Fig 2 - uploaded by Yanzhong Tian
Content may be subject to copyright.
EBSD maps of the 96% cold-rolled specimens after annealing at 300 o C for (a) 600s; (b) 1800s; (c) 3600s; and (d) 7200s, respectively. LAGBs (15° >θ≥2° ), HAGBs (θ≥15° ) and TBs (Σ3) are drawn by green lines, black lines and red lines, respectively. The dark regions in (a) correspond to the unrecrystallized deformed structures and the bright regions correspond to the recrystallized structures.
Source publication
A single-phase Cu–Al alloy with a low stacking fault energy was processed by cold rolling and subsequent annealing. Fully recrystallized microstructures composed of ultrafine grains were obtained after isothermal annealing at different temperatures. The minimum mean grain sizes achieved were below 1 μm. It was found that the microstructures were ho...
Contexts in source publication
Context 1
... the 96% cold rolled sample is annealed at 300° C for 600s, only partial recrystallization has occurred, as shown in Fig. 2a. The dark regions correspond to the unrecrystallized deformed structures and the bright regions correspond to the recrystallized structures with low dislocation ...
Context 2
... drawn in red lines are found inside the recrystallized grains. Besides, high-angle grain boundaries (HAGBs) and low-angle grain boundaries (LAGBs) are drawn in black and green lines, respectively. In order to obtain a fully recrystallized microstructure, the sample was further annealed at 300° C for 1800s, of which EBSD boundary map is shown in Fig. 2b, where recrystallization has completed. It is found that annealing twins exist in almost every grain. However, the microstructure is not so homogeneous but has some larger grains. When the annealing time was further increased to 3600s and 7200s, it is found that the microstructure becomes more inhomogeneous, as shown in Figs. 2c and ...
Context 3
... recrystallized microstructures shown in Figs. 2-4 indicate that the starting time for recrystallization is different at each temperature. The distributions of the grain sizes in the fully recrystallized specimens are statistically analyzed by the OIM software and are shown in Fig. 5, where area fractions of the grains having various grain size ranges are displayed. In the specimen ...
Context 4
... the sample was annealed at 300° C for 600s, the strength decreases from 907 MPa of the as-rolled specimen to 703 MPa, but the total elongation recovers from 8.8% to 23.2% (Fig.8b), possibly due to the partial recrystallization shown in Fig. 2a. However, the uniform elongation of this specimen is still only 2.8%. After annealing at 300° C for 1800s, the uniform elongation considerably increases to 18%, and the yield strength and tensile strength are 506 MPa and 648 MPa, respectively. After annealing at 300° C for 7200s, the strength decreases slightly but the ductility ...
Similar publications
Among the various Severe Plastic Deformation (SPD) processes, Equal Channel Angular Pressing (ECAP) is one of the most applicable one which improves strength and ductility due to grain refinement and suitable texture development. In this study, cold rolling were carried out on the 4 pass ECAPed (in route A and C) strip shaped specimens of AZ31 magn...
The microstructural changes leading to nanocrystalline structure development and the respective tensile properties were studied in a 304L stainless steel subjected to large strain cold rolling at ambient temperature. The cold rolling was accompanied by the development of deformation twinning and martensitic transformation. The latter readily occurr...
Tensile properties have been evaluated for four kinds of Al-Mg-Si base alloys which were cold rolled by 90% and subsequently aged for 1 min, 30 min, 18 h at 170°C. To study the effect of alloy compositions and aging conditions on deformation behavior, fracture surface observations and strain distribution analysis during tensile deformation were per...
The development of nanocrystalline structures in austenitic stainless steels during large strain cold rolling and their tensile behavior were studied. The cold rolling to total equivalent strains above 2 was accompanied by the evolution of nanocrystalline structures with the transverse grain size of about 100 nm. The development of deformation twin...
Cu/Al corrugated clad plates were prepared by the novel corrugated cold roll bonding (CCRB) process to investigate the stress states, microstructures and mechanical behaviors of the corrugated clad plate adjacent to various corrugated interface positions by experimental and numerical simulation methods. The results show that the CCRB process induce...
Citations
... The hardening law parameters are identified using the results of the full-scale simple tensile tests, and the verification was carried out via the analysis of the results of shear and tensile tests. For identification and verification, the full-scale experimental data obtained in [10,13,14,51,52] are applied. ...
