Recrystallization Texture and Microstructure of Metal Substrate for Y123 Coated Superconductor

Thesecondgenerationofhigh temperaturesuper conductingtapesusingYBCO 12 3superconductorhavebeenanattractivesubjectinrecentyears .IncomparisonwithBibasedsuperconductors ,YBCOshowsbetterirreversibility ,lowAClosscapabilityandhighcriticalcurrentdensityJC inhighmagneticfields[1] .However ,owingtoitspropertyofphysicalmetallurgy ,YBCOtapescannotbeproducedbyOPIT(OxidePowderinTube)technique ,whichhasbeenusedinBibasedsuperconductorsuccessfully[2 ] .Fur thermore ,poorintergrainbondinginpolycrys…     

Fabrication of NiO Buffer Layer for YBCO Coated Conductors by Combining Sputtering and SOE Method

In research of YBCO coated conductors, the development of a oxide template for epitaxial growth of YBCO is very important. Matsumoto et al have demonstrated the potential of the surface oxidation epitaxial (SOE) route for formation a cube textured NiO layer on nickel tapes. The epitaxial NiO functions as a buffer layer of chemical reaction between YBCO and nickel, and as a template for the epitaxial growth of YBCO. However, the surface quality of NiO is difficult to control and defects such as crack, spall and deep grooves exist in SOE NiO layer. A new approach combining sputtering and SOE method to obtain crack-free and cube textured NiO layer were reported. Ni tapes prepared by the combination of rolling and recrystallization were used for this work. A coating of Ni was first deposited on the tapes via magnetron sputtering. Then on the coating tapes, continuous and textured NiO layer were achieved by SOE technology.     

Influence of deformation and annealing conditions on the recrystallization cube texture in the three-layer NiW/NiCr/NiW substrate tapes

The formation of a sharp cube texture in a three-layer composite tape with the outer (working) layers made of an Ni–4.8 at % W alloy and the inner layer made of an Ni–11 at % Cr alloy is studied after cold deformation by rolling at a reduction of 98.4–99.5% and subsequent recrystallization annealing at a temperature of 1000–1150°C. An analysis of the sharpness of the cube texture and the magnetic properties of the three-layer composite material shows that such tapes can be used as substrates to create second-generation HTSC. At a temperature of 80 K, the specific magnetization of the composite three-layer tape is lower than that of a widely used tape made of an Ni–5 at % W alloy.     

Influence of Hot Rolling on Cube Texture of Ni Substrate for Coated Conductor

Pure Ni and Ni alloy tapes with sharp cube texture and low-angle grain boundaries prepared by thermomechanical process were extensively used as substrates for coated conductor. The thermomechanical process usually includes hot forging and cold rolling. In this study, a hot-rolling process between hot forging and cold rolling was induced. The influence of hot rolling on the cube texture of pure Ni was discussed. Sharp cube texture on pure Ni was obtained by suitable hot rolling, cold rolling, and recrystallization treatment. This deformation texture of tape was studied using orientation distribution function （ODF）. Orientation mapping, content of the cube texture, and grain boundary distribution were performed using an EBSD system mounted on LEO-1450 SEM. The results show that the substrates that are hot rolled have a sharp cube texture and low-angle grain boundaries.     

The growth and structure of thin oxide films on cerium ion-implanted nickel

Cerium ions were implanted into a high purity polycrystalline Ni to a dose of 2 × 10¹⁶ Ce⁺/cm². The radiation damage and distribution of Ce in Ni substrate were modified by postimplantation vacuum annealing. The Ce implants significantly decreased the NiO growth rate at 973 K. Thin oxide films formed on implanted Ni were composed of three well-defined sublayers, each with an essentially different microstructure. Cerium was present in the near surface region of the oxide in the form of CeO₂ particles, randomly distributed in NiO matrix, and Ce ion segregants at NiO grain boundaries. The size of CeO₂ particles, formed during the initial stages of exposure to oxygen, affected the inhibition of oxide growth. Vacuum annealing following implantation decreased the beneficial effect of Ce implants by increasing the size of CeO₂ particles. The role of Ce implants in inhibiting grain boundary diffusion in NiO is analyzed. As a result of this study, the growth mechanism of thin NiO films on Ce-implanted Ni is proposed.     

