Dynamic Channel Angular Pressing Research Articles

Strength-ductility synergy in twinned titanium fabricated via dynamic equal channel angular pressing and heat treatment

Dynamic equal channel angular pressing (DECAP) and heat treatment are applied to pure Ti to achieve a strength-ductility synergy. DECAP induces a complex multiscale twin structure in Ti including four primary twin types, secondary twins and tertiary twins with multiple variants, and an increased yield strength (58% higher than the as-received Ti). Subsequent annealing at 200 ℃ and 400 ℃ leads to improved ductility and strength. The yield strength (σy) and total elongation (ɛt) for the Ti sample processed with DECAP and 400 ℃ annealing are 555 MPa and 30%, respectively, and its σyɛt product is ∼45% higher than the as-received Ti. DECAP and subsequent annealing lead to a superior strength-ductility synergy in twinned Ti, providing a novel approach to produce high strength and ductility materials via dynamic deformation and subsequent heat treatment.

The Dynamic Properties of Low-Alloyed Copper Alloys with a Submicrocrystalline Structure Obtained by High-Strain-Rate Deformation

Abstract—The mechanical properties of alloys Cu–0.03 wt % Zr and Cu–0.10 wt % Cr with a submicrocrystalline structure formed during dynamic channel-angular pressing and subsequent annealing. The properties of the alloys were studied under shock compression conditions with a pressure of 4.7–7.0 GPa and a deformation rate of (1.3–3.2) × 105 s–1. It is shown that grain grinding from 200–400 to 0.3–1.0 microns increases the dynamic elastic limit and the dynamic yield strength of the Cu–0.03% Zr alloy by 1.9 and 1.8 times, respectively, but reduces the shear strength by 1.4 times. Subsequent annealing at 400 and 450°C can increase the characteristics of the elastic-plastic transition by 3.0 and 3.7 times, respectively, and increase the shear strength to the level of a large-crystal analog. It is determined that the dispersion of the Cu–0.10% Cr alloy structure to 1.0–5.0 microns increases not only the dynamic elastic limit and dynamic yield strength by 3.7 and 2.6 times, respectively, and the shear strength by 1.5 times, compared with its value in the coarse-grained state.

Ultrafast severe plastic deformation in high-entropy alloy [formula omitted] via dynamic equal channel angular pressing

An extensively investigated high-entropy alloy (HEA), Al0.1CoCrFeNi, is processed by dynamic equal channel angular pressing (D-ECAP) and subsequent annealing. Severe shear deformation and ultrahigh strain rate give rise to simultaneous activation of the {111}〈112〉 macro deformation twins and kink bands with the 〈110〉 or 〈112〉 rotation axes. Secondary kink bands are also observed in primary kink bands. With increasing annealing temperature, the deformation twins and kink bands both become less or disappear. The yield strength is increased by ∼255% solely by D-ECAP compared to the as-cast HEA. A reasonable combination of high strength and good ductility is achieved through annealing twins in recrystallized grains via annealing the D-ECAP-processed alloy at 900 °C. It is the first observation on kink bands within a face-centered cubic HEA under various loading conditions. The strengthening in these D-ECAP-processed samples before and after annealing is discussed in terms of grain boundary strengthening and dislocation strengthening.

Исследование локализации пластической деформации слоистых металл-интерметаллидных композитов при динамическом канально-угловом прессовании

The method of mathematical modeling has been used to study the processes of plastic deformation localization of layered metal-intermetallic composites under dynamic channel-angular pressing. The deformation patterns of single-phase intermetallic samples and layered composites samples with the different arrangement of layers relative to the compression axis have been compared. The calculated stress-strain curves have been obtained. Three-dimensional modeling has been carried out on the basis of an approach combining two methods for the plastic flow description through the kinetics of deformation defects storage and the solid state mechanics. The numerical solution of the model equations has been carried out by the finite element method.

Microstructure evolution and peculiarities of strain hardening in aluminum processed by dynamic channel angular pressing

A study of aluminum subjected to high-rate shear deformation via dynamic channel angular pressing (DCAP) has been performed to investigate the main patterns of microstructure evolution and the peculiarities of strain hardening. A principal feature of the microstructure formed during the first DCAP pass is the occurrence of large misorientation deformation bands. Examination of their constitution and crystallography showed that at least some of them appear to be a product of deformation twinning. No indications of twinning were however found in the microstructure after 4 DCAP passes. At this stage of the processing, grain refinement occurs mainly through ordinary fragmentation, namely, a subdivision of crystallites into regions, whose misorientations gradually increase from low-angle to high-angle ones, while the role of deformation bands becomes less distinct. Nevertheless, despite considerable grain refinement, about 80% of strengthening after 4 DCAP passes is provided by the dislocation substructure, while the contribution of high-angle boundaries to the strengthening remains low.

