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It is generally known that equal channel angular pressing with back pressure (BP-ECAP) not only applies higher hydrostatic stress and more deformation compared to what a regular ECAP can apply to a workpiece, but also prevents surface defects in the workpiece during the processing. In this study, the plastic deformation behavior of the materials during the BP-ECAP process was investigated using the finite element method. The homogeneity within the workpiece was analyzed in terms of contours, path plot, and statistics of strain distribution under different conditions regarding back pressure, strain hardening, friction, and corner angle. The simulation results shed some lights on the optimum design of ECAP for homogeneous and large severe plastic deformation.

Equal channel angular pressing (ECAP) is the most promising and interesting process for refining the grain size to an ultrafine grain or nanosize by imposing severe plastic deformation into the workpiece and repeating the process while maintaining the original cross-section of the workpiece. In this paper, we simulated the batch type ECAP and the continuous type equal channel multi-angular pressing (ECMAP), which can impose large deformation by repeating the shear deformation, using the finite element method and investigated the similarity and difference of the two processes. In particular, modified die design of the continuous type ECMAP was proposed for strain uniformity.

Computational fluid dynamics (CFD) is nowadays a powerful and reliable tool for simulating different flow processes and temperature. CFD is used to analyze the various pot geometries and operative variables in 55% Al-Zn pot of CGL. In this research, different strip velocities were assumed and then shown the flow pattern in the pot that was similar in the different strip velocities. Temperature distribution in the pot depended on inductors and inlet strip temperature at the steady condition. Generation of dross particles and transport models were considered to describe dross particles evolution inside the pot. In order to observe dross influence by scrap location, dross particles were generated upon the sink roll. Floating time of dross particles is different by scraper locations above the sink roll.

In this study, consecutive workpiece equal channel angular pressing (ECAP) in solid-dies, where the second workpiece is successively deformed without splitting and reassembling the die after the first workpiece processing, is employed to reduce the processing time in ECAP. The plastic deformation behavior of the two workpieces was investigated in terms of strain homogeneity, load, and defects using the finite element method (FEM). The experimental deformations of the consecutive workpiece during ECAP were compared with the FEM results, and it was found that the deformation was more heterogeneous in the second workpiece when compared with the first workpiece. The primary reason behind these findings is that the deformed geometry of the second workpiece was a back slant type and the first deformed workpiece provided back pressure to the second workpiece. Furthermore, the folding defect was less pronounced in the second workpiece because of the back slant head shape. Despite the less homogeneity in strain, the ECAP of the consecutive workpieces is an effective process for less defective materials and increases process efficiency.

A constitutive relation based on the free volume model was developed to describe the strain-rate-dependent deformation behavior of bulk metallic glasses (BMG) at temperatures within the supercooled liquid region (SLR). Validity of the present approach has consequently been assessed by comparing the numerical results obtained from finite-element analyses with the experimental results previously obtained from compression tests of Vitreloy-1 BMG alloy. Finite-element-method simulations combined with free volume constitutive relations were found to reproduce well the plastic deformation behavior of Vitreloy-1 alloy, exhibiting a Newtonian viscous flow without stress overshoot and also a non-Newtonian viscous flow with stress overshoot at temperatures within the SLR. The present approach appears to provide a powerful means of understanding plastic deformation behavior in relation to localized and uniform deformation and also of making reliable formability estimations of BMG alloys.

Equal channel angular pressing (ECAP) process provides an efficient procedure for achieving ultrafine grained microstructures with excellent mechanical properties in metallic materials. In this article, a simulation scheme for predicting the mechanical behavior during and after ECAP was proposed. The proposed scheme was applied for interstitial-free (IF) steels, which are widely used for the automobile body applications. Plastic deformation behavior during several passes of ECAP in route Bc, including such aspect as deformed geometry, corner gap, forming load and strain uniformity, was predicted. Tensile testing responses of the ECAP-processed IF steel, including strain hardening, onset of necking, and post-necking behavior, were analyzed using the finite element method and compared with the experimental results. The predicted tensile curves, ultimate tensile strength, and elongation varying with the number of ECAP passes were in good agreement with experimental results. The computational scheme developed was demonstrated to successfully predict not only the plastic deformation behavior during ECAP but also the mechanical properties of the ECAP-processed material.