It is known that the meso- and microstructures of metals determine the physical, mechanical and operational properties of their final products. Scientific and technological progress of recent decades has given impetus to the elaboration and use of models capable of describing the evolving structure of materials. The most promising are multilevel models that include internal variables and are based on physical theories of elastoplasticity (elastoviscoplasticity). This paper presents the structure and basic relationships of a three-level (macro-, meso-1 and meso-2 levels) elastoviscoplastic model. The developed model operates on such internal variables as dislocation densities on slip systems, barriers on split dislocations and sources of edge dislocations. The model describes the mechanisms of production, annihilation, formation of barriers and sources of dislocations. The law of hardening directly takes into account the densities of dislocations and barriers. The mechanism of inelastic deformation is the gliding of edge dislocations along slip systems. Special emphasis is placed on the influence of split dislocations (prone to forming hard Lomer–Cottrell and Hirth barriers) on the deformation of the material. The model is used to describe the behavior of an elastoviscoplastic polycrystalline aggregate with an FCC lattice. Geometric nonlinearity is taken into account by utilizing decomposition of the crystallite motion into quasi-rigid and deformation components. For this purpose, a rigid moving coordinate system for the crystal lattice is introduced. Examples of the application of the model for analyzing the simple and complex deformation mechanisms of materials with different stacking fault energies and, consequently, with different tendencies toward the decomposition of dislocations and barrier formation are given.
... Significant grain refining effect was reported by employing MDF method in various metals, such as in the magnesium alloys [1,2], copper alloy [3], titanium alloy [4,5], as well as aluminum alloys [6]. Furthermore, the grain structure of these metals was regarded as a key factor affecting most of their properties, the strength and ductility were the primary properties that benefit from grain refinement [7][8][9][10][11][12]. Roven et al. [13] reported that grain refinement by forming fine grains greatly improved the ultimate tensile strength in the aluminum alloy. ...
Evolution of grain structure during isothermal multi-direction forging (MDF) of an Al-Zn-Mg-Cu alloy at 400 °C and 450 °C with strain rates from 10⁻³ s⁻¹ to 10⁻⁵ s⁻¹ was investigated with electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). The results demonstrated that the evolution of grain structure was dominated by discontinuous dynamic recrystallization (DDRX), during which the continuous forming of new recrystallized grains at grain boundaries was found. Characteristics of DDRX was enhanced with the decrease of MDF strain rate or temperature, which promoted the formation of recrystallized grains at grain boundaries. Besides, the increase of total strain enhanced such grain refinement effect until the grain structure reached the stable state, in which fine recrystallized grains replaced most of the initial coarse grains.
... Sarma et al. [29] found the optimum SFE to get UFG materials through cryorolling process. Tian et al. [30] achieved the superior strength and ductility of low SFE Cu-Al alloys by simple cold rolling and annealing which is due to an increase in the fraction of twin boundaries by annealing at 400 °C for 10 s. ...
Ultrafine-grained materials have an enormous scope of structural and functional applications owing to their higher mechanical properties compared to that of coarse-grained materials. The influence of room temperature and cryogenic temperature rolling of AA 3003 alloy and pure Cu on its mechanical properties and fracture behavior has been investigated in the present study. Both the materials are rolled to a thickness of 2 mm and 1 mm with a true plastic strain of 0.40 and 1.09, respectively. The deformed samples are characterized by tensile test, hardness test, and X-ray diffraction analysis. It has been observed that tensile strength and hardness of cryorolled (CYR) samples are higher than cold rolled (CR) samples and it is due to the fact that rolling at an extremely low temperature (− 196 °C) suppresses the dynamic recovery and hence mobility of dislocations becomes difficult as a result dislocation density increases. In CYR, low stacking fault energy material (Cu) has higher tendency to increase strength and work hardened compared to higher stacking fault energy materials (AA 3003) without much loss of ductility. SEM pictorial view of fractography revealed that CYR samples have mix mode of failure compared to CR samples. The dimple size is gradually decreased with increasing plastic strain and that is due to severe strain hardening and grain refinement.
... The high strength is deserved from the finer grain size and limited dislocation recovery process, whereas the improved ductility is attributed to the higher work hardening, which is also due to the difficulty of dynamic recovery. It was reported that both the strength and ductility of Cu-Al alloy were improved with increasing Al contents by severe plastic deformation (SPD) and annealing [6,[10][11][12]. This phenomenon was reported as twinning induced plasticity (TWIP) [6]. ...
Cryogenic high-speed rolling (C-HSR), where the specimen cooled in liquid nitrogen is supplied to rolls at rotating 1500 m/min at room temperature, was carried out with Cu - x Al (x = 3.1 and 6.8 mass%) alloy to investigate mechanical properties and electrical conductivities. After 2-pass rolling, the tensile strength was 665 MPa and 841 MPa in case of Cu-3.1 mass% Al and Cu-6.8 mass% Al, meanwhile, conventional low-speed (5 m/min) cold rolling (LSR) showed 605 MPa and 805 MPa, respectively. The balance of strength – electrical conductivity improved in the case of C-HSR compared to LSR. This trend was clearly observed in Cu-3.1 mass% Al. Yield strength and electrical conductivity were predicted using the modified Hall-Petch equation and modified Mayada and Shatzkes (MS) model. It is formed C-HSR increased the accumulation of dislocation density as well as decreasing mean grain size and activation of deformation twins. On the other hand, increase of dislocation density was dominant to contribute the electrical resistivity.
