Orientations of recrystallization nuclei developed in columnar-grained Ni at triple junctions and a high-angle grain boundary

A directionally solidified, high-purity nickel sample with a strong 〈0 0 1〉 fiber texture was cold rolled to 40% reduction. Electron backscattered diffraction (EBSD) was used to identify triple junctions (grain edges) before annealing the sample at 430 °C, after which further EBSD was performed to identify 17 recrystallization nuclei at the initially characterized triple junctions on the rolling plane. In addition, a longitudinal section was cut on which a further seven recrystallization nuclei were found and characterized. This characterization of all nuclei revealed that the majority of nuclei could be broadly associated with a 40° 〈1 1 1〉 misorientation to the matrix in which they formed, while a much lower percentage were found to have orientations as those of the local deformation substructure. However, a substantial fraction (around one-third) could not be associated with either of these types. Mechanisms for the formation of nuclei with new orientations are discussed, as is evidence of reorientation of material ahead of the recrystallization front.     

Observation and modeling of the through-thickness texture gradient in commercial-purity aluminum sheets processed by accumulative roll-bonding

The texture evolution in commercial-purity aluminum (AA1070) processed by accumulative roll-bonding (ARB) is investigated with the aid of X-ray diffraction and crystal plasticity modeling. The experimental results indicate strong texture gradients through the sheet thickness, from rolling-type textures with orthorhombic symmetry at the center to shear-type textures with monoclinic symmetry near the surface. The experimental textures are reproduced well by polycrystal plasticity modeling carried out with deformation histories from finite element simulations. The observations of a relatively strong {4 4 11}〈11 11 8〉 component at the center and a {0 0 1}〈1 1 0〉 component at the surface are attributed to their higher orientation stability than the other rolling- and shear-type orientations. Examination of the average through-thickness textures suggests that the ARB technique may not be an effective means to develop apparent {1 1 1}〈u v w〉 components and thus to enhance the normal anisotropy of plasticity of the bulk sheet materials.     

Influence of anisotropy of the magnesium alloy AZ31 sheets on warm negative incremental forming

Single point incremental forming of the magnesium alloy AZ31 sheets, which were fabricated by hot extrusion, slab + hot/cold rolling, strip-casting rolling and cross-rolling, respectively, was investigated at elevated temperatures. The results show that the anisotropy of the sheets fabricated by casting slab + hot/cold rolling and cross-rolling is not remarkable, and the formability is improved significantly. The circular, square and rotary cone parts were performed with satisfactory surface quality and without any microcracks successfully, and which is superior to those of the extruded sheet and the one-way rolled sheet. Therefore, anisotropy of the sheets has remarkable effects on the surface quality of the formed parts, and the effect becomes weakened with increasing temperature. It is proposed that cross-rolling sheet is much more suitable for warm SPIF process.     

Effect of redundant shear strain on microstructure and texture evolution during accumulative roll-bonding in ultralow carbon IF steel

Accumulative roll-bonding (ARB) is a severe plastic deformation process that can effectively produce ultrafine grained (UFG) structures in metals and alloys. In previous investigations, the ARB process has often been carried out under high-friction conditions without any lubricant between materials and rolls, which may cause a large amount of redundant shear strain near the sheet surface. Owing to repetition of cutting, stacking and roll-bonding in the ARB, a complicated redundant shear strain distribution is expected through the sheet thickness. The purpose of the present study is to clarify the effect of the redundant shear strain on the microstructure and texture evolution during ARB. A Ti-added ultralow carbon interstitial free steel was deformed by up to seven cycles of ARB (a thickness reduction of 99.2%) at 500 °C, with or without lubrication, in order to investigate the effect of shear strain. Microstructural characterization by electron backscatter diffraction analysis was carried out at various thickness locations of the ARB processed sheets. The sheet processed by one cycle of ARB with good lubrication showed typical deformation microstructures uniformly throughout the thickness. In contrast, the specimen processed by one ARB cycle without lubrication had an inhomogeneous microstructure, and the fraction of deformation-induced high-angle boundaries increased close to the surface. Non-lubricated ARB caused through-thickness microstructural heterogeneity in low numbers of cycles, but repetition of ARB above five cycles finally produced quite uniform UFG structures. It was established that the microstructural parameters of the deformation structures can be basically understood in terms of the total equivalent strain, taking account of the redundant shear strain.     

