Equal Channel Angular Pressing Method Research Articles

Issledovanie prochnosti, relaksatsionnoy i korrozionnoy stoykosti ul'tramelkozernistoy austenitnoy stali 08Kh18N10T, poluchennoy metodom RKU-pressovaniya. II. issledovanie relaksatsionnykh svoystv i stoykosti protiv mezhkristallitnoy korrozii

Relaxation resistance and corrosion resistance of samples of ultrafine-grained steel 08H18N10T obtained by the method of equal-channel angular pressing at temperatures of 150 and 450 °C are investigated. For ultrafine-grained steel with high values of the limit of macroelasticity and yield strength, a decrease in the Hall—Petch coefficient due to fragmentation of δ-ferrite particles at the method of equal-channel angular pressing is shown. It is established that the samples of ultrafine-grained steel have 2-3 times higher relaxation resistance compared to coarse-grained steel. It is noted that the method of equal-channel angular pressing leads to an increase in the rate of general corrosion. At the same time, despite the decrease in corrosion resistance, samples of ultrafine-grained steels have high resistance to intercrystalline corrosion. It is established that the decrease in corrosion resistance of ultrafine-grained steel is due to an increase in the volume fraction of martensite deformation at the method of equal-channel angular pressing.

Оценка схемы многоканального углового прессования прутков и возможности ее применения на практике

Introduction. Deformation of low-plastic materials requires a high degree of compressive stress. This requirement is implemented, for example, in the process of equal channel angular pressing (ECAP). However, the products obtained by the ECAP method have a cross-section identical to the initial blank, which is one of the disadvantages of this method. The method of nonequal channel angular pressing (NECAP), in contrast to ECAP, makes it possible to change the shape of the initial blank towards closer to the shape of the finished product. However, the well-known NECAP device allows obtaining products only in the form of a thin strip of rectangular cross-section. Well-known devices for multichannel pressing of non-angular type also have a disadvantage — it is implemented only on horizontal type presses, where it is possible to receive long products on the workshop areas. The aim of the work is the evaluation of the bars’ multichannel angular pressing scheme, combining a change in the shape of the initial workpiece in cross-section, as well as the accumulation of a high level of strain during deformation. Research methods: finite element modeling using the DEFORM software module. Results and discussion. The paper considers the scheme of the angular pressing process with the use of a device that allows, for example, to obtain magnesium bars with a diameter of d = 4.1 mm with the number of matrix channels n = 3 from a blank of round cross-section. The container of this device in its lower part has a rectangular groove where the matrix is inserted. Modeling of the process under study using a matrix with the axes of its channels located in the plane of the orthogonal axis of the container and, in the first variant, along the axis of a rectangular groove, and in the second variant, along the radius of the container, allowed us to estimate the distribution of the average stress. It is established that the metal of the blank in both variants of the deformation process is affected by compression stresses at a high level (1,600 MPa). The assessment of the degree of deformation of the pressed bars allowed us to find out that at the initial stage of both process variants, the maximum strain degree can reach 2.6, and at the steady stage it reaches 5.0. It is established that in the case of the first variant of the matrix, the strain level along the length of the bars is lower than when using the second variant of the matrix. The difference reaches 20 %. By evaluating the distribution of the strain degree in the cross section of the pressed bars near the deformation site, it was found that in the case of the first variant of the matrix, the pressed bars of the first and third channels have an uneven dimensions, and the greater value of the strain degree is on the peripheral part of the rods from the side bordering the central bar. This difference in the strain degree reaches 20 %. When placing the second version of the matrix, this unevenness decreases to 12 %. Thus, in the case of using a matrix with the arrangement of the channel axes along the radius of the container, the strain degree is distributed more evenly compared to the strain degree when using a matrix with the arrangement of the channel axes along the axis of a rectangular groove.

Creep and microstructure stability of different purity aluminium and its alloy processed by ECAP method

Severe plastic deformation (SPD) is a perspective method for preparation of ultrafine-grained materials. A coarse-grained aluminium with different purity and Al-0.2Sc alloy were processed by equal-channel angular pressing (ECAP) to evaluate the effect of severe plastic deformation on the thermal stability of resulting ultrafine-grained (UFG) microstructure and on creep behaviour of the SPD processed samples. These materials were subjected to ECAP up to 8 passes by route BC at room temperature with a die that had an internal angle of 90° between the two parts of the channel. The microstructural investigations were performed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with an electron back-scatter diffraction (EBSD) unit. Tension creep tests in constant load regime were conducted at temperature of 473 K on a both coarse-grained and UFG states of materials. It was found that creep behaviour of aluminium and its alloy is influences by their grain size, stability during creep test, material purity, solid solution and precipitate strengthening and fraction of high-angle grain boundaries development during ECAP process. While creep resistance of pure aluminium at elevated temperatures is improved already after 1 ECAP pass, further ECAP passes lead to degradation of creep life in case of low purity Al and Al-0.2Sc alloy.

