Cu-Cr Alloys Research Articles

Grain Refinement of Hypereutectic Immiscible Cu-50Cr Alloy during Rapid Melting and Solidification Induced by High Power Density Laser Beams

The microstructure of hypereutectic immiscible Cu-50Cr alloy (wt%) was effectively refined and homogenized by a high power density Nd:YAG continuous laser beam (power density 104–105 MW/m2). The average grain size of Cr was effectively refined from ~100 μm to ~1 μm, and some of the Cr particles even decreased to a few hundred nanometers. The high cooling rate (7.29 × 106 K/s) effectively inhibited the coarsening effect on Cr particles during liquid phase separation (LPS). The spherical Cr particles were preferably dispersed in the melt layer, and the thickness of the layer was up to ~150 μm. The refinement and dispersion of the Cr phase contributed to improving the interruption capability of the Cu-Cr contacts. Compared with the untreated samples, the arc duration and the withstanding voltage of the laser surface melting (LSM) treated contacts with refined microstructure increased to 21% and 33%, respectively. The results demonstrated that the LSM method was an effective approach to optimize the microstructure of Cu-Cr alloy, which made it a promising modification method for Cu-Cr vacuum contact applications.

Sliding Wear Behavior of Spark Plasma-Sintered Cu–6 Wt Pct Cr Alloy at Room and Elevated Temperatures

Although dilute Cu-Cr alloys are frequently used for applications involving sliding contacts, their wear mechanism at elevated temperatures has rarely been explored. We fabricated a bulk Cu-6 wt pct Cr alloy using high-energy ball milling and spark plasma sintering, and systematically investigated its dry sliding wear behavior against 440C stainless steel at room temperature and 300 °C. The alloy had a heterogeneous microstructure consisting of coarse-grained Cu (average grain size: 1.5 µm) distributed into a nanocrystalline Cu-Cr matrix (average Cu grain size: 77 nm; Cr-rich precipitate size: 18 nm), which gave high strength and plasticity (ultimate compressive strength: 1020 MPa; strain-to-failure: 26.0 pct) at room temperature. At 300 °C, the strength was significantly reduced, the coefficient of friction and wear rate increased, and the dominant wear mode switched from adhesive wear to oxidative/abrasive wear. Uniformly distributed nanoscale Cr-rich and Cr oxide precipitates hindered severe plastic deformation near the sliding surface during wear at room temperature; at 300 °C, severe plastic deformation was observed, with elongated Cu grains and uniformly dispersed Cr-rich and Cr oxide nanoparticles. Formation of a discontinuous glaze layer consisting of equiaxed nanograins of Cu, Cu oxides, and Cr oxides resulted in severe abrasion-assisted wear, and reduced the wear resistance at 300 °C.

Synthesis, microstructure, and hardness of rapidly solidified Cu-Cr alloys

Cu-Cr alloys with ∼32 at.% Cr were rapidly solidified by splat quenching or laser melting techniques with the intention to form a very fine grained, non-equilibrium nanostructure similar to those obtained by severe plastic deformation or thin film deposition. The rapidly solidified Cu-Cr alloys were analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Both synthesis techniques lead to a similar two-phase microstructure with a nearly pure fcc Cu matrix with μm grain sizes and bcc Cr particles highly supersaturated with Cu. Splat quenching provides finer bcc particles with dimensions of less than 50 nm compared to laser melting with particle sizes of 100–2000 nm. In case of laser melting, (14 ± 2) at.% Cu are contained in the bcc phase, while splat quenching freezes (20 ± 2) at.% Cu in the bcc particles. The microstructures are discussed and compared to the non-equilibrium microstructures reported in literature using severe plastic deformation and thin films deposition.

