EBSD Investigation on Oriented Nucleation in IF Steels

The mechanism responsible for the formation of recrystallization texture in cold-rolled Ti bearing interstitial free （IF） steel sheets was investigated using electron back-scatter diffraction （EBSD）. In addition, the origin of nuclei with specific orientations was studied. The formation of recrystallization texture was explained by oriented nucleation. Most nuclei have a high misorientation angle of 25-55° with the surrounding deformed matrices, but no specific orientation of misorientation axis between the nucleus and the surrounding deformed matrix is observed. The stored energy of deformed grains is in the decreasing order of the {111}〈112〉,{111}〈110〉, {112}〈110〉 and {001}〈110〉 orientations. New {111}〈110〉 grains are nucleated within deformed {111}〈112〉 grains and new {111}〈112〉 grains originate in the deformed {111}〈110〉 grains.     

Nucleation of Cold Rolled FeCo Alloy during Annealing and Its Influence on the Formation of Recrystallization Texture

1. IntroductionNumerous research works have been conductedon recrystallization mechanisms in conventional metalmaterials, where certain recrystallization textures areusually formed[1], of which the characteristics couldbe explained by the theory of oriellted nucleation[21or by that of oriented grain growth[3]. However,in maily illtermetallics based alloys random orientation distributions have been frequently observed afterrecryst allizat ion [4-61, and the corresponding mecha-nisms are not cle…     

3%Si电工钢铸坯中柱状晶的形变、再结晶行为及织构演变规律

利用电子背散射衍射(EBSD)技术和X射线衍射仪(XRD)研究3%(质量分数)Si电工钢铸坯中柱状晶的形变、再结晶行为及织构演变规律。结果表明:柱状晶长轴分别沿轧向、横向和法向放置,具有不同的初始织构。热轧后,表层形成的3种剪切取向中高斯取向较容易形成。中心区,RD样品中的α和γ线轧制取向,TD样品中的强γ线取向,ND样品中的强{100}取向以及各样品中的立方取向,均表现出明显的初始取向依赖性。冷轧后,RD,TD样品中的强{111}〈112〉取向来自热轧板中的高斯取向,ND样品中的强旋转立方取向遗传自初始{100}取向。受初始取向偏差及大晶粒尺寸影响,ND样品中的旋转立方取向晶粒内取向梯度较大。退火后,样品中心大尺寸的{100}取向晶粒是柱状晶初始取向遗传性的表现。     

镁合金AZ31高温形变机制的织构分析

利用X射线衍射和背散射电子衍射方法测定了镁合金AZ3l高温动态再结晶和超塑形变时的宏观和微观织构,分析了晶粒内部的形变机制.结果表明,在动态再结晶和超塑形变过程中,晶粒内部的滑移机制仍起重要作用,表现为再结晶晶粒出现择优取向以及一些晶粒可充分均匀形变成长条状.宏观织构的测定表明,具有不同初始织构的两类样品高温动态再结晶时,新晶粒有不同的取向择优过程,形成相似的织构;长条形变晶粒内部开动的滑移系也有一定的差异.分析了不同温度下相同的织构对应的不同塑变机理取向成像分析表明,基面织构取向的晶粒间总伴随着较高比例的小角晶界和30°(0001)的取向关系,这是六方结构的六次对称性限制了动态再结晶时(亚)晶粒间取向差的有效增大的缘故.     

Analysis of Micro-texture during Secondary Recrystallization in a Hi-B Electrical Steel

The understanding of Goss texture in Hi-B electrical steels possesses significant industrial and academic value, thus attracts worldwide attention. The prevailing models for sharp Goss texture formation during secondary recrystallization are CSL (coincident site lattice) boundary theory and HE (high energy) boundary theory. These theories stress the key factor of preferred growth and the difference between them only lies in the specific selection manner. This work examined the texture gradient in primarily recrystallized sheet and demonstrated its possible influence on the formation of secondary grains, and then determined the micro- texture during different stages of secondary recrystallization using EBSD (electron back-scattered diffraction) technique, finally analyzed a special type of secondary grains with near Brass orientation, which were detected in the later stage of secondary recrystallization, and discussed its origin and effect in terms of surface energy effect. The results indicate that texture gradient in primarily recrystallized sheet will lead to a multi-stage formation of Goss texture, namely, early stage of secondary grains with various orientations in subsurface region, intermediate stage of preferred growth of Goss grains into center layer and re-grow back to the surface and the final stage of Goss grain growth by swallowing slowly the island grains with the help of H2 atmosphere.     

