电子背散射衍射分析技术在钢铁及管线钢研究领域中的应用

介绍了电子背散射衍射（EBSD）分析技术在钢铁研究领域的应用,提出了利用其在高钢级管线钢领域进行研究的切入点和一些研究结论,并对原位EBSD新技术进行了介绍。     

EBSD测定钛合金中氢化物的取向关系

提出了一种新的基于扫描电镜背散射电子衍射花样的测定析出相取向关系的分析方法,这种方法的精度约为2．5°。实验中还使用该方法对钛合金中氢化物与基体的取向关系进行了分析,其结果与用选区衍射分析得到的结果一致。     

EBSD analysis of melt-textured YBCO with embedded Ag-2411 nanoparticles

Nanoparticles of the type M-2411 (with M = U, Nb, Zr, Ag, etc.) can be embedded within the superconducting YBCO matrix to provide flux pinning sites. Among all these types of nanoparticles, the Ag-2411 particles are special in the sense that they may provide also metallic Ag particles to be formed within the superconductor. The addition of metallic Ag (or silver oxide) was shown to be a means to create a more stable system by filling cracks and voids. Using the advanced polishing method of the YBCO surfaces, we achieve a high EBSD image quality of the recorded Kikuchi patterns. In this contribution, we perform a four-phase EBSD analysis including YBa₂Cu₃O_x, Y₂BaCuO₅, Ag-2411 and metallic Ag. As a result, we find nanometer-sized Ag particles being distributed within the YBCO matrix, and a reduced amount of Ag-2411 particles as compared to the nominal composition. The Ag-2411 particles are well oriented with the surrounding YBCO matrix as found earlier, but the metallic silver particles as detected by EBSD do not exhibit a preferred orientation.     

Orientations of nuclei during static recrystallization in a cold-rolled Mg-Zn-Gd alloy

The static recrystallization process of a cold-rolled Mg-Zn-Gd alloy was tracked by a quasi-in-situ electron backscatter diffraction method to investigate the orientations of nuclei.The results show that orientation distribution of nuclei is associated with nucleation mechanism.The continuous static recrystallization nuclei display similar orientations to the parent grains with TD orientation.Differently,discontinuous static recrystallization nuclei formed within the parent grains(TD-45~0 orientation) show random orientations and a variety of misorientation angles but preferred axes <5273> or <5270>.Interestingly,a special oriented nucleation is found.Discontinuous static recrystallization nuclei originated from boundaries of the parent grain(TD-70° orientation) show concentrated TD orientations in another side due to the preferred misorientation relationship 70°<1120>(∑18 b).It is speculated that these two special misorientation relationships are related to the dislocation type.     

Microstructural Characterization of the Shear Bands in Fe-Cr-Ni Single Crystal by EBSD

An investigation has been made into the microstructural characterization of the shear bands generated under high-strain rate （≈10^4 s^-1） deformation in Fe-15%Cr-15%Ni single crystal by EBSD-SEM （electron backscatter diffraction-scanning electron microscopy）, TEM （transmission electron in microscopy） and HREM （high- resolution electron microscopy）. The results reveal that the propagation of the shear band exhibits an asymmetrical behavior arising from inhomogenous distribution in plasticity in the bands because of different resistance to the collapse in different crystallographic directions; The γ-ε-α′phase transformations may take place inside and outside the bands, and these martensitic phases currently nucleate at intersections either between the twins and deformation bands or between the twins and ε-sheet. Investigation by EBSD shows that recrystallization can occur in the bands with a grain size of an average of 0.2μm in diameter. These nano-grains are proposed to attribute to the results of either dynamic or static recrystallization, which can be described by the rotational recrystallization mechanism. Calculation and analysis indicate that the strain rate inside the shear band can reach 2.50×10^6 s^-1, which is higher, by two or three orders of magnitude, than that exerted dynamically on the specimen tested.     

Particle effects on recrystallization in magnesium-manganese alloys: Particle pinning

Dispersoid particles are widely used in wrought aluminium alloys to control grain structure during thermomechanical processing. The aim of this work was to investigate whether this approach could be utilized in wrought magnesium alloys to obtain better control of recrystallization. A binary magnesium-manganese alloy was heat treated to produce a fine dispersion of manganese precipitates. The effect of this dispersion on dynamic and static recrystallization during channel die deformation (at a slow strain rate), hot rolling, and annealing was studied and compared with that of an alloy free of fine particles. It was found that the presence of particles did not suppress dynamic recrystallization during channel die deformation. Fine particles did lead to a much reduced recrystallized fraction after hot rolling, attributed to a retardation of static recrystallization kinetics. Although the presence of pinning particles greatly slowed recrystallization kinetics on annealing, for no conditions studied was it possible to prevent recrystallization of the as-deformed structure using particles.     