Simulation of deformation behaviour of Aluminium 7075 during Equal Channel Angular Pressing (ECAP)

This paper presents a finite element simulation of equal channel angular pressing (ECAP) since it is one of the most common and successful severe plastic deformation techniques. This study reports the influence of the most significant factors influencing the ECAP technique. Through finite element simulation, the effect of the die geometry, workpiece geometry, and the pressing speed on the effective strain distributions, damage, and pressing loads, were investigated. The influence of the ECAP method on different material models is also presented. Additionally, the prospective expansion and future applications of ECAP are herein highlighted. From the results, the die geometry of a 90° channel imparts the highest strains during ECAP. Additionally, specimens of rectangular geometry are susceptible to cracking and damage as compared to circular samples. It was found that very high processing speeds (>7mm/sec) are undesirable during ECAP since they cause very high internal stresses to the structure of the workpieces. Besides, processing at room temperature can achieve homogeneous strain distribution with minimum sample damage.

An Overview of Deformation Path Shapes on Equal Channel Angular Pressing

In recent years, research on ultra-fine grain materials has gained attention. While attempts have been made to improve the properties of the material, it has also become increasingly important to decrease the costs. Studies on improving material properties have revealed new production methods or have required the revision of existing production methods. In this direction, severe plastic deformation methods have come to the fore as a good alternative, and by improving the methods with new variations, materials with grain sizes below 1 µm have been obtained. In addition, this method positively affects the mechanical properties of the material. In this study, the Equal Channel Angular Pressing (ECAP) method, one of the severe plastic deformation methods, which has attracted great attention among researchers, was examined and the development stages of the method were investigated according to recent studies. The effective parameters in the method were examined and the effects of these parameters on the grain structure and mechanical properties of the material were discussed. Channel shapes, which are open to innovation and increase the efficiency of the ECAP method, were kept in the foreground among the prominent parameters in the ECAP process, and the results of the design changes made with new variations were examined.

INVESTIGATION OF MICROSTRUCTURAL AND HARDNESS CHANGES OF AA7075 ALLOY PROCESSED BY ECAP

This study aims to examine the change in microstructural and hardness values AA7075 aluminum alloy, which is frequently preferred in the aviation industry by applying the Equal Channel Angular Pressing (ECAP) method. ECAP method, one of the plastic deformation methods, has been successfully carried out by applying 0.025mm/sec pressing speed and 200°C temperature for a different route (A, Bc, C) and the different number of passes (2, 4, 8). The characterization of the aluminum alloy obtained by applying ECAP process was carried out by optical microscope (OM), X-ray diffraction (XRD), and scanning electron microscope (SEM) analysis. Hardness tests have been applied to examine the mechanical properties of the material. The microstructures of the materials obtained as a result of the application were examined. It was observed that precipitation occurred in the AA7075 alloy depending on the applied temperature, pressing, and grain breakage. Moreover, it is seen that the grain size of the materials produced by the ECAP method has been reduced, and consequently the strength of the material increases. As a result of the ECAP process, it was seen that the existing phases were α-Al, -MgZn2, S-Al2CuMg, and Al7Cu2Fe. The grain size of 288.4 nm obtained after 8 repeated passes using the Bc route was the smallest grain size obtained.

Influence of large and severe plastic deformation mechanisms on structure formation in metals

A comparison of structural changes during large deformation accumulation in a metal billet by the example of longitudinal rolling and super large intense plastic deformation (SPD) by the case of equal-channel angular pressing (ECAP) has been carried out. It is shown that during rolling large monotonic deformation leads to formation of extremely thin microstrip structure with weakly oriented cells inside, and nonmonotonic SPD by ECAP method to formation of ultrafine grained (UFG) structure. A kinetic equation for the growth of the fraction of extremely thin micro- bands with small cells in them during strain accumulation was obtained in agreement with the experiment. It has been revealed that the reason why it is not possible to refine grains to sizes corresponding to extremely small cells even after superlarge strains at ECAP is the instability of the latter and non-uniform distribution of deformation origin boundaries over the sample cross-section. Recommendations are given to increase the efficiency of the SPD methods.