Growth of CeO2, Y2O3 Buffer Layers for YBCO Coated Conductor

The liquid citrate method was used to synthesize perovskite-type SrCe0.9 Y0.1O3-α powder. SrCe09Y01O3-α membranes were prepared from the powder by sintering at 1450℃ for 10 h. The reactions in the process of the heat treatment were studied by XRD and DSC/TG. The microstructure of the powder and the membrane was observed by SEM. The results indicate that the perovskite-type SrCe0.9Y0.1 O3-α can be synthesized at 1100℃. The particle size of the synthesized SrCe0.9Y0.1O3-α powder is less than 1μm. The powder can be densified at 1450℃.     

Deposition of Biaxially Aligned YSZ Layers on Polycrystaline Metallic Substrate

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On the origin of cube texture in copper

A crystallographic etch in which 111 planes are exposed in copper has been used to determined the orientation of the neighbouring substructures sorrounding cube oriented microbands in heavily cold rolled copper. These, after characterisation into orientation groups, were compared with the neighbourhoods of undeveloped cube oriented microbands in lightly annealed material in which almost all well developed recrystallised grains were of cube orientation. By inspection of the two sets of orientation neighbourhoods it is demonstrated that only cube microbands sorrounded by material with a φ° <111> orientation relationship provide cube nuclei. Thus the cube texture arises from competition between nuclei in a variety of orientation environments, the successful nuclei having environments into which they initially grow characterised by a φ° <111> relationship. The process is best described as micro-growth selection, in which the local texture determines the viability and competitive advantage of nuclei, while the global deformation texture (i.e. that determined by traditional diffraction methods) is that which is consumed by those nuclei, with the possibility of further growth selection as recrystallisation proceeds.     

无取向电工钢织构的演变及其沿带钢宽度方向上的差异

采用EBSD检测技术,分析了50W800无取向电工钢在重要生产工序间织构的演变以及织构沿带钢宽度方向上的差异性。结果表明:热轧板织构沿带钢宽度方向上的差异性主要体现在表层织构。带钢边部表层织构主要由旋转立方织构、α纤维织构以及少量的γ纤维织构组成,带钢宽度1/4处的表层织构主要存在高斯织构,带钢宽度1/2处的表层织构主要为(110)面织构以及少量的铜型织构。各处的带钢宽度1/4处和1/2处的织构类型基本一致,都以α纤维织构和旋转立方织构为主。冷轧后,各处的表层织构类型差异较小,均为γ纤维织构和α纤维织构。由板宽边部至中心处织构强度值逐渐降低。退火后,各处织构的组分基本一致,为较强的γ纤维织构和较弱的(100)面织构。各处织构强度值差异较小,变化趋势与冷轧板一致。     

Oxidation Mechanism of Ni-0.5Y Microcrystal CoatingSputtered by Magnetron at 1 000 ℃

The isothermal and cyclic oxidation behaviors of bulk pure nickel and its Ni-0.5Y microcrystal coating sputtered by magnetron at 1 000 ℃ in air were studied. The scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) were used to examine the structures of the coating and the NiO oxide films. The laser Raman spectrum was also used to measure the stress level in NiO films formed on bulk nickel and the coating. It is found that the Ni-0.5Y microcrystal coating has lower oxidation rate, and the grain size of NiO formed on Ni-0.5Y coating is also relatively smaller than that formed on bulk nickel. Meanwhile, the compressive stress level of oxide film formed on Ni-0.5Y coating was lower than that formed on bulk nickel, and the high temperature plasticity of oxide film was much improved in coating case. The improvements of anti-oxidation properties of the sputtered Ni-0.5Y coating are due to the microcrystal structure and yttrium.     

Microstructure and crystallographic texture of strip-cast and hot-rolled austenitic stainless steel

The microstructure and texture of a strip-cast as well as a hot-rolled austenitic stainless steel (18 pct Cr, 8.5 pct Ni) are investigated by the use of optical metallography and quantitative X-ray texture analysis. In the hot band, a homogeneous microstructure is revealed together with a through-thickness texture gradient consisting of a weak cold rolling type of texture in the center layer and a shear texture close to the surface layers. The result is discussed in terms of the through-thickness shear profile that is generated during hot rolling. In the strip-cast material, a random orientation distribution as well as the development of martensite close to the center layer is attributed to the impingement and deformation of the films that are solidified on the surfaces of the casting rolls. The texture close to the surface is attributed to the growth selection of {001}〈uvw〉 oriented grains.     

