Equal Channel Angular Pressing Method Research Articles

Investigation of Steel 09G2S Processed by Equal Channel Angular Pressing

Severe plastic deformation is a well known procedure for fabrication considerable grain refinement in metal materials. Equal channel angular pressing (ECAP) is one of these severe plastic deformation techniques which allows the receiving of the bulk ultrafine grained (UFG) metals. It is well known that the ECAP method leads to significant improvement of strength of investigated materials, but the fracture mechanisms of UFG metals at low temperature are not enough studied. The investigation was performed on low-alloy constructional steel 09G2S (GOST) after application of ECAP. Fracture toughness tests were performed on Charpy impact testing specimens at low temperature. The experiments demonstrate that ECAP treatment has the effect on increasing of fracture resistance of steel 09G2S at low temperature.

The Influence of ECAP Geometry on the Effective Strain Distribution

Equal channel angular pressing (ECAP) is one of the most well-known severe plastic deformation (SPD) method for formation the UFG (ultrafine-grained) structures. This method provides very high strains leading to the extreme work hardening and microstructural refinement. To increase the efficiency of ECAP method, there is necessary to design the geometry of ECAP die with focus on high degree of plastic deformation homogeneity. The present study deals with the influence of channel angle on the deformation behavior and strain homogeneity in the transverse direction of sample after two ECAP passes. This analysis was carried out through finite element simulations in the Deform program. In the simulation, three main factors such as an intersecting angle of Ф = 90°, 100°, 110° a 120°, outer corner angle R (ψ) and inner corner angle (r) were being varied. The equation describing the dependence of R and r on average value of the effective plastic strain for different channel angles was established. Moreover, strain inhomogeneity index (Ci) in the transverse direction of sample was also calculated. The results from simulations have indicated that if the outer corner angle increases, mean effective strain decreases. After two ECAP passes (route C), there was seen the increase in strain homogeneity of the sample's cross section.

Synthesis, Characterization, and ECAP Consolidation of Carbon Nanotube Reinforced AA 4032 Nanocrystalline Composites Produced by High Energy Ball Milling

In the present work, multiwalled carbon nanotubes (MWNTs) were synthesized by electric arc discharge method in open air atmosphere. The synthesized nanotubes were subjected to multistep purification followed by characterization using Raman spectroscopy and transmission electron microscopy (TEM). These carbon nanotubes (CNTs) have inner and outer diameters of the order of 3.5 nm and 16 nm with an aspect ratio of 63. AA 4032 nanocomposites reinforced with MWNTs were produced by high energy ball milling using elemental powder mixtures. X-ray diffraction (XRD) and scanning electron microscope (SEM) studies showed different phases of composite with and without CNTs. The crystallite size and lattice strain were calculated using an anisotropic model of Williamson–Hall peak broadening analysis, which showed in decreased crystallite size with increasing milling time. TEM studies reveal that the MWNTs were uniformly distributed in the matrix. Thermal stability of the nanocrystalline powders was studied using a differential thermal analyzer (DTA). The mechanically alloyed powders were consolidated using a novel method called equal channel angular pressing (ECAP) at room temperature. The consolidated samples were sintered at 480 °C in argon atmosphere for 90 min. ECAP method was investigated as an alternative to conventionally sintered powder composites. CNT addition has shown significant improvement in the hardness of the system, even though the observed density is relatively low compared with a base alloy. Thus, the results show that ECAP enables sufficient shear deformation results in good metallurgical bonds between particles at lower compaction pressures. Hence, it is proven that ECAP can be effectively used as one of the consolidation technique especially for powders that are difficult to consolidate by other means.

Effect of Hot Rolling and Equal-Channel Angular Pressing on Generation of Globular Microstructure in Semi-Solid Mg-3%Zn Alloy

A combination of hot rolling and equal channel angular pressing (ECAP) was explored to generate globular microstructures in the Mg-3%Zn alloy after re-heating to the semisolid state. It was found that the single-step deformation of as-cast alloy via hot rolling at 350°C with a thickness reduction of 50% refined the alloy microstructure by creating deformation bands of the Mg (α) phase with a size of the order of tenths of micrometers. After re-heating to 630 °C, the microstructure transformed into spheroidal morphologies with an average globule size of 82 μm. An additional deformation of the hot-rolled alloy by the ECAP method at 250 °C further refined the alloy microstructure to sub-micrometer grains of lath and equiaxed shapes. After re-heating of this microstructure to 630 °C the average globule size reached 62 μm, which is roughly 25% smaller than that achieved for the hot-rolled precursor. The role of strain-induced melt activation (SIMA) techniques in generation of globular morphologies in Mg-based alloys after partial re-melting is discussed.

