Effect of equal-channel angular pressing on the precipitation kinetics in Cu-Cr-Hf alloys

Fu H., Xu S., Li W., Xie J., Zhao H., Pan Z.

The effects of rolling deformation, rolling temperature and aging treatment on microstructure and mechanical properties of Cu-Cr-Zr alloy were investigated and the relevant influencing mechanism was also discussed in this study. The results showed that the tensile strength of the Cu-Cr-Zr alloy increased with an increase of rolling deformation at room temperature. The elongation to failure of the alloy decreased until the rolling reduction is up to 80% and then increased with the reduction, which is related to the grain orientation change from Copper texture with poor plasticity to the Goss/Brass texture with good plasticity. A large amount of Cr precipitates were identified during rolling at 300 °C in Cu-Cr-Zr alloy, which resulted in much higher electrical conductivity and tensile strength exceeded that of the room-temperature rolling with the rolling reduction over 80%. Aging treatment of 450 °C for 1 h led to the formation of massive Cr and Cu 4 Zr precipitates, which can significantly improve the tensile strength from 591.1 MPa to 669.1 MPa and electrical conductivity from 30.3%IACS to 74.5%IACS of the room-temperature rolled alloy. These results provide a guideline for exploring efficient preparation methods of high-performance Cu-Cr-Zr alloys.

Suzuki H., Kanno M.

Dobatkin S.V., Bochvar N.R., Shangina D.V.

The aging processes in Cu-0.7% Cr, Cu-0.9% Hf, and Cu-0.7% Cr-0.9% Hf alloys after equal channel angular pressing have been studied. ECAP leads to strong grain refinement (200 nm for Cu-0.7% Cr-0.9% Hf alloy). It was shown that the Cu5Hf particles are more efficient as strengthening phase than the particles of Cr-based solid solution. Alloying with hafnium also improves the thermal stability of hardening and minimizes recrystallization processes at aging temperatures. Temperature-time aging regimes of bronzes for achieving optimal combination of strength, ductility, and electrical conductivity were also determined. Ternary alloy after aging at 500 °C for 2.5 h has a tensile strength of 582 MPa, an elongation of 18%, and an electrical conductivity of 75% IACS.

Shangina D., Maksimenkova Y., Bochvar N., Serebryany V., Raab G., Vinogradov A., Skrotzki W., Dobatkin S.

Equal channel angular pressing (ECAP) results in grain-subgrain structure formation in Cu0.75 %Cr alloy with the average size of structure elements of 320 ± 73 nm Addition of hafnium into the Cu-Cr alloy leads to decrease of average size down to 225±82 nm and to increase of the high angle boundaries fraction from 40% to 53%. Microhardness of the Cu-0.7 %Cr-0.9 %Hf alloy is higher, than of the Cu-0.75 %Cr alloy, as after ECAP, so after heating when the aging processes occur in the temperature interval 400–550 °С. The strength in the tension tests of the Cu-0.7 %Cr-0.9 %Hf alloy after ECAP rises in 2.2 times compared with the quenched state. The aging leads to additional strength growth by 19%.

Wongsa-Ngam J., Kawasaki M., Langdon T.G.

Experiments were conducted on a Cu–0.1% Zr alloy to evaluate the potential for achieving homogeneity when processing by equal-channel angular pressing (ECAP). Billets of the alloy were processed by ECAP for up to 8 passes at room temperature using a die with a channel angle of 110°. This processing reduced the grain size from an initial value of ∼30 μm to a value of ∼500 nm after 8 passes. Values of the Vickers microhardness were recorded on both the cross-sectional or X planes and the longitudinal or Y planes after ECAP. The results reveal the presence of lower hardness values adjacent to the lower surfaces of the billets in the early stages of processing but there is an evolution towards a hardness homogeneity throughout the billets after pressing through 8 passes. The measurements show this evolution occurs at similar rates on the X and Y planes.

