Effect of deformation texture on the anisotropy of elasticity and damage of two-phase steel sheets

The effect of small tensile deformation (3, 6, and 10%) on the texture of preliminary annealed sheets of two-phase DP600 steel (0.10 C, 0.15 Si, 1.4 Mn, 0.007 P, 0.008 S, 0,009 N, 0.02–0,06 Al, 1 Cr–Mo–Ni (wt %)) is studied. Against the background of the annealing texture in the sheets, the {001} <110>, {111} <110>, {111} <112>, {111} <312> components of the slip texture and {115} <110>, {115} <552>, {221} <110>, {221} <114> orientations are developed, which can be associated with the twinning processes. The anisotropy pattern of the Young’s modulus (E) in the sheet plane remains the same after tensile deformation of the annealed sheets. After tension, the values of E decrease in all directions as a result of the onset and development of microdamages. The anisotropy of damage (D) in the plane of the steel sheets after tension is characterized by a maximum in the transverse direction (TD) and a minimum in the rolling direction (RD).     

初始织构对差厚板非均匀塑性变形的影响

CR340轧制差厚板（TRB）在轧制过程中,其不同的厚度区形成了不同的织构,分别是薄区的{111}<01>和{141}<22>织构,过渡区的{225}<10>和{211}<01>织构,厚区的{876}<5>和{411}<01>织构。根据EBSD测试结果,建立了各厚度区的多晶体塑性有限元模型,研究了单向拉伸时各厚度区的晶粒织构对滑移系开动情况和应力应变分布的影响规律。结果表明,薄区的{111}<01>织构和厚区的{876}<5>织构有利于滑移系的开动,开动的数量分别为9和8组,这使得等厚区在变形中的应力集中弱化,具有良好的塑性变形行为。而过渡区的{225}<10>、{211}<01>织构的晶粒滑移系开动较少,开动的数量分别为6和7组,导致应力集中,其塑性变形行为较差。差厚板各厚度区织构的差异导致其塑性变形呈现明显的不均匀性,其断裂位置发生在单轴拉伸时塑性变形较差的过渡区。     

Study on the cold rolling deformation behavior of polycrystalline tungsten

Tungsten is paid special attention due to its superior properties, especially in nuclear field. Meanwhile it is suitable for texture simulation investigation of BCC metals and alloys as it's near elastically isotropic. This study investigates the cold rolling deformation texture of polycrystalline tungsten using RS model, in which the stress and strain consistence is realized simultaneously. The texture evolution and effects of deformation parameters, including external as well as internal reaction stress, strain and activation of different slip, on texture during rolling are discussed by comparing the simulated results and reported experimental results in literatures. The results show that, the cold rolling deformation texture could be simulated statistically based on RS model. The accumulation of each reaction stress is different. The up-limit of reaction stress σ'₁₂ is found to be medium, meaning that σ'₁₂ exerts important effect on texture evolution. Much lower accumulation level of σ'₁₃ as well σ'₂₃ is displayed, each of which within certain range contributes to the increase of different γ-fiber texture components. The effect of σ'₂₂ can't be ignored during rolling, especially in the case of obtaining {111}<110> texture. Regarding the deformation textures of tungsten rolled to true strains of −1.7 and −2.91, {001}<110> texture is strengthened with the increasing strain and becomes dominant, implying the easier activation of {112}<111> slip systems; γ-fiber texture is weakened at higher strain, and the formation of {111}<112> texture shows significant effect of surface shear stress σ₁₃, which is due to the nonnegligible surface friction when rolling at high temperature.     

2A14-T4铝合金T形接头静轴肩搅拌摩擦焊组织结构与力学性能

采用静轴肩搅拌摩擦焊接法（SSFSW）在不同的焊接速度下制备了2A14-T4铝合金T形接头。在优化的焊接工艺参数下,可以得到光滑的T形接头焊缝表面。结果表明：焊接熔核区（WNZ）的显微组织为完全动态再结晶产生的细小等轴晶,第2次焊核区（WNZ2）的平均晶粒尺寸最大,焊接重合区（WNOZ）次之,第1次焊核区（WNZ1）的平均晶粒尺寸最小。WNZ的再结晶机制主要是几何动态再结晶,并伴有部分连续动态再结晶。WNZ1和WNZ2织构类型为弱{111}<110>,而WNOZ经过2次搅拌后织构类型为弱{100}<001>。热机械影响区（TMAZ）发生塑性变形,而热影响区（HAZ）只受到焊接热循环作用,不发生塑性变形和晶粒的动态再结晶。WNZ的硬度较高,硬度最低的区域位于靠近TMAZ的HAZ。随着焊接速度的增加,接头抗拉伸强度先增大后减小。底板和加强板的主要断裂形式是脆性/韧性混合断裂。     