Microstructures and electrical and mechanical properties of Cu-Cr alloys fabricated by selective laser melting

In this study, the microstructures and electrical and mechanical properties of Cu-1.3 mass%Cr (1.3Cr) and Cu-2.5 mass%Cr (2.5Cr) alloy specimens fabricated by selective laser melting (SLM) were investigated. The effects of heat treatment on the microstructures and properties of the SLM specimens were also studied. Cu-Cr SLM specimens with a relative density of >99.7% were obtained. By annealing at 600 °C, the electrical conductivity of the SLM specimens significantly increased to maximum values of 91% IACS and 73% IACS for the 1.3Cr and 2.5Cr SLM specimens, respectively. Further, by annealing at 450 °C, the tensile strength and Vickers hardness of the SLM specimens also increased, with the tensile strength reaching maximum values of 640 and 777 MPa for the 1.3Cr and 2.5Cr SLM specimens, respectively. A close relationship was found between the changes in the properties and the nanostructures. By annealing, a fine Cr phase precipitated from the supersaturated solid solution, which formed through rapid solidification by local laser irradiation. Therefore, the electrical conductivity increased because of the decrease in the solid-solute Cr. Meanwhile, the SLM specimens were strengthened because of age hardening by the precipitation of the fine Cr phase.

Microstructure and properties of CuCr alloy manufactured by selective laser melting

CuCr alloys with Cr contents of 20 wt% and 25 wt% were prepared by selective laser melting (SLM) using mixed powders. Microstructural evolution and effect of aging on the microstructure and properties (electrical conductivity and hardness) of SLM CuCr alloys were investigated. The results show that because of rapid solidification during SLM, the Cr-rich phase can be refined to 50–800 nm, and Cu is supersaturated. The electrical conductivity and hardness were improved by an aging treatment, and both are superior to those of CuCr alloys fabricated by the current methods.

ПРОЦЕСС ОКИСЛЕНИЯ В ТЕКСТУРОВАННЫХ ТОНКИХ ЛЕНТАХ ИЗ БИНАРНЫХ СПЛАВОВ НА МЕДНОЙ ОСНОВЕ

In the present work, the authors studied the development of the oxidation process in some binary copper alloys (Cu - 40 % Ni, Cu - 30 % Ni, Cu - 1.6 % Fe, Cu - 0.4 % Cr). The authors determined the principal locations for the formation of corrosion centers on the surface of textured tape substrates of Cu-Me alloys (where Me=Ni, Cr, Fe) after annealing in an oxidizing atmosphere for 5, 30, and 250 min at the temperature of 700 °С. The study established that the oxidation of the surface of thin tapes of Cu - 0.4 % Cr and Cu - 1.6 % Fe alloys is not homogeneous, in contrast to the Cu - 40 % Ni and Cu - 30 % Ni alloys. The corrosion centers formed more intensively on the segregated particles of the alloying element - pure chromium or iron with a bcc lattice. The study discovered that the oxide film formed as a result of prolonged annealing, in Cu-Cr and Cu-Fe alloys, has a greater thickness in the zone of grain boundaries. According to the X-ray spectrum analysis, in the spectra taken from the boundaries, the higher oxygen content is registered than in the central zone of a grain. The study shows that in the textured tapes of Cu-Cr and Cu-Fe alloys, both the surface oxidation and internal oxidation of tapes occur in the process of short-term annealing (700 °С, 5 and 30 min). As a result of electron-diffraction analysis, the authors identified that, in the course of oxidation, a layer of complex spinel-type CuMe 2 O 4 (Me=Cr, Fe) oxide appears on the alloying element particles during the annealing, and the dispersed copper oxides, mainly Cu 2 O with a small quantity of CuO, are produced in the copper matrix.

Microstructure and properties of high strength and high conductivity Cu-Cr alloy components fabricated by high power selective laser melting

Although different kinds of metal materials have been built in the past years, it is difficult to fabricate the components of copper alloys with high strength and high conductivity due to their high reflectivity and thermal conductivity. In this paper, Cu-Cr alloy with high strength and high conductivity was successfully manufactured by high laser power selective laser melting. The microstructure, mechanical properties and conductivity were studied and compared before and after the heat treatment. The microstructure of the as-built sample was columnar grains with very fine cellular sub-structures and precipitates of Cr and Cr2O3. After heat treatment, the Cr particles precipitated from Cu matrix, resulting in simultaneous increase in strength and conductivity. The ultimate tensile strength of 468 MPa, yield strength of 377.33 MPa, and electrical conductivity of 98.31% IACS were achieved, which is even better than the samples fabricated by rolling with post heat treatment.