Chbihi A., Sauvage X., Blavette D.

The early stage of chromium precipitation in copper was analyzed at the atomic scale by atom probe tomography (APT). Quantitative data about the precipitate size, three-dimensional shape, density, composition and volume fraction were obtained in a Cu–1Cr–0.1Zr (wt.%) commercial alloy aged at 713 K. Surprisingly, nanoscaled precipitates exhibit various shapes (spherical, plates and ellipsoid) and contain a large amount of Cu (up to 50%), in contradiction to the equilibrium Cu–Cr phase diagram. APT data also show that some impurities (Fe) may segregate along Cu/Cr interfaces. The concomitant evolution of the precipitate shape and composition as a function of the aging time is discussed. Special emphasis is given to the competition between interfacial and elastic energy, and to the role of Fe segregation.

Jayakumar P.K., Balasubramanian K., Rabindranath Tagore G.

The structure, thermal stability and diffusion bonding behaviour of oxygen free high conductivity copper (OFHC), and Cu–Cr–Zr alloy (CRZ) with ultra fine grains (UFG) produced by severe plastic deformation through equal-channel angular pressing (ECAP) are investigated. Microstructural study reveals a grain refinement from 150 μm to 200 nm sized grains after 8 ECAP passes. Thermal stability of ECAP processed OFHC and CRZ has been investigated. Both OFHC and CRZ show hardness reduction at temperatures above 100 °C. However CRZ exhibits grain size stability up to a temperature of 500 °C. Diffusion bonding studies reveal that bond strengths of ∼54 MPa are developed between ECAP processed CRZ and OFHC at a lower temperature of 500 °C when compared to annealed materials.

León K.V., Muñoz-Morris M.A., Morris D.G.

The microstructure and mechanical behaviour of a Cu–Cr–Zr alloy has been examined after severe plastic deformation, and giving both prior and subsequent age hardening treatments. Dislocation subgrain structures are produced by deformation leading to high strength and reduced ductility. Mild annealing following deformation leads to slight substructural coarsening, some loss of dislocations, and simultaneous precipitation, resulting in an increase of strength with some improvement of ductility. The same heat treatments for precipitation before deformation lead to finer substructures, with shear reducing particle size and leading to partial dissolution. Strength and ductility are analysed in terms of the deformation substructures and the role of precipitate particles.

Liu Q., Zhang X., Ge Y., Wang J., Cui J.

A new series of Cu-Cr-Zr alloys to be used as railway contact wire, Cu-0.26 wt pct Cr-0.15 wt pct Zr, Cu-0.13 wt pct Cr-0.41 wt pct Zr, and Cu-0.34 wt pct Cr-0.41 wt pct Zr, were studied. The results indicated that processing and aging treatment had an effect on the microstructure, tensile strength, and electrical conductivity behavior of the Cu-Cr-Zr alloys. Process I (solution treatment + cold work + aging) was superior to process II (cold work + solution treatment + aging), because precipitation can occur heterogeneously at the dislocations and subcells. An appropriate processing and aging treatment may improve the properties of the alloys due to the formation of fine, dispersive, and coherent precipitates within the matrix. It is demonstrated that the best combination of tensile strength and electrical conducitivity, on the order of 599 MPa and 82 pct IACS (International Annealed Copper Standard), respectively, can be obtained in alloy Cu-0.34 wt pct Cr-0.41 wt pct Zr in the solution-heat-treated, cold-worked, and aged condition. The mechanism of tensile and conductive properties of Cu-Cr-Zr alloy is also discussed.

VINOGRADOV A., ISHIDA T., KITAGAWA K., KOPYLOV V.

