Search

In this study, the accumulative roll bonding (ARB) method, a severe plastic deformation (SPD) process, was used to fabricate copper-2 wt% silicon carbide composite strips. The ARB process was successfully conducted for up to nine cycles on pure copper strips with silicon carbide particles distributed between them, as well as on monolithic copper. Equiaxed tensile and Vickers hardness tests were conducted to evaluate the mechanical properties of the samples. SEM was utilized to study the fracture surfaces and to determine the fracture mechanism of ARB processed monolithic copper and composite samples after the tensile test. Texture parameters were calculated through X-ray analysis. The Rietveld method using MAUD software were employed to assess the crystallite size of the samples. Results indicated that average amount of porosity decreased and interface bonding between copper strip layers improved with increasing the number of ARB cycles. Moreover, an increased number of cycles led to homogeneous distribution of SiC particles within the copper matrix. The tensile strength of the fabricated composites improved with an increase in the number of cycles, ultimately reaching 483 MPa after nine cycles, compared to 388 MPa for the composite processed with a single cycle of ARB and 194 MPa for annealed copper strips. Initially, the elongation of the composite samples decreased dramatically to about 6% after applying five cycle of ARB process from the 46% observed for annealed pure copper strip. However, it improved as the process continued, reaching 8.9% after the ninth cycle. Investigation of fracture surfaces after the tensile test using SEM revealed that the dominant failure mode was shear ductile fracture. Analysis of sample textures demonstrated that the dominant texture was (100). Crystallite sizes for pure copper and nine cyclesrolled composites, as determined by Reitveld method, reached 111 nm and 89 nm, respectively. [ABSTRACT FROM AUTHOR]

In the present study, the effect of different accumulative roll bonding (ARB) process routes was investigated on microstructure and mechanical properties for commercially pure copper strips. Scanning electron microscope equipped with EBSD detector, optical microscope, tensile and hardness tests were used. Copper strips were ARBed up to 8 cycles both in route A (conventional ARB) and also in route BC (rotated 90° anti-clockwise before each cycle). Higher bonding quality was achieved when strips ARBed in route BC. However, tensile strength increased in both routes by proceeding ARB process. The orientation maps of specimens subjected to route A showed bimodal grain size, whereas the ones ARBed in route BC, a relatively equiaxed grain, were obtained. Rotation of specimens between different cycles (i.e., route Bc) resulted in lower strength as a result of lower dislocation density as well as lower accumulative strain hardening. Fractography results showed that by increasing the number of ARB cycles, the failure mode in the specimens changed from a ductile fracture to a shear–ductile fracture with shear dimples. [ABSTRACT FROM AUTHOR]

CoCrFeMoTi high-entropy alloy (HEA) was synthesized using mechanical alloying and spark plasma sintering. The corresponding microstructural features and phase composition were compared with those of CoCrFeNi, CoCrFeNiTix (x = 0, 0.3 and 0.5) and CoCrFeNiMox (x = 0, 0.3, 0.5 and 0.85) HEAs. Co, Cr, Fe, Mo and Ti elemental powders were mixed in equiatomic ratio and mechanically alloyed in a planetary ball mill at 300 rpm for up to 80 h. The influence of the milling duration on the evolution of microstructure, constituent phases and morphology was studied. After 40 h of ball milling, two supersaturated BCC solid solution phases were obtained. Milling time increasing resulted in grain refinement and higher solid solution homogenization characterized by a high internal strain. A partial phase transformation from BCC to intermetallic phases when the temperature exceeds 660 °C was revealed. After SPS consolidation, the Vickers hardness was 778 ± 10 HV, in combination with an ultimate shear stress of 216 ± 20 MPa and a yield shear stress of 81 ± 15 MPa for the material sintered at 950 °C and 65 MPa. Further increasing in the sintering temperature resulted in enhanced hardness value of 1600 ± 5 but reduced yield shear stress. The failure analysis revealed a brittle fracture of the synthesized materials. [ABSTRACT FROM AUTHOR]

Dynamic recrystallization behavior of the FeCrCuMnNi high entropy alloy (HEA) was investigated through hot compression test at different temperatures and at constant strain rate. The results revealed that during hot deformation of FeCrCuMnNi HEA, flow stress and work hardening rate rapidly decreased with increasing the deformation temperature. Discontinuous dynamic recrystallization (dDRX) was found to be the main active mechanism during hot deformation, which was the governing mechanism even at higher temperatures. In addition, bulging was an effective mechanism for inducing new recrystallized nuclei. Grain growth was occurred at slow strain rate in comparison to conventional alloys and other HEAs. This behavior was attributed to the continuous nucleation during dDRX, sluggish diffusion, high solution hardening characteristics of HEAs, and the presence of multiple phases in the FeCrCuMnNi HEA. Texture analysis showed that at lower temperatures, deformation texture including < 110 > // CA fiber was formed. By increasing the deformation temperature, the formation of recrystallization texture fibers such as < 100 > // CA and < 211 > // CA rapidly intensified. • Flow stress and work hardening rate decreased with deformation temperature. • Recrystallization occurred through dDRX and bulging mechanisms. • The FeCrCuMnNi HEA revealed a sluggish grain growth compared to other alloys. • The < 100 > // CA fiber was the main texture in fully recrystallized samples. [ABSTRACT FROM AUTHOR]

