Accumulative Roll Bonding Cycles Research Articles

Ultrafine-Grained Austenitic Stainless Steels X4CrNi18-12 and X8CrMnNi19-6-3 Produced by Accumulative Roll Bonding

Austenitic stainless steels X4CrNi18-12 and X8CrMnNi19-6-3 were processed by accumulative roll bonding (ARB). Both materials show an extremely high yield strength of 1.25 GPa accompanied by a satisfactory elongation to failure of up to 14% and a positive strain rate sensitivity after two ARB cycles. The strain-hardening rate of the austenitic steels reveals a stabilization of the stress-strain behavior during tensile testing. Especially for X8CrMnNi19-6-3, which has an elevated manganese content of 6.7 wt.%, necking is prevented up to comparatively high plastic strains. Microstructural investigations showed that the microstructure is separated into ultrafine-grained channel like areas and relatively larger grains where pronounced nano-twinning and martensite formation is observed.

Electrochemical and Passive Behaviors of Pure Copper Fabricated by Accumulative Roll-Bonding (ARB) Process

In the present work, electrochemical and passive behaviors of pure copper fabricated by accumulative roll-bonding (ARB) process in 0.01 M borax solution (pH = 9.1) have been studied. Before any electrochemical measurements, evaluation of microstructure was obtained by Vickers microhardness, x-ray diffraction (XRD), and transmission electron microscopy. The results of microhardness tests revealed that microhardness values increased with the increasing number of ARB cycles. Also a sharp increase was seen in microhardness after the first ARB cycle, whereas mediocre additional increases were observed afterward up to the seven cycles. Moreover, XRD patterns showed that the mean crystallite size values decrease with the increasing number of ARB cycles. To investigate the electrochemical and passive behaviors of the samples, the potentiodynamic polarization, Mott-Schottky analysis and electrochemical impedance spectroscopy (EIS) were carried out. Polarization plots revealed that as a result of ARB, the corrosion behavior of the specimens improves compared with the annealed pure copper. Also, the Mott-Schottky analysis and EIS measurements showed that the increasing number of ARB cycles offer better conditions for forming the passive films with higher protection behavior, due to the growth of less-defective films.

Growth of TiO2 Nanotube Layers on Ti Substrates with Different Microstructures

Since the reports on self-organized tubular oxide layers on Ti and its alloys by Assefpour-Dezfuly et al[1] and Zwilling et al[2,3], TiO2 nanotube layers have been widely studied in several application fields owing to its unique chemical and physical properties. It was reported that the morphology of the oxide layers is strongly influenced by anodization parameters such as electrolytic composition, applied voltage and electrolyte temperature. However, among the many anodization parameters, the influence of titanium substrate on oxide layer growth has not been clear yet. In the present study, the growth behavior of nanotubular oxide layers was examined by using Ti substrates with various microstructures. As-received Ti sheets (purity: 99.5%) were heat-treated at 500 °C for 12 h to ensure homogeneity. After the homogenization, some Ti sheets were heat-treated at various temperatures in argon atmosphere. Also, the other sheets were subjected to ARB (Accumulative Roll Bonding) process up to 6 cycles to change the microstructures. Anodization was carried out at 50 V for 3 h in ethylene glycol containing 2 wt% H2O and 0.05 M NH4F. After the anodization, the morphology of oxide layers was characterized by FE-SEM. Nanotubebular oxide layers were formed on all Ti sheets whereas the growth of nanotubular oxide layer was affected by the microstructure of Ti substrate that can be controlled by heat treatment and ARB process. The grain size increased with increasing heat-treatment temperature, duration while increasing the number of ARB cycle decreased the grain size. Consequentially, nanotubular oxide layer thickness increased with decreasing grain size. Therefore, it was found that the growth behavior may be affected by the numerous lattice defects in substrate introduced by heat-treatment and ARB process.

Production of nanograin microstructure in steel nanocomposite

In this study, microstructure and mechanical properties of steel/2vol% 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 (55nm) 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 84MPa to 689MPa which is almost 8.2 times greater than that of the initial sample. After final cycle, the yield strength value increased to 1189MPa. 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.

