrasive wear with the increase in the V content.

Deformation induced grain boundary segregation in nanolaminated Al–Cu alloy

A gradient nanostructured surface layer was formed in an Al–4 wt%Cu alloy processed by means of surface mechanical grinding treatment at liquid nitrogen temperature. Within the deformed surface layer, laminated structures with a wide range of thickness were formed. With a decreasing depth from the treated surface, lamellae thickness decreases accompanied by an increased fraction of high angle grain boundaries (HAGBs) from 10% to 70%. In the topmost surface layer, nanolaminated (NL) structures were found with an average thickness as small as 28 nm and a HAGB fraction of 70%. Composition analysis indicated that Cu atoms segregate at NL boundaries in the as-prepared sample, Cu concentration is about 3–4 times higher than that in the lattice. The obvious grain boundary (GB) segregation of Cu induced by cryogenic plastic deformation is attributed dynamic interaction between solute atoms with gliding dislocations. GB segregation of Cu is responsible for the stabilization of the NL structures with a much finer structural size than that in pure Al, resulting in higher hardness. The deformation-induced GB segregation provides an alternative strategy to achieving stable high strength nanostructures in Al alloys.

Density-functional tight-binding approach for the structural analysis and electronic structure of copper hydride metallic nanoparticles

We perform a theoretical investigation using the density functional tight-binding (DFTB) approach for the structural analysis and electronic structure of copper hydride (CuH) metallic nanoparticles (NPs) of different size (from 0.7 to 1.6 nm). By increasing the size of CuH NPs, the number of bonds, segregation phenomena and radial distribution function (RDF) of binary Cu-Cu, Cu-H and HH interactions are analyzed using new implementations in R code. The results reveal that the number of Cu-Cu bonds is more than that of Cu-H while the number of HH bonds are the less. Thus, a large amount of H atoms prefers to connect to Cu atoms. The increase in the size of the NPs contributes to their stabilization because of the increase in the interaction of HH bonding. The segregation of Cu and H atoms shows that Cu atoms tend to co-locate at the center, while H atoms tend to reside on the surface. From the density of state (DOS) analysis, CuH NPs shows a metallic character which is compatible with experimental data. HOMO and Fermi levels decrease from -3.555 to -3.443 eV and from -3.510 to -3.441 eV. Herein, an increase in the size contributes to the stabilization of CuH NP due to decrease in the HOMO energies.