Papers by Ebad Bagherpour
Metallurgical and Materials Transactions A
A combination of experiment and numerical simulation was employed to study the healing mechanism ... more A combination of experiment and numerical simulation was employed to study the healing mechanism of fatigue crack via a novel route of electropulsing treatment (EPT) named dual-step EPT processing. By applying cyclic loads, similar cracks were generated in 316L stainless steel samples. Then, cracked specimens were subjected to electropulsing treatment under different conditions in order to find the optimum EPT condition to effectively heal the crack. The geometry of the fatigue crack before and after EPT was investigated in 3D by Micro-CT. SEM-EBSD was used to evaluate the microstructure of the healed region. To understand the dominant mechanism of crack healing by EPT, the temperature and stress/strain fields were evaluated by the finite element method (FEM) considering non-uniform Joule heating. The results demonstrate that complete crack healing requires a balanced combination of melting and compressive stress as well as increased peak current density regarding the reduced crack ...
The present paper is the second part of a previously published overview entitled “ten years of se... more The present paper is the second part of a previously published overview entitled “ten years of severe plastic deformation (SPD) in Iran”. Part I concentrates on the equal channel angular pressing (ECAP). In this part, the focus is on the accumulative roll bonding (ARB) because, currently, Iran is ranked the first in the world by the total number of publications in this field. In the present section, the emphasis is not on the microstructure and ultrafine-grained materials produced by ARB. Instead, its focus is on several aspects of ARB to which small attention has been paid so far. The impact and contribution of Iran to each category is evaluated in comparison to researchers from other countries. The main interest of Iranian researchers in the field of ARB is to fabricate the composite materials, particularly metal matrix composites (MMCs). The Iranian researchers were the first who introduced ARB as an effective method to produce particulate MMCs.
Crystals, 2020
The effect of reverse straining on the microstructure, texture, and hardness of the pure Al durin... more The effect of reverse straining on the microstructure, texture, and hardness of the pure Al during the single cycle of the simple shear extrusion (SSE) process is investigated. Electron backscattering diffraction (EBSD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) are used for microstructural evaluations. Due to the nature of the SSE process, the direction of the shear is reversed in the second half channel. As a result, the mean misorientation angle, dislocation density, and hardness decrease. The grain size increases to some extent in the exit of the channel compared with that in the middle. The structural evolution during the single pass of SSE is described in terms of the dislocation cancelling, “untangling” of the cell walls and disintegration of the “forward” cell structure due to the reverse straining in the second half channel. Some simple shear components replace the first texture component in the middle of the channel. At th...
International Journal of Minerals, Metallurgy, and Materials, 2019
Commercial A7020-T6 plates in the overaged state were subjected to friction stir welding with fou... more Commercial A7020-T6 plates in the overaged state were subjected to friction stir welding with four different tool rotational speeds of 500, 710, 1000, and 1400 r/min and a single traverse feed rate of 40 mm/min. The resultant changes in the welding heat input, microstructure, and the mechanical properties of the joints were investigated. The changes were related to the processes of growth, dissolution, and reformation of precipitates. The precipitate evolution was examined by differential scanning calorimetry, and the microstructural analysis was conducted using optical, scanning, and transmission electron microscopes. The results showed that the grain size in the stirred zone (SZ) decreased substantially compared with the base metal, but increased with tool rotational speed because of the rise in temperature. We found that the width of the heat-affected zone increased with tool rotational speed. The hardness and the tensile strength in the SZ increased with increasing heat input compared with the base metal in the overaged condition. This recovery in mechanical properties of the joints can be attributed to the dissolution and reformation of precipitates in the SZ and the thermomechanically affected zone. This process is referred to as an "auto-aging treatment."