In vitro comparison of commercial and ultrafine-grained titanium osteosynthesis miniplates used on mandibular fractures.

Implants called miniplates, with different geometries, are used for the treatment of a fractured or diseased mandible. Generally, Ti-based miniplates in various quantities and with various geometries are fixed into the bone tissue according to the location and shape of the fracture by embedding. The aim of this study was to increase the strength of the material used in the production of miniplates by means of the equal-channel angular pressing (ECAP) treatment, and to provide a highrigidity fixation system with fewer miniplates. In this study, the ECAP method, which is one of the methods of severe plastic deformation, was applied at 4 passes at 300°C in route Bc to increase the strength of pure Ti. Then, miniplates were produced with 2 different geometries (regular and long) and 2 different properties of the Ti material (untreated and ECAP-treated). The produced miniplates were placed in the fracture line formed in the angular region of an artificial, synthetic-bone mandible. The 2-point and 3-point bending and torsion tests were conducted on these fixation systems. As a result, after the ECAP process, the yield and tensile strength of pure Ti increased by 65%, while elongation decreased by 13%. After the ECAP process, the grain size of the material was reduced from 110 μm to 200 nm. This study showed that the fixation system became more rigid due to using ECAP-treated miniplates, and this ensured lesser displacement of the fixation system.

Influence of equal-channel angular pressing on the functional characteristics of biodegradable Fe-based alloys

In this work samples of Fe-Mn alloys were subjected to equal-channel angular pressing (ECAP) in order to study the effect of the resulting microstructure on the mechanical properties, biodegradation rate, and biocompatibility in vitro of the alloys. The microstructure of the alloys was studied by scanning and transmission electron microscopy, as well as by X-ray diffraction analysis. Mechanical properties were studied by microhardness and tensile tests. It is shown that as a result of deformation by the ECAP method, a predominantly austenitic ultrafine-grained (UFG) structure is formed, shear bands up to 600 nm thick and nanosized twins up to 40 nm thick were observed. The release of α-Mn particles in the ECAP process was revealed. Due to the structure refinement and twinning during ECAP, the strength characteristics of Fe-Mn alloys were significantly increased compared to the corresponding alloys in the initial annealed state. An increase in the propensity to biodegradation of UFG alloys with their satisfactory hemocompatibility was observed.

Prediction of Shortening and Material Grain Size after Extrusion Using the ECAP Method

Equal channel angular pressing (ECAP) is a widespread severe plastic deformation (SPD) method to fabricate ultrafine-grained bulk materials. In the field of materials engineering, this method has already experienced rapid development over the past few decades. In this research, the authors sought to create a prediction of shortening and the material particle size after extrusion using ECAP. Behaviours of essential functions are analysed here on samples of pure copper Cu 99.9. It is the measurement and analytical processing of changes in the values of selected structural and mechanical parameters depending on the reduction of the structural granularity. Parameters such as deformation speed, deformation work and ECAP mechanical performance are also included in the results. The change in structure and mechanical parameters is also newly demonstrated by measuring the change in the velocity of the longitudinal ultrasound wave during the experimental passes. Based on the results obtained, new computational algorithms for Excel and Matlab were developed. The algorithms developed here contain many new findings, conclusions and derivations addressing the integrity of the surface with the inner structure of materials. Algorithms are very well-suited for obtaining results on different materials quickly, for predicting and checking measured values, and for designing optimal measurement technology parameters for the ECAP method.

Features of the structure and properties formation of AMG6 alloy under the equal channel angular pressing

The results of experimental studies of changes in the structure, microhardness, and wear resistance of the AMG6 aluminum alloy during equal channel angular pressing (ECAP) are presented in this work. The evolution of the fine structure and the formation of secondary phases in the AMG6 alloy during ECAP were studied. The dark-field image of the structure of the AMg6 alloy in the matrix reflex showed the splitting of the material into small disoriented fragments of about 0.5 μm in size with a small-angle disorientation boundary (about 2–5°). Optimal method and modes of ECAP of the AMG6 aluminum alloy were selected of the bases of experimental research, which make it possible to obtain a workpiece with enhanced tribological and mechanical characteristics. It was established that the most intensive grinding of the grain structure in the AMG6 alloy occurs at ECAP-12 at a channel angle intersection of 120°. It is shown that with a decrease in grain size, the microhardness of the alloy AMG6 after ECAP increases by 4 times, compared with the initial state.The results of the test samples for abrasive wear showed a decrease in mass loss after 12 passes of ECAP, which indicates an increase in the wear resistance of the alloy AMG6 by 13–14 %, compared with the initial state.

