The heterophase interface character distribution of physical vapor-deposited and accumulative roll-bonded Cu-Nb multilayer composites

We present a method for characterizing the full five parameter heterophase interface character distributions (HICD) using two-dimensional electron back-scatter diffraction (EBSD) images. We apply the HICD method to determine the orientation relationships and three-dimensional normal vectors of Cu-Nb interfaces in both physical vapor-deposited (PVD) pure Cu-Nb (4 μm individual layer thickness) and accumulative roll-bonded (ARB) alloyed Cu-Nb multilayer composites (200-600 nm layer thickness). The HICD analysis shows that {1 1 2}_Cu planes are most preferentially and frequently bonded with {1 1 2}_Nb planes with Kurdjumov-Sachs and Nishiyama-Wasserman misorientations in the ARB alloyed Cu-Nb multilayers. These interfaces differ from the {1 1 1}_Cu||{1 1 0}_Nb interfaces predominantly found in the PVD pure Cu-Nb multilayered thin films. Also, pure tilt type interfaces with a [1 1 1]/30° misorientation and {1 1 0}_Cu planes bonded to {1 1 2}_Nb planes were found in ARB alloyed Cu-Nb multilayers. In the ARB material the observed Cu-Nb interfaces differ from what would be obtained from random pairings of the Cu and Nb orientations in terms of the relative intensities (in multiples of random distribution) and shapes of the interface normal peaks, which indicates that these interfaces were preferentially selected during the high strain ARB process. The measured ARB textures along the interface also differ from the theoretical rolling textures for each bulk single phase metal, suggesting that during ARB layer refinement these interfaces have some influence on slip activity by constraining grain deformation or through the kinetics of dislocation-interface interactions.     

累积叠轧Nb/Zr层状复合板的微观组织与力学性能研究

采用累积叠轧法制备了初始Zr层厚度不同的两种Nb/Zr金属层状复合板并对其在叠轧过程中的微观结构、织构演化和力学性能进行了研究。结果显示, Nb/Zr层状复合材料的界面结合良好,异质界面处无金属间化合物产生。随着叠轧道次增加,层状复合结构内部形成了贯穿于多个金属层的剪切带组织,初始Zr层厚度为1 mm的复合板较Zr层厚度为2 mm的复合板易于发生Zr层的颈缩、断裂和分离。Nb层内主要为位错胞状结构, Zr层内为高位错密度晶粒与动态回复晶粒的混合组织。此外,不同初始Zr层厚度的复合板中Nb层的织构演化特征不同：当初始Zr层厚度为1 mm时,Nb表现为强立方取向;当初始Zr层厚度为2 mm时,随着叠轧道次增加,旋转立方取向始终为主导的织构组分。两种复合板中Zr层的织构演化特征一致,即经一道次叠轧后,{0001}基面双峰织构为主要织构组分。随着叠轧道次增加,基面双峰织构略有减弱,同时出现了较弱的{11-20}丝织构。单轴拉伸测试表明,随着叠轧道次增加两种不同Zr层厚度的复合板屈服强度和抗拉强度均逐渐增大,而塑性延伸率呈现先减小后增大的趋势。经三道次叠轧后两种复合板的最大延伸率分别为14.2%和16.5%。叠轧过程中各金属显著的晶粒细化、Zr层内高位错密度晶粒与动态回复晶粒共存的混合组织以及Zr织构的特征演化是贡献于复合板具有高强度和良好塑性的原因。     

Texture evolution of the γ- and the α/α2-phase during hot rolling of γ-TiAl based alloys

Multiple hot rolling experiments were performed in the upper area of the α+γ phase field of the γ-TiAl based alloy Ti46Al9Nb (in atomic percent). The texture evolution for both the γ- and the α/α₂-phase has been investigated by X-ray diffraction. In the γ-phase textures comparable to those known from fcc-metals evolve. The texture components and fibers were separated and described with respect to the lower symmetry of the L1₀-structure. Computer simulations of the deformation texture evolution allow to attribute specific texture components to the predominant activity of ordinary dislocations, super dislocations and twinning, respectively. The accompanying recrystallization appears to be orientation dependent. In the α/α₂-phase transversal and basal type textures similar to those found after hot rolling of two-phase titanium based alloys have been identified. Based on the literature about titanium-based alloys specific orientations were correlated with characteristic slip activity. The underlying mechanisms of texture evolution and orientation dependent recrystallization are discussed for both phases.     