深冲IF钢再结晶{111}纤维织构形成机制探讨

为了探讨深冲IF钢再结晶织构与退火温度之间的关系及{111}再结晶织构形成机制,采用X射线衍射三维取向(ODF)和背散射电子衍射(EBSD)分析技术并结合金相组织观察,利用Gibbs-Thom son方程对冷轧IF钢在不同退火温度下的再结晶织构演变规律及形成机制进行研究.实验结果表明:随着退火温度的增加,再结晶量逐渐增多,γ纤维织构强度亦相应增强,同时,α纤维织构强度则逐渐降低;冷轧IF钢再结晶初期的织构转变主要发生在γ纤维织构之间.研究表明,再结晶核心的形成主要以"显微择优形核"为主,晶核的长大则主要以择优生长为主,而Σ重位点阵晶界在再结晶γ纤维织构形成过程中起着重要作用.     

基于EBSD技术对NiW合金复合基带表面微取向的分析

采用EBSD技术对大冷轧变形量、再结晶退火后的Ni-W复合基带的表面织构进行了表征，对其晶粒取向信息、晶界特征等信息进行采集和分析。该基带经过冷轧和再结晶退火后，无需抛光，即可获得具有花样质量较高的Ni基复合基带表面的EBSD图像。经Orientation Imaging Microscopy^TM（OIM）4．6软件分析，结果表明该Ni基复合基带表面10°以内立方织构晶粒百分含量为97．9％。     

Reconstruction of parent grains from EBSD data

The limits of the parent grain reconstruction by the neighbor-to-neighbor method are shown. A new method of parent grain reconstruction from EBSD data is proposed for any phase transformation. It is based on the theoretical groupoid structure formed by the variants and their operators. It tolerates materials with high levels of intragranular deformation. It is quick and robust because it does not imply solving any equation, and mainly consists in the comparison of numbers. It has satisfactorily been applied to the reconstruction of austenitic grains in martensitic steels.     

On the origin of recrystallization textures

The development of recrystallization textures has been debated for the past 50 years. Essentially the rival theories of evolution of recrystallization textures i.e. oriented nucleation (ON) and oriented growth (OG) has been under dispute. In the ON model, it has been argued that a higher frequency of the special orientation (grains) than random occur, thus accounting for the texture. In the OG model, it has been argued that the specially oriented grains have a high mobility boundary and thus can migrate faster and grow to a larger size as compared to random orientations thus contributing to the final recrystallization texture. In FCC metals and alloys like aluminium, cube orientation [(001) 〈100〉] is the recrystallization texture component. In the classic OG model, cube orientation is supposed to be misoriented fromS-orientation [(123) ] which is a deformation texture component by a 40° about 〈111〉 relationship which is supposed to be a high mobility boundary leading to faster growth of cube grains. Stereographic calculations and analytical calculations are presented in this paper to the effect that theS-orientation (123) is not misoriented from cube (100) 〈001〉 by 40° 〈111〉 whereas another deformation texture component (123) which is termed theR-component is misoriented from cube component by 40° 〈111〉,R-component is also seen in deformation textures of aluminium and hence the classic OG model remains valid with respect to theR-component.     

Recrystallization of the ODS superalloy PM-1000

The primary recrystallization of a 1 0 0-fiber textured coarse-grained oxide dispersion strengthened nickel-based superalloy (PM-1000) has been investigated by high-resolution electron backscatter diffraction. The annealing behavior of this alloy is quite complex. Even at high annealing temperatures (e.g. 1200 °C), recrystallization is only partial. The microstructure of this superalloy in the annealed state consists of a blurred subgrain structure, coarse grains with sizes of about 10–20 μm at the pre-existing grain boundaries and a significant fraction of small crystals in the interior of the recovered grains. These small grains are elongated and display anisotropic growth. In the present paper we present a detailed explanation for this peculiar microstructure. Particular focus is placed on the origin of the new grains in the recovered structure in a [1 0 0]-oriented grain.     