Microstructure,texture and grain boundaries character distribution evolution of ferritic stainless steel during rolling process

In order to better understand the texture, microstructure and grain boundaries character distribution evolution of ferritic stainless steel, the texture, microstructure and grain boundaries character distribution of ferritic stainless steel (hot rolled sheet, cold rolled sheet and annealing sheet) with 11 wt%Cr content were studied using X-ray diffraction and electron back scattered diffraction technique. The texture of the hot and cold rolled sheets has a through-thickness texture gradient. In the center layer of the hot and cold rolling sheet, α-fiber texture was observed which was attributed to ideal plane strain deformation. Close to the surface a Gross orientation was detected which was attributed to shear deformation. During annealing, the γ-fiber was formed attributed to recrystallization process. The microstructure of the hot and cold rolled sheets was non-homogeneous through the sheet thickness, while, the microstructure of annealing sheets was homogeneous through the sheet thickness. Grain boundaries character distribution results show that there are many low angle grain boundaries in hot and cold rolled sheets and many high angle grain boundaries and coincidence site lattice after annealing. The above results indicated that the changes in texture are closely related to the grain boundaries type.     

Texture and mechanical properties of Al-0.5Mg-1.0Si-0.5Cu alloy sheets manufactured via a cross rolling method

The relationship between the texture and mechanical properties of 6xxx aluminum alloy sheets processed via cross rolling was investigated. The microstructures of the conventional rolled and cross rolled sheets after annealing were analyzed using optical micrographs (OM). The texture distribution across the thickness in the Al-Mg-Si-Cu alloy, conventional rolled sheets, and cross rolled sheets both before and after annealing was investigated via X-ray texture measurements. The texture was analyzed in three layers from the surface to the center of the sheet. The β-fiber texture of the conventional rolled sheet was typical of the texture obtained using aluminumoll ring. After annealing, the typical β-fiber orientations were changed to recrystallization textures: cube{001}〈100〉 and normal direction (ND)-rotated cubes. However, the texture of the cross rolled sheet was composed of an asymmetrical, rolling direction (RD)-rotated cubes. After annealing, the asymmetrical orientations in the cross rolled sheet were changed to a randomized texture. The average R-value of the annealed cross rolled sheets was higher than that of the conventional rolled sheets. The limit dome height (LDH) test results demonstrated that cross rolling is effective in improving the formability of the Al-Mg-Si-Cu alloy sheets.     

摩擦轧压表面处理及退火处理中纯钛的微观组织与织构演化(英文)

通过一种新的摩擦轧压表面处理工艺(FRSP)对纯钛板材表面进行加工,引入的应变沿材料厚度方向成梯度分布。采用光学显微镜、X射线衍射对FRSP加工后的纯钛的微观组织进行观察发现在钛材表面形成了超微细晶粒,且具有明显织构,其方向与FRSP的加工方向有关。另外,对FRSP处理后的钛材在不同温度和时间下进行退火处理,通过EBSD研究织构的形成及其在退火过程中的演变规律。结果表明:在低温退火过程中,钛板材表层主要存在FRSP后形成的织构,而原有的典型轧制织构减少,可见,通过FRSP及后续退火可有效地控制钛材表面的微观组织与织构。     

Linking recovery and recrystallization through triple junction motion in aluminum cold rolled to a large strain

