Mehdi Mehdi - Academia.edu (original) (raw)

Papers by Mehdi Mehdi

TMS 2022 151st Annual Meeting & Exhibition Supplemental Proceedings, 2022

Materials Science Forum, 2021

Cube texture ({001}<100>) is a desired final texture in non-oriented electrical steel sheet... more Cube texture ({001}<100>) is a desired final texture in non-oriented electrical steel sheets used as magnetic cores because it contains two easy <100> axes in the sheet plane, which is beneficial to the magnetic properties. However, the cube texture is very difficult to form in non-oriented electrical steels through conventional rolling and annealing. It has been shown that after conventional rolling, the deformed <111>//ND (normal direction) grains provided nucleation sites for the unfavourable <111>//ND texture during recrystallization, leading to a final <111>//ND texture. To eliminate the <111>//ND texture and promote the {001}<100> texture, an uncommon rolling process, i.e. inclined rolling, was adopted in this study. By rotating the hot rolling direction by 60° around the ND, an uncommon initial texture, the rotated Goss ({110}<110>), was intentionally generated. This was intended to change the orientation flow during plastic def...

Non-oriented electrical steels are widely used in electric motors and generators as core material... more Non-oriented electrical steels are widely used in electric motors and generators as core materials to amplify magnetic flux and thus enhancing the conversion of energy. The efficiency of the motors and generators is closely related to the magnetic properties of the lamination core. In order to produce the magnetically favourable //ND texture (θ-fibre) and suppress the unfavourable //ND (γ-fiber) components in non-oriented electrical steels, two unconventional cold rolling schemes (inclined and skew rolling) were employed to process the steel. These rolling schemes have shown great potential in altering the texture of non-oriented electrical steel, especially for the 60° (inclined rolling) and 22.5° (skew rolling) angles. In this paper the effect of annealing time on the texture evolution of a 2.8 wt% Si steel was investigated using EBSD techniques. It was found that, all the unconventional rolling schemes were able to produce a strong θ-fiber texture, but the annealing time to achie...

Materials Characterization, 2021

Abstract Magnetic Barkhausen noise (MBN) analysis is a relatively new technique used to character... more Abstract Magnetic Barkhausen noise (MBN) analysis is a relatively new technique used to characterize the magnetic properties of electrical steels. Not only has it been utilized to evaluate the overall core loss of electrical steel sheets, but it has also been employed as a non-destructive testing (NDT) tool to assess the magnetocrystalline anisotropy of ferromagnetic materials. In this study, non-oriented electrical steel sheets produced by inclined and cross rolling were characterized by both MBN and electron backscatter diffraction (EBSD). The angular MBN measured on the surface of the steel sheet was directly compared to the magnetocrystalline anisotropy energy (MAE) calculated from the measured crystallographic texture. The MBN energy corresponding to the saturation-to-remanence part of the hysteresis loop was evaluated, which had been reported to have a close correlation to the MAE in pipeline steels. The results in this study showed that such a relationship did not exist in any of the electrical steel samples examined (including deformed, partially recrystallized, and completely recrystallized), although in some samples the polarities of the MBN and MAE partially coincide. It was shown that the residual stress in the material played an important role in determining the polarities of the angular MBN, which had been ignored in the previous studies when comparing the MBN to the MAE. Possible reasons that caused the discrepancies between the results of this study and those of the previous studies were given.

Tribology Letters, 2021

The load-induced dry-sliding wear behavior of alpha titanium (Ti) with low amount of boron (< ... more The load-induced dry-sliding wear behavior of alpha titanium (Ti) with low amount of boron (< 1 wt%) samples made through plasma transferred arc solid free form fabrication process were studied in the untreated and hardened shot-peened surface conditions. Shot peening conducted at 90 psi for two minutes for 100% coverage with S-550 steel shots, was found to lead to an increase in surface hardness, with a depth of penetration of approximately 1 mm. While shot peening in this scheme was found to have a limited influence on COF and wear rates, it did influence the wear mechanisms observed. Untreated samples had a shift in wear behavior from low to high loading conditions. Dominating wear mechanisms at low loads (≤ 10 N) for untreated samples were oxidative and abrasive wear accompanied by weight gain of the steel counterface balls. At higher loads (> 10 N), untreated samples experienced weight loss of the steel counterface balls and severe plastic deformation with the formation and onset delamination of mechanically mixed layers (MML). Comparatively, shot-peened samples exhibited limited changes in wear behavior, remaining dominated by oxidation wear over the loading range. With oxidation wear dominating and the shot peening treatment inhibiting the formation of a MML and its delamination, it is hypothesized that the transition to severe wear may be delayed to higher loads from this treatment.