Carbon nanotubes (CNTs) are expected to be ideal reinforcements of composite materials used in aircraft and sports industries due to their high modulus and low density. In the present paper, severe plastic deformation by high pressure torsion (HPT) of powders at elevated temperature (473 K) was employed to achieve both powder consolidation and grain refinement of aluminum-matrix nanocomposites reinforced by 5 vol% CNTs. Before the HPT, the powders were ball milled using planetary ball mill in order to achieve molecular level mixing. Aluminum was treated by the same process for a reference. The HPT processed disk were composed of considerably equilibrium grain boundaries with high misorientation angles. The CNT-reinforced ultrafine grained microstructural features resulted in high strength and good ductility.

Bulk nanostructured metallic materials are generally synthesized by bottom-up processing which starts from powders for assembling bulk materials. In this study, the bottom-up powder metallurgy and High Pressure Torsion (HPT) approaches were combined to achieve both full density and grain refinement at the same time. After the HPT process at 473K, the disk samples reached a steady state condition when the microstructure and properties no longer evolve, and equilibrium boundaries with high angle grain boundaries (HAGBs) were dominant. The well dispersed alumina particles played important role of obstacles to dislocation glide and to grain growth, and thus, reduced the grain size at elevated temperature. The small grain size with HAGBs resulted in high strength and good ductility.

The plastic deformation behavior of forward extrusion, equal channel angular pressing, and a combination of the forward extrusion and equal channel angular pressing processes are analyzed by the finite element method. Simulations were carried out under realistic conditions by considering the strain hardening of the material and the degree of friction. Strain homogeneity in the combined processes is also compared to that of the individual forward extrusion and equal channel angular pressing processes. The plastic flow is more complicated and the strain induced is non-uniform in the combined processes. However, the combined processes show no corner gap formation. Moreover, it led to the development of higher strains in a single step compared to the individual processes. In addition, the load requirements for the combined processes are higher than the summation of loads of the individual processes. © 2010 The Japan Institute of Metals.

In current studies, equal channel angular pressing process (ECAP) and modified ECAP processes are simulated under ideal conditions to compare the deformation characteristics. The deformation behaviour is more complicated and the strain induced during the processes is highly non-uniform in the modified ECAP processes except in the equal channel multi-angular pressing (ECMAP) process with Route C. The strain homogeneity is more of a possibility with ECAP and ECMAP with Route C processes. The deformation stress state is widely distributed in nature in modified ECAP processes than in conventional ECAP. In addition, the load requirements are also higher in modified ECAP processes with that of the ECAP process.

Strain hardening of pure copper and friction between the sample and die channels is considered for finite element modelling. To validate the FEM results, the FEM calculated effective strain variations were compared with the hardness measurements. Simulated load-stroke curve and peak load calculations were also compared with the experimentally recorded load-stroke curve and peak load. Different stages of the load-stroke curve of the ECAP process was explained in detail. In over all, good conformity is observed between the FEM calculations and experimental results.

Magnesium and its alloys are attractive as light weight structural/functional materials for high performance application in automobile and electronics industries due to their superior physical properties. In order to obtain high quality products manufactured by the magnesium powders, it is important to control and understand the densification behavior of the powders. The effect of the sheath surrounding the magnesium powders on the plastic deformation and densification behavior during equal channel angular pressing was investigated in the study by experimental and the finite element methods. A modified version of Lee-Kim`s plastic yield criterion, notably known as the critical relative density model, was applied to simulate the densification behavior of magnesium powders. In addition, a new approach that extracts the mechanical characteristics of both the powder and the matrix was developed. The model was implemented into the finite element method, with which powder compaction under equal channel angular pressing was simulated.

For the first time, a detailed and systematic finite element study was carried to identify the parameters which cause the bending of the workpiece in equal channel angular pressing. These simulations were carried out by using commercial finite element code Abaqus with different materials behavior, processing parameters, and die geometries. The results showed that the optimal ways to reduce the bending of strain rate sensitive materials in ECAP without varying the strain homogeneity are the usage of lower processing speed and the increase in length of the die exit-channel.