FeCrCuMnNi multiphase high entropy alloy was cold-rolled to 85% reduction and annealed at different temperatures. Recrystallization behavior of the alloy was investigated using XRD, SEM-EBSD, hardness, microhardness, and tensile tests. The results revealed variation in phase distribution due to annealing and earlier recrystallization of the FCC1 phase. Recrystallization of FCC1 and FCC2 phases initiated at 873 and 1073 K, respectively, and a fully recrystallized microstructure was seen after 1273 K. Deformation texture components eliminated slowly with increase in annealing temperature, and D and Cube components formed as a result of recrystallization. Faster decrease in FCC1 microhardness was seen due to earlier recrystallization. In addition, an excellent combination of strength and elongation was achieved in the partially recrystallized samples compared to conventional alloys. The strength was affected more after annealing at temperatures higher than 1073 K. Fracture behavior of FCC2 phase changed from a brittle fracture to a ductile fracture with increase in annealing temperature; however, FCC1 phase revealed a ductile fracture even at low annealing temperatures. • A fully recrystallized microstructure was achieved after annealing at 1273 K. • Fast elimination of residual strain in FCC1 led to earlier recrystallization. • D and Cube texture components formed as a result of recrystallization. • The alloy preserved its strength during partial recrystallization. [ABSTRACT FROM AUTHOR]

Hybrid composites of Al/Al2O3/TiC were produced by anodizing and accumulative roll bonding processes. We implemented 3D imaging of the composites using synchrotron radiation tomography at Biomedical Imaging and Therapy's 05B1-1 beamline at Canadian Light Source to collect information on internal structure of these hybrid composites i.e. distribution of particles and voids, particle/matrix interface and surface area distribution after different accumulative roll bonding passes. The volume and interface surface area distribution are responsible for strength and toughness of the composites along with other factors such as strain hardening and formation of ultrafine grains. We found that the mechanical properties improved as the number of accumulative roll bonding passes increases and the internal homogeneity of structure also improved. The composites after different accumulative roll bonding passes are studied where the number of reinforced particles and voids and their shape and size distribution were accurately being quantified in 3D to relate with mechanical properties of the composite. Such information should be of importance in analysis and improvement of the manufacturing process of these types of composites. [ABSTRACT FROM AUTHOR]

Equiatomic FeCoCrNi (Zr0) and non-equiatomic FeCoCrNiZr0.4 (Zr0.4) high-entropy alloys (HEAs) were synthesised by mechanical alloying and spark plasma sintering. XRD analysis verified the formation of FCC and BCC solid solution phases in both alloys after 30 h of ball milling. While the SPS FeCoCrNi alloy contains both FCC and BCC solid solution phases, the FeCoCrNiZr0.4 presents an FCC solid solution. The thermodynamic analysis showed that FeCoCrNiZr0.4 is more stable with respect to the FeCoCrNi alloy. The phase stability of FeCoCrNiZr0.4 was revealed up to ∼800°C. The shear strength and hardness of the FeCoCrNi HEA improved with Zr addition. Failure analysis of the shear punch tested samples revealed a ductile fracture with dimple structure for FeCoCrNi and a brittle fracture with a smooth featureless surface for FeCoCrNiZr0.4. [ABSTRACT FROM AUTHOR]

In the present work, aluminum‐3% brass composite sheets are produced by accumulative roll bonding (ARB) process up to nine passes at ambient temperature. Evolution of rolling texture is studied by texture measurement using X‐ray diffraction method. The results show that ARB process leads to the formation of copper ({112} <111>) and Dillamore ({4 4 11} <11 11 8>) as the major texture components. The intensity of copper and Dillamore components enhances to values as high as 19 times that of random with increasing number of passes to 9. It is observed that the 5th pass is a transition in development of the texture components, after which the intensities undergo a drop. The textures are comparable to ARB process of high purity aluminum, indicating that the addition of 3% brass particles do not cause any significant change in the deformation behavior. Electron backscatter diffraction (EBSD) technique is used to examine the microstructure; the results reveal formation of ultrafine grains (UFG), starting in the 3rd pass and covers the entire structure after the 5th pass. The major mechanisms involved are identified as rotation of the sub‐grains, as well as grain boundary migration. [ABSTRACT FROM AUTHOR]

In this investigation, commercial purity titanium (CP–Ti) was subjected to accumulative roll bonding (ARB) process up to 8 cycles (equivalent strain of 6.4) at the ambient temperature. Transmission electron microscopy (TEM) and X–ray diffraction line profile analysis (XRDLPA) were utilized to investigate the microstructure and grain size evolution. Both characterization techniques could clarify the non–uniform microstructure in the early stages and the uniform microstructure in the final stages of the process. The effectiveness of ARB for the fabrication of the nano–grained structure in CP–Ti was revealed. It was found that the SFE is not the only factor affecting grain refinement, as compared with other studies on ARB of FCC materials. Influence of other factors such as the melting temperature and the crystalline structure of the material was determined on the grain refinement. [ABSTRACT FROM AUTHOR]

FeCrCoNiCu high entropy alloy (HEA) was produced through mechanical alloying (MA) and spark plasma sintering (SPS) processes. Using X-Ray diffraction, scanning electron microscopy, differential scanning calorimetry, and shear punch testing, the structural, microstructural, and mechanical properties of the milled and SPSed samples were evaluated. After 50 h of milling, a dual-phase solid solution HEA formed consisting of a major FCC phase and a minor BCC phase. Increasing milling time and repeated deformation of the powders led to increased strain and dislocation density, and eventually, an alloy with a uniform distribution of particles with reduced size was achieved. Sintering of the alloy at 750 °C resulted in the annihilation of the BCC phase and the formation of a sigma phase. Moreover, segregation of the elements due to the different mixing enthalpies led to the formation of a new FCC phase. Results revealed that the SPSed alloy that was properly sintered had a porosity of less than 8%, which resulted in good final mechanical properties such as ultimate shear strength of 300 MPa and ultimate tensile strength of 540 MPa. • 50 h milling of FeCrCoNiCu, led to formation of a dual-phase HEA (FCC + BCC). • Increasing milling time led to increased strain and dislocation density. • A new FCC phase formed during sintering due to the segregation of the elements. • The sintered alloy revealed 300 MPa τ USS and 540 MPa σ UTS with 8% porosity. [ABSTRACT FROM AUTHOR]