Thermal stability of hafnium bronze subjected to dynamic channel angular pressing

Thermal stability of the structure of Cu-0.8%Hf alloy subjected to severe plastic deformation by 2 passes of dynamic channel angular pressing (DCAP) has been investigated. It is demonstrated that after such deformation the microstructure of the hafnium bronze is non-uniform, where areas of cell structure are neighboring with thin-lamellar structure of twinning type. Such structure indicates the action of two deformation mechanisms, dislocation sliding and twinning. It has been revealed that doping with hafnium has considerably affected susceptibility of copper to relaxation processes under the DCAP and following annealing. It has been found that the microstructure formed under the deformation can be retained at the annealing up to 500°C without noticeable changes, and the microhardness changes only slightly in this temperature range. At the same time, at heating up to 600°C and higher the relaxation processes are developed in the structure which is accompanied with a drastic drop of microhardness.

Influence of the Initial Treatment on the Structure of Hafnium Bronze upon High-Speed Pressing

It is shown that initial treatment (quenching or annealing) has a significant effect on the evolution of the structure of hafnium bronze upon dynamic channel-angular pressing (DCAP). Upon annealing, hafnium becomes bound into particles of the intermetallic compound Cu5Hf, and the annealed samples are only insignificantly strengthened upon DCAP. Upon quenching, Hf remains in the solid solution, and the strengthening effect upon DCAP is much greater. Twinning becomes the main deformation mechanism for quenched bronze upon DCAP.

Modeling of Plastic Flow Localization and Crack Formation in Dynamic Channel Angular Pressing

The paper studies the phenomenon of localized-deformation macrobands and crack formation in metal alloys under dynamic channel-angular pressing. The numerical calculations are carried out using a threedimensional model of plastic deformation, which combines mathematical models of dislocation kinetics and mechanics of solids. Various scenarios of strain hardening the deformable medium element and the geometry of pressing channels are considered in relation to localized-deformation macrobands and crack formation during dynamic channel angular pressing. It is shown that non-monotonous strain hardening of the deformable medium element and the angle of channel connection are the important factors that form localized-deformation macrobands and cracks.

Dynamic Strength of Submicrocrystalline and Nanocrystalline Copper Obtained by High-Strain-Rate Deformation

Abstract—The dynamic properties of commercial copper (99.8 wt % purity) with a submicrocrystalline and nanocrystalline structure obtained by high-strain-rate deformation using the dynamic channel-angular pressing (DCAP) method have been studied in this work. The tests were carried out under conditions of shock compression at a pressure of 5.6−6.8 GPa at a strain-rate of (0.9−2.0) × 105 s–1. The analysis of the evolution of the structure and mechanical properties, namely, the dynamic elastic limit, dynamic yield stress, and the spall strength of copper before and after DCAP in different regimes, made it possible to evaluate the influence of the dispersity and imperfection of the crystal structure on its resistance to the high-strain-rate deformation and fracture. It has been shown that the grain refinement from 100 to 0.5−1.0 μm increased the dynamic elastic limit and the dynamic yield stress of copper by six times, but only slightly decreased the spall strength. The further refinement of the structure (up to 0.05−0.40 μm) increases the spall strength of copper by 1.4 times as compared to its value in the initial coarse-grained state.

Orientation-dependent microstructure development during high-rate shear deformation of copper

ABSTRACT The microstructure transformations in copper subjected to high-rate deformation via dynamic channel angular pressing (DCAP) have been examined after one and four DCAP passes using electron backscattering diffraction. The focus was on the interrelation between microstructure and texture evolution and on the role of deformation twinning in these processes. During the first pass, a mesoscopic banding is shown to be the main mechanism of grain fragmentation, while the texture is qualitatively similar to that of face-centered cubic metals subjected to equal channel angular pressing, including the presence of characteristic texture components C, A1 and A2. A correspondence between structural elements and texture components occurs. Specifically, the mesobands have orientations near either an A1 or A2 ideal orientation, whereas the matrix has an orientation near C. Inside the A1-bands, microtwins with orientations near A2 are observed. Detailed analysis of the A2-bands suggests that they may be of twinning origin. Similar orientation dependence of microstructure, though on a much finer scale, is observed after four DCAP passes. Based on the microstructure examination, it was suggested that mesoscopic banding together with deformation twinning continue to be principal mechanisms of grain refinement until the fourth pass, resulting in the formation of ultrafine-grained structure.