Numerical simulations of the powder extrusion need an appropriate pressure-dependent constitutive model for densification modeling of the magnesium powders. The present research investigated the effect of representative powder yield function of the critical relative density model. We could obtain reasonable physical properties of pure magnesium powders using cold isostatic pressing. The proposed densification model was implemented into the finite element code. The finite element analysis was applied to simulation of powder extrusion of pure magnesium powder in order to investigate the densification and processing load at room temperature.

【In this study, bottom-up powder processing and top-down severe plastic deformation processing approaches were combined in order to achieve both full density and grain refinement with least grain growth. The numerical modeling of the powder process requires the appropriate constitutive model for densification of the powder materials. The present research investigates the effect of representative powder yield function of the Shima-Oyane model and the critical relative density model. It was found that the critical relative density model is better than the Shima-Oyane model for powder densification behavior, especially for initial stage.】

Elasto-plastic finite element analysis was carried out for analyzing the severe plastic deformation behavior of copper specimens during groove pressing. Deformation localization was studied in terms of strain variations along the longitudinal direction. Plastic strain is lower at the local interface between the shear and the flat regions, which receives very little shear during the pressing cycle. Strain localization is more intensified with the number of groove pressing cycles, although the average strain level increases. � 2008 Elsevier B.V. All rights reserved.

The inner corner angle (ICA) is one of the major factors affecting deformation homogeneity in workpieces during equal channel angular pressing (ECAP). In this study, the effect of the ICA on the plastic deformation behavior in ECAP was investigated using the finite element method. A round ICA induces highly inhomogeneous deformation in the head, tail, top and bottom regions of the workpiece due to increasing compressive and decreasing shear deformation components. It was found that a round inner corner with an angle up to 9° is acceptable in finite element simulations for reproducing a sharp inner corner. These results can serve as a design guide for processing and dies of ECAP.

In this paper, the finite element method (FEM) was applied to analyze the plastic flow and strain hardening behavior of pure copper, subjected to rotary-die equal channel angular pressing (RD-ECAP) up to four passes. The die was rotated 90° counter clockwise between the passes in the simulation. The effective strain distribution and load–stroke curves were investigated. The load was increased with the number of rotary-die equal channel angular pressing passes. The results show that, plastic deformation becomes inhomogeneous with the number of passes due to an end effect, which was not found seriously in conventional equal channel angular pressing (ECAP). Especially, decreasing corner gap with increasing the number of passes was observed and explained by the strain hardening effect.

Aluminum alloys are not only lightweight materials, but also have excellent thermal conductivity, electrical conductivity and workability, hence, they are widely used in industry. It is important to control and enhance the densification behavior of metal powders of aluminum. Investigation on the extrusion processing combined with equal channel angular pressing for densification of aluminum powders was performed in order to develop a continuous production process. The continuous processing achieved high effective strain and full relative density at . Optimum processing conditions were suggested for good mechanical properties. The results of this simulation helped to understand the distribution of relative density and effective strain.

Recently, several methods of severe plastic deformation were developed to process bulk nanostructured materials with a grain size from 20 to 200 nm depending on a number of factors. The high pressure torsion (HPT) process has been subject of many investigations as a new method of processing bulk nanostructured materials. Nanostructures of materials can be formed both by the consolidation of nanopowders and the refinement of the coarse-grained microstructures. Because the mechanical properties of the deformed material are directly related to the amount of plastic deformation, i.e. the developed strain, understanding the phenomenon associated with strain development is very important in severe plastic deformation processes. The knowledge of absolute values and the homogeneity of internal stress and strain distributions is still very desirable in order to optimize the processes of grain size refinement and nanostructure development in the HPT process. In this study, the results of the rigid-plastic finite element analysis of the plastic deformation behavior of bulk materials during the HPT processing are presented. The deformation geometry of the workpiece was investigated. This approach of continuum mechanics for the analysis of the HPT process can be a useful tool if the material parameters are incorporated.