Surface nanocrystallization of Cu-Cr alloy by a high power density continuous laser beam

A nanostructured surface layer of ∼300 μm thickness was fabricated on Cu-30Cr (wt%) hypereutectic alloy by a continuous laser beam with high power density (1.08 × 107 W/cm2). The average grain size of Cr-rich particles was refined to ∼40 nm, and the solid solubility limit of Cr in Cu was extended to 1.96 at. %. Experimental results show that the dispersion of nano-sized Cr-rich spheroids in Cu-rich matrix was attributed to the Brownian motion of Cr-rich spheroids, and the high cooling rate (5.75 × 106 K/s) during liquid phase separation which inhibits the collisions between Cr-rich spheroids.

Phase separated characteristics affected by cooling rate of immiscible Cu-Cr alloy by laser surface melting

The effect of cooling rates on the solidified microstructure of Cu-50Cr (wt. %) produced by laser surface melting (LSM) was studied. Layered structure transformed into a dispersed structure when the cooling rate increased from ∼105 K/s to ∼106 K/s. The average diameter of the Cr-rich spheroids in the homogenous layer was reduced to less than 1 μm, and the migration velocity by Marangoni motion was ∼103 times higher than the velocity by Stokes sedimentation, suggesting that the movements of α-Cr droplets containing supersaturated Cu phase during liquid phase separation (LPS) were dominated by Marangoni motion. Although the collisions and coagulations between Cr droplets couldn't be eliminated, the growth was suppressed by high cooling rate. The melt layer presented improved homogenous microhardness and the well-dispersed melt layer exhibited higher withstanding voltage than that of the untreated.

Comparison of Ag and Zr with same atomic ratio in Cu-Cr alloy

In order to compare the effect of Ag and Zr with same atomic ratio on mechanical properties and electrical conductivity improvement of Cu-Cr system alloys, three alloys (CuCrZr, CuCrAg and CuCrZrAg) were prepared. And the mechanical properties and electrical conductivity during different aging process had also been studied. The results showed that the tensile strength of CuCrAg and CuCrZrAg were similar at various aging temperature better than CuCrZr. While the electrical conductivity of CuCrZr was better than others.

Analytical Modeling of Strength and Electrical Conductivity of Nanostructured Cu-Cr Alloys

The analysis of the strength characteristics and electrical conductivity of annealed Cu-1.0wt.%Cr-0.1wt%Zr alloy subjected to subsequent deformation under various conditions was carried out by analytical modeling methods. The contributions of the regions with nanotwins, as well as such defects of the crystal structure as vacancies, alloying atoms, dislocations, and particles of the secondary phase to the strength and electrical conductivity of the material were estimated.

Microstructure and properties of Cu-Cr powder metallurgical alloy induced by high-current pulsed electron beam

The purpose of paper is to investigate the microstructure and properties of Cu-Cr alloys induced by high-current pulsed electron beam (HCPEB) irradiation. Microstructure of the alloying layer was studied by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM). The microhardness and friction property were also tested. The microstructure reveals that craters were formed which were fused and eliminated to form flat surface with increase of the pulse number. Additionally, the inter-diffusion of Cu and Cr elements caused component homogenization of the surface melted layer. Besides, the fine grains/particles and Cu (Cr) solid solution were formed. Those factors accounted for a significant increase in microhardness. The lowest COF and wear rate were attributed to the ultrafine Cr particles in the hard Cu matrix.

Effect of Ag addition on the microstructure and mechanical properties of Cu-Cr alloy

Effect of Ag addition on the microstructure and mechanical properties of as-cast, cold-rolled and aging treated Cu-Cr alloys were investigated in this study. The results indicated that adding a small amount of Ag significantly improve the mechanical properties of the Cu-Cr alloys with little effect on electrical conductivity. Besides the solution strengthening mechanism of Ag, the distribution changes of Cr precipitates from the chain along grain and dendritic boundaries to homogeneously dispersed sphere in the as-cast Cu-Cr-Ag alloys, and more fibrous Cr precipitates obtained in the cold-rolled Cu-Cr-Ag alloys also played key roles in the performance improvement of the alloys. By intermediate frequency induction melting with non-vacuum melting condition, 1000 °C − 60 min solution treatment, 95% cold-rolling deformation, and 400 °C − 90 min aging treatment, the Cu-0.89Cr-0.44Ag alloy exhibited excellent mechanical-electrical properties with the tensile strength of 541.5 MPa and electrical conductivity of 83.2%IACS. Meanwhile, the Cu-0.94Cr-0.11Ag alloy showed a better cost performance (tensile strength*conductivity/raw material price per kg) about 800 MPa*%IACS/Yuan. These relevant results provided important references for research and development of the high-performance Cu-Cr-Ag alloy.