Metals, 2021

In this work, fatigue improvement through shot peening of an additive manufactured Ti–TiB block p... more In this work, fatigue improvement through shot peening of an additive manufactured Ti–TiB block produced through Plasma Transferred Arc Solid Free-Form Fabrication (PTA-SFFF) was investigated. The microstructure and composition were explored through analytical microscopy techniques such as scanning and transmission electron microscopy (SEM, TEM) and electron backscatter diffraction (EBSD). To investigate the isotropic behavior within the additive manufactured Ti–TiB blocks, tensile tests were conducted in longitudinal, diagonal, and lateral directions. A consistent tensile behavior was observed for all the directions, highlighting a nearly isotropic behavior within samples. Shot peening was introduced as a postmanufacturing treatment to enhance the mechanical properties of AM specimens. Shot peening led to a localized increase in hardness at the near-surface where stress-induced twins are noted within the affected microstructure. The RBF-200 HT rotating-beam fatigue machine was util...

IOP Conference Series: Materials Science and Engineering, 2018

Metallurgical and Materials Transactions A, 2019

A 2.8 wt pct Si non-oriented electrical steel was thermomechanically processed using conventional... more A 2.8 wt pct Si non-oriented electrical steel was thermomechanically processed using conventional hot rolling, hot band annealing, cold rolling and final annealing routes. The evolution of texture during these processes was investigated using electron backscatter diffraction (EBSD) techniques. The final annealing was conducted at 750°C for various times (10 to 120 minutes), and it was found that by simply changing the annealing time, the texture shows significantly different features, i.e. depending on the annealing time, the Goss ({011}h100i), the h-fiber (h001i//normal direction, ND) or the c-fiber (h111i//ND) may dominate the texture. Annealing for 60 or 90 minutes can essentially eliminate the magnetically unfavorable h111i//ND texture while promoting the desired h001i//ND texture. On the other hand, annealing at the same temperature for 30 or 120 minutes, the h111i//ND texture is strengthened and the favorable h001i//ND texture is weakened. The formation of the typical textures observed in each process was examined with respect to known mechanisms existing in the literature. The formation of the various textures during annealing at different times was discussed against the oriented growth theory based on a statistic analysis of the grain boundary misorientation and grain size. It is seen that during annealing at different times, the grain boundary character (e.g. mobility) and the grain size may determine the growth of certain orientations, which give rise to the different textures after annealing for different times.

Acta Materialia, 2019

Abstract Due to the alignment of two easy 〈100〉 axes in the sheet plane, the cube orientation ({0... more Abstract Due to the alignment of two easy 〈100〉 axes in the sheet plane, the cube orientation ({001} ) is an ideal texture for non-oriented electrical steel sheets used as core lamination for electric motors. However, this magnetically favorable texture was rarely able to be produced using conventional rolling and annealing routes in non-oriented electrical steels. In this research, inclined cold rolling − a simple rolling scheme to alter the initial texture before cold rolling − was applied to a 2.8 wt% Si non-oriented electrical steel, in order to intentionally “create” a rotated Goss ({110} ) texture before cold rolling, which was not commonly observed in hot-rolled electrical steels. Plane-strain compression (rolling) of the rotated Goss was able to produce cube crystallites within the matrix, at the grain boundaries and within the shear bands of the deformed rotated Goss grains. The cube crystallites within the shear bands had lower stored energy than their surroundings, and served as the initial seeds for nucleation. Upon annealing, the cube crystallites preferentially nucleated from the shear bands and competitively grew out of the surrounding substructure, forming a strong cube texture in the final sheet. The formation of the initial cube crystallites within the shear bands of the deformed microstructure was believed to be necessary for the development of a final cube texture in the annealed electrical steel sheet. Although inclined rolling may be difficult to be implemented in industrial production, its unique capability to produce uncommon initial texture before cold rolling provides an interesting technique for the study of texture involution during thermomechanical processing.