In this study, microstructure and mechanical properties of steel/2 vol% SiC nanocomposite fabricated via accumulative roll bonding (ARB) process were investigated. Microstructure of nanocomposites was studied by scanning transmission electron microscopy (TEM). Tensile test also applied for determination of properties. In addition, the dislocation density was estimated from hardness measurement. The results indicated that continuously dynamic recrystallization (CDRX) and discontinuously dynamic recrystallization (DDRX) occurred in the microstructure of steel-based nanocomposite and the nanograins (55 nm) were obtained after the final cycle. With increasing the number of ARB cycles, the dislocation density of nanocomposite increased. In addition, after the first cycle, a significant increase observed in the yield strength, from 84 MPa to 689 MPa which is almost 8.2 times greater than that of the initial sample. After final cycle, the yield strength value increased to 1189 MPa. The yield strength improvement was mostly due to the grain refinement and dislocations and to a lesser extent to the load bearing effects of second phase (SiC nanoparticles) and precipitates. The contribution of each of these mechanisms was evaluated. [ABSTRACT FROM AUTHOR]

The evaluation of mechanical properties, like yield and ultimate shear strengths from shear punch tests, is important when availability of material, is limited. A shear punch test setup was built, and the mechanical properties of different strips of hot rolled pure aluminum, post-rolling annealed pure aluminum, as-milled pure aluminum, and 4 wt% Al 2 O 3 were investigated. The materials were first manufactured using powder metallurgy and then processed by hot rolling procedure. Microstructures of the samples were investigated by optical and scanning electron microscopes. It was found that by increasing alumina content in the matrix, shear strength and hardness were increased; also, the percentage of shear elongation was decreased. The results, also, indicated that by applying mechanical milling on pure aluminum powders before the hot rolling process, shear strength and hardness increased more than other samples. Moreover, shear strength was increased by increasing the amount of alumina particles in composite strips. SEM observations demonstrated that the amount of flat surface in shear failure micrographs increased by increasing the amount of shear strength and hardness. [ABSTRACT FROM AUTHOR]

Abstract: In this study, microstructure and mechanical properties of Al/1.6vol% Al2O3/1.5vol% B4C hybrid composite produced by anodizing and accumulative roll bonding (ARB) processes were investigated. Microstructural observations and fractography were performed by scanning electron microscopy (SEM). Also, the mechanical properties were investigated by tensile and microhardness tests. It was found that with increasing the number of ARB cycles, a better distribution of Al2O3 and B4C particles was obtained in the aluminum matrix. The hybrid composite after the tenth cycle demonstrated a uniform distribution and a strong bonding between the particles and the matrix without any porosity. Furthermore, ARB-processed monolithic and also, the hybrid composite showed much higher tensile strength than the annealed aluminum sample. In addition, elongation of ARB-processed monolithic and also, the hybrid composite was decreased in the first step and then increased as a result of increasing the number of cycles. Moreover, the ARB-processed monolithic and the hybrid composite exhibited higher hardness than the annealed aluminum. Finally, it was realized that the monolithic and hybrid composite samples had a shear ductile fracture, dimples and shear zones. However, the number of sources in the void nucleation of the composite was more than that of the monolithic sample. [Copyright &y& Elsevier]

Abstract: In this investigation different thicknesses of Cu and Al strips were accumulative roll bonded (ARBed) to form five dissimilar multilayered Al–Cu composites. Also, to investigate the effect of annealing on the mechanical properties, selected ARBed composites were annealed at three different temperatures (300, 400 and 500°C) for four different periods (10, 30, 60 and 360min). Different microstructural characterizations were conducted on the produced composites. The results demonstrated that by increasing the amount of Cu in the composites, tensile strength improved while elongation deteriorated. By increasing the annealing time and temperature, the tensile strength of the composites was remarkably decreased, after which it was increased while the elongation was increased rapidly and then decreased. This behavior was considered to be due to the restoration of the work-hardened metallic layers as well as formation of intermetallic compounds during annealing process. Corresponding fracture surfaces also revealed a brittle fracture in most of the annealed composites. [Copyright &y& Elsevier]

Abstract: In the present work, a comparison of microparticles and nanoparticles effects on the microstructure and mechanical properties of steel-based composite and nanocomposite fabricated via accumulative roll bonding (ARB) process was studied. The microstructure of the fabricated composite and nanocomposite after fourth cycle of the ARB process exhibited an excellent distribution of SiC micro/nano particles in the IF steel matrix without any porosity. Unlike the nanocomposite, the particle breaking (cracking) was one of the most important phenomena that occurred during ARB process of composite. The findings revealed that with increasing the number of ARB cycles, the tensile strength of the ARB-processed composite and especially nanocomposite improved, but their elongation decreased at first step and then increased at second step. In addition, the ARB-processed composite and especially nanocomposite exhibited a higher hardness than the annealed IF steel so that the hardness values of the composite and nanocomposite were 4.18 and 4.44 times higher than that of the annealed IF steel, respectively. [Copyright &y& Elsevier]