Deformation characteristics of Cu-30 % Zn alloy subjected to dynamic equal channel angular pressing (DECAP)

Abstract In this study, the applicability of dynamic equal channel angular pressing for grain refinement and improvement in the properties of a two-phase Cu-30 %Zn alloy was investigated. Simulation and experiments were performed to study the deformation characteristics. The parameters for the multi-pass extrusion simulation were consistent with those in the experiments. The experimental results are in good agreement with the simulation. A homogeneous microstructure and grain refinement are readily achieved. The hardness increases rapidly by 170 % compared to the annealed samples, and its distribution is approximately uniform throughout the 2-pass deformation. Microstructural analysis indicates nanotwins of ~5–10 nm width and high-density dislocations.

Simulation of dynamic channel angular pressing of copper samples using experimental data of loading

The paper represents the numerical simulation of severe plastic deformation of a copper sample under dynamic channel-angular pressing. The initial sample velocity and the value of pressure acting on the back surface of the sample during the process were determined based on the analysis of experimental data. Numerical computations were carried out using the author’s numerical code created in the integrated development environment Delphi. A modified finite element method (without constructing a global stiffness matrix) was used as a numerical method. The behavior of the material was described by an elastic-plastic model using the active type fracture model. Testing of the numerical code was carried out on the Taylor problem. The velocity and pressure values required for the successful dynamic channel-angular pressing were determined. A uniform distribution of the ultrafine-grained structure in almost the entire volume of the copper sample was revealed.

Investigation of Cu5Zr particles precipitation in Cu-Zr and Cu-Cr-Zr alloys subjected to quenching and high strain rate deformation

The paper studies the decomposition of a supersaturated solid solution with a precipitate of particles of the copper-zirconium phase in the Cu-0.06 wt.% Zr and Cu-0.21 wt.% Cr-0.20 wt.% Zr alloys in two initial states, i. e. after solid-solution quenching and after high strain rate deformation (105 s−1) by the method of dynamic channel-angular pressing (DCAP). It has been shown that the decomposition of the supersaturated solid-solution of zirconium in copper in the quenched micro-alloyed Cu-Zr and low-alloyed Cu-Cr-Zr alloys occurs in two stages. At the first stage, nanoparticles of a metastable copper-zirconium phase are formed. The crystal structure of the nanoparticles is close to the structure of the copper matrix. At the second stage, particles of the equilibrium Cu5Zr phase are formed in the form of rods. Annealing (aging) of the alloys deformed by DCAP is characterized by the predominance of heterogeneous precipitation of Cu5Zr nanoparticles at sub-grain boundaries and dislocations, and the decomposition begins at a lower temperature. The particle size is less by an order of magnitude than that in the quenched state. The precipitation of nanoparticles at dislocations retards the formation of recrystallization centers. It has been shown that the treatment including DCAP and annealing at 450°C for 1 h substantially increases microhardness of the micro-alloyed Cu-0.06 %Zr alloy by a factor of 2.7 as compared to the initial quenched state. This behavior is related to substantial structure refinement during DCAP and decomposition of the supersaturated α-solid solution of copper.

Effect of high-speed dynamic channel angular pressing and aging on the microstructure and properties of Cu-Cr-Zr alloys

The microstructure, mechanical and functional properties, including electrical and wear resistances have been investigated for the Cu-0.09%Cr-0.08%Zr and Cu-0.14%Cr-0.04%Zr alloys subjected to high-speed dynamic channel angular pressing (DCAP) followed by annealing (aging). It was shown that DCAP led to the formation of a submicrocrystalline (SMC) structure (d = 200–400 nm) with second-phase precipitates up to 5 nm in a size. The sequence of decomposition of a copper based α solid solution, accompanied by recrystallization and precipitation of second-phase nanoparticles during annealing (aging), was determined. DCAP and aging at 400-450 °C led to a decrease in the electrical resistance of the Cu-Cr-Zr alloys from 4.2 to 2.1 µΩ·cm and to a drastic increase in their strength properties (σu from 197 to 542 MPa, σ0.2 from 94 to 464 MPa), while retaining reasonable ductility. It was revealed that the SMC structure processed by DCAP and annealing (aging) at 400 °C can be additionally strengthened after sliding friction tests due to the formation of a nanocrystalline structure in the surface layer.

Hardening mechanisms of aluminum alloys under dynamic-channel angular pressing

An experiment on high-speed deformation of aluminum alloy A3003 by dynamic channel angular pressing is described. During dynamic pressing, the material is exposed to two deformation modes. They are compression-tension due to the interaction of shock and rarefaction waves when the sample hits the bottom of the first channel, and a simple shear localized at the joint of the channels. The features of structure formation under the action of each deformation mode are determined. It was found that a high dislocation density and the presence of localized deformation zones caused by shock-wave loading, have a significant influence on the formation of the structure upon dynamic channel-angular pressing. The mechanisms of hardening and the contribution of dislocation and grain-boundary components to the overall hardening of the alloy are determined.