Mg and Mg alloys are promising materials for light weight high strength applications. In this paper, grain refinement of pure Mg using severe plastic deformation was tried to enhance the mechanical properties of the hard-to-deform metallic material. The microstructure and the mechanical properties of Mg processed by equal channel angular pressing(ECAP) at various processing temperatures were investigated experimentally. ECAP with channel angle of and corner angle of was successful at without fracture of the samples during the processing. The hardness of the ECAP processed Mg decreased with increasing ECAP processing temperature. The effect of temperature on the hardness and microstructure of the ECAP processed Mg were explained by the dislocation glide in the basal plane and non-basal slip systems and by the dynamic recrystallization and recovery.

Equal channel angular pressing (ECAP) is so far the most viable severe plastic deformation procedure to extrude material by using specially designed channel dies without any substantial changes in geometry and to prepare an ultrafine grained material. Magnesium is the lightest of all structural metallic materials, but a typical hard-to-deform metallic material due to its HCP structure and associated slip systems. ECAP has been applied for a processing method of severe plastic deformation to achieve grain refinement of magnesium and to enhance it's low ductility. In particular, we investigated the deformation and fracture behavior of pure magnesium workpiece using experimental and numerical methods. The finite element method with different ductile fracture models was employed to simulate plastic deformation and fracture behavior of the workpiece.

In order to obtain high-quality products in powder metallurgy, it is important to control and understand the densification behavior of metallic powders. The effect of the powder characteristics of magnesium powders on the compaction behavior was investigated in this study by experimental and theoretical methods. A modified version of Lee-Kim’s plastic yield criterion, known as the critical relative density model, was applied to simulate the densification behavior of magnesium powders, and a new approach that extracts both the powder and the matrix characteristics was developed. The model was implemented via the finite element method, and powder compaction under upsetting conditions was simulated. The calculated and experimental results are in good agreement. [doi:10.2320/matertrans.MC200724]

Magnesium and magnesium alloys are promising materials for light weight and high strength applications. In order to obtain homogeneous and high quality products in powder compaction and powder forging processes, it is very important to control density and density distributions in powder compacts. In this study, a model for densification of metallic powder is proposed for pure magnesium. The mode] considers the effect of powder characteristics using a pressure-dependent critical density yield criterion. Also with the new model, it was possible to obtain reasonable physical properties of pure magnesium powder using cold iso-state pressing. The proposed densification model was implemented into the finite element method code. The finite element analysis was applied to simulating die compaction of pure magnesium powders in order to investigate the density and effective strain distributions at room temperature.

In this study, a deformation mechanism map of metallic nanocrystalline materials(NCMs) using the phase mixture model is proposed. It is based on recent modeling that appears to provide a conclusive description of the phenomenology and the mechanisms underlying the mechanical properties of NCMs. The proposed models adopted the concept of a `phase mixture` in which the grain interior and the grain boundaries are treated as separate phases. The volume fraction of this grain boundary `phase` may be quite appreciable in a NCM. Based on the theoretical model that provides an adequate description of the grain size dependence of plasticity covering all grain size range from coarse down to the nanoscale, the tensile deformation response of NCMs, especially focusing on the deformation mechanisms was investigated. The deformation mechanism map is newly proposed with axes of strain rate, grain size and temperature.

Manufacturing bulk nanostructured materials with least grain growth from initial powders is challenging because of the bottle neck of bottom-up methods using the conventional powder metallurgy of compaction and sintering. In this study, bottom-up type powder metallurgy processing and top-down type SPD (Severe Plastic Deformation) approaches were combined in order to achieve both full density and grain refinement of metallic powders. ECAP (Equal-Channel Angular Pressing), one of the most promising processes in SPD, was used for the powder consolidation method. For understanding the ECAP process, investigating the powder density as well as internal stress, strain and strain rate distribution is crucial. We investigated the consolidation and plastic deformation of the metallic powders during ECAP using the finite element simulations. Almost independent behavior of powder densification in the entry channel and shear deformation in the main deformation zone was found by the finite element method in conjunction with a pressure dependent material yield model. Effects of processing parameters on densification and density distributions were investigated.