Highlights: [•] Al/Al2O3/SiC hybrid composite was fabricated by anodizing and ARB processes. [•] With no. of ARB cycles, the uniformity of particles in the Al matrix improved. [•] With no. of ARB cycles, the bonding quality between particles and matrix improved. [•] The UTS of Al/1.6vol.% Al2O3/1vol.% SiC was 3.1 times higher than annealed Al. [•] Increasing the amount of the SiC up to 2vol.% in matrix decreased UTS and El%. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, Al/Al2O3/TiC hybrid composite was produced using anodized strips and accumulative roll bonding (ARB) process. Alumina layers with various thicknesses were firstly obtained by anodizing the aluminum strips at different times. The anodized strips were then used along with certain amount of TiC particles (1vol%) as dispersed layer in order to fabricate Al/Al2O3/TiC hybrid composite. The resulting microstructures as well as the corresponding mechanical properties of the composites in different cycles of ARB process were studied. It was found that after one ARB cycle, departing and fracturing phenomena occurred in brittle alumina layer, followed by breaking down the alumina fragments to finer particles as the number of rolling cycles increased. In addition, by applying eight ARB cycles, the distribution of reinforcement particles (Al2O3, TiC) in aluminum matrix became highly uniform. It was shown that the mechanical properties of the hybrid composite such as tensile strength and elongation were enhanced as the number of ARB cycles increased. The results also showed that adding of up to 1.6vol% alumina in aluminum matrix enhanced considerably the yield and tensile strength of hybrid composite, whereas increasing the amount of alumina to 2.1vol% deteriorated the tensile properties. Finally, the fracture surfaces of the samples after the tensile tests showed that the fracture mode of composite was shear ductile rupture. [Copyright &y& Elsevier]

• A constitutive relationship was extracted to analyze behavior of HEA at peak stress. • For the initiation of DRX of this alloy, ε c /ε p = 0.60 and σ c /σ p = 0.86. • σ values showed that developed constitutive equations had high predictive accuracy. In this study, hot deformation behavior of an as-cast FeCrCuNi2Mn2 high-entropy alloy (HEA) was evaluated. For this purpose, hot compression tests were carried out in the temperature range of 600–1000 oC and initial strain rate range of 0.001–0.1 s-1. Flow stresses under different deformation conditions were then friction-corrected. Work hardening rate analysis was used to evaluate the occurrence of dynamic recrystallization. Microstructures of the hot compressed specimens were characterized using optical microscopy. Strain-dependent constitutive equations were developed using the data obtained from the Sellars–Tegart–Garofalo equation. The critical and peak strain and the critical and peak stress, as dynamic recrystallization parameters, were extracted from the work hardening rate versus stress curves. The results indicated that the modeled flow stresses were generally lower than the measured ones, which could be attributed to the impact of friction on the flow stress. Microstructural observations after hot compression tests as well as evaluation of work hardening rate versus stress curves showed typical dynamic recrystallization characteristics under different deformation conditions. In addition, with increase in deformation temperature and decrease in strain rate, more DRX grains were formed along grain boundaries and shear bands, resulting in a decrease in the flow stress. The size of the DRX grains was strongly affected by deformation temperature and increased with increase in temperature. The normalized critical stress and strain for the initiation of DRX were calculated as ε c /ε p = 0.60 and σc/σp = 0.86, respectively. The activation energy of hot deformation was determined to be 708 kJ/mol. It was noticed that the developed constitutive equations could accurately predict the flow stress behavior of the studied alloy over a wide range of experimental conditions. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effect of stacking fault energy on the formation of nanostructure in aluminum, copper, and brass fabricated via the accumulative roll bonding (ARB) process was investigated. Evolution of microstructure of the samples was investigated by transmission electron microscopy (TEM). Occurrence of the recrystallization (both continuous and discontinuous) in the copper and brass led to the formation of nano grains with mean sizes of 80, and 40nm, respectively; while, the mean grain size of aluminum was 250nm. Differences in microstructural evolution during processing of aluminum, copper, and brass was related to their stacking fault energies. In order to facilitate nanostructure formation in the commercial purity aluminum, the second phase particles (alumina) were added to aluminum matrix. In this case, the mean grain size of the aluminum changed down to 90nm. [Copyright &y& Elsevier]

Abstract: In the present study, the silicon carbide particles (SiCp) dispersion-strengthened copper matrix composites (Cu/SiCp) were successfully fabricated in the form of sheets by continual annealing and roll-bonding (CAR) process. The microstructure and mechanical properties of the Cu/ 2vol% SiC composite during various CAR cycles were evaluated by optical and scanning electron microscopes and tensile test. The composite showed an excellent distribution of silicon carbide particles in the matrix after nine cycles. It was found that by increasing the number of cycles, the strength of composite strips was improved and reached 315MPa after nine cycles, which is 1.6 times larger than that of the raw materials (annealed copper). Elongation declined up to four cycles, which was about 26%, and by proceeding the CAR cycles, it was enhanced slightly, reaching 34% after nine cycles. In order to clarify the failure mode, fracture surfaces after tensile tests were observed by scanning electron microscopy (SEM). Observations revealed that the failure mode in CARed Cu/ 2vol% SiC composite was a shearing ductile rupture with elongated shallow shear dimples. [Copyright &y& Elsevier]