Effects of microstructure evolution on discharge properties of AZ31 alloy as anode for seawater battery

AbstractIn recent years, many researchers have been focusing on improving the discharge properties of AZ31 magnesium alloy for battery applications. In this paper, the equal‐channel angular pressing (ECAP) is used as a preferred way of refining the microstructure to enhance the discharge characteristics of AZ31 alloy as the anode for seawater batteries. The electrochemical discharge behaviors of ECAP‐processed AZ31 alloy are investigated along extrusion surfaces, normal cross‐sections, and transverse cross‐sections and compared with as‐cast and homogenized samples. On the basis of the findings, the anode efficiency is improved effectively through the ECAP method, with approximate isotropy in the discharge behaviors of refined AZ31 alloy. The enhanced discharge performance can be attributed to the refined grains, uniform grain sizes, and dispersed β‐Mg17Al12 after ECAP processing.

Texture evolution and strengthening mechanism of single crystal copper during ECAP

For finding a process for improving the strength of single crystal Cu while still maintaining good plasticity and electrical conductivity, the die with an internal angle (Ф) = 105° and an outer curvature angle (ψ) = 37°was used to prepare the equal channel angular pressing (ECAP) deformation by route Bc. The deformation behavior of single crystal copper during ECAP was investigated through electron backscatter diffraction (EBSD), optical microscope (OM) and X-ray diffraction (XRD). The mechanical properties and electronic conductivity after deformation were tested. The results show that the texture evolution is {111}<112> (intital)→ {111}<110>→ {111}<112>→ {112}<110> during 4 passes deformation. The tensile strength and the hardness of single crystal copper increased 123% and 115% respectively after four passes, the electrical conductivity has no obvious decrease. This result indicates that ECAP method can significantly improve the strength of single crystal copper, simultaneously, the plasticity and conductivity of the material remains at an excellent level.

Mechanical behaviour of the St. 20 Steel after equal chanel angular pressing

The mechanical properties of low-carbon (0.2% C) St. 20 steel with conventional and ultrafine-grained (UFG) structures have been studied. The UFG structure of 340-448 nm in grain size was prepared by the method of equal-channel angular pressing (ECAP) for different numbers of passes (N = 4, 8 and 12) and subsequent annealing at 400 and 450°C. The study included static tension, impact bending at room and lower temperatures, fatigue tests, and the examination of the development of plastic deformation zones by replicas. It was established that an increase in the number of ECAP passes increases strength, but decreases plasticity and impact toughness, decreases strain hardening coefficient, and increases yield strength to the level of ultimate tensile strength. The ECAP for 8 passes leads to an increase in fatigue strength by 25%. Annealing does not substantially change mechanical properties. The optimum set of properties is characteristic of the steel after ECAP for 8 passes and annealing at 400°C. The shear instability revealed in the UFG steel upon static loading as the formation of a network of localized deformation bands inclined at an angle of ~ 55° to the loading axis of the specimen depends on the number of passes.

Numerical Modeling of Nanostructured Tube Produced by ECAP

— tailoring material properties to specific application requirements is one of the major challenges in materials engineering. Grain size is a key factor affecting physical and mechanical properties of polycrystals materials. Grain size reduction in the metals and alloys can be achieved using Equal channel angular pressing (ECAP) method. In this work, Nanostructure thin walled copper tube specimens with 1 mm wall thickness and 23mm diameter have been produced successfully with ECAP method using flexible polyurethane rubber pad to prevent the tube walls from collapsing. Furthermore, this paper details the development of a numerical simulation to analyse the fabrication of thin walled tube through ECAP process. A copper tube was pushed through a channel with a series of 90° bends. During each successive bend, the magnitude of plastic strains accumulate in the copper tube. A three dimensional numerical simulation was used to model the process and determine the extent of plastic deformation that takes place during each bend process. The numerical simulation was developed using the finite element (FE) code, ABAQUS V6.13, and analysed using the explicit solver.