IOP Conference Series: Materials Science and Engineering, 2019

The magnetic properties of non–oriented electrical steel (NOES) vary significantly with respect t... more The magnetic properties of non–oriented electrical steel (NOES) vary significantly with respect to the microstructure and crystallographic texture of the final steel sheets, which, in turn, are highly dependent upon the thermomechanical processing parameters used during hot rolling, cold rolling and annealing. This paper performs an exploratory performance analysis of NOES for use in high–speed traction motors, emphasizing the importance of obtaining an appropriate crystallographic texture to achieve the desired magnetic properties by controlling the annealing temperature and holding time. A 3.2% Si NOES annealed at 860°C for 24 hours after hot rolling can result in reduced core losses after cold rolling and final annealing. This material was chosen for the performance analysis of a laboratory scale high–speed, high–power traction motor (45 kW, 10,000 rpm) using finite element analysis (FEA). The motor using the NOES is compared to that using a commercially available grain–oriented ...

Journal of Magnetism and Magnetic Materials, 2019

A 3.2 wt% Si non-oriented electrical steel (NOES) was processed using conventional rolling and an... more A 3.2 wt% Si non-oriented electrical steel (NOES) was processed using conventional rolling and annealing routes, i.e. hot rolling, hot band annealing, cold rolling, and final annealing. The evolution of texture during all the thermomechanical processing stages was investigated using electron backscatter diffraction (EBSD) techniques. It was found that the final annealing temperature and holding time had a profound effect on the texture. At higher temperatures and shorter holding times, the desired <100>//ND (normal direction) texture was promoted, while the magnetically unfavorable <111>//ND texture was weakened. The magnetic properties of the steel sheets were measured by Epstein frame method and magnetic Barkhausen noise (MBN) analysis, and it was found that the AC (alternating current) core losses of the NOES annealed at 850C for 60 minutes were comparable to grain-oriented electrical steel (GOES) with the same silicon content and the same sheet thickness, even in the rolling direction (RD). The DC (direct current) core losses and the MBN decreased with increasing grain size, due to the decrease in pinning sites (grain boundaries). The good magnetic properties of the processed NOES were attributed to a combination of an optimized texture and an appropriate grain size, which was, in turn, the result of proper hot band annealing, fast heating during annealing and a good selection of the annealing temperature and holding time.

steel research international, 2019

During the manufacturing of non-oriented electrical steel laminations for electric motor or gener... more During the manufacturing of non-oriented electrical steel laminations for electric motor or generator applications, the Goss ({110}<001>) texture frequently appears in several stages of the processing. To understand the origin and the evolution of this texture, a non-oriented electrical steel (2.8 wt% Si) is processed through hot rolling, hot band annealing, cold rolling and final annealing, and the origins of the Goss orientation and the evolution of the Goss texture in these processes are investigated by electron backscatter diffraction (EBSD) techniques. It is seen that hot rolling results in a high volume fraction (%30%) of the Goss grains near the surfaces of the rolled plate, but the subsequent hot band annealing significantly reduces it to less than 10%. After cold rolling, the Goss volume fraction further decreases to only about 1%. Three locations of the Goss grains are observed in the coldrolled matrix, that is, those within the shear bands of two symmetrically equivalent {111}<112> grains, those embedded in the microbands of one of the {111}<112> grains, and those at the grain boundaries between the {111}<112> and {113}<361> grains. The formation mechanisms of these three types of Goss grains are explained using a transition band model and a rigid inclusion model.