... Recently, it was reported that Cu-Al alloys processed by severe plastic deformation and annealing shows excellent tensile properties due to TWIP (Twinning Induced Plasticity) [2 -4]. Tian et al. [5] aimed at optimization of balance between strength and elongation by heat treatment after 96% heavy rolling, resulted in yield strength of 520 MPa with uniform elongation of 15% after annealing at 673 K for 10 s. In this study, microstructural evolution and changes in mechanical properties with rolling without heat treatment were investigated. ...
... The results of this experiment, which was only cold rolling, were compared with the severely deformed and annealed references as shown in Fig. 9. Fig 9a shows the relationship between 0.2% proof stress and uniform elongation. It is found the balance between uniform elongation and 0.2% proof stress is very similar to those of references [2,5]. Fig 9b shows the relationship between UTS and total elongation. ...
... Fig 9b shows the relationship between UTS and total elongation. It is found that the balance between strength and total elongation of this study is comparable to the results by high pressure torsion (HPT) followed by annealing [2] and 96% rolling followed by annealing [5]. The balances are much higher than that of 70:30 brass sheets [6]. ...
Recently, it was reported that Cu-Al alloys of low stacking fault energy (SFE) processed by severe plastic deformation show excellent tensile properties due to TWIP (Twinning induced Plasticity) phenomenon. In this study, Cu-15at% Al sheets were heavily processed by conventional multi-pass cold rolling up to 90% in reduction in thickness without annealing. In order to reveal the change in mechanical properties and the microstructure evolution, tensile test, hardness test, optical microscopy (OM) and electron backscattering diffraction (EBSD) analysis were performed. Deformation twinning due to low SFE is observed even in the case of low reduction in thickness. As the reduction increases, grains are refined by intersections of shear bands. It is found that the balance of strength and elongation of the processed sheets is comparable to those by severe plastic deformation followed by annealing in literature.
... This indicates that each position along the radial direction of the torsional CuAl6-UCG alloy possesses gradient hardening rate during the tensile processing and the hardening capacity becoming similar only before fracture. Fig. 13 shows the relationship between yield strength and uniform elongation for Cu\ \Al alloys, and the mechanical data are obtained from homogenously structured Cu\ \Al alloys in the literatures and gradient Cu\ \Al alloys in present work [29,32,[47][48][49][50][51][52]. It can be seen that the gradient CuAl6-CG400, CuAl4-UCG and CuAl6-UCG alloys introduced by torsional treatment can enhance the strength without sacrificing the ductility. ...
... Relationship between yield strength and uniform elongation for Cu\ \Al alloys, with the mechanical data being obtained from homogenously structured Cu\ \Al alloys in the literatures[29,32,[47][48][49][50][51][52] and gradient Cu\ \Al alloys in present work. ...
Gradient structures were introduced via torsional treatment to Cu and CuAl alloys with different starting grain sizes and stacking fault energies (SFEs). Systematic investigations showed that the original grain sizes and SFEs of these materials play vital roles in affecting the formation of gradient structures and their corresponding mechanical properties. Large grain size and relatively low SFE are two critical requirements for the formation of the optimum gradient structure. A superior combination of high strength and good ductility can be achieved by torsional treatment in ultra-coarse-grained materials with low SFEs, which is attributed to the hierarchical structures that led to the simultaneous activations of different deformation mechanisms from full dislocation activities to partial dislocation slip and nano-twinning along the radial direction.
... ii) Strain-hardening ability derives from the capacity of newly nucleated dislocations. For the AN-UFG/FG specimens, on the one hand, the moderate grain size created good conditions for both the nucleation and storage of dislocations [30]; on the other hand, the rather low initial dislocation density [44] leaves sufficient space for the dislocation multiplication. In contrast, the nano-scaled grain size and high dislocation density of SPD-NG materials made them difficult to store more dislocations during cyclic loading; thus the strain-hardening ability is limited. ...
... iii) Microstructure stability of the AN-UFG/FG materials has been efficiently improved through the annealing treatment. During the recrystallization process [44], the metastable boundaries have been replaced by the low-energy microstructures such as coherent twin boundaries, together with the elimination of oversaturated dislocations. As a result, the materials exhibit satisfactory microstructure stability during cyclic loading, without obvious grain coarsening, as displayed in Figs. ...