Effect of High Strain-Rate Deformation and Aging Temperature on the Evolution of Structure, Microhardness, and Wear Resistance of Low-Alloyed Cu–Cr–Zr Alloy

The effect of the preliminary high strain-rate deformation, performed via the method of dynamic channel-angular pressing (DCAP), and subsequent annealings on the tribological properties of a dispersionhardened Cu–0.092 wt % Cr–0.086 wt % Zr alloy has been investigated. It has been shown that the surfacelayer material of the alloy with a submicrocrystalline (SMC) structure obtained by the DCAP method can be strengthened using severe plastic deformation by sliding friction at the expense of creating a nanocrystalline structure with crystallites of 15–60 nm in size. It has been shown that the SMC structure obtained by the high strain-rate DCAP deformation decreases the wear rate of the samples upon sliding friction by a factor of 1.4 compared to the initial coarse-grained state. The maximum values of the microhardness and minimum values of the coefficient of friction and shear strength have been obtained in the samples preliminarily subjected to DCAP and aging at 400°С. The attained level of microhardness is 3350 MPa, which exceeds the microhardness of the alloy in the initial coarse-grained state by five times.

Effect of Equal Channel and Dynamic Channel Angular Pressing of Ni and Further Heat Treatment on its Structure and Grain Boundary Diffusion

Formation of microstructure in Ni under equal-channel angular pressing (ECAP) and dynamic channel-angular pressing (DCAP), its thermal stability and diffusion properties of grain boundaries are investigated. Grain boundary diffusion in the ultrafine-grained Ni is found to be significantly faster than in the coarse-grained Ni, which indicates a 'non-equilibrium' (deformation-modified) state of grain boundaries in the former. The effect of non-equilibrium state of grain boundaries on the level of internal stresses is analyzed.

The formation of friction-induced nanocrystalline structure in submicrocrystalline Cu–Cr–Zr alloy рrocessed by DCAP

The effect of high strain-rate (100000 s-1) deformation by the method of dynamic channel-angular pressing (DCAP), annealing and quasi-static severe plastic deformation (SPD) by sliding friction on the evolution of structure and properties of a low-alloyed dispersion-hardened Cu–Cr–Zr alloys have been investigated. It is shown that the alloying of copper with chromium (0.09–0.14%) and zirconium (0.04–0.08%) microadditions changes the mechanisms of submicrocrystalline (SMC) structure formation and elastic energy relaxation during DCAP: a cyclic character of structure formation due to alternation high-rate processes of fragmentation and dynamic recrystallization, is changed by the processes of fragmentation and partial strain aging with the precipitation of second-phase nanosized particles. The temperature-time annealing (aging) conditions of Cu-Cr-Zr SMC alloys obtained by DCAP for improvement of mechanical properties and electrical conductivity was established. In particular, for the Cu-0.14Cr-0.04Zr SMC alloy, it has been shown that the optimal combination of microhardness (HV=1880 MPa), electrical conductivity (80% IACS) and strength (σ0.2=464 MPa, σu =542 MPa) at retaining satisfactory plasticity was obtained by treatment: DCAP+400°C, 1 h. The increased level of mechanical properties of alloys, compared to copper, is associated with additional strengthening due to precipitation of nanoparticles (5-10 nm) of the Cu5Zr and Cr during DCAP and aging. It has been shown that the low-alloyed Cu–Cr-Zr alloys possess a high ability to strengthen via the methods of DCAP and SPD by sliding friction. It has been determined based on the example of Cu–0.09Cr–0.08Zr alloy that the wear rate of samples with the SMC structure obtained by the DCAP method decreases by a factor of 1.4 compared to coarse-grained state. It was established that the combined treatment DCAP + 400°С + SPD by friction of the alloy gives rise to the friction-induced NC structure with grains 15– 60 nm in size in the surface-layer material, which provides a high level of the microhardness (3350 MPa) and satisfactory tribological properties.

Effect of high-rate deformation on the structure, the properties, and the thermal stability of copper alloyed with chromium and zirconium

The deformation behavior and the properties of copper alloyed with chromium and zirconium (0.04–0.14 wt %) are studied during high-rate deformation (~105 s–1) by dynamic channel angular pressing (DCAP). The sequence of the decomposition of the α solid solution of copper accompanied by the precipitation of second-phase nanoparticles and recrystallization in annealing (aging) is determined. The influence of DCAP and aging on the mechanical and physical properties of the copper alloys is investigated.

Evolution of the structure of tin bronze under dynamic channel-angular pressing

The study of the evolution of the structure of tin bronze under dynamic channel-angular pressing (DCAP) has been performed. For comparison, the evolution of the structure of commercial copper subjected to the same treatment has been investigated. A comparison of the microhardness of copper and bronze has been carried out after one and two DCAP passes