Journal of Magnetism and Magnetic Materials, 2018

Magnetic Barkhausen noise (MBN) signals were measured on a non-oriented electrical steel through ... more Magnetic Barkhausen noise (MBN) signals were measured on a non-oriented electrical steel through all the thermomechanical processing stages, i.e. hot rolling, hot band annealing, cold rolling and final annealing. The temperature of the final annealing was varied from 600°C to 750°C so that the steel consisted of partially or completely recrystallized microstructures and different levels of residual stresses. The angular MBN rms (root mean square) values were compared to the texture factors in the same directions, the latter being calculated from the crystallographic texture measured by electron backscatter diffraction (EBSD). It was found that, in the cold-rolled, hot-rolled and completely recrystallized steels, the angular MBN rms followed a cosine function with respect to the angle of magnetization, while in partially recrystallized state such a relation does not exist. After cold rolling, the maximum MBN rms was observed in the rolling direction (RD) and the minimum MBN rms was in the transverse direction (TD), which was inconsistent with the magnetocrystalline anisotropy as indicated by the texture factor. After hot rolling, the maximum and minimum MBN rms values were observed in the TD and RD, respectively, exactly opposite to the cold-rolled state. If the steel was completely recrystallized, the maximum MBN rms was normally observed at a direction that was 15°-30° from the minimum texture factor. If the steel was partially recrystallized, both the magnetocrystalline anisotropy of the material and the residual stress contributed to the angular MBN rms , which resulted in the deviation of the relationship from a cosine function. The relative strength of the two factors determined which factor would dominate the overall magnetic anisotropy.

IEEE Transactions on Magnetics, 2018

Non-oriented electrical steels are indispensable materials for use in electric motors as magnetic... more Non-oriented electrical steels are indispensable materials for use in electric motors as magnetic cores. It is desired that the magnetic properties of the steel sheets be optimal and uniform in all the directions in the sheet plane. Thus, knowing the magnetic properties of the steel sheets in all the directions is crucial for the design of the motors. However, the magnetic properties of non-oriented electrical steels are usually measured by the standard Epstein frame method, which normally only gives the overall magnetic properties in the rolling and transverse directions and those in other directions are usually unknown. In this paper, magnetic Barkhausen noise (MBN) analysis is utilized to characterize the local magnetic response of non-oriented electrical steel. By aligning the MBN sensor to all the directions in the sheet plane, angular magnetic response is obtained. The measured MBN is then directly compared to the texture factor evaluated in the same direction. In this way, the local magnetic response of the steel is correlated with the crystallographic texture. It was found that MBN technique was able to detect the difference in magnetic response induced by magnetocrystalline anisotropy if the effect of the residual stress can be eliminated. This would provide a potential technique for the characterization of magnetic properties of non-oriented electrical steel.

Materials Characterization, 2018

Steel samples cut from two line pipes with unknown processing history were analyzed using magneti... more Steel samples cut from two line pipes with unknown processing history were analyzed using magnetic Barkhausen noise (MBN), electron backscatter diffraction (EBSD) and Vickers hardness techniques on the pipe surface and on sections through the wall thickness. The results show that the MBN responses vary significantly not only between the two pipe steels, but also among different thickness layers of each steel. Both steels show considerable variations in MBN at different locations on the surfaces. For one steel, the surface MBN illustrates an inverse linear relationship with respect to the hardness, while the other does not depict such a relation since the variation in hardness at different locations is very small. Across the thickness, the microstructure (phase and grain size) of both steels is quite similar, but the texture shows significant differences. Again, there is a large difference in hardness across the thickness for one steel, while the other only shows very small variation in hardness across the thickness. The variations in average MBN across the wall thickness for both steels are quite large. Angular MBN measurements on the sectioned samples revealed significant discrepancies in the magnetic anisotropy in the two steels. Based on the analysis of the angular MBN data with respect to the single and dual easy axis models, one pipe can be determined to have been manufactured through a seam welding process, while the other may have been formed by spiral welding. Due to the residual stresses in the steel samples, the effect of the crystallographic texture on the anisotropy in MBN response has essentially been suppressed. (1) where K 0 and K 1 are constants related to a particular material, and α 1 ,