As a significant scientific problem directly impacting on the long-term safety of engineering materials and facilities, the improvement of fatigue strength under fully-reversed cycling was comprehensively explored in this study. Advantageous material characteristics for the improvement of fatigue strength were summarized from the achievements of the previous researches, followed by a new attempt to combine them in material design. As the model material, α-Cu-Al alloys with clean ultrafine-grains as well as large proportions of twin boundaries were thus produced, which exhibited a notable fatigue strength improvement (up to 155 % higher than the coarse-grained counterparts and 40 % higher than the counterparts produced by severe plastic deformation). Furthermore, a general principle briefly summarized as localized fatigue damage reduction was proposed based on the analysis of the optimizing methods including microstructure optimization and composition optimization. Accordingly, several recommended features to obtain such high fatigue strength materials were finally listed for further anti-fatigue design, such as uniform grains with small size and stable boundaries; low initial dislocation density, and proper alloying composition.
... However, there are only few studies on UFG Cu with recrystallized structures since recrystallized UFG grains have been difficult to obtain by conventional plastic deformation and subsequent annealing treatment [11]. Recent research results in some metals and alloys indicate that the yield strength changes greatly when the grain size approaches 1 m, and superior strength-ductility can be obtained when the recrystallized grain size is smaller than 1 m [12,13]. Besides, some unconventional phenomena appear which can be related to the grain structure and dislocation density [14,15], i.e. clear yield drop and Lüders deformation in Al and Al alloys [5,16,17] and interstitial free (IF) steels [16]. ...
... The change of the TB fraction with annealing temperature is consistent with a Cu-6.8wt.%Al alloy processed by cold rolling and annealing treatments [12]. Tensile engineering stress-strain curves of the Cu specimens after HPT and subsequent annealing are shown in Fig. 2. For the as-HPT sample ( =0.2 m), the tensile stress-strain curve showed a high peak stress at a small tensile strain, and gradual decrease in the flow stress owing to necking, which was a typical feature of severely deformed materials and due to the high-density dislocations that limited strain-hardening capability. ...
Fully recrystallized ultrafine-grained (UFG) pure Cu specimens were fabricated by high-pressure torsion (HPT)
and controlled annealing. The recrystallized UFG Cu with a minimum mean grain size of 0.51 μm showed high
yield strength, good ductility, obvious yield drop and large Lüders strain during tensile test. The mechanical behavior of the Cu specimen became sensitive to the change in the grain size from 0.2 μm to 4.2 μm. The continuous transitions of yield behavior and Lüders deformation with grain sizes were discussed.
... Nowadays, ultrafine-grained (UFG) metals have gained more attention in the steel industry because of its excellent mechanical properties such as high tensile strength and good elongation [1][2][3][4][5][6]. In previous studies, UFG metals were fabricated by severe plastic deformation (SPD) processes [7][8][9][10]. ...
The microstructures and properties of the ultrafine-grained low-carbon steel were investigated. Martensite microstructure was obtained by quenching a low-carbon steel, followed by 50% strain cold rolling and then annealing at 500–650 °C for 2 and 30 min, respectively. Microstructures were observed, and tensile properties were measured for the specimens treated with cold rolling and annealing. The effects of annealing parameters on the microstructure and mechanical properties were analyzed. It shows that the microstructure of specimen annealed at 550 °C for 30 min consists of ferrite grains with an average size of 330 nm. The ultrafine-grained low-carbon steel exhibits not only high tensile strength (867 MPa), but also good elongation (16.7%).
... Note that in all these studies mentioned above [15,18,24], the grain sizes of the TWIP steels and Cu alloys always fall in the coarsegrained regime larger than several-tens micro-meters. In contrast, fully recrystallized TWIP steels and CueAl alloys with grain sizes smaller than 1 mm have been successfully fabricated [20,26], which makes it feasible to study the deformation mechanisms from the ultrafine-grained regime to the coarse-grained regime. ...
Fully recrystallized Cu-4 at.%Al alloy and Cu-11 at.%Al alloy with grain sizes ranging from 0.5 μm to 80 μm were fabricated by cold rolling and annealing. Tensile tests showed that yield strength, ultimate tensile strength and uniform elongation of the two Cu–Al alloys had linear relationships with the inverse square root of the grain size, and both the tensile strength and uniform elongation were ameliorated with decreasing the stacking fault energy. The strain-hardening curves of the Cu-4 at.%Al alloy shifted slightly with increasing the grain size, but the strain-hardening curves of the Cu-11 at.%Al alloy were very sensitive to the grain size. Microstructures of both alloys deformed to different tensile strains showed that the Cu-4 at.%Al alloy was favored by dislocation slip; in contrast, dislocation slip, stacking faults and deformation twins were widely observed in the Cu-11 at.%Al alloy, and their roles changed at different strain levels in the specimens with different grain sizes. Finally, mechanisms of achieving high strength and ductility in low-SFE materials were analyzed based on the strain-hardening behavior and deformation patterns. Optimal grain size ranges of 0.2–1 μm for the Cu-4 at.%Al alloy and 1–3 μm for the Cu-11 at.%Al alloy were proposed to achieve superior comprehensive mechanical properties.