The effect of strain path during severe plastic deformation via equal-channel angular pressing on grain refinement and structural features of a model Cu–Cr alloy is investigated in terms of grain shape, dimensions, preferred crystallographic orientation and distribution of grain boundaries with respect to the angle of misorientation. The mechanical behavior of differently processed specimens is assessed in both monotonic and cyclic tests aimed at clarification of the role played by different structural factors in the resultant mechanical properties. It is shown, that despite the considerable microstructural differences in the grain morphology and texture, the tensile and fatigue strength is only slightly affected by the processing routes chosen in the present study. However, the strain path and, therefore, the grain shape and texture have some effect on ductility and strain localization, which is particularly pronounced during cyclic loading.

Vinogradov A., Patlan V., Suzuki Y., Kitagawa K., Kopylov V.I.

The structure, thermal stability and properties are investigated of a Cu–Cr–Zr alloy with ultra fine grains (UFG) of 160 nm diameter produced by severe plastic deformation through equal-channel angular pressing (ECAP). Special attention is paid to optimization of multi-functional thermal, electrical and mechanical properties of this alloy by aging after ECAP. Fatigue life and cyclic response under strain-controlled experiments are investigated aiming at clarification of mechanisms of plastic deformation and fracture in the precipitation hardened ECAP materials. It is shown that the precipitation strengthened UFG structure remains stable both under elevated temperatures as high as 500°C and under cyclic loading at room temperature. Substantial improvement of fatigue life is evidenced in comparison with conventional coarse-grain materials. The appearance of cyclic softening is noticed and its nature is discussed in terms of dislocation–particle interaction and possible dissolution of precipitates during fatigue.

Dölling J., Gruber S., Kovermann F., Stepien L., Beeh E., Lopez E., Leyens C., Wobker H., Zilly A.

Copper alloys with chromium and hafnium offer the possibility of precipitation hardening and combine enhanced strength with high electrical and thermal conductivities. The production process, which starts with raw materials, involves powder production by gas atomization and leads to additive manufacturing by laser powder bed fusion with different parameter sets. The aim is to utilize precipitation reactions afterwards in CuHf0.7Cr0.35 during temperature exposure for further property optimization. This research focuses on the low-alloyed copper alloy with hafnium and chromium, compares this with conventionally manufactured specimens, and relates the alloy to additively manufactured specimens of other benchmark alloys such as CuCr1Zr. Measurements of hardness and electrical conductivity are accompanied by metallographic investigations to understand the behavior of CuHf0.7Cr0.35 manufactured by generative methods. In the as-built condition, melting traces remain visible in the microstructure, and hardness values of 101 HV and an electrical conductivity of 17.5 MS/m are reached. Solution annealing completely recrystallizes the microstructure, and the following quenching holds further alloying elements in supersaturated solid solution, resulting in 73 HV and 16.5 MS/m. Subsequent target-oriented precipitation reactions enable peak values of about 190 HV and 42 MS/m. Future research will assess mechanical and physical properties at elevated temperatures and evaluate possible applications.

Dölling J., Kuglstatter M., Prahl U., Höppel H.W., Ortner P., Ott B., Kracun S.F., Fehlbier M., Zilly A.

Copper alloys containing chromium and hafnium combine elevated mechanical strength and high electrical and thermal conductivity. For the simultaneous enhancement of both material properties, precipitation hardening is the utilized mechanism. Therefore, the aim is to analyze the influence of chromium and hafnium in binary and ternary low-alloyed copper alloys and to compare the precipitation processes during temperature exposure. Atom probe tomography (APT) and differential scanning calorimetry (DSC) measurements enable to understand the precipitation sequence in detail. CuCr0.7 starts to precipitate directly, whereas CuHf0.7 is highly influenced by prior diffusion facilitating cold rolling. Within the ternary alloy, hafnium atoms accumulate at the shell of mainly Cr-containing precipitates. Increasing the local hafnium concentration results in the formation of intermetallic CuHf precipitates at the sites of mainly Cr-containing precipitates. Indirect methods are utilized to investigate the materials’ properties and show the impact of cold rolling prior to an aging treatment on binary alloys CuCr and CuHf. Finally, ternary alloys combine the benefits of facilitated precipitation processes and decelerated growing and coarsening, which classifies the alloys to be applicable for usage at elevated temperatures.