Strain-Rate Dependence of Compressive Yield Strength of Titanium Grade 4 with Coarse-Grained and Ultrafine-Grained Structures: Experimental Results and Theoretical Calculation

The nanocrystalline (NC) and ultrafine-grained (UFG) structures of metallic materials can lead to their extraordinary high strength. However, most of the papers on this topic consider deformation parameters of NC and UFG materials only for the case of quasi-static tensile tests. Characteristics of dynamic strength and fracture of such materials remain unexplored. This paper presents a study of the mechanical behavior of pure titanium Grade 4 with a coarse-grained (CG) and UFG structure under uniaxial compression with different strain rates. The UFG structure was provided using the method of equal-channel angular pressing. The dynamic compression was carried out on a setup with the Split-Hopkinson pressure bar. It is found that in the observed range of strain rates 10–3-3×103 s–1, the yield stress of the CG titanium increases by 20%, and does not exceed the yield stress of the UFG titanium. However, the yield stress of the UFG titanium remains close to a quasi-static value. It is shown that these strain-rate dependencies of the yield strength can be predicted by the incubation time approach. The calculated curves show that at strain rates above 104 s–1 the yield stress of the CG titanium becomes higher than the yield strength of the UFG titanium.

Fracture and wear of the Sn11Sb5.5Cu Babbitt after equal-channel angular pressing

A computer simulation and natural experiments on the rod from babbit Sn11Sb5.5Cu deformation by the method of equal-channel angular pressing (ECAP) were carried out. Two structural states of the material were investigated. The first, obtained by usual crystallization, is characterized by large particles of intermetallic- and -phases. The second, obtained by rapid crystallization, has fine particles. ECAP was carried out in a matrix with a vertical and horizontal channels intersecting at a right angle. With the aim to ensure the least damage at the ECAP the computer simulation of the process in the software product DEFORM-2D was made, the deformation rate was selected. The wear was determined by the loss of the sample weight. Dependence of wear of babbitt, obtained by usual crystallization, had stages of running-in and stable wear. Wearing of the samples obtained by rapid crystallization showed that the running-in stage is absent. It was found that severe plastic deformation (SPD) by the ECAP method leads to the dispersion of intermetallic particles and the weakening of the adhesive bond of the particles with the matrix. In the case of coarse particles, their milling causes a decrease in wear. In the case of fine particles, the weakening of adhesion to the matrix causes an increase in wear. It can be said that for a material such as babbit Sn11Sb5.5Cu, an attempt to improve the tribological characteristics by means of the SPD method is untenable. There are less costly and simpler ways to obtain in babbits a structure with small intermetallic particles, which fully complies with the Charpy rule and has high tribological characteristics.

CHANNEL CROSS-SECTION INFLUENCE ON EFFECTIVE STRAIN DISTRIBUTION IN ECAP PROCESS

This study compares the numerically determined strain distributions after the application of the method of equal-channel angular pressing. The calculations were performed for four variants of the channel cross-sectional shapes – square, circular, and two rectangular ones with the same transverse surface area. The calculation results have been demonstrated as maps of effective strain distribution in the stabilized process.

Microstructure Evolution and Coarsening Mechanism of 7075 Semi-Solid Aluminum Alloy Pre-Deformed by ECAP Method

To investigate the influence of refined grains on the microstructure of 7075 aluminum alloy in semi-solid state, a new strain induced melting activation (SIMA) method was put forward containing two main stages: pre-deformation with equal channel angular pressing (ECAP) method and isothermally holding in the semi-solid temperature range. The breaking up and growth mechanisms of the grains and kinetics of equiaxed grains coarsening during the semi-solid holding were investigated. The results showed that the average grain size after ECAP extrusion decreased significantly, e.g., microstructure with average globular diameter less than 5μm was achieved after four-pass ECAP extrusion. Obvious grain coarsening had been found during isothermal holding in the semi-solid state and the roundness of the grains increased with the increasing holding time. The proper microstructure of 66.8μm in diameter and 1.22 in shape factor was obtained under proper soaking condition (at 590°C for 15 min). Two coarsening mechanisms, namely, coalescence in lower liquid fraction and Ostwald ripening in higher liquid fraction contributed to the grain growth process.

Analysis of Microstructure and Mechanical Properties Changes in AA1050 Aluminum Subjected to ECAP and KoBo Processes / Analiza Zmian Mikrostruktury I Własności Mechanicznych Aluminium AA1050 Po Procesie ECAP I KoBo

Analysis of the results of the microstructure and the mechanical properties change in AA1050 aluminum alloy of technical purity processed using ECAP (Equal Channel Angular Pressing) and KoBo deformation methods are presented in the paper.. ECAP process was performed according to Bc scheme in the range from 1 up to 10 passes. Changes of microstructure were analyzed using scanning electrone microscope equipped with electron backscattered diffraction (EBSD) system. Microstructure and fraction of high-angle grain boundaries in KoBo processed samples were similar to those observed in ECAP processed samples after four passes. The most significant microstructure refinement was observed in ECAP processed sample submitted to 10 passes. In ECAP method the systematic increase of mechanical properties was observed along with increase of deformation degree.