Finite element analysis of planar twist channel angular extrusion (PTCAE) as a novel severe plastic deformation method

A new severe plastic deformation (SPD) method based on equal channel angular pressing (ECAP) is introduced for producing ultrafine grains in bulk alloys, entitled as “Planar twist channel angular extrusion (PTCAE)”. In PTCAE method, there is additional angle, α, (plus φ and ψ angles in ECAP method) which represents angle associated with the lateral reversal arc of curvature in deformation zone. Three dimensional finite element method (FEM) simulations of both ECAP and PTCAE processes were performed in order to investigate the plastic deformation state of processed samples and, moreover, the effect of different die geometry (in terms of variation of planar twist angle) on plastic strain distribution and magnitude. Results revealed that PTCAE process related with ECAP process can impose higher strain values in different shear planes simultaneously in one deformation zone. Therefore, PTCAE can produce UFG or nanostructured materials better than ECAP method which has simpler design and significantly higher efficiency compared with other new SPD processes.

New way to take control of a structural grain size in the formation of nanomaterials by extrusion

AbstractProduction of nanomaterials by formation of extreme plastic deformation ECAP (Equal‐Channel Angular Pressing) is a way of preparing nano‐structures of engineering materials. A development of a nanostructure in steel AISI 309 (EN X15CrNiSi20.20) with the technology of ECAP, and a new method for determination of the grain size are analysed here. In this study, we also make a comparison, analysis and prediction of the grain size with other technologies. Samples of steel of AISI 309 type were deformed by ECAP method using up to 35 passes.

The Comparison between Continuous Confined Strip Shearing (C2S2) and ECAP Conform in Regard to Equivalent Plastic Strain Distribution for Al 1100

During the last years lots of efforts have been done to industrialize equal channel angular pressing (ECAP) technique. Both Continuous Confined Strip Shearing (C2S2) and ECAP-Conform methods are rather recent techniques, making a continuous process from ECAP method. In present study both mentioned processes were simulated with ABAQUS Finite Element software for commercially pure aluminum. During C2S2 process the sample gradually experienced equivalent plastic strain (PEEQ) of 0.13 at initial stages of bending, while during ECAP-Conform the sample underwent rather sudden magnitude of strain of about 0.52 at primary stages, and it remained constant during the rest of the process. The final magnitude of the PEEQ differed significantly between two processes, as it was 0.86 and 1.36 in C2S2 and ECAP-Conform, respectively. Therefore, in the same processing condition employing the ECAP-Conform method led to a finer microstructure in comparison with C2S2 technique.

A Comparison Between ECAP and Conventional Extrusion for Consolidation of Aluminum Metal Matrix Composite

In this study, two powder consolidation techniques, equal channel angular pressing (ECAP) and extrusion, were utilized to consolidate attritioned aluminum powder and Al-5 vol.% nano-Al2O3 composite powder. The effect of ECAP and extrusion on consolidation behavior of composite powder and mechanical properties of subsequent compacts are presented. It is found that three passes of ECAP in tube at 200 °C is capable of consolidating the composite to 99.29% of its theoretical density whereas after hot extrusion of the composite the density reached to 98.5% of its theoretical density. Moreover, extrusion needs higher temperature and pressing load in comparison to the ECAP method. Hardness measurements show 1.7 and 1.2 times higher microhardness for the consolidated composite and pure aluminum after ECAP comparing with the extruded ones, respectively. Microstructural investigations and compression tests demonstrate stronger bonds between the particles after three passes of ECAP than the extrusion. Furthermore, the samples after three passes of ECAP show better wear resistance than the extruded ones.

Mechanical properties of ferrite-perlite and martensitic Fe–Mn–V–Ti–C steel processed by equal-channel angular pressing and high-temeperature annealing

Using the method of equal-channel angular pressing (ECAP), submicrocrystalline structure is formed in lowcarbon Fe–Mn–V–Ti–C steel with the average grain size 260 nm in the ferrite-perlite state and 310 nm in the martensitic state. It is established that the ECAP treatment gives rise to improved mechanical properties (Hμ = 2.9 GPa, σ0 = 990 MPa in the ferrite-perlite and Hμ = 3.7 GPa, σ0 = 1125 MPa in martensitic states), decreased plasticity, and results in plastic flow localization under tensile loading. The high strength properties formed by the ECAP are shown to sustain up to the annealing temperature 500°C.