Abstract: Al–Ni–Cu composite was produced using accumulative roll bonding (ARB) and electroplating processes. Nickel was electroplated on copper substrate for a certain time and voltage. In this study, the microstructural evolution and mechanical properties of the Al–Ni–Cu composite during various ARB cycles were studied by optical and scanning electron microscopes, microhardness, tensile and bending tests. It was observed that at first, nickel layers and then copper layers, were necked, fractured and distributed in aluminum matrix as accumulative roll bonding cycles were increased. Finally, after 11 cycles of ARB process, a completely uniform composite was produced with a homogeneous distribution of copper and nickel particles in aluminum matrix. The results showed that by increasing the number of ARB cycles, the bending strength of produced composite was increased. Also, it was found that when the number of cycles was increased, not only elongation was increased but also the tensile strength of the composite was improved. Microhardness for different elements in different cycles was also evaluated. Finally, fracture surfaces of samples were studied, using scanning electron microscopy (SEM), to reveal the failure mechanism. [Copyright &y& Elsevier]

Abstract: Accumulative roll-bonding (ARB) process is a severe plastic deformation (SPD) process capable of developing grains below 1μm in diameter. In this study, the ARB process was applied on 6061 aluminum alloy up to 5 cycles at ambient temperature without any lubrication. Microstructural characterizations were performed by transmission electron microscopy (TEM). The dislocation density changes during deformation were calculated using a recently developed JAVA based software, Materials Analysis Using Diffraction (MAUD), based on Rietveld''s whole X-ray pattern fitting methodology. It was found that the presence of Mg in solid solution efficiently promoted and increased the dislocation density in the alloy during ARB process. This resulted in a continuous recrystallization phenomenon, leading to a microstructure consisting of small recrystallized grains with an average diameter of about 100nm. The tensile tests were conducted on the ARBed strips. The tensile strength increased 2.5 times more than the initial value. However, the elongation dropped abruptly at the first cycle, and then decreased slightly. [Copyright &y& Elsevier]

Abstract: The anodizing and accumulative roll bonding (ARB) processes are used in this paper as a new, effective alternative for manufacturing high-strength and highly-uniform aluminum/alumina composites. Four different thicknesses of alumina layers are grown on the substrate using an anodizing process and the microstructural evolution and mechanical properties of the resulting aluminum/alumina composite are investigated. Microscopic investigations of the composite show a uniform distribution of alumina particles in the matrix. It is found that alumina layers produced by the anodizing process neck, fracture, and depart as the number of accumulative roll bonding passes increases. During ARB, it is observed that as strain increases with the number of passes, the strength and elongation of the produced composites correspondingly increase. Also, by increasing alumina quantity, tensile strength improves so that the tensile strength of the Al/3.55vol.% Al2O3 composite becomes ∼3.5 times greater than that of the annealed aluminum used as raw material. [Copyright &y& Elsevier]

Abstract: In the present work, accumulative roll bonding (ARB) process was used as an effective alternative method for manufacturing high-strength, finely dispersed and highly uniform copper/alumina metal matrix composite (MMC). The microstructural evolution and mechanical properties of the Cu/15vol.% Al2O3 composite during various ARB cycles are reported. The produced MMC by nine ARB cycles showed a homogeneous distribution and strong bonding between particles and matrix without any porosity. Also, it was found that when the number of cycles increased, not only did elongation increase but also the tensile strength of the composite improved by 2.5 times compared to that of the annealed copper used as the original raw material. Strengthening in the produced composites was explained by strain hardening, grain refinement, reinforcing role of particles, uniformity, bonding quality and size of particles. The findings also revealed that after the first cycle, hardness rapidly increased, then dwindled and finally saturated by further rolling. [ABSTRACT FROM AUTHOR]

Abstract: The ARB process used as a technique in this study provides an effective alternative method for manufacturing high-strength aluminum/alumina composites. The microstructural evolution and mechanical properties of the aluminum/15vol.% alumina composite are reported. The composite shows an excellent alumina particle distribution in the matrix. It is found that by increasing the number of ARB cycles, not only does elongation increase in the composites produced but also the tensile strength of the Al/15vol.% Al2O3 composite improves by 4 times compared to that of the annealed aluminum used as the original raw material. Fracture surfaces after tensile tests are observed by scanning electron microscopy (SEM) to investigate the failure mode. Observations reveal that the failure mode in both ARB-processed composites and monolithic aluminum is of the shear ductile rupture type. [Copyright &y& Elsevier]

Abstract: Accumulative roll-bonding process is the only severe plastic deformation (SPD) process using rolling deformation itself, and has been used for 70/30 brass up to 6 cycles at ambient temperature under unlubricated conditions. Microstructural characterizations were done by transmission electron microscopy (TEM). After 6 cycles it was found that continuous recrystallization occurred and the microstructure covered with small recrystallized grains with an average diameter below 100nm. The tensile tests and Vickers macro- and microhardness were conducted on the ARBed 70/30 brass. A scanning electron microscopy (SEM) study was performed in order to observe the shear bands and also to clarify the failure mechanism. The tensile strength and hardness became two and three times greater than the initial value respectively. However, the elongation dropped abruptly at the first cycle, then increased slightly. Strengthening in ARBed 70/30 brass explained by strain hardening in the first step and grain refinement at high strains. Observations revealed that the failure mode in ARBed 70/30 brass was a shearing ductile rupture with elongated shallow shear dimples. [Copyright &y& Elsevier]