Mechanical properties of ultrafine-grained AlZnMg(Cu)-alloys AA7020 and AA7075 processed by accumulative roll bonding

Ultrafine-grained AA7020 (AlZnMg) and AA7075 (AlZnMgCu) were produced by accumulative roll bonding (ARB) with up to 6 cycles. Different pre-heating treatments and their effect on the mechanical performance of the materials were investigated by means of hardness measurements and uniaxial tensile testing. It was found for AA7020 that by pre-heating at 230 °C for 2.5 min prior to each rolling step, an UTS of 550 MPa can be achieved, which is 51 % higher compared to the peak-aged T6 reference. For AA7075, pre-heating at 280 °C for 2.5 min leads to a very high UTS of 720 MPa after four ARB passes. A negative strain rate sensitivity was found for both alloys, which shifts toward zero with increasing number of ARB cycles. Post-ARB heat treatment was performed in order to overcome the reduced ductility after ARB. This leads to an enhanced strain hardening capacity after 4 cycles, resulting in an increase of the uniform elongation from 1.4 to 2.0 % for AA7020 and from 0.9 to 2.1 % for AA7075.

Evolution of microstructure and texture during annealing of Al-2.5%Mg-0.2%Sc severely deformed by a combination of accumulative roll bonding (ARB) and conventional rolling

Evolution of microstructure and texture during heavy cold-rolling and annealing of Al-2.5%Mg-0.2%Sc alloy was investigated. For this purpose recrystallized sheets of 1mm thickness having finely dispersed precipitates were processed to 3 cycles of ARB (equivalent strain, εeq=2.4) followed by conventional rolling to a final thickness of 200μm resulting in total equivalent strain of 4.0. Evolution of ultrafine microstructure and strong copper or pure metal type texture were observed during deformation. During annealing very stable microstructure was observed up to 400°C but further annealing resulted in formation of a layered microstructure with deformed layer sandwiched between recrystallized layers. Formation of strong cube texture is not observed in the recrystallized layers. Isothermal annealing for longer time at 500°C leads to abnormal growth of Q orientation ({013}<213>) within the deformed layer.

EBSD characterization of an IF steel processed by Accumulative Roll Bonding

The objective of this work is to study the texture and microstructure evolution of an IF steel deformed by Accumulative Roll Bonding (ARB) using Electron Backscatter Diffraction. Texture changes occur with increasing number of ARB cycles. For the early cycles, the main components are the α and γ fiber components characteristic of steels. With increasing the number of ARB cycles a tendency towards a random texture is obtained. In the initial state, the mean grain size is 30 μm and after 5 cycles it decreases to 1.2 μm. For the first ARB cycles, the fraction of high angle grain boundary is low but it increases with the number of cycles to about 80% for 5 cycles. The Kernel Average Misorientation (KAM) has no appreciable changes with the number of ARB cycles for all the texture components.

Effect of accumulative roll bonding process on the electrochemical behavior of pure copper

In this study, the effect of accumulative roll bonding (ARB) process on the electrochemical behavior of pure copper in 0.01M borax solution has been investigated. The microhardness tests showed that by implementing the ARB process the values of microhardness improve with increasing the number of ARB cycles. Moreover, a drastic increase of microhardness was seen (∼100%) after the second ARB cycle. Potentiodynamic polarization plots and electrochemical impedance spectroscopy (EIS) measurements showed that increasing the number of ARB cycles offer better conditions for forming the passive films. In the Mott–Schottky analysis, no evidence for n-type behavior was obtained, indicating that the oxygen vacancies and the copper interstitials do not have any significant population density in the passive films. Also, this analysis revealed that with increasing the number of ARB cycles, the acceptor density of the passive films decreased.

Application of accumulative roll bonding and anodizing process to produce Al–Cu–Al2O3 composite

Abstract In the present investigation, production of Al–Cu–Al 2 O 3 composite by means of Accumulative Roll Bonding (ARB) coupled with the anodizing process was studied. For this purpose, the alumina was grown on Al sheets by electrolyte technique and then the coated Al was laid between two Cu sheets followed by roll bonding to a specific reduction. This process was repeated up to seven times in order to achieve a bulk composite. The microstructure was characterized by SEM and optical microscopy while the mechanical properties were measured by microhardness, triple point bending and tensile testing. Microstructural evolution of the produced composite revealed that alumina was fractured in the primary sandwich and distributed non-uniformly throughout the composite. However, the alumina distribution was improved as the ARB cycles proceeded. It was also found that the tensile strength was improved up to the third cycle, after which it was decreased for the fourth and fifth cycles and again, it was increased for the last cycles. The bend strength showed the same trend as the tensile strength, while the elongation represented weak values for almost all cycles. Moreover, it was observed that as strain was increased (more ARB cycles), the microhardness for both Al and Cu layers was increased by two different trends. Additionally, failure analysis revealed that the mode of fracture was governed by two mechanisms: micro crack initiation between the metallic layers and formation of micro voids mainly around the alumina particles followed by their coalescence.