形变诱导Inconel 625合金管材静态再结晶行为

使用室温压缩变形与再结晶退火处理研究了Inconel 625高温合金冷变形及再结晶行为,采用EBSD技术分析冷变形过程中的应变分布、晶粒尺寸变化、组织与织构演变,分析冷变形Inconel 625合金再结晶过程中再结晶分数、晶粒尺寸、组织及织构演变。研究表明,Inconel 625合金在变形量为35%~65%时具有良好的塑性,随着变形量的增加,晶粒尺寸减小,应变分布越均匀,{111}<112>织构和{110}<001>织构逐渐减弱,而{001}<110>织构和{112}<111>织构略为增强。冷变形Inconel 625合金再结晶退火处理后,随着退火温度与保温时间的升高,再结晶分数增大;随着变形量的增大,Inconel 625合金发生完全再结晶时温度减小,且发生完全再结晶时的晶粒尺寸变小,变形量为35%时,再结晶过程主要是{112}<111>织构{123}<634>变形织构转变为{110}<112>织构、{001}<100>织构与{124}<211>织构。随着变形量增加到50%及65%时,冷变形产生的{123}<634>织构在再结晶过程中转变成了{124}<211>织构。     

Micromechanical mechanism of texture formation in γ-TiAl

Texture evolution in TiAl depends on the type of deformation such as uniaxial compression, tension or rolling as well as on the initial microstructure. Cast TiAl shows a lamellar microstructure with an alignment of the lamellae and exhibits a strong texture. Deformation parallel to the aligned lamellae results in a plane-strain deformation which leads to a brass type texture. From room temperature up to 700 °C, compression tests of TiAl specimens with equiaxed microstructures result in <110>-fiber textures where the <101> component is shifted to <302>. At higher temperatures the orientation <302> is caused by dynamic recrystallization. In rolled sheets of TiAl with equiaxed microstructure the main texture component is a modified cube texture {100}<010> where the tetragonal c-axis is aligned in transverse direction of the sheet. This texture component is caused by dynamic recrystallization and appears to be stable against further rolling.     

The effect of texture on ridging of ferritic stainless steel

Ferritic stainless steel sheets exhibit ridging parallel to the rolling direction when subjected to tension or deep drawing. The origin of ridging behavior has not been clearly explained yet. Many people agree that ridging originates from different plastic anisotropies of grains. In this study, 430 and 409L stainless steels having columnar and equiaxed structures were chosen as initial specimens to elucidate the role of microstructure and composition on ridging. The specimens initially having the columnar structure showed severe ridging and 409L stainless steel showed an inferior surface quality. The existence of band-like colonies of similar orientations was found in the center of the sheets by electron back-scattered diffraction measurement. In addition, the previous models suggested by other researchers were examined quantitatively by the crystal plasticity finite element method. In order to obtain a more realistic ridging simulation, the specimens containing variously oriented colonies in a textured matrix were also considered. The simulated results showed that the lower plastic strain ratio of {001}<110> colonies and different shear deformations of {111}<110> or {112}<110> colonies resulted in ridging.     

Recrystallisation of channel die deformed single crystals of typical rolling orientations

The effect of deformation microstructure heterogeneity on recrystallisation behaviour has been studied using channel die deformed single crystals of typical f.c.c. rolling texture components. These orientations exhibit a wide range of both spatial and orientational heterogeneity. The likelihood of recrystallisation nuclei developing from within the deformed microstructure is found to be directly related to the extent of this heterogeneity. The recrystallisation textures comprise both a retained deformation texture component, as well as a component close, but beyond, to one extreme of the deformation texture spread. The growth of recrystallised grains, regardless of orientation, is affected by the degree of heterogeneity of the deformation microstructure. For randomly oriented nucleation, and under equivalent annealing conditions, recrystallisation proceeds two orders of magnitude faster in the lower stored energy homogeneous {110}<112> orientation than in the {123}<634> orientation, with a much more heterogeneous microstructure and higher stored energy, even after recovery.     