Dynamic oxidation behavior of TD-NiCr alloy with different surface pretreatments

Oxidation tests of TD-NiCr alloy with different surface pretreatments were conducted in a Mach-5 arc-jet at 1200°C and 0.002 lb/s flowing air environment. Extensive scanning electron microscopy and X-ray analyses were carried out to determine the mechanisms responsible for the observed oxidation behavior. The presence of atomic oxygen in the air stream plays a significant role in determining the oxidation characteristic of the alloy. The rate of Cr₂O₃ vaporization by formation of volatile CrO₃ is greatly enhanced by the flowing conditions. The typical microstructure of oxides formed in the dynamic tests consists of an external layer of NiO with a porous “mushroom”-type morphology, an intermediate layer of NiO and Cr₂O₃ oxide mixture, and a continuous inner layer of Cr₂O₃ in contact with the Cr-depleted alloy substrate. The formation of mushroom-type NiO is attributed to three basic processes: 1) vaporization of NiO by dissociation into its elements, 2) reoxidation of Ni vapor predominantly with atomic oxygen, and 3) condensation of NiO at elevated sites on the specimen surface. The oxidation rate is determined by the rate of vaporization of NiO. Surface pretreatment has a significant effect on the oxidation behavior of the alloy in the early stage of oxidation, but becomes less important as exposure time increases. Mechanical polishing induces surface recrystallization, which enhances the formation of Cr₂O₃ in static environment, but promotes the concurrence of external growth of NiO and internal oxidation of the alloy in the dynamic atmosphere. C. T. Young and H. W. Herring were formerly Research Fellow and Materials Engineer, respectively, NASA-Langley Research Center, Hampton, VA. D. R. Tenney was formerly Assistant Professor of Metallurgical Engineering, Division of Mineral Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA.     

Corrosion and Microstructure Correlation in Molten LiCl-KCl Medium

Pyrochemical reprocessing in molten chloride salt medium has been considered as one of the best options for the reprocessing of spent metallic fuels of future fast breeder reactors. The unit operations such as salt preparation, electrorefining, and cathode processing involve the presence of molten LiCl-KCl eutectic salt from 673 to 1373 K (400 to 1100 °C). The present work discusses the corrosion behavior of electroformed nickel (EF Ni) without and with nickel-tungsten (Ni-W) coating, 316L SS, and INCONEL 625 alloy in molten LiCl-KCl eutectic salt at 673 K, 773 K, and 873 K (400 °C, 500 °C, and 600 °C) in the presence of air. The weight percent loss of the exposed samples was determined by the weight loss method and surface morphology of the salt exposed, and product layers were examined by scanning electron microscopy (SEM). X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) analysis were also carried out on the exposed and corrosion product layers to understand the phases present and the corrosion mechanism involved. The results of the present study indicated that INCONEL 625 alloy showed superior corrosion resistance compared to electroformed nickel (EF Ni), EF Ni with nickel-tungsten (Ni-W) coating (EF Ni-W), and 316L SS. The EF Ni with Ni-W coating exhibits better corrosion resistance than EF Ni without tungsten coating. Based on the surface morphology, XRD, and EDX analysis of corrosion product layers, the mechanism of corrosion of INCONEL 625 and 316L involves formation of chromium-rich compound at the surface and subsequent spallation. For the EF Ni, the porous thick NiO corrosion product allows the penetration of salt, thus accelerating the corrosion. Improved corrosion resistance of EF Ni-W was attributed to the W-rich NiO layer, while for INCONEL 625, the adherent and protective NiO layer improved the corrosion resistance. The article highlights the results of the present investigation.     

Recrystallization and grain growth of cold-rolled gold sheet

Recrystallization and grain growth of a cold-rolled gold sheet with 98 pct reduction in area (RA) were investigated with electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Gold with some dopants (Be, Ca, and La) was used in this research and its recrystallization temperature was 320 °C. Isothermal annealing experiments at 400 °C, 500 °C, and 600 °C were carried out for the cold-rolled gold sheet, and recrystallization texture was examined. In the cold-rolled gold sheet, α- and β-fibers were measured mainly and some shear texture components were found on the surface. Shear texture components remained on the surface for 2 hours at 400 °C and were consumed by other recrystallized grains after 24 hours at 400 °C. Microstructure and texture evolution during in-situ annealing at 400 °C were investigated from the cold-rolled state to the fully recrystallized state using EBSD. Most of the newly, recrystallized grains came from the deformed β-fiber regions and consisted of β-fiber, cube, and other random orientations.     