Carbon nanotubes (CNTs) have been the subject of intensive studies for applications in the fields of nanotechnologies in recent years due to their superior mechanical, electric, optical and electronic properties. Because of their high Young’s modulus (≈ 1 TPa), tensile strength (≈ 200 GPa) and high elongation (10-30%) as well as high chemical stability, CNTs are considered to be attractive reinforcement materials for light weight and high strength metal matrix composites. In this paper, we described a scheme for multi-scale modeling for the elastic and plastic properties of CNT/metal nanocomposites using the numerical analyses of the three-dimensional finite element method based on the continuum mechanics of a unit cell. In particular, the quantitative effects of the distribution and the array of the CNT reinforcement (viz. cross-over, vertical and horizontal distributions) on the elasticity and plasticity of the nanocomposites were investigated and the anisotropic characteristics of elasticity and plasticity of the nanocomposites were linked with the extremely high aspect ratio of CNTs.

Microstructure and microhardness of metallic powders of pure copper were studied after high pressure torsion(HPT) processing with 10 turns of die rotation and high pressure of 6 GPa. The grain size of copper decreases drastically after HPT and reaches nanometer size ranges. During HPT, the hardness of consolidates of copper powders increases with increasing the temperature of HPT processing. Examinations of the fracture surfaces indicated evidence of ductile fracture. The results proved that HPT of copper powders has a beneficial effect for homogeneous deformation with reducing grain size.

It is well known that deformation during equal channel angular pressing (ECAP) is not as perfectly homogeneous as simple shear, although the inhomogeneity is not as distinct as the other metal forming processes. The sources of this inhomogeneity are (i) external conditions such as die geometries, loading modes, temperature, ram speed and die frictions and (ii) internal conditions such as material's strain hardenability and strain rate sensitivity. In spite of a lot of recent research results, factors and mechanisms of the inhomogeneous deformation were not elucidated systematically. In this paper, the effects of external and internal factors on the deformation inhomogeneity during ECAP are investigated. The finite element analyses of plastic deformation are employed for this purpose in conjunction with die corner angle and strain hardenability of metallic workpieces. Optimum die corner angles with strain hardening exponent are presented.

Manufacturing bulk nanostructured materials with least grain growth from initial powders is challenging because of the bottle neck of bottom-up methods using the conventional powder metallurgy via compaction and sintering. In the study, densification behavior of nano Cu powders during pressureless sintering was investigated using an in-situ optical dilatometer technique. The initial heating and steady temperature stages during the sintering of nano Cu powder compacts were observed. At the initial heating stage, the powder compact has many porosities and full densification needs high temperature and/or high pressure sintering. In the experimental analysis, changes in geometry and density were measured and discussed for optimal consolidation and densification by the in-situ optical dilatometer.

For the usage and shaping of engineering parts of nanocrystalline (NC) materials, deformation behavior at both the service temperature and the forming temperature is necessary. For characterization of the mechanical properties of metallic NC materials, NC nickel has been synthesized using electrodeposition processing. In this study, experimental uniaxial tensile testing was performed to elucidate the deformation behavior of NC nickel of 12 nm grain size under various strain rate conditions. In addition to the experimental approach, we provide an account of the mechanical properties of NC nickel materials from our current viewpoint. This is based on recent modeling that appears to provide a conclusive description of the phenomenology and the mechanisms underlying the mechanical properties of NC materials. The experimental results indicate that the deformation in an elastic range is large (∼2%) and strain rate insensitive whereas in a plastic deforming range the deformation is small and strain rate sensitive. The fracture strain and stress increases with increasing strain rate. Overall, limited fracture strain results from the absence of strain hardening soon after the elastic limit. Phase mixture modeling could simulate the absence of strain hardening associated with the grain boundary mediated plastic deformation mechanism.

The processing and mechanical properties of rapidly solidified and consolidated hypereutectic Al-20 wt% Si alloys were studied. A bulk form of rapidly solidified Al-20 wt% Si alloy was prepared by extruding gas atomized powders having a powder size of 106–145 μm. Powder extrudates were subsequently equal channel angular pressed up to eight repetitive route C passes to refine matrix microstructure and Si particles by imposing severe plastic deformation. The microstructures of the gas atomized powders, extrudates and equal channel angular pressed samples were investigated via a scanning electron microscope. The mechanical properties of the bulk samples were measured by compressive tests. Equal channel angular pressing was found to be effective in matrix grain and Si particle refinement, which enhanced the strength of the Al-20 wt% Si alloy without deteriorating ductility in a range of experimental strain of up to 30%.