Rolling textures in nanoscale Cu/Nb multilayers

Rolling textures in nanoscale multilayered thin films are found to differ markedly from textures observed in bulk materials. Multilayered thin films consisting of alternating Cu and Nb layers with columnar grains were produced by magnetron sputtering, with individual layer thickness ranging from 4 μm to 75 nm and Cu/Nb interfaces locally satisfying the Kurdjumov–Sachs (K–S) orientation relations. After rolling to 80% effective strain, samples with a larger initial layer thickness develop a bulk rolling texture while those with a smaller initial layer thickness display co-rotation of Cu and Nb columnar grains about the interface normal, in order to preserve the K–S orientation relations. The resulting K–S texture has 0 0 1Nb parallel to and 1 1 0Cu approximately 5° from the rolling direction. A crystal plasticity model based on the Principle of Minimum Shear captures the K–S texture approximately and suggests that Nb drags Cu along in the rotation process.     

Meso-Scale Modeling the Orientation and Interface Stability of Cu/Nb-Layered Composites by Rolling

Metallic-based multilayered nanocomposites are recognized for their increased plastic flow resistance and indentation hardness, increased ductility, improved radiation damage resistance, improved electrical and magnetic properties, and enhanced fatigue failure resistance compared to conventional metallic materials. One of the ways in which these classes of materials are manufactured is through accumulated roll bonding where the material is produced by several rolling and heat-treatment steps during which the layer thickness is reduced through severe plastic deformation. A single rolling pass of the accumulated roll bonding process in which a Cu/Nb-layered composite with an initial average layer thickness of 24 μm subjected to a 50% height reduction is modeled. A single-crystal model based upon thermally activated dislocation motion is used. Nanohardness tests for both the Cu and Nb layers are used to help initialize the model for each of the two materials. Electron backscatter diffraction (EBSD) data of the heat-treated material is used to characterize the initial state of the composite and to produce 40 combined morphological and crystallographic numerical model realizations of the material. The results suggest very good agreement between the predicted and experimental textures for both the materials. Highly oriented microstructure develops during severe plastic rolling deformation of Cu/Nb nanocomposites. The deformation textures significantly deviate from those expected when rolling Cu or Nb alone, and the Cu/Nb interfaces do not correspond to those with the lowest possible formation energies. We study the interfacial stability of specific Cu/Nb bicrystal configurations under rolling conditions using a finite-element crystal plasticity model. Specifically, we examine how slip activity and lattice reorientation are affected by the kinematic constraint imposed by the interface. Our results show that for certain configurations the slip activity and lattice rotation of the individual crystallites display some sensitivity to the kinematic constraint, yet the overall stability of a given bicrystal can be predicted by the stability of the individual single-crystal orientations. Future work will account for the influence of the bimetal interface on the interface stability and development of enhanced properties.     

Electron back scattered diffraction (EBSD) characterization of warm rolled and accumulative roll bonding (ARB) processed ferrite

An interstitial free (IF) steel was severely deformed using accumulative roll bonding (ARB) process and warm rolling. The maximum equivalent strains for ARB and warm rolling were 4.8 and 4.0, respectively. The microstructure and micro-texture were studied using optical microscopy and scanning electron microscopy equipped with electron back scattered diffraction (EBSD). The grain size and misorientation obtained by both methods are in the same range. The microstructure in the ARB samples after 6 cycles is homogeneous, although a grain size gradient is observed at the layers close to the surface. The through thickness texture gradient in the ARB samples is different from the warm rolled samples. While a shear texture (〈1 1 0〉//rolling plane normal direction (ND)) at the surface and rolling texture at the center region is developed in the ARB samples, the overall texture is weak. The warm rolled samples display a sharp rolling texture through the thickness with increasing the sharpness toward the center. These differences are attributed to the fact that the central region of ARB strip is comprised of material that was once at the surface. The ARB process can suppress the formation of shear bands which are conventional at warm rolled IF steels. EBSD study on the sample with 6th cycle of ARB following the annealing at 750 °C verified a texture gradient through the thickness of the sheet. The shear orientations at the surface and at the quarter thickness layers can be identified even after annealing. The overall weak texture and existence of shear orientations make ARB processed samples unfavorable for sheet metal forming in compare with warm rolled samples.     

A new consideration on reinforcement distribution in the different planes of nanostructured metal matrix composite sheets prepared by accumulative roll bonding (ARB)

Recently, a number of novel methods based on accumulative roll bonding (ARB) have been introduced to produce particulate metal matrix composites. Nonetheless, the microstructure uniformity from the reinforcement distribution viewpoint in the different planes of ARBed composite sheets has not been focused up to date. This paper aims to compare the evolution of the B₄C particles distribution in nanostructured Al-10 vol.% B₄C composites prepared by ARB in the rolling direction-normal direction (RD-ND) and transverse direction-normal direction (TD-ND) planes. From optical microscopic evaluations quantified by the radial distribution function analysis, it is realized that the homogeneity in the RD-ND planes is in excess of the TD-ND planes. In addition, transmission electron microscopy reveals the development of nanostructures in the Al matrix after seven ARB passes.     