Influence of an accumulative roll bonding (ARB) process on the properties of AA5083 Al-Mg alloy sheets

In this study, fully annealed AA5083 type alloy sheets with 1 mm in thickness were processed by accumulative roll bonding (ARB) at room temperature, up to 6 ARB cycles. It was found that microstructure was refined and mechanical properties were significantly improved with ARB processing. The maximum achieved values of hardness and tensile strength were two and three times greater than that of the initial material, respectively. This was attributed to the intensive strain hardening and grain size refinement which occurred during ARB deformation. However, the uniform elongation values were decreased by increasing the number of ARB cycles, and early fracture was registered. SEM fractography of fractured surfaces after tensile tests revealed a typical ductile fracture of ARB processed specimens, which was changed with ARB deformation. It was observed that ductile area on the fractured surfaces and the amount of necking, which occured before fracture, were decreased with increasing the number of ARB cycles.

Microstructure and mechanical properties of Tri-metal Al/Ti/Mg laminated composite processed by accumulative roll bonding

Metal matrix composites are of great interest in automotive and aerospace applications due to their superior properties that help in designing light weight structures. In the present work, tri-metal Al/Ti/Mg laminated composite was processed by accumulative roll bonding (ARB). Al, Ti, and Mg strips were sandwiched as alternate layers and rolled at 150°C up to 5 passes. In order to study microstructural evolution and mechanical properties of the Al/Mg/Ti composite during different ARB cycles, various tests such as optical and scanning electron microscopes, energy dispersive spectrometer, X-ray diffraction, micro-hardness, and tensile tests were performed. The results showed that at the first ARB cycle, Mg and Ti layers were necked and fractured, respectively. Layer thickness was decreased and the process was completed in the early cycles, and the cycles of heterogeneous distribution of the final distribution made a more uniform layer. This showed the influence of the concentration profiles of adjacent layers as an adjunct link. In this process, the preheat temperature did not form an intermetallic layer at the interface. Maximum ultimate tensile strength was 335.9MPa after imposing four deformation passes. After five ARB cycles, a tri-metal Al/Ti/Mg multilayer composite with homogeneous distribution was formed and hardness was increased gradually while the elongation to failure was decreased with increasing the ARB cycles.

Fabrication and characterization of hybrid composite strips with homogeneously dispersed ceramic particles by severe plastic deformation

In the present work, accumulative roll bonding (ARB) process was used as an alternative method for manufacturing Al/B4C/SiC hybrid composites. Uniaxial tensile tests and microhardness measurements were carried out on ARBed specimens and their characteristics were investigated by means of scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and the Archimedes method. It was found that with increasing the ARB cycles, the distribution of B4C and SiC particles was improved in the aluminum matrix. After the 11th cycle, the hybrid composite demonstrated a uniform distribution of the reinforcement particles with strong bonding between the particles and the matrix material without any trace of porosities. The tensile strength of the composite increased with ARB cycle and reached to maximum value of 255MPa at 11th cycle; which was 3.19 and 1.35 times higher than the annealed aluminum and monolithic aluminum, respectively. The microhardness results suggested that by increasing the number of cycles, hardness increased rapidly at first stages and then dwindled at last stages. Finally, fractography results indicated that the fracture mode in hybrid composites consisted of shear ductile rupture, dimples and shear zones.