Prediction of Change of Energy Supplied to Materials in Equal Channel Angular Pressing Method Technology

Prediction of Change of Energy Supplied to Materials in Equal Channel Angular Pressing Method Technology

Improvement of Mechanical Properties of Semi-Solid Alloys by ECAP Processing

Recently, semi-solid processing is paid to attention in the field of the light alloys. By this method, it is improved ductility and fatigue strength. Although, because of those mechanical properties of the elongation and toughness is not excellent, the range that can be the application to parts is limited. On the other hand, it is reported that grain refinements cause improvement of ductility and appearance of super plasticity. Then, Equal-Channel Angular Pressing (ECAP) method is reported to be effective to the sample making of a bulk and ultra fine grain in various alloys in recent years. In this study, it tried to improve ductility and durability due to making ultra fine grain in AC4CH alloys by the ECAP method, and the influence of ECAP processing on the mechanical property of AC4CH was investigated. As the result, the ductility of AC4CH has improved by ECAP processing. However, the tensile strength of AC4CH declined along with the increase in the number of passes. So, for the purpose of additional improvement of tensile strength, ECAP-Back Pressure (ECAP-BP) method that was reported to be more effective for grain refinements than ECAP method was applied to semi-solid AC4CH and compared with ECAP method. As the result, the tensile strength of AC4CH was maintained by use of ECAP-BP. Moreover, both ductility and toughness of that have been also improved.

Study of the grain-boundary structure in submicrocrystalline niobium after equal-channel angular pressing

The method of Mossbauer emission spectroscopy on 119mSn nuclei was used to study grain boundaries in submicrocrystalline Nb produced by the method of equal-channel angular pressing (ECAP) of poly-crystalline Nb (99.9%). ECAP included 16 passes at room temperature.

Improving corrosion resistance of RE-containing magnesium alloy ZE41A through ECAP

Significant grain refinement was achieved in rare earth (RE) containing aeronautic magnesium alloy ZE41A through equal-channel angular pressing (ECAP) using rotary die at 603 K. Influence of ECAP pass number on its microstructure change and corrosion behavior was investigated by optical microscope (OM)/scanning electron microscope (SEM) observation and potentiostatic polarization tests in aqueous solution of NaCl, respectively. The results showed that ultrafine equiaxial grains (about 2.5 μm) were obtained over 16 passes due to plastic-induced grain refinement accommodated by dynamic recrystallization. The lower corrosion current density and nobler corrosion potential correlated with large number of pressing passes were attributed to the low tendency toward localized corrosion with broken secondary phase after homogenization on ultrafine-grained Mg matrix. The multi-pass ECAP method made the ZE41A aeronautic magnesium alloy more attractive since severe plastic deformation may significantly improve its corrosion resistance besides superior mechanical properties.

Structure and properties of aluminum alloy 1421 after equal-channel angular pressing and isothermal rolling

Sheets from the aluminum alloy 1421 with an ultrafine-grained (UFG) structure and a weak crystallographic texture were prepared by the method of equal-channel angular pressing (ECAP) through a die with channels of a rectangular cross section and by subsequent isothermal rolling. Both operations were carried out at a temperature of 325°C. It is shown that severe plastic deformation (SPD) leads to the formation of a completely recrystallized uniform microstructure with an average grain size of 1.6 µm in the alloy. At room temperature the alloy 1421 demonstrates high static strength (σu = 545 MPa, σ0.2 = 370 MPa) in the absence of a significant anisotropy. At temperatures of hot deformation, the alloy showed ultrahigh elongations under superplasticity (SP) conditions. At a temperature of 450°C and initial deformation rate of 1.4 × 10−2 s−1 the maximum elongation at fracture was ∼2700%. At static annealing at a temperature of SP deformation, the UFG structure formed in the process of SPD remains stable. The SP deformation is accompanied by an insignificant grain growth and pore formation.

Study of ECAP Processing Routes on Semi-Solid Microstructure Evolution of A356 Alloy

Semi- solid (SS) processing technologies provide the production of metal parts with homogeneous, fine and globular – grained microstructure. This is one of the most successful and reliable methods to produce near net shape products exhibiting good mechanical properties. Production of feed stock with non-dendritic and spherical structure is the critical factors in semisolid forming. Among several processes to obtain a globular microstructure, the SIMA (strain induced melt activated) process is simple and advantageous with respect to equipment and eliminating the melting stage before reheating. In this research, Al (A356) has been used and in order to induce strain, ECAP (equal channel angular pressing) method has been applied. ECAP is a method in which a great strain is induced and severe plastic deformation without any changes in cross section area occurs. To induce larger strain, ECAP process was carried out on annealed specimens up to several passes in route A (no rotation of samples around linear axis between each pass) and Bc (90◦ rotation of samples around linear axis between each pass), in ambient temperature. The reheating condition was optimized and the comparison between different routes and number of passes was investigated. The microstructure evolution of deformed and reheated Al (A356) was characterized by SEM (Scanning electron microscopy) and optical microscopy. In addition, the relation between the induced strain with size and shape of particles has been studied.