Zhang X., Jiang Y., Cao F., Yang T., Gao F., Liang S.

A dual-scale hybrid HfB2/Cu-Hf composite with HfB2 microparticles and Cu5Hf nanoprecipitates was designed and prepared. The contribution of the hybrid effect to the mechanical properties and high-temperature performances was studied from macro and micro perspectives, respectively. The hybrid of dual-scale particles can make the strain distribution of the composite at the early deformation stage more uniform and delay the strain concentration caused by the HfB2 particle. The dislocation pinning of HfB2 particles and the coherent strengthening of Cu5Hf nanoprecipitates simultaneously play a strengthening role, but the strength of the hybrid composite is not a simple superposition of two strengthening models. In addition, both Cu5Hf nanoprecipitates and HfB2 microparticles contribute to the high-temperature performance of the composite, the growth and phase transition of nanoprecipitates at high temperature will reduce their contribution to strength, while the stable HfB2 particles can inhibit the coarsening of matrix grains and maintain the high-density geometrically necessary dislocations (GNDs) in the matrix, which ensures more excellent high-temperature resistance of the hybrid composite. As a result, the hybrid structure can simultaneously possess the advantages of multiple reinforcements and make up for the shortcomings of each other. Finally, a copper matrix composite with high strength, high conductivity, and excellent high-temperature performance is displayed.

Martynenko N., Rybalchenko O., Straumal P., Tabachkova N., Lukyanova E., Rybalchenko G., Prosvirnin D., Beletsky E., Prokofiev P., Yusupov V., Dobatkin S., Straumal B.

The effect of cold rotary swaging (RS) and subsequent aging on the structure, electrical conductivity, mechanical characteristics and fracture toughness of the Cu-0.77%Cr-0.86%Hf alloy was studied. RS leads to the formation of a microstructure elongated along the direction of deformation with grains width of 8.0 ± 0.2 μm. An ultrafine-grained structure with shear bands of 370 ± 10 nm in width and subgrains of 500 ± 13 nm in size is formed inside these elongated grains. The refinement of the microstructure after RS leads to an increase in ultimate tensile strength (UTS) from 300 ± 5 to 505 ± 12 MPa and a decrease in ductility from 54.0 ± 2.4 to 12.9 ± 0.3%. A subsequent aging of the alloy leads to the precipitation of fine particles of Cr and Cu5Hf phases. The precipitation of these particles leads to an additional increase in UTS of RS-treated alloy up to 558 ± 11 MPa and ductility up to 15.4 ± 2.4%. In this case, the decomposition of the supersaturated solid solution, which accompanies the particles precipitation, leads to an increase in the electrical conductivity of the deformed alloy up to 77.7 ± 1.6%IACS. The combination of RS and subsequent aging at a temperature of 450 °C for 4 h leads to an increase in the fatigue limit from 220 to 393 MPa. In addition, this treatment allows to increase the fracture toughness coefficient by 6 times.

Shi B., Hong D., Wang W., Su L., Wang C., Xiao L., Ma T., Zhou J.

The Cu‐1.1 wt.% Hf‐0.1 wt.% Si alloy containing various precipitates was studied as a novel precipitation‐strengthened alloy with high strength and high electrical conductivity. The Cu‐Hf‐Si alloy prepared by solution, cold rolling and aging processes, exhibits a hardness of 238.92 HV, a tensile strength of 691.01 MPa, a breaking elongation of 15.09 % and an electrical conductivity of 62.34 % IACS. The optimal peak aging parameter for Cu‐Hf‐Si alloy is 430 °C for 90 min. The precipitation of Hf and Si atoms from the Cu matrix is helpful to enhance the electrical conductivity. The precipitation of Hf can produce fibrous G.P. zone and γ' precipitate, as well as spherical Cu10Hf7 phases. In addition, the co‐precipitation of Si and Hf can also produce Hf3(Cu2Si)2 and HfCuSi phases. The high strength of Cu‐Hf‐Si alloy is mainly due to the multi‐precipitates synergistic strengthening.This article is protected by copyright. All rights reserved.