Journal of Magnetism and Magnetic Materials, 2017

In order to promote the magnetically favourable < 001 > //ND texture (θ-fibre) and minimize the u... more In order to promote the magnetically favourable < 001 > //ND texture (θ-fibre) and minimize the unfavourable < 111 > //ND fibre (γ-fibre) in non-oriented electrical steel, an unconventional cold rolling scheme was employed in this study, in which the cold rolling was carried out at an angle (i.e. 30°, 45°, 60°, and 90°) to the hot rolling direction (HRD). After annealing, two steel sheets (i.e. those after cold rolling at 60°and 45°to the HRD) were found to have considerably different textures from other sheets, i.e. showing the strongest and the weakest θ-fibre textures, respectively. These two sheets were then subjected to skin pass rolling to various reduction rates from 5-20% to investigate the effect of rolling reduction on the evolution of texture. It was found that during skin pass rolling, the cube texture ({001} < 100 >) was gradually weakened and the rotated cube orientation ({001} < 110 >) was strengthened. With the increase of the reduction rate, the {112} < 110 > orientation on the α-fibre became a major component. Upon final annealing, the cube texture was slightly restored, but the volume fraction was considerably lower than that before skin pass rolling.

Wear, 2016

Abstract The dry sliding wear behavior and wear mechanisms of near-β Ti–10V–2Fe–3Al alloy were in... more Abstract The dry sliding wear behavior and wear mechanisms of near-β Ti–10V–2Fe–3Al alloy were investigated with respect to its superelastic characteristics. The β-annealed Ti–10V–2Fe–3Al alloy exhibited high recoverable elastic deformation, e.g., maximum recovery ratio of 90% at 200 mN load during indentation tests using a diamond Rockwell stylus (200 µm radius). Wear tests were carried out under unlubricated conditions using a ball-on-disk tribometer under unidirectional sliding (single pass) and rotational conditions within a load range of 1–5 N against AISI 52100 steel counterface. The dominant wear mechanism, at low loads (≤2 N), was oxidative wear and superelasticity enhanced the wear resistance mainly due to the high strain recovery of the alloy. A transition to severe wear occurred at higher loads (>2 N) characterized by higher wear rates, adhesion, and transfer of titanium alloy to the counterface. After the transition, superelasticity did not contribute to wear enhancement.

Metallurgical and Materials Transactions A, 2015

With the objective of optimizing the crystallographic texture of non-oriented electrical steel, i... more With the objective of optimizing the crystallographic texture of non-oriented electrical steel, i.e., reducing the h111i//ND and h110i//RD fibers and promoting the h001i//ND texture, a new rolling scheme was proposed and tested, in which the cold rolling direction (CRD) was intentionally inclined at an angle to the hot rolling direction (HRD) in order to change the orientation flow paths during cold rolling and alter the final texture of the annealed sheets. A non-oriented electrical steel containing 0.88 wt pct Si was hot rolled using conventional routes and annealed, and a number of rectangular plates were cut from the hot band with the longitudinal directions inclined at various angles, i.e., 0, 15, 30, 45, 60, 75, and 90 deg, to the HRD. These plates were then cold rolled along the longitudinal directions with a thickness reduction of 72 pct. The cold-rolled samples were annealed, temper rolled and annealed again (final annealing). The texture evolution during hot rolling, hot band annealing, cold rolling, and final annealing was characterized by electron backscatter diffraction and X-ray diffraction techniques. By changing the CRD with respect to the HRD, the initial texture and the orientation flow paths were altered, which resulted in apparent differences in the textures as compared to conventional cold rolling. After temper rolling and final annealing, the recrystallization textures consisted of mainly a h001i//ND fiber and there was almost no h111i//ND fiber. The sample cold rolled at an angle of 60 deg to the HRD had the strongest texture (intensity almost 29 of conventional rolling) with a maximum at the cube {001}h100i orientation-a magnetically favorable orientation for non-oriented electrical steels.