Strain reversal in simple shear extrusion (SSE) processing: Microstructure investigations and mechanical properties
AIP Conference Proceedings, 2018
Simple shear extrusion (SSE) is one of the severe plastic deformations which are based on the dir... more Simple shear extrusion (SSE) is one of the severe plastic deformations which are based on the direct extrusion of the samples. By passing the material through the deformation channel, gradually increased shear strain is imposed to the material. The direction of the shear is reversed at the middle of the channel after the maximum distortion angle is achieved. Therefore, the change in the direction of the shear affects the microstructure and texture of the sample in a unique way. Hence, in the present search role of shear reversal on microstructure and mechanical properties of pure copper after multi passes and during a single pass of the simple shear extrusion (SSE) process was investigated. For SSE processing an appropriate die with a linear die profile was designed and constructed. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) were used to evaluate the microstructure of the deformed samples. Strain reversal during the process results in a slight reduction in ...
JOM, 2019
Improvement of the functional properties of aluminium and its alloys by grain refinement is an ef... more Improvement of the functional properties of aluminium and its alloys by grain refinement is an effective way to increase their applications. The capability of severe plastic deformation methods to produce ultrafine-grained materials has been well established. However, their industrial application is limited because of the required additional equipment and limitation of the product size. Due to the direct extrusion characteristic of the simple shear extrusion (SSE) method and consequently the minimal additional tools and expenses, SSE is a good candidate for commercialization. The aim of this research is to scale up the SSE products to facilitate their potential use in practical applications. To overcome the limitation on the length of the plunger and reduce the load of the SSE process, a design is proposed in the current research. Microstructural investigations and mechanical tests of commercial pure aluminium (AA1050) workpieces confirm the effectiveness of the proposed design on t...
Metals, 2018
In this study, for the first time, the effect of large non-monotonic simple shear strains on the ... more In this study, for the first time, the effect of large non-monotonic simple shear strains on the uniformity of the tensile properties of pure Cu specimens was studied and justified by means of microstructural and textural investigations. A process called simple shear extrusion, which consists of two forward and two reversed simple shear straining stages on two different slip planes, was designed in order to impose non-monotonic simple shear strains. Although the mechanism of grain refinement is continuous dynamic recrystallization, an exceptional microstructural behavior and texture were observed due to the complicated straining path results from two different slip planes and two pairs of shear directions on two different axes in a cycle of the process. The geometry of the process imposes a distribution of strain results in the inhomogeneous microstructure and texture throughout the plane perpendicular to the slip plane. Although it is expected that the yield strength in the periphe...
Journal of Alloys and Compounds, 2018
In this study, Al/AlN in-situ nanocomposites were fabricated using Al/BN as the starting composit... more In this study, Al/AlN in-situ nanocomposites were fabricated using Al/BN as the starting composite powders. The impact of adding hexagonal boron nitride (BN) to the Al matrix of commercial purity on the microstructure and mechanical behavior of the fabricated in-situ nanocomposites was investigated. Samples including 1, 2, and 4 wt.% boron nitride nanoparticles were produced by planetary ball milling of the composite powders and a post-process of hot extrusion. Scanning transmission electron microscopy revealed that boron nitride nanoparticles dissolved as a solid solution of B and N in the Al matrix at the as-milled state. Through the process of hot extrusion, AlN as the in-situ phase was formed by a reaction between Al and N. These led to improve the mechanical properties as well as grain refinement of Al/AlN nanocomposite. The average grain size of the fabricated composites with the use of 1, 2 and 4 wt.% BN was measured about 910, 823, and 760 nm respectively. It was found that combined strengthening mechanisms of grain refinement, a solid solution of mostly B and AlN in-situ phase formation improved the mechanical properties of Al/AlN nanocomposite. With the use of 1, 2, and 4 wt.% BN, the tensile strength of nanocomposite samples increased approximately 40, 56, and 57% in comparison with pure Al, respectively. The remarkable change in microstructure and mechanical properties of the nanocomposite was obtained when the content of BN is up to 2 wt.%.
Advances in Materials Science and Engineering, 2018
Transition of dislocation structures in ultrafine-grained copper processed by simple shear extrus... more Transition of dislocation structures in ultrafine-grained copper processed by simple shear extrusion (SSE) and its effects on dissolution were manifested by simple immersion tests using a modified Livingston dislocation etchant, which attacks dislocations and grain boundaries selectively. The SSE process increased the internal strain evaluated by X-ray line broadening analysis until eight passes but decreased it with further extrusion until twelve passes. The weight loss in the immersion tests reflected the variation in the internal strain: namely, it increased until eight passes and then decreased with further extrusion to twelve passes. Taking our previous report on microstructural observation into account, it is suggested that variation in the internal strain is caused by both the variation in dislocation density and structural change of grain boundaries from equilibrium to nonequilibrium states or vice versa. Decreased dislocation density and structural change back to equilibriu...