工业纯铁自纳米化组织的EBSD分析

运用高能喷丸技术实现了工业纯铁表面自纳米化,利用电子背散射衍射（ElectronBackscatteredDiffraction,EBSD）对自纳米化组织的结构特征进行了分析,在此基础上探讨了工业纯铁自纳米化机理。结果表明,工业纯铁自纳米化组织由三个典型区域组成,分别含有大量残存住错,大角度晶界及大量小角度晶界。自纳米化组织含有再结晶织构和形变织构,但由于晶粒取向差不同,变形难易程度不同导致两种织构的比例不同。位错运动、晶粒取向差不同导致变形不同步及发生再结晶是工业纯铁表面自纳米化过程中晶粒细化的主要原因。     

Coupled simulations of texture evolution during deformation and recrystallization of fcc and bcc metals

Thermo-mechanical processing to produce optimum grain structure and texture is essential for the successful utilization of commercial aluminum alloys and steels as sheet products. Several modeling techniques have been developed in the past with a reasonably good predictive capability for bulk deformation textures. However, prediction of texture evolution during recrystallization remains very challenging because of uncertainties involved in predicting the mechanisms that lead to nuclei formation and crystallographic orientations of the nuclei, and the uncertainties involved in predicting the grain boundary properties that determine the growth kinetics of the nuclei. We present some of our recent work in modeling the recrystallization textures following cold deformation in polycrystalline bcc metals and hot-deformation in fcc metals.     

Treatment of misorientation data to determine the fraction of recrystallized grains in a partially recrystallized metal

A method has been developed to differentiate recrystallized from unrecrystallized grains in partially annealed samples based on the point-to-point misorientation within the grains. Recrystallized grains exhibit a low average point-to-point misorientation whereas the contrary is the case for deformed grains. The analysis for recrystallized fraction was calibrated based on this distinguishing feature, and it was found that the average point-to-point misorientation within a grain in a fully recrystallized sample was less than 0.7°. Based on this calibration, partially recrystallized samples were analysed for their degree of recrystallization, and the technique was validated using microhardness measurements. The analysis of the misorientation data was in excellent agreement with the hardness data. There are three factors which distinguish the current method in comparison to the earlier work: a fixed limit is maintained on the minimum number of pixels which may constitute a grain; pattern quality is not considered; and the recrystallization criterion is calibrated to the experimental data. Nevertheless, in the early stages of annealing, where recovery is likely to have the most influence on the drop in hardness, the analysis of electron backscattered diffraction (EBSD) data underpredicts the recrystallized fraction. The analysis was also conducted on a cold-rolled, nonannealed sample, and from this, the error of the technique is estimated to be a maximum of 0.06 recrystallized volume fraction.     

On the room-temperature annealing of cryogenically rolled copper

The electron-backscatter-diffraction (EBSD) technique was applied to investigate room-temperature annealing processes in cryogenically rolled copper during long-term (∼1.5 years) storage at ambient temperature. Static recrystallization appeared to be nucleated as result of both grain-boundary bulging and recovery. A bimodal recrystallized grain size distribution appeared to be a result of these two competing mechanisms. The ultra-fine grain copper produced via cryogenic deformation was deduced to be prone to abnormal grain growth after long static storage at room-temperature.     

Embedding of nanoparticles as flux pinning sites in superconducting samples

Crystallographic orientations of thin films and bulk, melt-textured YBa₂Cu₃O_x high-T_c superconductors with embedded Y₂Ba₄CuMO_x (M = Nb, Zr, Ag) nanoparticles are studied by electron backscatter diffraction. The Y₂BaCuO₅ particles exhibit no preferred orientation but have a strong negative influence on the matrix orientation. In contrast, the nanoparticles are not disturbing the texture of the YBCO matrix. For the bulk samples, depending on the preparation route, a different particle orientation with respect to the matrix is obtained. Untextured M-2411 nanoparticles are formed by solid state reaction during the melt process by adding oxides (Nb₂O₅ or Y₂O₃) to the precursor powder. Pre-formed Y₂Ba₄CuMO_x particles added to the precursor in the form of pre-reacted nanopowder, exhibit a dominant single orientation related to the surrounding YBCO matrix. In the case of thin films prepared using laser ablation with a bulk YBCO sample with embedded nanoparticles as a target, the nanoparticles are transferred into the thin film, but the transferred M-2411 particles are found to be randomly oriented. Nevertheless, these films exhibit increased flux pinning properties.