Reverse water gas shift reaction over Co-precipitated Ni-CeO2 catalysts

The Ni-CeO2 catalysts with different Ni contents were prepared by a co-precipitation method and used for Reverse Water Gas Shift （RWGS） reaction. 2wt.%Ni-CeO2 showed excellent catalytic performance in terms of activity, selectivity, and stability for RWGS reaction. Characterizations of the catalyst samples were conducted by XRD and TPR. The results indicated that, in Ni-CeO2 catalysts, there were three kinds of nickel, nickel ions in ceria lattice, highly dispersed NiO and bulk NiO. Oxygen vacancies were formed in CeO2 lattice due to the incorporation of Ni^2＋ ions into ceria lattice. Oxygen vacancies formed in ceria lattice and highly dispersed Ni were key active components for RWGS, and bulk Ni was key active component for methanation of CO2.     

CSP流程试制50W270高牌号无取向硅钢织构的演变

研究了CSP流程试制50W270高牌号无取向硅钢热轧→常化→冷轧→退火过程中织构的演变.利用电子背散射衍射技术对全流程织构进行测量和分析.发现热轧板织构在厚度方向上存在较大差异,表层主要为铜型、黄铜和高斯织构,1/4层存在微弱的高斯织构和旋转立方织构,中心层以γ纤维织构和旋转立方织构为主,还含有较弱的α纤维织构.与热轧板相比,常化板表层和1/4层织构变化不大,中心层旋转立方织构和α纤维织构增强.冷轧板各层均具有α纤维织构和γ纤维织构.与冷轧板相比,成品板各层中α纤维织构基本消失,还出现了立方织构和高斯织构.      

Quantitative analysis of texture evolution of cold-rolled direct-chill-cast and continuous-cast AA5052 and AA5182 aluminum alloys during isothermal annealing

The as-received direct-chill-cast (DC) and continuous-cast (CC) AA5052 and AA5182 hot bands were preheated at 454 °C for 4 hours, followed by cold rolling to an 80 pct reduction in thickness. The texture evolution of these cold-rolled samples during isothermal annealing was investigated by X-ray diffraction. The variation in texture volume fractions with annealing time was quantitatively analyzed by using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The differences in recrystallization textures between the AA5052 and AA5182 alloys and between the DC and CC alloys were compared. It was found that the AA5052 alloy possessed a stronger cube recrystallization texture than the AA5182 alloy for the DC and CC materials. The recrystallization textures of the AA5182 alloy were affected strongly by the annealing temperature. As the annealing temperature increased, the cube recrystallization texture strengthened, whereas the R texture weakened. The annealing temperature had little influence on the recrystallization textures of the AA5052 alloy. The DC AA5052 and 5182 alloys also exhibited stronger cube recrystallization textures than the corresponding CC alloys. For the DC and CC AA5052 alloys, the n value in the JMAK-type equation increased with an increase in the annealing temperature, while the n values varied only slightly with the annealing temperature for the DC and CC AA5182 alloys.     

7B04铝合金织构沿厚度变化的研究

采用X射线衍射法分析了7B04铝合金中厚板沿厚度方向的织构差异,结果表明织构沿厚度方向存在较大差异,变形织构R/S,brass,copper从表层到中心含量呈递增趋势;剪切织构r-cube和{111}<110>主要分布在表层;随机分布从表层的73%到中心的17%含量则快速下降;再结晶织构cube和cubeND在各层的含量基本不变,均维持3%和5%附近。织构沿厚度方向存在差异的主要原因在于热轧变形量和再结晶进程沿厚度的不均匀性。根据再结晶织构组分和变化趋势推测再结晶形核机制主要为粒子促进形核。     

Evolution of Microstructure and Texture During Deformation and Recrystallization of Heavily Rolled Cu-Cu Multilayer

A Cu-Cu multilayer processed by accumulative roll bonding was deformed to large strains and further annealed. The texture of the deformed Cu-Cu multilayer differs from the conventional fcc rolling textures in terms of higher fractions of Bs and RD-rotated cube components, compared with the volume fraction of Cu component. The elongated grain shape significantly affects the deformation characteristics. Characteristic microstructural features of both continuous dynamic recrystallization and discontinuous dynamic recrystallization were observed in the microtexture measurements. X-ray texture measurements of annealing of heavily deformed multilayer demonstrate constrained recrystallization and resulted in a bimodal grain size distribution in the annealed material at higher strains. The presence of cube- and BR-oriented grains in the deformed material confirms the oriented nucleation as the major influence on texture change during recrystallization. Persistence of cube component throughout the deformation is attributed to dynamic recrystallization. Evolution of RD-rotated cube is attributed to the deformation of cube components that evolve from dynamic recrystallization. The relaxation of strain components leads to Bs at larger strains. Further, the Bs component is found to recover rather than recrystallize during deformation. The presence of predominantly Cu and Bs orientations surrounding the interface layer suggests constrained annealing behavior.