Rybalchenko O.V., Bochvar N.R., Rybalchenko G.V., Martynenko N.S., Tabachkova N.Y., Dobatkin S.V.

The kinetics of phase precipitation during aging in the Cu – Cr – Hf and Cu – Cr – Zr alloys after high pressure torsion (HPT) has been studied and compared with quenching state. The effect of HPT on the kinetics of aging was revealed by the differential scanning calorimetry (DSC) and confirmed by changes in the microhardness and electrical resistivity. Analysis of the microstructure and phase precipitation after HPT and subsequent aging using a transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) revealed three types of phases in each of the alloys: Cu matrix, chromium and zirconium- or hafnium-rich phases. By measuring the microhardness, a higher degree hardening after HPT and subsequent aging was revealed in the Cu – Cr – Hf alloy compared to the Cu – Cr – Zr alloy.

Guo T., Qian D., Huang D., Li K., Gao Y., Ding Y.

Cu-0.6Cr alloy was extruded by liquid nitrogen cooling equal channel angular pressing (ECAP) route-Bc and aging treated at 400 °C–500 °C; the structure and orientation distribution of the alloy were detected by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), electron back-scattered diffraction (EBSD) and TEM. The purpose is to detect the influence of deformation conditions and aging treatment on the microstructure and properties of the materials, and to analyzed the microscopic mechanism of the precipitates formation process and transformation. The results show that the cryo-ECAP-Bc deformation will accelerate the interaction between the microstructure and texture of the Cu-0.6Cr alloy, and reduce the limitation size of the grains after deformation. Strain increase can promote increasing the amounts of micro/nano precipitates discontinuous distribution on the grain boundaries. After 4 passes of extrusion and aging at 450 °C, the tensile strength, hardness and elongation of the material reach to 555.0 MPa, HV 167.3 and 13.1%, respectively, and the conductivity exceeds 84%IACS. The synergistic effect of microalloying, solid solution, cryo-ECAP and aging, and the formation of {111} <112> and {111} <110> textures are beneficial to improving the conductivity of the alloy simultaneously.

Martynenko N.S., Bochvar N.R., Rybalchenko O.V., Prosvirnin D.V., Rybalchenko G.V., Kolmakov A.G., Morozov M.M., Yusupov V.S., Dobatkin S.V.

Abstract—The structure, electrical conductivity, and mechanical properties (including fatigue strength) of a Cu–0.8% Hf alloy after rotary swaging (RS) at various strains and subsequent aging are investigated. RS is shown to cause the formation of a microstructure elongated in the deformation direction. When the strain increases, the average grain width decreases and grains acquire an increasingly elongated shape. After RS at ε = 2.77, the formation of an ultrafine-grained structure with an average subgrain size of 173 ± 12 nm is observed inside the elongated grains. When the strain increases, the strength of the alloy increases and the plasticity decreases. Subsequent aging causes an increase in the strength of the quenched alloy and the alloy after RS at ε = 0.58 and 1.39; hardening is absent after RS at ε = 2.77. In all cases, aging increases the electrical conductivity of the alloy as a result of the decomposition of a supersaturated solid solution and the precipitation of the Cu5Hf phase. The best combination of the mechanical and functional properties is achieved after RS at ε = 2.77 and subsequent aging at 475°C for 2 h: the ultimate tensile strength is 461 ± 28 MPa, the ductility is 12.5 ± 2.4%, the fatigue limit is 325 MPa, and the electrical conductivity is 90.4 ± 1.9% IACS.

Dölling J., Kracun S.F., Prahl U., Fehlbier M., Zilly A.