基于VPSC仿真的ZK60镁合金拉伸变形行为

通过实验和粘塑性自洽（VPSC）模型,研究了在室温下挤压态ZK60镁合金沿不同方向拉伸时的变形机制开动情况,及其与流动曲线、织构演变和显微组织的对应关系。通过调节VPSC模型的参数,建立了滑移和孪生耦合的晶体塑性力学模型。比较了不同方向拉伸过程中织构演变的差异,分析了变形机制对屈服不对称性的影响。实验和模拟结果表明：当沿垂直于挤压方向（PED）拉伸时,由于｛102｝孪晶开动,大部分晶粒发生大角度旋转（约90°）。柱面<a>滑移是导致ZK60合金沿不同方向拉伸时出现明显屈服不对称的主要变形机理。当ZK60合金沿挤压方向（ED）拉伸时,由于晶粒的择优取向分布,｛101｝孪晶难以开动,导致ZK60挤压态镁合金拉伸屈服强度较高。ZK60镁合金沿着与ED成45°的方向拉伸时,屈服应力高于沿PED拉伸,但随着拉应力逐渐增大,由于沿PED拉伸时柱面<a>滑移逐渐开动,沿PED应变后期的应力曲线逐渐高于沿与ED成45°方向应变的应力曲线。     

Lattice orientation dependence of the stored energy during cold-rolling of polycrystalline steels

During cold deformation, about 10% of the energy spent is stored in the polycrystalline material in the form of the elastic energy associated to crystal defects. The latter can be measured experimentally by calorimetry, X-ray diffraction. In this work, we propose a direct calculation based on an elastic-plastic self-consistent model. The part of the stored energy related to second order (intergranular) stresses is estimated for a cold-rolled Ti–IF steel. The stored energy as well as the accumulated plastic strain are reported as a function of the final crystallographic orientation of the grains. Along the α-fiber, the stored energy increases from {001}<110> to {111}<110> while the plastic strain decreases. This dependence with the crystallographic orientation is in good agreement with experimental results. With respect to recrystallization, experiments show that {111}-grains nucleate first. This highlights the specific role of second order (intergranular) stresses for recrystallization.     

Interpretation of hot rolling and cold rolling texture in high purity aluminium

In high purity aluminium two different types of hot band textures were produced by changing the final hot rolling temperatures. The texture of the hot bands was found to be inhnmogeneous through thickness. The strong preferred orientation of {001}<110> developed in the surface layer of the hot band which had been rolled at the higher finishing temperature. For the lower finishing temperature sample, the cold rolling type of texture was formed in the hot band. The cold rolling texture was dependent on the initial hot rolling texture. The hot band which had strong {001}<110> at the surface layer led to the maximum orientation density at {44 11}<11 11 8> after the subsequent cold rolling. Preferred orientations near {123}<634> in the hot band caused the maximum at {123}<634> in the cold rolling texture. The experimental results were discussed based on the simulation test of deformation texture in which the rotation of orientations was calculated from the Taylor model. In this calculation, the strain state of the deformation zone in the rolling gap is assumed to vary with shears induced from the geometry and the friction.     

Ti-2Al-2.5Zr单道次皮尔格轧制过程中显微组织和织构的演化

研究了单道次皮尔格轧制过程中Ti-2Al-2.5Zr材料的变形行为和织构的演变规律。结果表明,在轧制过程中,｛102｝孪晶和柱面滑移是最容易被激活的2种变形模式,｛102｝孪晶的产生使得晶粒在轴向上的位向从<100>转向<110>。并且,在不同瞬时Q值和等效应变量下,滑移和孪生导致｛0001｝极图中最大极密度点在切向上发生变化。     