In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve both full density and grain refinement of metallic powders with least grain growth, which is considered as a bottle neck of the bottom-up method that uses the conventional powder metallurgy of compaction and sintering. ECAP (Equal channel angular pressing), one of the most promising method in SPD, was used for the powder consolidation. In the ECAP process of not only solid but also powder metals, it is important to get a good understanding of the density as well as internal stress, strain and strain rate distribution. We investigated the consolidation, plastic deformation and microstructure evolution behavior of the metallic powders during ECAP using an experimental method. It was found that high mechanical strength could be achieved effectively due to the well bonded powder contact surface during ECAP process of gas atomized Al-Si powders. The experimental results show that SPD processing of powders is a viable method to achieve both fully density and nanostructured materials.

Carbon nanotubes (CNTs) have been the subject of intensive study for applications in the fields of nanotechnologies in recent years due to their superior mechanical, electric, optical and electronic properties. Because of their exceptionally small diameters (≈ several nm) as well as their high Young’s modulus (≈ 1 TPa), tensile strength (≈ 200 GPa) and high elongation (10-30%) in addition to a high chemical stability, CNTs are attractive reinforcement materials for light weight and high strength metal matrix composites. In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve full density of CNT/metal matrix composites with superior mechanical properties by improved particle bonding and least grain growth, which were considered as a bottle neck of the bottom-up method using the conventional powder metallurgy of compaction and sintering. ECAP (equal channel angular pressing), the most promising method in SPD, was used for the CNT/Cu powder consolidation. The powder ECAP processing with 1, 2, 4 and 8 route C passes was conducted at room temperature. It was found by mechanical testing of the consolidated CNT/Cu that high mechanical strength could be achieved effectively as a result of the Cu matrix strengthening and improved particle bonding during ECAP. The ECAP processing of powders is a viable method to achieve fully density CNT-Cu nanocomposites.

Nanostructured metallic materials are synthesized by bottom-up processing which starts with powders for assembling bulk materials or top-down processing starting with a bulk solid. A representative bottom-up and top-down paths for bulk nanostructured/ultrafine grained metallic materials are powder consolidation and severe plastic deformation (SPD) methods, respectively. In this study, the bottom-up powder and top-down SPD approaches were combined in order to achieve both full density and grain refinement without grain growth, which were considered as a bottle neck of the bottom-up method using conventional powder metallurgy of compaction and sintering. For the powder consolidation, equal channel angular pressing (ECAP), one of the most promising method in SPD, was used. The ECAP processing associated with stress developments was investigated. ECAP for powder consolidation were numerically analyzed using the finite element method (FEM) in conjunction with pressure and shear stress.

Although equal channel angular pressing (ECAP), imposing large plastic shear strain deformation by moving a workpiece through two intersecting channels, is a promising severe plastic deformation method for grain refinement of metallic materials, its batch type characteristic makes ECAP inefficient for multiple-passing. Rotary-die ECAP (RDECAP) proposed by Nishida et al. can achieve high productivity by using continuous processing without taking out the samples from the channel. However, plastic deformation behavior during RD-ECAP has not been investigated. In this study, material plastic flow and strain hardening behavior of the workpiece during RD-ECAP was investigated using the finite element method. It was found that plastic deformation becomes inhomogeneous with the number of passes due to an end effect, which was not found seriously in ECAP. Especially, decreasing corner gap with increasing the number of passes was observed and explained by the strain hardening effect.

Carbon nanotubes (CNTs) have been the subject of intensive studies for applications in the fields of nano technologies in recent years due to their superior mechanical, electric, optical and electronic properties. Because of their exceptionally small diameters () as well as their high Young`s modulus (), tensile strength () and high elongation (10-30%) in addition to a high chemical stability, CNTs are attractive reinforcement materials for light weight and high strength metal matrix composites. Although extensive researches have been performed on the electrical, mechanical and functional properties of CNTs, there are not many successful results on the mechanical properties of CNT dispersed nanocomposites. In this paper, we applied equal channel angular pressing for consolidation of CNT/Cu powder mixtures. We also investigated the hardness and microstructures of CNT/Cu nanocomposites used experimental for metal matrix composites.