Recovery mechanisms and kinetics have been studied in commercial purity aluminum (AA1050) cold rolled to a true strain of 5.5 (99.6% thickness reduction) and annealed at low temperatures from 140 to 220 °C. Transmission electron microscopy, electron backscatter diffraction (EBSD) and electron channeling contrast (ECC) are used to characterize the microstructural evolution during annealing. The microstructural characterization shows that a deformed lamellar structure coarsens uniformly during annealing by triple junction motion while maintaining the lamellar morphology, leading to a gradual transition into a more equiaxed structure, where recrystallization nuclei start to evolve. The apparent activation energy for the microstructural coarsening is estimated separately for different stages characterized by an increase in the lamellar boundary spacing measured by EBSD and ECC. The apparent activation energy increases during annealing, from 110 kJ mol^?1 at the beginning to 230–240 kJ mol^?1 at the end of uniform coarsening, linking the recovery stages to recrystallization. The increase in activation energy underpins operation of different diffusion mechanisms for migration of boundaries and their junctions during coarsening, and solute drag may become increasingly important as the structure coarsens. These findings form the basis for a discussion of the thermal behavior of a fine lamellar structure produced by cold rolling to a large strain of both scientific and applied interest.     

Microstructure and mechanical properties of AZ31 magnesium alloy sheets produced by differential speed rolling

The as-extruded AZ31 alloy sheets of 10 mm in thickness were subjected to differential speed rolling (DSR) process performed on a mill, of which the rotation speed ratio of the lower roll and upper one is kept at constant 1.05 by using the different upper and lower roller diameters. The influence of the billet temperature, pass and total thickness reduction ratio on the microstructures, mechanical properties and crystal orientation of the specimens were examined by optical microscopy, tensile test and X-ray diffraction. The present process was found to be effective to refine the grain size and restrain the twinning. Grain refinement became more marked and uniform when the pass and total thickness reduction ratio increased, and the sheets processed by DSR exhibited higher elongation and lower strength than those of the conventional rolled sheets under the same testing conditions. Especially, the AZ31 sheet with elongation of 32% at room temperature was prepared. Moreover, anisotropy was diminished by further annealing at 573 K for 30 min. The DSR does not alter the basal texture but leads to the incline of the basal plane from the sheet surface plane to some extent.     

Texture and mechanical properties evolution of a deep drawing medium carbon steel during cold rolling and subsequent recrystallization

Medium carbon steels are mostly used for simple applications; however, new applications have been developed for which good sheet metal formability is required. These types of steels have an inherent low formability. A medium-carbon hot-rolled SAE 1050 steel was selected for this study. It has been cold rolled with thickness reductions varying between 7 and 80%. The samples obtained were used to evaluate the strain hardening curve. For samples with a 50 and 80% thickness reduction, an annealing heat treatment was performed to achieve recrystallization. The material was characterized in the “as-received”, cold rolled and annealed conditions using several methods: optical metallography, X-ray diffraction (texture), Vickers hardness, and tensile testing. For large thickness reductions, the SAE 1050 steel presented low elongation, less than 2%, and yield strength (YS) and tensile strength (TS) around 1400 MPa. Texture in the “as-received” condition showed strong components on the {0 0 1} plane, in the 〈1 0 0〉, 〈2 1 0〉 and $〈1\overline{1}0〉$ directions. After cold rolling, the texture did not present any significant changes for small thickness reductions, however. It changed completely for large ones, where gamma, 〈1 1 1〉//ND, alpha, 〈1 1 0〉//RD, and gamma prime, 〈2 2 3〉//ND, fibres were strengthened. After annealing, the microstructure of the SAE 1050 steel was characterized by recrystallized ferrite and globular cementite. There was little change in the alpha fibre for the 50% reduction, whereas for the 80% reduction, its intensity increased. Both gamma and gamma prime fibres vanished upon annealing for 50 and 80% reductions alike.     