In this study, the influence of prior cold deformation on recrystallization behavior of FeCrCuMnNi high entropy alloy was studied. Homogenized samples were cold-rolled up to 85% reduction in thickness and then, annealed for 60 min at 900 °C. The results showed that initiation of recrystallization in different phases of the alloy requires different amounts of prior cold deformation, which is related to their deformation behavior. Microstructure evolution revealed an enhancement in recrystallized nuclei with increase in prior cold deformation, and it seems that the distinct characteristics of HEAs such as sluggish diffusion can promote this process. Increasing prior cold deformation led to a greater decrease in deformation texture components after annealing and formation of annealing texture components. Mechanical test results revealed that increasing prior cold deformation leads to a greater decline in hardness, ultimate tensile strength (UTS), and yield strength (YS) as a result of annealing. With increase in prior cold deformation fracture mode changed to a bimodal fracture in which FCC1 and FCC2 phases, respectively, revealed a ductile and brittle fracture. Moreover, it was seen that variation in hardness of the annealed alloy is directly related to the recrystallized fraction and there is a linear relation between the hardness and UTS of the alloy. • Recrystallization in different phases requires different amounts of prior cold deformation. • Increasing prior cold deformation led to a greater decrease in deformation texture. • Fracture mode changed to a bimodal fracture with increase in prior cold deformation. • A sharper drop in hardness, UTS, and YS was seen with increase in prior cold-rolling. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the characteristics of the AlCrCuFeNi high-entropy alloy (HEA) synthesized through mechanical alloying (MA). In addition, effects of Process Control Agent (PCA) amount and milling time were investigated using X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The results indicated that the synthesized AlCrCuFeNi alloy is a dual phase (FCC + BCC) HEA and the formation of the phases is strongly affected by the PCA amount. A high amount of PCA postponed the alloying process and prevented solid solution formation. Furthermore, with an increase in the PCA amount, lattice strain decreased, crystallite size increased, and the morphology of the mechanically alloyed particles changed from spherical to a plate-like shape. Additionally, investigation of thermal properties and annealing behavior at different temperatures revealed no phase transformation up to 400 °C; however, the amount of the phases changed. By increasing the temperature to 600 °C, a sigma phase (σ) and a B2-ordered solid solution formed; moreover, at 800 °C, the FCC phase decomposed into two different FCC phases. [ABSTRACT FROM AUTHOR]

• The FexCoCrNi high entropy alloys were produced by powder metallurgy. • The structure of the alloys consisted of BCC and FCC solid solutions. • The addition of Fe led to increases the BCC volume fraction. • As the Fe content increased, Hardness and shear strength increased. • The high wear resistance of the Fe 1.6 CoCrNi alloy was attributed mainly to the BCC Solid solution. In the present study, the Fe x CoCrNi (x = 1, 1.3, 1.6) high entropy alloy (HEA) system was prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The effect of iron content on the microstructure, mechanical properties, thermal behavior, and wear resistance of the FexCoCrNi (x = 1, 1.3, 1.6) HEA system was separately studied. It was found that all 3 alloys showed body-centered cubic (BCC) and face-centered cubic (FCC) solid solutions after 50 h of milling and an increase in the iron content was accompanied by an increase in the fraction of the BCC solid solution. Thermal stability of the Fe x CoCrNi (x = 1, 1.3, 1.6) HEA system was evaluated in the temperature range of 973–1273 K. The FCC structure was retained even after thermal exposure at 973, 1123, and 1273 K for all 3 alloys. The increase in Fe content led to a decrease in the sigma phase (FeCr or CoCr) formation temperature. The results of mechanical tests indicated that increasing Fe (1–1.6 mol) resulted in enhancement of ultimate tensile strength and hardness from 480 to 560 MPa and 320–400 Vickers, respectively. Wear resistance results demonstrated that the coefficient of friction (COF) and weight loss of this system decreases with increased Fe content. Moreover, the dominant wear mechanism changed from abrasive wear to adhesive wear. [ABSTRACT FROM AUTHOR]

Plasma electrolytic oxidation (PEO) coatings were grown on AZ31 Mg alloy in a silicate-based electrolyte containing KF using unipolar and bipolar (usual and soft-sparking) waveforms. The coatings were dual-layered consisting of MgO, MgF2 and Mg2SiO4 phases. Surface morphology of the coatings was a net-like (scaffold) containing a micro-pores network, micro-cracks and granules of oxide compounds. Deep pores were observed in the coating produced by unipolar and usual bipolar waveforms. The soft-sparking eliminated the deep pores and produced the lowest porosity in the coatings. It was found that the corrosion performance of the coatings evaluated using EIS in 3.5 wt. % NaCl solution is mostly determined by the inner layer resistance, because of its higher compactness. After 4 days of immersion, the inner layer resistances were almost the same for all coatings. However, the coatings produced by unipolar and usual bipolar waveforms showed sharp decays in inner layer resistances after 1 week and even the barrier effect of outer layer was lost for the unipolar-produced coating after 3 weeks. The low-frequency inductive loops appeared after a 3-week immersion for all coatings indicated that the substrate was under local corrosion attack. However, both coatings produced by soft-sparking waveforms provided the highest corrosion performance. [ABSTRACT FROM AUTHOR]

A study was conducted to determine the impact of cold rolling on the evolution of the microstructure of the CuCrFeNi 2 Mn 0.5 high entropy alloy. Cold rolling resulted in the development of crystallographic textures and microstructure evolution. It was observed that the main deformation mechanism during cold rolling of the mentioned alloy is the movement of dislocations and the formation of mechanical twins, which lead to the formation of shear bands by increasing the amount of deformation. Microstructural studies suggest that the decrease in the microhardness of cold-rolled samples is caused by the formation of strain-free grains on the shear bands. The development of strain-free grains is aided by the rotation of subgrains on the shear bands. [Display omitted] • CuCrFeNi 2 Mn 0.5 low-cost FCC high entropy alloy. • Shear bands Formation as the main deformation mechanism during cold rolling. • Rotational dynamic recrystallization as a recrystallization method on shear bands. [ABSTRACT FROM AUTHOR]