Effect of magnesium on microstructure and properties of Cu-Cr alloy

Magnesium was added into Cu-Cr alloy to overcome the traditional limitations of high-cost and large-scale manufacturing of Cu-Cr alloys and to unveil the acting mechanism of Mg on the microstructure and properties of Cu-Cr alloy. Effect of magnesium on microstructure and properties of Cu-Cr alloy has been investigated by means of hardness test, electrical conductivity measurement, transmission electron microscopy, three-dimension atom probe tomography technique and X-ray diffraction analysis. The precipitation sequence of Cu-Cr-Mg alloy was similar with that of binary Cu-Cr alloy. Additional magnesium in Cu-Cr alloy accelerated the process of precipitates nucleation, restrained the growth of the precipitates by segregating along precipitates surface during aging. This enhanced the stability of the deformation microstructure and improved the mechanical properties of the alloy. Cu-Cr-Mg alloy showed a better comprehensive properties and softening resistance performance than Cu-Cr alloy at elevated temperature. After aged at 480 °C, Cu-Cr-Mg alloy had a tensile strength of 540 MPa and an electrical conductivity of 79.2 %IACS for the peak aging states, and it still maintained a tensile strength of 515 MPa and an electrical conductivity of 80.8 %IACS after 4 h aging.

Simulation of cathode spot crater formation and development on CuCr alloy in vacuum arc

The two-dimensional (2D) rotary axisymmetric model is used to describe the formation and development of a cathode spot on a copper-chromium alloy (CuCr) in a vacuum arc. The model includes hydrodynamic equations and the heat transfer equation. Parameters used in this model come from experiments and other researchers' work. The influence of parameters is analyzed, and the simulation results are compared with pure metal simulation results. In simulation, the depth of the cathode crater is from 0.5 μm to 1.1 μm, the radius of the cathode crater is from 1.6 μm to 2.6 μm, the maximum velocity of the droplet is from 200 m/s to 600 m/s, and the maximum temperature is from 3500 K to 5000 K which is located in the area with a radius of 0.5–1.5 μm. The simulation results show that a smooth cathode surface is advantageous for reducing ablation, the ablation on the CuCr alloy is smaller than that on the pure metal cathode electrode, and the cathode spot appears on the chromium grain only on CuCr. The simulation results are in good agreement with the experiment.

Combining Cr pre-coating and Cr alloying to improve the thermal conductivity of diamond particles reinforced Cu matrix composites

Weak interface bonding inhibits high thermal conductive potential of diamonds in metal matrix composites reinforced with diamond particles (Cu/diamond composites). With an attempt to modify the Cu/diamond interface, we combine Cr pre-coating and Cr alloying to produce Cu-Cr/Cr-diamond composites by gas pressure infiltration. High resolution transmission electron microscopy (HRTEM) results reveal that Cr pre-coating on the diamond surface before infiltration promotes the formation of highly active graphite-like structures. These structures enhance the interfacial reaction and intensify the formation of a uniform and dense carbide layer on the diamond surface. By altering the Cr concentration in the Cu-Cr alloy matrix, the thickness of interfacial carbide layer is tailored. As a result, a maximum thermal conductivity of 810 W m-1 K-1 is achieved in the Cu-0.5 wt%Cr/Cr-diamond composite, which is the highest value among Cr-modified Cu/diamond composites reported so far. The high thermal conductivity is attributed to optimal interface conditions: moderate thickness of interfacial carbide layer, uniform and dense carbide layer on the diamond surface, and crystallographically aligned interfacial graphite layers. This study offers a new route to modifying interface bonding and to enhancing thermal conductivity of Cu/diamond composites.