The International Journal of Advanced Manufacturing Technology, 2018
The present overview gives a new approach toward developments and recent achievements in severe p... more The present overview gives a new approach toward developments and recent achievements in severe plastic deformation. The review focuses on several subjects. First, an outline of SPD research status in the world is presented by literature analysis based on the total number of publications, citations and the contribution of the topranked countries. Second, the mechanisms of grain refinement and grain growth during SPD processing are discussed by means of the latest concepts. Third, all SPD methods invented so far are classified based on a new approach. Up to now, the growing tendency of researchers to introduce new SPD techniques results in a large number of SPD methods which can be considered as new or modified techniques or a combination of previous ones. Such a reference can help to prevent the future duplication to introduce the SPD processes, which are technically similar. At the end, the practical applications of ultrafine/nanostructured materials and industrial commercialization of SPD methods are summarized.
Procedia Manufacturing, 2018
Under the concept of "Industry 4.0", production processes will be pushed to be increasingly inter... more Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization's profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization's value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity optimization might hide operational inefficiency.
IOP Conference Series: Materials Science and Engineering, 2017
Tube channel pressing (TCP), which is one of the severe plastic deformation (SPD) technologies to... more Tube channel pressing (TCP), which is one of the severe plastic deformation (SPD) technologies to refine grain size into submicron size for tubular materials, have been applied to ferritic stainless steel tubes for one pass, in order to alleviate ridging and enhance the hydroformability. It was found that grain-scale shear bands were introduced by one-pass TCP, and texture and microstructure was successfully modified by promoting recrystallization of deformation microstructure, which is otherwise hard-to-recrystallize, in the post-TCP annealing. Elongation to failure, strain-hardening exponent (n-value) and Lankford values of both longitudinal and circumferential directions increased in comparison to with the tube fabricated by conventional process.
Materials Science and Engineering: A, 2016
In the present paper the role of shear reversal on microstructure, texture and mechanical propert... more In the present paper the role of shear reversal on microstructure, texture and mechanical properties of pure copper during a single pass of the simple shear extrusion (SSE) process was investigated. For SSE processing an appropriate die with a linear die profile was designed and constructed, which imposes forward shear in the first half and reverse shear in the second half channels. Electron back-scattering diffraction (EBSD), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) were used to evaluate the microstructure of the deformed samples. The geometrical nature of this process imposes a distribution of strain results in the inhomogeneous microstructure and the hardness throughout the plane perpendicular to the extrusion direction. Strain reversal during the process results in a slight reduction in dislocation density, the hardness and mean disorientation angle of the samples, and an increase in the grain size. After a complete pass of SSE, dislocation density decreased by $ 14% if compared to the middle of the process. This suggests that the dislocation annihilation occurred by the reversal of the shear strain. The simple shear textures were formed gradually and the strongest simple shear textures were observed on the middle of the SSE channel. The degree of the simple shear textures decreases with the distance from the middle plane where the shear is reversed, but the simple shear textures are still the major components after exit of the channel. Hardness variation was modeled by contributions from dislocation strengthening and grain boundary strengthening, where dislocation density is approximated by the misorientation angle of LAGBs which are regarded as dislocation cell boundaries. As a result, the hardness can be predicted successfully by the microstructural features, i.e. the low-angle boundaries, the mean misorientation angle and the fraction of high-angle grain boundaries.