In this research, the microstructure, texture, and work hardening behavior of the Al/IF composite were investigated. The composites were produced through up to 7 cycles of accumulative roll bonding (ARB). The microstructure evolution revealed that the IF layer fractured during the process and distributed within the Al matrix due to its higher hardness and higher work hardening rate, as well as formation of shear bands. The main deformation textures formed in the Al layer were the {001} <110>, {4,4,11} <11,11,8>, and {111} <112> components. In the IF layer, preferred orientations of {001} <110>, {110} <112>, and {111} <110> were observed. The produced composite exhibited typical tensile behavior, with strength increasing and elongation decreasing during the process due to an increment in dislocation density and hardening. Additionally, the results revealed that the hardening capacity of the composite decreased during the process; however, the strain hardening rate increased. A noticeable increase in dislocation density and a decrease in crystallite size were found to be the main governing parameters of these variations. Moreover, the fracture mode of the composite changed from ductile fracture to a more brittle mode as a result of hardening. [ABSTRACT FROM AUTHOR]

In this work, 2 vol% carbon nanotubes (CNTs) reinforced aluminum (Al) matrix composites of superior microstructural homogeneity are successfully synthesized using Bc equal-channel angular extrusion (ECAP) route. The key step in arriving at high level of homogeneous distribution of CNTs within Al was preparation of the powder using simultaneous attrition milling and ultra-sonication processes. Microstructure as revealed by electron microscopy and absence of Vickers hardness gradients across the material demonstrate that the material reached the homogeneous state in terms of CNT distribution, porosity distribution, and grain structure after eight ECAP passes. To facilitate comparison of microstructure and hardness, samples of Al were processed under the same ECAP conditions. Significantly, the composite containing only 2 vol% exhibits 20% increase in hardness relative to the Al samples. [ABSTRACT FROM AUTHOR]

Abstract: Continual annealing and roll-bonding (CAR) process was used in this study as a very effective method for fabrication of the Al/15vol.% SiO2 metal matrix composite. The microstructure of the produced composites after 6 cycles of the CAR process was showed an excellent distribution of SiO2 particles in the AA1100 matrix without any porosity. Particle breaking was one of the most important phenomena that can occur in CAR process. The results also were indicated that when the number of CAR cycle was increased, the tensile strength of the manufactured composites was improved, but their elongation was decreased at first step and then was increased. The tensile strength of the composite was 1.77 and 1.63 times higher than the same values was obtained for annealed and monolithic aluminum strips, respectively, while the elongation value was decreased slightly. [Copyright &y& Elsevier]

Abstract: Continual annealing and roll-bonding (CAR) process was used in this study as a very effective method for improving the microstructure and mechanical properties of the A356/SiC metal matrix composite produced by semi-solid metal processing. The results showed that the increase in the number of cycles led to the following points: (a) the uniformity of the silicon and silicon carbide in the aluminum matrix was improved, (b) the Si particles became finer and more spheroidal in appearance, (c) the porosity was decreased, (d) the bonding quality between the reinforcement (SiC particles) and the matrix (A356 aluminum) was improved, (e) the particle free zone disappeared, and therefore (f) the tensile strength, elongation, and formability index of the samples were improved. The microstructure of the manufactured A356/SiC composite after ten cycles indicated a totally modified structure so that its tensile strength, elongation, and formability index values reached 166.7MPa, 23.9%, and 3984MPa·% which were 1.74, 4.19, and 7.29 times greater than those of the as-cast composite, respectively. [Copyright &y& Elsevier]

Abstract: Accumulative roll bonding (ARB) process was used in this study as an effective method for manufacturing high-strength, finely-dispersed and highly-uniform A356 alloy. It was found that when the number of ARB cycles was increased, the uniformity of silicon particles in the aluminum matrix improved, the particles became finer and spheroider and therefore, the tensile strength (TS) and ductility of the samples improved. The microstructure of the manufactured A356 alloy after five ARB cycles indicated a totally modified structure such that it''s TS and elongation values reached 269MPa and 5.3% which were 2.6 and 2.5 times greater than those of the as-cast material, respectively. Also, the hardness value increased from 55.4 (for as-cast sample) to 100.2HV (after the fifth cycle of ARB), and registered 81% increase. [Copyright &y& Elsevier]

Abstract: In the present work, Al/10vol.% SiC metal matrix composite (MMC) was manufactured by accumulative roll bonding (ARB) process. The silicon carbide particles with two various particle sizes of 40 and 2μm were used. Effect of particle size on microstructure (by scanning electron microscopy) and mechanical properties (tensile strength and elongation) at various ARB cycles was investigated. It was found that the microstructural evolution in MMC with 40μm particle size was more salient compared to the MMCs with 2μm particle size. Also, the composite strip with 40μm particle size became uniform with high bonding quality and without any porosity sooner than the strip of 2μm particle size. Moreover, when the number of cycles was increased, the tensile strength for both samples was improved. The tensile strength of the composite strip with 40μm particle size was more than the composite strip with 2μm up to the seventh cycle. By increasing the number of cycles after the seventh cycle, the value of tensile strength of MMC with 40μm particle size became saturated and then decreased, and its tensile strength became less than that of the composite with 2μm particle size for the ninth and eleventh cycles. Up to the seventh cycle, when the number of ARB cycles was increased, the elongation of composite strips was decreased, but after the ninth cycle, the tensile elongation for both samples was improved. [Copyright &y& Elsevier]