Copper alloys with chromium, hafnium, and scandium combining enhanced strength as well as high electrical and thermal conductivity are analyzed in depth. The aim is to compare the precipitation process during temperature exposure to meet increasing material requirements. This research focuses on alloying elements having a limited, maximum 1 wt.%, and with temperature decreasing solubility in copper. For the simultaneous enhancement of mechanical strength and conductivity, precipitation hardening is the utilized mechanism during the processing of as-casted annealed and quenched specimens and in combination with optional cold-rolling prior to the aging process. Extensive DSC measurements, accompanied by metallographic investigations, and the analysis of hardness and electrical conductivity, lead to a versatile description and comparison of different alloying systems. CuCr0.7 starts to precipitate early and is mainly influenced by the temperature of aging. Provoking the solid solution with cold deformation has a less significant influence on the following precipitation. CuSc0.3 and CuHf0.7 precipitate at higher temperatures and are highly influenced by cold deformation prior to aging. Furthermore, CuHf0.7 and CuSc0.3 show advantages regarding the recrystallization behavior, making them especially applicable for higher operating temperatures. Future research will assess ternary alloy combinations to further scoop the potential.

Alateyah A.I., El-Shenawy M., Nassef A., El-Hadek M., Ahmed M.M., Kouta H., El Sanabary S., El-Garaihy W.H.

Abstract The main aim of the current work is to investigate the effect of equal channel angular pressing (ECAP) processing parameters, namely, number of passes, ECAP die angle, route type, and processing temperature on the mechanical and electrical properties of pure copper (Cu). The finite element method was used to simulate the homogeneity of stress and plastic strain distribution during ECAP processing. The response surface methodology (RSM) was used to identify the optimum ECAP processing parameters by analyzing the impact of ECAP conditions on responses. A second-order regression model and analysis of variance were created to analyze the ECAP condition of optimum responses. A genetic algorithm (GA) was also applied to optimize the ECAP condition. Finally, a hybrid RSM–GA was created to improve the optimization of ECAP responses and corresponding conditions evaluated using GA. The developed models were validated and compared with the experimental findings to prove that they are reliable as predictive tools. The optimization findings revealed that route Bc was more effective in improving the hardness, yield stress, ductility, and impact energy whereas route A was more effective in improving the ultimate tensile strength and the electrical conductivity of the Cu billets. Furthermore, the optimum die angle, number of passes, and processing temperature for the mechanical and electrical properties were also identified individually.

Rybalchenko O., Anisimova N., Martynenko N., Rybalchenko G., Kiselevskiy M., Tabachkova N., Shchetinin I., Raab A., Dobatkin S.

In this work, a Fe–Mn–Pd alloy was produced by methods of equal channel angular pressing (ECAP) in order to obtain an alloy with a high rate of degradation for the development of biodegradable devices. Special efforts were made to the obtaining of an ultrafine-grained structure of alloys in a fully austenitic state at temperatures of 300 °C and 450 °C. Further investigation of its effect on the corrosion rate and mechanical properties was carried out. The formation of an austenitic structure with structural element sizes of 100–250 nm after deformation was confirmed by X-ray diffraction analysis. ECAP proved to be the reason for a significant increase in strength with maximum σUTS = 1669 MPa and σYS = 1577 MPa while maintaining satisfactory plasticity. The alloy degradation rate was investigated using the potentiodynamic polarization analysis. The corrosion rate of the alloy after ECAP (~1 mm/y) is higher than that of the coarse-grained state and significantly higher than that of annealed iron (~0.2 mm/y). ECAP in both modes did not impair the biocompatibility of the Fe–Mn–Pd alloy and the colonization of the sample surface by cells.

Shaban M., Alsharekh M.F., Alsunaydih F.N., Alateyah A.I., Alawad M.O., BaQais A., Kamel M., Nassef A., El-Hadek M.A., El-Garaihy W.H.