Preform design is an effective means of achieving the homogeneous deformation of workpiece materials and decreased load in metal forming. However, this approach has not been applied to equal channel angular pressing (ECAP). In this paper, the plastic deformation behavior of workpieces having three different preform shapes during ECAP was investigated using experimental and finite element analyses. The results indicated that a preform design slant at the back part of the workpiece head is beneficial to homogeneous deformation, reducing the maximum pressing load at the initial stage and eliminating folding defects at strain concentration points.

In this study, bottom-up type powder processing and top-down type SPD (severe plastic deformation) approaches were combined in order to achieve both full density and grain refinement of metallic powders with least grain growth, which was considered as a bottle neck of the bottom-up method using the conventional powder metallurgy of compaction and sintering. ECAP (Equal channel angular pressing), one of the most promising method in SPD, was used for the powder consolidation. In the ECAP process of not only solid but also powder metals, knowledge of the density as well as internal stress, strain and strain rate distribution is important for understanding the process. We investigated the consolidation, plastic deformation and microstructure evolution behavior of the metallic powders during ECAP using experimental and theoretical methods. Almost independent behavior of powder densification in the entry channel and shear deformation in the main deformation zone was found by the finite element method in conjunction with a pressure dependent material yield model. It was found that high mechanical strength could be achieved effectively as a result of the well bonded powder contact surface during ECAP process of gas atomized Al-Si powders. The SPD processing of powders is a viable method to achieve both fully density and nanostructured materials.

Equal-channel angular (ECA) pressing is the main technique of the severe plastic deformation (SPD) method, applied for fabrication of bulk nanostructured metal materials. At the same time the practical realization of this technique is a rather challenging task. This is connected with the fact that the material during the ECA pressing is subjected to large strains under high imposed pressure at relatively low temperatures. Simulation with the help of the finite element method (FEM) or the variation-difference (VDM) method is widely applied to analyze the process of ECA pressing. A variety of as commercial as well as in-house developed programs are used by researches, when conducting this analysis. As a result the correlation between the modeling results, obtained at different laboratories as well as their adequacy, i.e. possibilities of their application for the analysis of the experimental data become topical issues. In order to find answers to the questions put by there has been performed computer simulation of 1st pass of ECA pressing by an example of pure copper at 4 different laboratories, engaged in SPD problems. Meanwhile, the investigators used different software packages, however, initial simulation conditions were set equal. This refers in particular to geometry sizes and the form of the die-set possessing square transverse section of the channels, as well as to the inner and outer curvature radii of the channels in the point where they intersect, and to the form and dimensions of the billet, strain rate, strain curve, isotropic model of the material. The modeling temperature was ambient. The die-set and the punch were assigned as absolutely solid non-deformable bodies. Taking into account the symmetry of the solving task, the modeling was conducted for a half of the billet, cut along the vertical plane, coming through its geometrical center. The friction coefficient was assigned equal to zero, in order to avoid influence of friction on the character of the material flow as well as not to complicate the problem at the given stage of comparison. Other modeling parameters were chosen by each researcher on his own, basing on his experience and conventional approaches to modeling. Comparison of the obtained modeling results was made by means of matching of the calculated values of the level of the accumulated strain along the bulk of the billet, pressing efforts, and the geometrical form of the billet after ECA pressing. Modeling results were compared with the results of the experimental researches.

Plastic deformation behavior during equal channel multi-angular pressing (ECMAP) was analyzed using the three dimensional finite volume method of the commercial code MSC.Superforge. In order to understand local and global deformation characteristics, effective strain and pressing load histories were investigated. The predicted plastic deformation behavior of the workpiece material during ECMAP of route A, route B and route C with a theoretical total strain of ~2.2 upon a single pass at three different friction factors (m=0, 0.1 and 0.2) was compared. The predicted strain results show different values in outside and similar values in central regions of the processed workpieces with different friction and forming routes. The pressing loads are higher under higher friction condition, showing almost no difference with three different pressing routes.