Journal of Materials Science, 2016
The effect of particle distribution non-uniformity on the microstructure and flow stress in nanos... more The effect of particle distribution non-uniformity on the microstructure and flow stress in nanostructured metal matrix composites produced by severe plastic deformation was investigated. The Al/SiC composite fabricated by accumulative roll bonding was considered as a case. Transmission electron microscope (TEM) and scanning transmission electron microscope (STEM) were used for microstructural characterizations. Based on the particle distribution, three different zones were considered: particle-free zone, single particle zone, and cluster zone. In comparison to the particle free zone, finer grain sizes with higher boundary misorientation angle were observed in the single particle zone. The lowest grain size (342/260 nm by TEM/STEM) was obtained in the cluster zone approximately between two near particles. The selected area diffraction showed the highest misorientation angle at these regions. A combined microstructure strengthening analysis was considered for the prediction of the flow stress. The flow stress is predicted based on the grain sizes at various microstructural zones, and the results were compared with the experimental yield stress of the composite.
Materials Science and Engineering: A, 2016
Materials Science and Engineering: A, 2017
In the present paper the variation of microstructural parameters and tensile properties of ultraf... more In the present paper the variation of microstructural parameters and tensile properties of ultrafine-grained copper processed by simple shear extrusion (SSE) via namely route C in 1, 2, 4, 6, 8 and 12 passes is described. TEM analysis showed that the microstructure evolves from lamellar boundaries and elongated cells towards a more equiaxed homogeneous microstructure. After 12 passes, the grain fragmentation occurred in all the directions without any significant elongation in the grains. The minimum cell size is achieved after eight passes. Evaluation of dislocation density using scanning transmission electron microscopy observations shows a gradual increase of dislocation from one to eight passes following a reduction afterward. Yield stress and ultimate tensile stress reach a maximum after eight passes. The uniform elongation attains its minimum after eight passes. Reduction in dislocation density, grain growth, formation of Moiré fringes and twinning after twelve passes of SSE are some of the evidences for the
MATERIALS TRANSACTIONS, 2016
In the present paper texture changes of pure copper during and after a single pass of simple shea... more In the present paper texture changes of pure copper during and after a single pass of simple shear extrusion (SSE) was studied. For this reason, the samples were taken out from an SSE die during the process and investigated by electron back-scattering diffraction (EBSD). From the beginning to the middle of the deformation channel, the simple shear textures were formed gradually and the strongest one was observed on the 0.5 pass sample. The degree of the simple shear textures decreases with the distance from the middle plane where the shear is reversed, but the simple shear textures are still the major components after the exit of the channel. The major orientation component of the 0.5 pass sample was C component, whereas, it was A * 2 component of the 1 pass sample.
Consolidation of aluminum powders through equal channel angular pressing-forward extrusion (ECAP-FE)
In the present work, a new method, named as equal channel angular pressing-forward extrusion (ECA... more In the present work, a new method, named as equal channel angular pressing-forward extrusion (ECAP-FE), is introduced for consolidation of metallic powders. Al particles were successfully consolidated at 200ºC by this method. To evaluate the capability of the new process, properties of the samples produced by this method were compared with that produced through conventional forward extrusion process. Results showed that combination of ECAP and forward extrusion process could refine the microstructure and significantly improve the physical and mechanical properties of the produced material
Materials & Design, 2015
In the present work, for the first time, an analytical approach based on upper-bound theorem is p... more In the present work, for the first time, an analytical approach based on upper-bound theorem is proposed to analyze the simple shear extrusion process. In this regard new die parameter named maximum inclination angle is introduced. By this model, the power dissipated on all frictional and velocity discontinuity surfaces is determined and the total power is optimized for two types of die, fixed and movable inlet channel die. To check the validation of the upper-bound model, the process is simulated by the commercial finite element code, Deform-3D. To compare the theoretical results with experiments, a fixed inlet channel die and two dies with movable inlet channel are used to determine the processing force for different cross sections. The developed model predicts that the relative extrusion pressure increases with increasing the constant friction factor; also, for a given value of the constant friction factor and the maximum distortion angle, there is an optimized maximum inclination angle which minimizes the power. Comparing the fixed inlet channel die with the movable inlet channel one, it is seen that the optimized maximum inclination angle is higher in the FIC die.
IOP Conference Series: Materials Science and Engineering, 2014
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Papers by Ebad Bagherpour