Copper and its related alloys are frequently adopted in contemporary industry due to their outstanding properties, which include mechanical, electrical, and electronic applications. Equal channel angular pressing (ECAP) is a novel method for producing ultrafine-grained or nanomaterials. Modeling material design processes provides exceptionally efficient techniques for minimizing the efforts and time spent on experimental work to manufacture Cu or its associated alloys through the ECAP process. Although there have been various physical-based models, they are frequently coupled with several restrictions and still require significant time and effort to calibrate and enhance their accuracies. Machine learning (ML) techniques that rely primarily on data-driven models are a viable alternative modeling approach that has recently achieved breakthrough achievements. Several ML algorithms were used in the modeling training and testing phases of this work to imitate the influence of ECAP processing parameters on the mechanical and electrical characteristics of pure Cu, including the number of passes (N), ECAP die angle (φ), processing temperature, and route type. Several experiments were conducted on pure commercial Cu while altering the ECAP processing parameters settings. Linear regression, regression trees, ensembles of regression trees, the Gaussian process, support vector regression, and artificial neural networks are the ML algorithms used in this study. Model predictive performance was assessed using metrics such as root-mean-squared errors and R2 scores. The methodologies presented here demonstrated that they could be effectively used to reduce experimental effort and time by reducing the number of experiments runs required to optimize the material attributes aimed at modeling the ECAP conditions for the following performance characteristics: impact toughness (IT), electrical conductivity (EC), hardness, and tensile characteristics of yield strength (σy), ultimate tensile strength (σu), and ductility (Du)

Martynenko N.S., Rybal’chenko O.V., Rybal’chenko G.V., Ogarkov A.I., Bazhenov V.E., Koltygin A.V., Belov V.D., Dobatkin S.V.

Bodyakova A., Tkachev M., Raab G.I., Kaibyshev R., Belyakov A.N.

The effect of severe plastic deformation by the conforming process of equal channel angular extrusion (ECAE-Conform) followed by cold rolling on the microstructures developed in a Cu-0.1Cr-0.1Zr alloy was investigated. Following the ECAE-Conform of 1 to 8 passes (corresponding strains were 0.8 to 6.4) cold rolling to a total strain of 4 was accompanied by substantial grain refinement and strengthening. An average grain size tended to approach 160 nm with an increase in the rolling reduction. An increase in the ECAE-Conform strain promoted the grain refinement during subsequent cold rolling. The fraction of the ultrafine grains with a size of 160 nm after cold rolling to a strain of 4 increased from 0.12 to 0.52 as the number of ECAE-Conform passes increased from 1 to 8. Correspondingly, the yield strength increased above 550 MPa. The strengthening could be expressed by a Hall–Petch type relationship with a grain size strengthening factor of 0.11 MPa m0.5.

Martynenko N.S., Bochvar N.R., Rybalchenko O.V., Bodyakova A.I., Morozov M.M., Leonova N.P., Yusupov V.S., Dobatkin S.V.

The effect of rotary swaging (RS) at various strains and subsequent aging at various temperatures on the structure and the mechanical properties of a Cu–0.5% Cr–0.08% Zr alloy is studied. RS is shown to form a microstructure with grains extended along the deformation axis. The grain size decreases with increasing strain. Subgrains 300–400 nm in size and shear bands 200 nm in width are observed inside the elongated grains formed upon RS at ε = 2.77. Microstructural refinement significantly increases the strength of the alloy but decreases its plasticity. Subsequent aging further increases the strength and the electrical conductivity of the alloy due to the precipitation of fine chromium and Cu5Zr-phase particles. Quenching, RS at ε = 2.77, and subsequent aging at 500°C for 1 h result in the best combination of strength (557 ± 18 MPa), plasticity (17.1 ± 2.6%), and electrical conductivity (83.4 ± 1.6% IACS) of the Cu–0.5%Cr–0.08%Zr alloy.