Microstructure and mechanical properties of AM31 magnesium alloys processed by differential speed rolling

Ingot casted AM31 alloys were rolled at a warm temperature of 350 °C and subsequently rolled at 300 °C using equal speed rolling (ESR) and differential speed rolling (DSR) with speed ratios of top roll to bottom roll, 1.2 and 1.5, respectively. Microstructures, textures and mechanical properties of the as-rolled AM31 sheets were examined. Ductility was improved by DSR due to inclination of basal poles and weakened texture. The sheets produced by DSR with a speed ratio of 1.2 showed highest strength and ductility at room temperature, which can be attributed to homogeneous fine grain distribution and tilted basal texture.     

Zr-4合金板材冷轧过程材料变形晶体塑性分析与织构演变

选取厚度为3.6mm具有典型双峰织构的Zr-4合金板材,利用电子背散射衍射（EBSD）技术对板材冷轧后的织构进行表征,利用粘塑性自洽（VPSC）模型对板材冷轧后的变形机理进行分析。VPSC模型预测了轧制道次数量、每道次压下量以及总变形量对冷轧织构以及变形机理的影响规律,结果表明Zr-4合金板材在冷轧后,织构保持典型的基面双峰织构;轧制道次数、单道次压下量对冷轧后的织构以及变形机理无明显影响;总变形量对冷轧后的织构有明显影响,随着轧制总变形量减小,大部分晶粒的c轴由法向（ND）向宽向（TD）转动;当变形量低于临近变形量39%时,法向科恩系数（Fn）随着变形量的增大而快速增大,柱面滑移开启快速降低,当变形量超过39%时,法向科恩系数（Fn）的增长趋于平缓,柱面滑移的开启趋于稳定。     

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.     

Finite element polycrystal model simulation of cold rolling textures in deformation processed two-phase Nb／Al metal-metal composites

The finite element polyerystal model (FEPM) was extended and applied to simulate the development of the cold rolling textures of matrix aluminum in deformation processed two-phase 10% and 20% Nb/Al(in volume fraction) metal-metal composites on the basis of slip deformation of individual grains. This simulation method can assure the continuity of stress and displacement at the boundary during heterogeneous deformation and take arbitrary boundary conditions into consideration. The starting hot-extruded textures, as initial input condition, were taken into account in the FEPM simulation. The simulation results show that the main texture components and their evolution after various cold rolling reductions in 10% and 20% Nb/Al metal-metal composites are well qualitatively in agreement with the experimental ones. The initially extruded textures are rather weak, so they have no much influence on the simulated final cold rolling textures of the matrix aluminum for Nb/Al composites.     

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.     

Addition of catalysts to magnesium hydride by means of cold rolling

In this paper we compare the techniques of cold rolling and ball milling as a mean to synthesized nanocomposites MgH₂ + 2 at.%X where X = Co, Cr, Cu, Fe, Mn, Nb, Ni, Ti, V. High energy ball milling was performed under argon for 30 min while cold rolling was done in air with a number of roll limited to five. Particle and crystallite sizes are smaller in the ball milled compounds than in the cold rolled ones. The hydrogen sorption kinetics of the ball milled compounds was also faster than the cold rolled samples but not by a wide margin. Because cold rolling was done in air, this limited the number of rolls that could be performed. It is expected that rolling under protective atmosphere will enable a higher number of rolls and better sorption kinetics.     

不同轧制方法制得镁合金板材的组织和织构特点

介绍了热轧、冷轧、交叉轧制、累积叠轧、不对称轧制等不同的镁合金板材轧制工艺。分析了不同轧制工艺对应板材的组织特点及晶粒细化机制。分析了不同轧制工艺下板材织构特点及形成原因。对提高镁合金板材性能,改进轧制工艺提供参考借鉴。     

Analysis of texture and R value variations in asymmetric rolling of IF steel

Asymmetric rolling (ASR) is a potential process to reach better grain refinement than in conventional rolling, thus, can lead to better mechanical properties. It is not known, however, how the introduction of a shear component will change the ideal orientations of the textures, and consequently, the evolution of plastic anisotropy. To understand the effect of the added shear on texture evolution in ASR, a stability analysis is carried out in orientation space and the variations in the position and strength of the ideal orientations are analysed as a function of the shear component. Then, modelling of R values is presented for various cases. On that basis, it is shown that there is an upper limit for the shear component in asymmetric rolling that still retains the 〈1 1 1〉 || ND fibre (ND: direction normal to the sheet) which is good for formability. It is also found that better persistence of the ND fibre can be obtained by cyclically alternating the shear component. The theoretical results are well supported by comparison to experimental evidences.     