Pore Characteristics of Lotus-Type Porous Cu-Fe and Cu-Cr Alloys Fabricated by Unidirectional Solidification.

Lotus-type porous Cu-Fe and Cu-Cr with long cylindrical pores was fabricated by centrifugal casting under hydrogen atmosphere and the effect of alloying elements on pore characteristics of lotus-type porous Cu was investigated. For the lotus type porous Cu-Fe alloy, the porosity slightly decreased and the average pore diameter slightly increased with increasing Fe content. For the lotus-type porous Cu-Cr alloy, the porosity sharply decreased and the average pore diameter drastically increased with an increase in the Cr content. From these results, it was found that the pore evolution and growth are affected by alloying element and this leads to the change in the pore characteristics of lotus-type porous Cu-Fe and Cu-Cr alloys.

Using precipitated Cr on the surface of Cu-Cr alloy powders as catalyst synthesizing CNTs/Cu composite powders by water-assisted CVD

Given that the conventional catalyst is easily soluble in the matrix to result in the poor performance of the CNTs/Cu composite materials, the Cr nano-particles precipitated on the surface of Cu-Cr particles are first used as catalysts to prepare the CNTs/Cu composite powders by means of water-assisted chemical vapor deposition in situ synthesis. The results show that the morphological difference of the precipitated Cr nano-particle is obvious with the change of solution and aging treatment, and the morphology, length and diameter of the synthetic CNTs are also different. The catalyst of Cr nano-particle has the best morphology and the synthesized CNTs had a good wettability with Cu particles when the Cu-Cr composite powders was solution-treated at 1023 K for 60 min and then was aged at 723 K for 120 min. The length, diameter, yield and purity of the synthesized CNTs can be also affected by the moisture content in the reaction gas. It is the most suitable for the growth of CNTs when the moisture content is 0.4%, and the high purity and defect-free CNTs with the smooth pipe wall, a diameter of 20 ∼ 30 nm and a length of up to 1800 nm can be obtained. The yield of CNTs with the moisture content of 0.4% reached to 138%, which was increased by 119% to compare with that without moisture. In this paper, a feasible technology was offered for the preparation of high performance CNTs/Cu composites.

Graphite fiber/copper composites prepared by spontaneous infiltration

The major bottleneck in developing graphite fiber reinforced copper (GF/Cu) composites is the poor wettability of Cu/graphite system. Alloying element of chromium (Cr) is introduced to improve the wettability of liquid copper on graphite. Sessile drop method experiments illustrate that the contact angle of liquid Cu-Cr (1.0 wt.%) alloy on graphite substrate decreases to 43° at 1300 °C. The improvement of wettability is related to the formation of chromium carbide layer at interface zone. Based on the wetting experiment, a spontaneous infiltration method for preparing GF/Cu composites is proposed. Unidirectional GF preforms are infiltrated by Cu-Cr alloys without external pressure in a tubular furnace. Results reveal that the GF preform can be fully infiltrated by Cu-Cr alloy (8 wt.%) spontaneously when fiber volume fraction is 40%. The coefficient of thermal expansion (CTE) of GF/Cu-Cr (8.0 wt.%) composites is 4.68 × 10−6/K along the longitudinal direction.

Investigation on the microstructure and properties of Cu-Cr alloy prepared by in-situ synthesis method

In this work, Cu-Cr alloys have been prepared by reducing reaction of Cr2O3 with Cu-Mg melt. The thermodynamic analysis of the reaction system and the microstructures of alloys were carried out. The results show that Cu-Cr alloys with around 0.57 wt%∼4.92 wt% chromium content can be prepared by in-situ synthesis technique. And Cr particles with anomalies forms have been observed, which illustrated that part of Cr particles is not formed by classical nucleation and crystal growth. In addition, the influence of thermomechanical treatments on microstructure and properties of the Cu–Cr alloy was also discussed. The results show that cold rolled before aging can accelerate the speed of decomposition of Cr from supersaturated matrix and finer precipitates are obtained in CR-80%-A sample than STA sample. Moreover, the good combination of the properties, such as microhardeness of around 171HV, tensile strength of around 475 MPa as well as electrical conductivity of around 86.2% IACS were obtained in CR-80%-A sample.