Preparation of Ag-Ni-Cu Composite Material by Ultrasonic Arc Spray Forming and Accumulative Roll Bonding and the Evolution of Its Microstructure

We prepared a layered composite material by subjecting a deposition billet of AgNiCu15-5 formed by ultrasonic arc spray forming (UASF) to extrusion at 773 K (500 °C), rolling at 673 K (400 °C), and accumulative roll bonding (ARB). The evolution of the microstructure of the formed AgNiCu15-5 strips was analyzed through X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive spectrometry. The deposition billet had a rapid solidification microstructure consisting of β-Ni particles dispersed in α-Ag matrix. ARB significantly refined the microstructure of the AgNiCu15-5 samples. There was no further decrease in the grain size after the 9th ARB cycle. Thus, UASF combined with extrusion and ARB is suitable for producing high-performance AgNiCu15-5-based electrical contact materials efficiently and economically.

Microstructural Evolution Analysis in Thickness Direction of An Oxygen Free Copper Processed by Accumulative Roll-Bonding Using EBSD Measurement

Abstract Microstructural evolution in the thickness direction of an oxygen free copper processed by accumulative roll-bonding (ARB) is investigated by electron back scatter diffraction (EBSD) measurement. For the ARB, two copper alloy sheets1 mm thick, 30 mm wide and 300 mm long are first degreased and wire-brushed for sound bonding. The sheets are then stackedand roll-bonded by about 50 % reduction rolling without lubrication at an ambient temperature. The bonded sheet is then cutto the two pieces of the same dimensions and the same procedure was repeated on the sheets up to eight cycles. The specimenafter 1 cycle showed inhomogeneous microstructure in the thickness direction so that the grains near the surface were finerthan those near the center. This inhomogeneity decreased with an increasing number of ARB cycles, and the grain sizes ofthe specimens after 3 cycles were almost identical. In addition, the aspect ratio of the grains decreased with an increasingnumber of ARB cycles due to the subdivision of the grains by shear deformation. The fraction of grains with high angle grainboundaries also increased with continuing process of the ARB so that it was higher than that of the low angle grain boundariesin specimens after 3 cycles. A discontinuous dynamic recrystallization occurred partially in specimens after 5 cycles.Key wordsaccumulative roll-bonding, oxygen free copper, microstructure, electron back scatter diffraction(EBSD).

Microstructure and Texture of Al-2.5wt.%Mg Processed by Combining Accumulative Roll Bonding and Conventional Rolling

Evolution of microstructure and texture during severe deformation and annealing was studied in Al-2.5%Mg alloy processed by two different routes, namely, monotonic Accumulative Roll Bonding (ARB) and a hybrid route combining ARB and conventional rolling (CR). For this purpose Al-2.5%Mg sheets were subjected to 5 cycles of monotonic ARB (equivalent strain (eeq) = 4.0) processing while in the hybrid route (ARB + CR) 3 cycle ARB-processed sheets were further deformed by conventional rolling to 75% reduction in thickness (eeq = 4.0). Although formation of ultrafine structure was observed in the two processing routes, the monotonic ARB—processed material showed finer microstructure but weak texture as compared to the ARB + CR—processed material. After complete recrystallization, the ARB + CR-processed material showed weak cube texture ({001}〈100〉) but the cube component was almost negligible in the monotonic ARB-processed material-processed material. However, the ND-rotated cube components were stronger in the monotonic ARB-processed material-processed material. The observed differences in the microstructure and texture evolution during deformation and annealing could be explained by the characteristic differences of the two processing routes.

Texture Development of ARB-Processed Steel-Based Nanocomposite

In this study, the evolution of deformation texture in steel-based nanocomposite fabricated via accumulative roll bonding (ARB) process was investigated. Textural evolution during the ARB process was evaluated using x-ray diffraction. It was found that with increasing number of ARB cycles, first, intensity of α-fiber, γ-fiber, and θ-fiber decreased and then increased, while ζ-fiber exhibited the opposite trend compared to these fibers. Also, there were texture transitions in e-fiber and η-fiber. It was realized that with increasing the number of ARB cycles, volume fraction of low-angle grain boundary decreased and the fraction of high-angle grain boundary increased. In addition, shear texture was predominant after first cycle, while for other samples, rolling texture was dominant. When recrystallization occurred, the intensity of ζ-fiber increased, the intensity of α-fiber and γ-fiber decreased, and the intensity of {011}〈100〉 orientation in e-fiber and η-fiber remarkably increased. Indeed, the transition from rolling texture to shear texture was a sign of occurrence of discontinuous recrystallization after the first ARB cycle. Moreover, in the one-cycle sample, nucleation of discontinuous recrystallization had occurred. Finally, with increasing the number of cycles, the intensity of rolling texture increased and the intensity of shear texture decreased.