Simulation of deformation twins and deformation texture in an AZ31 Mg alloy under uniaxial compression

To investigate deformation twins and the evolution of deformation texture during plastic deformation, uniaxial compression tests on a hot-rolled AZ31 Mg alloy were carried out at 200 °C. Cylindrical specimens were then compressed in both the rolling and the normal directions. The findings revealed that texture evolution, work hardening and macroscopic anisotropy are strongly dependent on the loading direction. Electron backscattered diffraction analysis was used to examine the orientation of parent grains and twin bands in the AZ31 Mg alloy under uniaxial compression. A viscoplastic self-consistent model (VPSC) was theoretically employed to calculate the relative activities of slip and twin systems in polycrystalline hexagonal aggregates under uniaxial compression. Each deformed grain exhibited an independent number and type of twin variants under uniaxial compression. Neutron diffraction was used to measure the macroscopic texture of the AZ31 Mg alloy. The VPSC model was used to simulate texture evolution, work hardening and macroscopic anisotropy during the uniaxial compression. A modified predominant twin reorientation (PTR) scheme was suggested to explain the gradual increase in twin volume in deformed grains.     

Comparison of earing behavior between continuous cast and direct chill cast AA 5182 aluminum alloys during cold rolling and annealing

The evolution of texture and earing during rolling of continuous cast (CC) and direct chill (DC) cast AA 5182 aluminum alloys was investigated. The results showed that the CC alloy possessed a significantly weaker cube texture than the DC alloy after annealing at 454 °C for 3 h. The evolution of texture and earing during rolling was strongly affected by the initial texture. The 45° earing value of the CC alloy increased with increasing rolling reduction, while the 0/90° earing value of the DC alloy decreased. After 45% cold rolling reduction, the deep-drawn cup of the DC alloy exhibited eight ears at 0°, 45° and 90° to the rolling direction. The DC sheet with minimum earing was obtained at about 83% rolling reduction. The evolution of texture and earing during annealing of the CC and DC alloys was compared. An empirical relationship between the earing value and texture volume fractions was established. Minimization of earing could be achieved by balancing the cube, r-cube and β fiber components.     

Effect of plane strain on microstructures and texture, through the reduction ratio of AZ31 Mg alloy

Structural evolution of warm-rolled AZ31 alloy sheets was investigated with respect to various reduction ratios. In order to examine the effect of rolling pass on deformation of the sheet, one-pass rolling was applied to the AZ31 alloys for various 6/1/2011reduction ratios. When the applied reduction ratio was ∼85% of the initial thickness, significant grain refinement and texture development were achieved with dynamic recrystallization. Moreover, with the increase of the rolling reduction ratio from 30% to 85%, the warm rolled sheets exhibit plane strain mode displaying uniform 〈0 0 0 1〉//ND basal textures throughout the whole sheet thickness. The two-dimensional finite element method simulation showed that the current lubrication rolling results in a uniform plane strain deformation through the whole warm rolled sheet.     

The effect of texture and strain conditions on formability of cross-roll rolled AZ31 alloy

The effect of texture evolution of AZ31 Mg sheet on cross-roll rolling process has been investigated for the commercial AZ31 Mg sheet. The large ?₂₃ was operated for the cross-roll rolled sample throughout the whole thickness, leading to the homogeneity of the (0 0 0 2) basal texture. After recrystallization annealing at 673 K for 30 min, cross-roll rolled sample showed uniform texture intensity from surface layer to middle layer different from the normal-roll rolled sample. An excellent formability of the cross-rolled specimen was achieved due to the developed homogeneity of the texture and microstructure refinement for the cross-roll rolled specimen. The strain conditions of surface and center layers were discussed in terms of experimental evaluations and three-dimensional finite element method (FEM) for conventional rolling and cross-roll rolling.     

Structure and Property of Interfaces in ARB Cu/Nb Laminated Composites

Bulk Cu/Nb multilayered composites with high interfacial content have been synthesized via the accumulative roll bonding (ARB) method. Experimental characterization shows that these multilayers with submicronmeter and nanometer individual layer thicknesses contain a predominant, steady-state interface with the Kurdjumov?CSachs orientation relationship joining the mutual {112} planes of Cu and Nb. In this article, we overview microscopy and simulation results on the structure of this interface at an atomic level and its influence on interface properties, such as interface shear resistance and its ability to absorb point defects and nucleate dislocations nucleation.