Effect of the grain size on the macroscopic response of aluminum to shock loading

Shock tests of two lots of a 1420 aluminum-lithium alloy are performed. The mean grain size is 24 µm in the first lot and 1.6 µm in the second lot obtained by the method of equal-channel angular pressing. Two characteristics of dynamic strength of the material were determined in experiments on the high-velocity impact of flat samples: threshold of dynamic stability with respect to compression on the fore front of the compression pulse and spall strength of the material. The materials of both types have an identical threshold of dynamic stability with respect to compression, whereas the spall strength of the microcrystalline alloy is 20% greater than the spall strength of the polycrystalline alloy. The reason is the consumption of energy on structure formation in the coarse-grain material in passing to a larger-scale structural level (in the case with a fine-grain material, such a structure is available in the initial state). The experiments reveal the presence of a second plastic front whose amplitude is approximately 10% of the first plastic front.

Compaction of Ti-6Al-4V Powder by ECAE with Back-Pressure

Powder metallurgy is widely used to produce alloys with low cost of production. The main drawback using powders is the level of residual porosity of final product which often implies the application of a complicated and costly hot isostatic pressing process. However, this issue can be overcome by using equal channel angular pressing (ECAE) with back pressure (BP). The use of severe shear deformation, with imposed hydrostatic pressure, allows a reduction in the range of compaction temperatures compare to those used in conventional practice. The compaction of Ti-6Al-4V powder by the ECAE method has been investigated. The compaction has been performed at temperatures starting from room temperature (RT) and increasing up to 400°C with various back pressures ranging from 0 to 350MPa. A billet processed by ECAE with 43MPa back-pressure at 400°C was found to have improved relative density of 97.5% and increased Vickers hardness of 369HV, compared to values of 96.7% and 325HV respectively obtained at RT. A relative density of 98.2% and 426HV hardness were measured for billets processed with BP = 262MPa at 400°C. A fully compact billet was obtained by applying 350 MPa of BP at 400°C.

Noncombustible Magnesium Alloy Processed by Rotary-Die Equal Channel Angular Pressing Method

Noncombustible Mg-8Al-2Ca rods were processed by RD-ECAP. The magnesium alloy rod had Mg matrix and Al2Ca second phase. Grains with about 20 μm in diameter were observed in the matrix of the raw materials. The grains in matrix had no anisotropy. On the other hand, positions of second phase particles had anisotropy and the second phase particles formed lines. The samples processed by RD-ECAP had no crack and the samples had 20mm diameter. Grains in matrix of the 4 pass RD-ECAP sample had no anisotropy and the grains had under about 5 μm in diameter. The second phase particles had round shapes and were uniformly distributed as compared with the raw material rod. Therefore, the RD-ECAP is useful for forming noncombustible Mg-8Al-2Ca alloy with fine-grains.

Severe Plastic Deformation of Commercially Pure Titanium by Rotary-Die Equal Channel Angular Pressing Method

The commercially pure titanium cylindrical samples with a diameter of 11.5mm and a length of 24mm were processed by a new severe plastic deformation process, called the rotary-die equal channel angular pressing (RD-ECAP), under the condition of 773K, 2.4mm/s punch. By the RD-ECAP, ECAP processes of 1-4 passes were possible without sample removal and the temperature of cp-titanium could be simply controlled. After the RD-ECAP process, the cp-titanium samples had no crack. Fine-grained microstructures were observed in the sample on Y plane. Therefore the samples processed by RD-ECAP were expected to have high mechanical strength.

Crystallographic Orientation Observation and Mechanical Properties Evaluation of Fine-Grained Pure Aluminum

In order to improve the material characteristics of single and polycrystals of pure aluminum, the relationships between crystallographic orientations and microstructures, and the mechanical properties were examined. Several conventional grain-forming procedures, such as accumulative roll bonding (ARB), equal-channel angular pressing (ECAP) and accumulative forging bonding (AFB), were performed to obtain the ultrafine-grained structure. Furthermore, some analytical results, such as crystal direction maps, inverse pole figure (IPF), and texture, were obtained from the SEM-electron backscattered diffraction pattern (EBSP). As a result, (1) for the ARB method, increases of strength and ductility were shown, since the cube orientation was developed; (2) for the ECAP method, in the extrusion direction (ED) plane at the die angle Ψ=100°, peculiar distributions of microstructure and hardness were obtained; (3) for the AFB method, stratified inclination microstructures were obtained, and thus the typical texture was also observed.