Microtexture Development of Niobium in a Multilayered Ti/Al/Nb Composite Produced by Accumulative Roll Bonding

Multilayered Ti/Al/Nb composites were produced by the accumulative roll bonding (ARB) process utilizing pure Ti, Al, and Nb element sheets. Up to four cycles of ARB were applied to the composites. The microstructure and texture evolution on the Nb phase were studied by X-ray diffraction (XRD), transmission electron microscopy, scanning electron microscopy, and electron backscattered diffraction. Nb and Ti layers necked and fractured as the number of ARB passes increased. After four ARB cycles, a nearly homogeneous distribution of Nb and Ti layers in Al matrix was achieved. As-received Nb sheet exhibited a fully lamellar structure and had a strong cold-rolling texture. After subjecting to ARB, slight grain refining was observed and the high-angle boundary fraction was increased. The intensity of the α-fiber was weakened, while that of the γ-fiber was strengthened during ARB. The texture evolution was attributed to partial recrystallization during the ARB process as a result of adiabatic heating.

Analysis of Strain Rate Sensitivity of Ultrafine-Grained AA1050 by Stress Relaxation Test

Commercially pure aluminum sheets, AA 1050, are processed by accumulative roll bonding (ARB) up to eight cycles to achieve ultrafine-grained (UFG) aluminum as primary material for mechanical testing. Optical microscopy and electron backscattering diffraction analysis are used for microstructural analysis of the processed sheets. Strain rate sensitivity (m-value) of the specimens is measured over a wide range of strain rates by stress relaxation test under plane strain compression. It is shown that the flow stress activation volume is reduced by decrease of the grain size. This reduction which follows a linear relation for UFG specimens, is thought to enhance the required effective (or thermal) component of flow stress. This results in increase of the m-value with the number of ARB cycles. Strain rate sensitivity is also obtained as a monotonic function of strain rate. The results show that this parameter increases monotonically by decrease of the strain rate, in particular for specimens processed by more ARB cycles. This increase is mainly linked to enhanced grain boundary sliding as a competing mechanism of deformation acting besides the common dislocation glide at low strain rate deformation of UFGed aluminum. Recovery of the internal (athermal) component of flow stress during the relaxation of these specimens seems also to cause further increase of the m-value by decrease of the strain rate.

Dislocation Density of FCC Metals Processed by ARB

Accumulative roll bonding (ARB) was applied to three FCC metals, such as Al, Cu and Ni. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were made to evaluate dislocation density ρ of the ARB processed FCC metals. The values of ρ of ARB processed Cu and Ni increased rapidly after the first ARB cycle, and then, tend to saturate after the following cycles. The evaluated values of ρ of both ARB 8-cycled Cu and Ni using DSC were around 2×1015 m−2. Whereas, those using XRD were around 5×1014m−2 (for Cu) and 3×1014m−2 (for Ni). Although the ρ values depend on the measurement methods, the trends that DSC values are about an order of magnitude higher than XRD values seem to be common. In the case of Al, dislocation density evaluated using XRD increased to about 1×1013m−2 at the first ARB cycle, and then gradually decreased to about 1×1012m−2 with increasing number of ARB cycles.

Texture development and microstructure evolution in metastable austenitic steel processed by accumulative roll bonding and subsequent annealing

In this paper, microstructure and texture development in a Fe–24Ni–0.3C metastable austenitic steel processed by accumulative roll bonding (ARB) and subsequent annealing was studied. Microstructural observations and crystallographic analysis were carried out by FE-SEM/EBSD. The results showed that elongated ultrafine-grained austenite having 300 nm in thickness surrounded by high angle boundaries was obtained after 6 cycles of the ARB process. It was found that 1-cycle ARB-processed specimen exhibited Copper ({112} 〈111〉) component as main texture, while by increasing the number of ARB cycles, it deviated to S component ({123} 〈634〉) at 2 cycles or Brass component ({110} 〈112〉) at 6-cycle. Annealing of 6-cycle ARB-processed specimen at 873 K for 1.8 ks resulted in the formation of an austenite with mean grain size of 2.5 µm having strong Cube recrystallization texture ({100} 〈001〉).