超低温等通道转角挤压高导电单晶铜的霍尔佩奇强化

分别采用光学显微镜、扫描电镜、X射线衍射仪和电子背散射衍射分析超低温等通道转角挤压(ECAP)中等应变量单晶铜的形变组织和织构演变，测试材料的力学和导电性能，分析材料组织转变机理及其对材料力学和导电性能的影响。结果表明，超低温ECAP早期形成的定向剪切带在后续变形过程中会严重影响材料组织的转变过程。增加应变量，A路径变形中剪切带内部会形成高密度的位错塞积，特征晶界占比增加；B_C路径变形时剪切带内部的位错发生强烈的交互作用；C路径变形后剪切带的取向发生分散。经过6道次变形后，单晶铜组织中形成强烈的{111}<112>织构，材料强度从初始126.0 MPa增加到400.2 MPa，而导电率仍保持在98%IACS以上。低温ECAP变形后组织内部形成定向剪切带并产生高密度的位错，位错间相互缠结，有效阻碍了位错滑移，而晶粒仍保持良好的单晶特性。     

Analysis of deformation textures of asymmetrically rolled aluminum sheets

Asymmetric rolling, in which the circumferential velocities of working rolls are different, imposes shear deformation and in turn shear deformation textures to sheets through the thickness. A component of ND//〈111〉 in the shear deformation textures can improve the plastic strain ratios of aluminum sheets. In order to understand the evolution of ND//〈111〉, the strain histories and distributions in the sheets and the texture evolution during the asymmetric rolling have been measured and calculated. The shear deformation texture can vary with the ratio of shear to normal strain increments. As the ratio increases from zero to infinity, the texture moves from the plane strain compression texture (β fiber) to the ideal shear deformation texture consisting of {001}〈110〉, {111}〈110〉, and {111}〈112〉. The ratio increases with rolling reduction per pass in asymmetric rolling. However, it is practically difficult to develop a rolling reduction per pass high enough to obtain the ideal shear deformation texture. Imposing the positive and negative shear deformations on the sheet by reversal of the shearing direction can give rise to the ideal shear deformation texture.     

Texture analysis of the transition from slip to grain boundary sliding in a discontinuously recrystallized superplastic aluminum alloy

Texture and microtexture measurements were correlated with mechanical property data for a superplastic 5083 aluminum alloy. Prior processing had included an overaging treatment followed by severe rolling deformation and the as-received material was annealed prior to mechanical testing. Discontinuous recrystallization by particle-stimulated nucleation during the annealing accounts for a predominantly random texture, although a weak {100}<0vw> component was present, as well as a random grain boundary disorientation angle distribution. During elevated temperature deformation under dislocation-creep-controlled conditions, a distinct <111> fiber component and a relatively weak {100}<001> cube orientation, which are mutually compatible during uniaxial tensile extension, became apparent in the texture. Also, low-angle boundaries became evident in the disorientation distribution. In contrast, the random texture component and the randomness of the disorientation distribution became more evident when the material was deformed under conditions of grain boundary sliding control of deformation. A transition from dislocation creep to grain boundary sliding observed in the microtexture measurements of this work may be predicted by treating constitutive equations for dislocation creep and grain boundary sliding in an additive manner.     

预变形对Al-Zn-Mg铝合金组织及力学性能的影响

系统研究了预变形温度对Al-Zn-Mg铝合金微观组织结构及力学性能的影响。运用光学显微镜和透射电镜观察了微观组织,扫描电镜表征了拉伸断口形貌,X射线衍射仪测试了宏观织构构成,万能拉伸试验机测试了力学性能。结果表明,在400 ℃的热轧温度下,力学性能指标最佳,屈服强度和抗拉强度分别达到325 MPa和455 MPa,伸长率达到14%。不同热轧温度下的拉伸试样断口均呈现为韧性断裂,断口处均存在数量和尺寸不一的韧窝。400 ℃热轧变形温度下,晶粒内部的位错缠结消失,形成了晶界附近规则排列的位错墙;450 ℃时,晶内的位错消失,主要为再结晶晶粒。在350 ℃和400 ℃热轧变形温度下,织构中存在明显的剪切织构,包括旋转立方织构{001}<110>和黄铜R织构{111}<112>和{111}<110>。450 ℃热轧变形温度下,出现明显的再结晶织构Cube_ND {001}<310>。     