IF钢铁素体区轧制对带钢最终性能的影响

采用铁素体区轧制工艺能够大大提高IF钢冷、热轧带钢的深冲性能。本研究通过工业试验验证了铁素体区轧制工艺的可行性。试制带钢组织、织构及性能检测的结果表明：热轧带钢1/4厚度处和芯部初步形成了γ织构,连续退火冷轧带钢中形成了强烈的γ织构,冷轧带钢的伸长率达到50%以上,r值达到3.15,具有优良的成形性能。     

The effect of β phase on microstructure and texture evolution during thermomechanical processing of α + β Ti alloy

Microstructure and texture evolution have been investigated in both α and β phases during the hot rolling of β-quenched Ti–6Al–4V at 800 and 950 °C, followed by annealing at 950 °C and air cooling using detailed electron backscattered diffraction mapping. The textures of primary and secondary α in the bi-modal microstructure were analysed separately, and the high-temperature β orientations were calculated by a variant based reconstruction from the inherited α_s orientations. Crystal plasticity finite element modelling has been employed to predict the rolling texture based on common α phase slip systems and compare with the measured α texture. It was found that despite the severe deformation during rolling, a large proportion of the primary α grains retain a Burgers relationship with the β phase. Consequently, the β phase in combination with a variant selection mechanism seems to control the α texture, which explains the discrepancy between predicted and measured rolling textures. The consequence of this mechanism for macrozone formation is also discussed.     

Microstructure and crystallographic texture of an ultrafine grained C–Mn steel and their evolution during warm deformation and annealing

The evolution of microstructure and texture of a 0.2%C–Mn steel during large strain warm deformation and subsequent annealing has been investigated. The process of grain subdivision during warm deformation is essential for the formation of ultrafine grains in such a material. The study reveals that pronounced recovery instead of primary recrystallization is required to obtain a large fraction of high-angle grain boundaries (HAGBs) as a prerequisite for the development of ultrafine grains in the course of warm deformation. The prevalence of primary recrystallization instead of recovery is not generally beneficial in this context since it reduces significantly the dislocation density and removes the substructure which is important for the gradual formation of subgrains and, finally, of ultrafine grains which are surrounded by HAGBs. Consistently, the texture of the ultrafine grained 0.2%C–Mn steel observed after large strain warm deformation and subsequent annealing, consists primarily of the α-(〈1 1 0〉∥RD) texture fiber which indicates strong recovery. The γ-(〈1 1 1〉∥ND) texture fiber which is typical of recrystallized rolled ferritic steels does not appear. The process occurring during the deformation and subsequent annealing can, therefore, be interpreted as a pronounced recovery process during which new grains are created without preceding nucleation.     

Shear banding and recrystallization texture development in a multilayered Al alloy sheet produced by accumulative roll bonding

A commercial purity Al alloy and an Al–0.3 wt.% Sc alloy, the latter in either the supersaturated or artificially aged condition, were accumulative roll bonded to produce 0.5-mm-thick sheet consisting of multiple alternating layers of Al and Al(Sc). The deformation mechanism of these two combinations was strongly influenced by the relative hardening behaviour of the adjacent layers. For the Al/Al(Sc)_aged material, a higher magnitude of in-plane shear stress, well exceeding the flow stress of Al(Sc), was operative at the interface between layers. This resulted in through-thickness shear banding and a marked curvature of the layers in the RD–ND sections. Shear banding also resulted in a reduction in intensity of the rolling texture components and had a randomizing effect on the recrystallization texture of the Al layers. In both conditions, the Al(Sc) layers were resistant to recrystallization after extended annealing at 350 °C and produced a microstructure of recovered equiaxed grains ～0.5–0.8 μm in diameter.     

Evolution of deformation microstructures of cold-rolled Ta–2.5W alloy with coarse grains at low to medium strains

Ta–2.5W alloy with coarse grains was cold-rolled to reductions ranging from 5 to 40%. The evolution of the microstructure was investigated by optical microstructure, electron backscatter diffraction (EBSD). A few microbands appear when the reduction reaches 20%. The density of microbands increases with increasing reduction. When the reduction reaches 40%, grains are composed of one or two groups of microbands except the {001}<110 > orientations. Most of the inclination angle between microbands and RD in this condition is 20–35°. As the strain increases, the inclination angle between microbands and RD gets smaller. The habit plane of microbands can be {110} plane. The microbands and matrix usually share a common < 110 > or < 111 >. The mature body-centered cubic rolling texture, including α and γ fibers, is not developed until the reduction reaches 40%. Meanwhile, shear bands appear. New grains can be seen in shear bands and a model is proposed to explain this process.     