In this study, aluminium sheets were processed through 8 cycles of accumulative roll bonding (ARB), and then, were annealed at 300 °C for different time periods to maintain the optimum annealing process for the formation of bimodal microstructure. Variations in microstructure, texture, and mechanical properties were studied using optical microscopy (OM), X-Ray diffraction (XRD), and hardness and uniaxial tensile tests. Microstructural observations showed that recrystallized grains formed after 10 s of annealing; however, recovery occurred after 1 s due to the high stacking fault energy (SFE) of aluminium. Fully recrystallized microstructure was seen after 900 s. A bimodal grain size was achieved after 3600 s and the ratio of the average size of the largest 2% grains to mean grain size (d max /) was 3. Abnormal grain growth took place with the increasing of annealing time to 18,000 s during which the d max / ratio reached 7. During annealing, Copper, Dillamore and S components remained the main texture components; however, their intensity reduced with increase in annealing time. In addition, the Cube component formed after the cessation of recrystallization and abnormal grain growth. After 18,000 s of annealing, ultimate tensile strength (UTS) decreased more than 70% and elongation increased 230%; however, the maximum toughness was achieved in the sample annealed for 3600 s. Formation of a bimodal grain size microstructure with d max / ratio of 3 was the main reason for this phenomenon. [ABSTRACT FROM AUTHOR]

Abstract: A major challenge in achieving the best potential of SiCp-reinforced aluminum composites is to homogeneously disperse SiC particles within the aluminum alloys. The presence of coarse Si fibers with non-uniform distribution in cast Al–Si alloys, which may lead to poor mechanical properties, is another important problem that limits the application of these alloys. In order to eliminate these problems, accumulative roll bonding (ARB) process was used in this study as a very effective method for improving the microstructure and mechanical properties of the Al356/SiCp composite. It was found that when the number of ARB cycles was increased, the uniformity of the Si and SiCp in the aluminum matrix improved, the Si particles became finer and more spheroidal, the free zones of Si and SiC particles disappeared, the porosity of composite decreased, the bonding quality between SiCp and matrix improved, and therefore mechanical properties of the composites were improved. The microstructure of the manufactured Al356/SiCp composite after six ARB cycles indicated a completely modified structure so that its tensile strength and elongation values reached 318MPa and 5.9%, which were 3.1 and 3.7 times greater than those of the as-cast composite, respectively. [Copyright &y& Elsevier]

Abstract: Metal matrix composite strips are conventionally produced by strip casting technology and ingot casting followed by secondary mechanical processes. These composites usually suffer from poor distribution of the reinforcement particles, presence of porosity, and unsuitable bonding between reinforcement and matrix, which result in low mechanical properties. In order to eliminate these problems, CAR (continual annealing and roll-bonding) process was used in this study as a very effective method for manufacturing Al/SiCp composite strip. The microstructure of the fabricated composite after fifteen CAR cycles showed an excellent distribution of SiC particles in the aluminum matrix without any noticeable porosity. The results also indicated that when the number of cycles increases, the tensile strength of the produced composites improves, but their ductility and formability index decreases at first and then increases. The tensile strength and formability index of the fifteen cycle CARed composite were 1.58 and 1.23 times higher than those of the initial alloy, respectively, while the elongation value decreased slightly. [Copyright &y& Elsevier]

Abstract: Some important problems associated with cast metal matrix composites (MMCs) include non-uniformity of the reinforcement particles, high porosity content, and weak bonding between reinforcement and matrix, which collectively result in low mechanical properties. Accumulative roll bonding (ARB) process was used in this study as a very effective method for refinement of microstructure and improvement of mechanical properties of the cast Al/10vol.% Al2O3 composite. The average particle size of the Al2O3 was 3μm. The results revealed that the microstructure of the composite after eleven cycles of the ARB had an excellent distribution of alumina particles in the aluminum matrix without any noticeable porosity. The results also indicated that the tensile strength and elongation of the composites increased as the number of ARB cycles increased. After eleven ARB cycles tensile strength and elongation values reached 158.1MPa and 7.8%, which were 2.54 and 2.36 times greater than those of the as-cast MMC, respectively. [Copyright &y& Elsevier]

Nanotructural evolution and grain refinement leading to heterogeneous bimodal structure were investigated during thermomechanical processing in carbon-containing FeMnCoCr twinning induced plasticity (TWIP) high-entropy alloy (HEA). The homogenized single-phase face-centered cubic alloy with the stacking fault energy of 19.4 ± 2 mJ m − 2 was cold rolled up to thickness reduction of 84 % and annealed at 850 °C. Planar slip with profuse nanoscale deformation twinning was the dominant deformation feature at low rolling reduction (32 %). The heterogeneous structure could be obtained through subdivision of microstructure, continuous dynamic recrystallization and static recrystallization described as follows: (i) Hierarchical mechanical twinning, (ii) Interaction of twin-matrix (T/M) lamellae with shear-bands and (iii) Continuous dynamic recrystallization (CDRX) within the strain-induced boundaries (SIBs), (iv) Subsequent static recrystallization of the region with twin-matrix (T/M) lamellae and shear-bands. The strength and ductility enhancement during deformation was attributed to the hierarchy of microstructural evolution consisting of TWIP and microband-induced plasticity (MBIP). The heterogeneous bimodal structure composed of ultra-fine grains and larger grains with an average grain size of 0.5 μm and 3 μm respectively was achieved by post-rolling (84 %) annealing at 850 °C. Favorable strength-ductility combination with the ultimate tensile strength of 840 MPa and elongation of ~88 % was achieved by formation of heterogeneous bimodal microstructure through thermomechanical processing. [ABSTRACT FROM AUTHOR]