Superplastic deformation mechanisms of high Nb containing TiAl alloy with (α2 + γ) microstructure

In this paper, superplastic deformation behaviour of a high Nb containing TiAl alloy with fine (α₂ + γ) microstructure, Ti–43.5Al–8Nb–0.2W–0.2B (at.%), has been examined and studied by means of hot tension from 850 °C to 1050 °C under an initial strain rate of 10⁻⁴ s⁻¹. The mechanical behaviour and microstructure evolution have been characterized and analyzed. Besides, to gain insight into deformation mechanisms, the texture evolution during deformation at ordinary (non-superplastic) and superplastic conditions has been systematically studied. The results showed that, the alloy exhibited impressive superplastic elongation at 1000 °C with a strain-rate sensitivity exponent (m) of about 0.5 and an apparent activation energy (Q_app) value of about 390 kJ/mol. The microstructural characterization showed that, when the alloy was deformed at ordinary condition (850 °C), severe grain refinement occurred and the fraction of low-angle grain boundary notably increased. Meanwhile, the textures were characterized by <100> and <111> double-fiber components parallel to the tensile direction. All these observations suggested a dislocation slip and twinning mechanism. However, if deformed at the superplastic condition (1000 °C), it was found that the microstructure was fairly stable in terms of grain size, morphology and grain boundary characteristics during tension, but a continuous weakening of the initial <110> fiber texture (resulted from canned-forging) was observed. This was believed to be an indication of grain boundary sliding mechanism. Moreover, the deformation texture (<100> + <111>)—though is very weak—was simultaneously appeared. According to a detailed discussion on the deformation kinetics and microstructure evolution, it was believed that the slip/twinning-accommodated grain boundary sliding was responsible for superplastic deformation and the dislocation climb inside of γ grains was the rate-controlling step.     

Phase transformation of pure tungsten subjected to multi-directional compression

Multi-directional compression (MDC) under the reduction of 30% with 1, 2 and 3 passes was subjected to tungsten at the temperature of 900 °C. The microstructure characteristics of the initial sintered and MDC-processed tungsten (W) specimens were comparatively investigated by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The phase transformation from α-W to γ-W was observed during the MDC deformation due to the crossed-shear deformation mode and high stored strain energy. An obvious crystallographic relationship of {110} α // {111} γ was found between α-W and γ-W. And a new crystalline slip path along [101] direction was presented. Molecular dynamics simulations were performed to investigate the phase transformation mechanism of pure W during MDC. A large number of defect clusters and shear bands were formed along 〈110〉 direction. Defect clusters huddled around the slip bands with the accumulation of strain, which caused dislocation tangling with the slip bands, resulting in stress concentration leading to phase transformation. The crystalline slip direction of α-W to γ-W phase transformation was a complex of [100] and [001]. The simulation results showed that the process of microstructural evolution under multiple passes of MDC was in good agreement with the experiment. This study is significant for the phase transformation path and mechanism of pure W during plastic forming.     

Effect of extrusion ratios on hardness,microstructure, and crystal texture anisotropy in pure niobium tubes subjected to hydrostatic extrusion

Nb tubes were fabricated through hydrostatic extrusion at extrusion ratios of 3.1 and 6.1 at ambient temperature, and then their microstructure, texture, and Vickers hardness were investigated based on electron back-scattered diffraction (EBSD) data. The fraction of low-angle boundaries (LABs) largely decreased with a sharp decrease in mean grain sizes after hydrostatic extrusion and was not proportional to extrusion ratios, assuming that mixed-asymmetrical junctions forming LABs dissociate at high extrusion ratios from the external stress (>981 MPa) with thermal activation by the generated heat. The correlation between grain size and Vickers hardness followed the Hall?Petch relationship despite the texture gradient of the 〈111〉 cyclic fiber textural microstructure at low extrusion ratios and the 〈100〉 true fiber textural microstructure at high extrusion ratios. The increase in hydrostatic pressure on the Nb tubes contributed to texture evolution in terms of extrusion ratios due to the difference between {110}〈111〉 and {112}〈111〉 components based on EBSD data.