Microstructure,texture and magnetic properties of strip casting Fe–6.2 wt%Si steel sheet

An Fe–6.2 wt%Si strip with equiaxed grains and mild {0 0 1}〈0 v w〉 fiber texture was produced by twin-roll strip casting process. Then the as-cast strip was treated with or without the hot rolling prior to the warm rolling and annealing. When the hot rolling was not introduced, a fine and heterogeneous warm-rolled microstructure was produced and led to a fine recrystallization microstructure and very weak {0 0 1}〈0 v w〉 fiber texture in the annealed sheets. When the hot rolling was introduced, a coarse and homogeneous warm-rolled microstructure was produced and led to a very coarse recrystallization microstructure and much stronger {0 0 1}〈0 v w〉 fiber texture in the annealed sheets. The annealed sheets with hot rolling showed a higher magnetic induction and a higher core loss than those without hot rolling.     

Cold rolling and recrystallization textures of a Ni–5 at.% W alloy

The formation of recrystallization texture has been studied in a sintered Ni–5 at.% W alloy after heavy cold rolling (～95%) and annealing. Although the cold-rolled texture is a typical pure metal or Cu-type deformation texture on a global scale, variations in microstructure and microtexture are found in the deformed material between locally sheared regions and away those from these regions. The primary recrystallization texture consists of the cube ({1 0 0}〈0 0 1〉), a RD-rotated cube ({0 1 3}〈1 0 0〉) and twin-related orientations of these two components. The presence of both cube and the RD-rotated orientations are identified in thin bands of materials in the deformed matrix. However, predominantly cube-oriented grains nucleate and grow in regions away from the locally sheared regions. In contrast, the nucleation and growth of non-cube grains are observed in the vicinity of locally sheared regions. The formation of cube texture in Ni–5 at.% W alloy appears to occur primarily via the oriented nucleation of cube grains owing to the special properties of the cube bands.     

Deformation-induced grain coalescence in an electrodeposited pure iron sheet studied by in situ neutron diffraction and electron backscatter diffraction

The plastic deformation behavior of an ultrafine-grained electrodeposited pure iron sheet with a strong {1 1 1}〈h k l〉 texture was studied by in situ neutron diffraction during tensile deformation at room temperature and by electron backscatter diffraction (EBSD). The combination of volume-averaged crystallographic orientation changes determined by neutron diffraction and the local orientation relationship determined by EBSD reveals a texture change to {1 1 1}〈1 1 0〉 and corresponding microstructural changes with tension deformation. Related to such grain rotation, grain coalescence on deformation was found using semi in situ EBSD. The results obtained are explained using a characteristic slip model, which also gives a reason for the ultrahigh Lankford value of this material.     

The influence of rolling temperature on texture evolution and variant selection during α → β → α phase transformation in Ti–6Al–4V

The role of starting texture in variant selection has been studied during α → β → α transformation in Ti–6Al–4V. By hot rolling at different temperatures followed by recrystallization, material with either a strong basal texture or a strong transverse texture was generated. Subsequently, both conditions were heat-treated above the β transus followed by slow cooling. The degree of variant selection was assessed by comparing the strength of the measured and predicted α texture from high temperature β texture, assuming equal occurrence of all possible variants during β → α transformation. It was found that, even though the material rolled originally at 800 °C displayed a stronger α texture after β heat treatment, it was the material rolled originally at 950 °C that showed greater variant selection. The variant selection mechanism is discussed in terms of the generated β texture and common 〈1 1 0〉 poles in neighbouring β grains selecting a similar α variant on both sides of the prior β grain boundary. Predictions of possible 〈1 1 0〉 pole misorientation distributions for the two investigated β textures showed that the combination of texture components generated during rolling Ti–6Al–4V at 950 °C increases the likelihood of having β grain pairs with closely aligned (1 1 0) planes compared to rolling at 800 °C. Therefore, it can be proposed that avoiding the generation of certain combinations of β texture components during thermomechanical processing has the potential for reducing variant selection during subsequent β heat treatment.