Grain morphology and texture evolution of TC21 titanium alloy during annealing with different time

A homogeneous equiaxed‐structure TC21 titanium alloy is hot rolled and annealed for different time ranging from 1 h to 6 h. The grain morphology and texture evolution of α and β phases during annealing are mainly investigated using the electron back‐scattered diffraction characterization. In the early annealing stage, the α grain mainly maintains the elongated morphology generated in the rolling. With increasing annealing time, more and more elongated α grains become equiaxed due to enhanced static recrystallization and boundary splitting. Differently, the β grain exhibits a fully equiaxed morphology all the time due to the sufficient static recrystallization, and get a coarsening with increasing annealing time. The α phase exhibits a (0001) basal texture in the early annealing stage, and then forms a TD‐split texture with increasing annealing time. The β phase exhibits the {001}<110> texture at every annealing time. Based on the analysis about the texture of different grain sizes, the effects of recrystallization nucleation and oriented growth on texture evolution are discussed. It suggests that TD‐split texture in α phase is originated from both the recrystallization nucleation and oriented growth. The formation of {001}<110> texture in β phase is mainly originated from the oriented growth.     

Q235碳素钢应变强化相变中铁素体的取向特征

利用背散射电子衍射取向成像技术分析了在热模拟单向压缩条件下Q235碳素钢应变强化相变中铁素体晶粒的取向（差）变化特点。结果表明，奥氏体的状态影响应变诱导出的铁素体的取向，奥氏体的动态再结晶使应变诱导出的铁素体的取向随机分布，在铁素体的内部基本上没有小角晶界，随着形变温度的降低和应变量的增大，铁素体取向的择优性变强，铁素体内部的小角晶界增加，这是细小铁素体动态再结晶的表现，相变，形变以及铁素体的动态再结晶都影响＜111＞方向线织构的形成。     

Microstructure and texture evolution in Mg–1 %Mn–Sr alloys during extrusion

Microstructure and texture evolution in Mg–1 %Mn–Sr alloys during extrusion has been investigated. At 350 °C, the extrusion of Mg–1 %Mn (M1) alloy exhibits the progressive formation of basal texture from the undeformed zone to the die opening. The extruded microstructure of M1 consists of recrystallized grains nucleated by grain boundary bulging and elongated parent grains along with extensive twinning. At 350 °C, the extrusion of M1–1.6Sr alloy results in progressive elongation of Mg–Sr precipitates in the form of stringers from the undeformed zone to the die opening. The final extruded microstructure of this alloy shows extensive recrystallization occurring at the intermetallic stringers by particle-stimulated nucleation (PSN). M1–(0.3–1.6)%Sr alloys display weaker textures due to PSN which creates new grains with random orientations. At 250 °C, the extrusion of M1 creates necklace of small recrystallized grains around large elongated parent grains. M1–1.6Sr alloy extruded at 250 °C exhibits continuous dynamic recrystallization (CDRX) in the Mg matrix and PSN at Mg–Sr precipitates. PSN is less extensive at lower temperature. Both CDRX and PSN grains have random orientations, and therefore, alloy develops random texture.     

Formation mechanism of large grains inside annealed microstructure of GH4169 superalloy by cellular automation method

In authors’ previous work [Mater. Charact. 141 (2018) 212–222], it was found that the heterogeneous deformed microstructures can be replaced by the relatively homogeneous recrystallized grains through an annealing treatment. However, there are still some relatively large recrystallized grains. To find the reasons for the formation of large grains, some new annealing treatment tests were done, and the cellular automation (CA) simulations were carried out in the present work. The experimental results showed that the microstructural evolution during annealing treatment is significantly affected by the content of δ phase. So, the effects of δ phase on the nucleation and growth of grains are carefully considered in the CA model to accurately simulate the microstructural evolution behavior. By the CA simulation, it is found that the dislocation density rapidly decreases due to the nucleation of static recrystallization (SRX) and the growth of dynamc recrystallization (DRX) nuclei at the early stage of annealing. The high initial dislocation density can provide the high velocity for the growth of DRX nuclei, which is responsible for the formation of coarse grains. However, the growth rate of SRX nuclei is relatively small due to the low dislocation density and pinning effects of δ phase.     

Grain boundary migration: misorientation dependence

The ability of grain boundaries (GB) to move has been found to be strongly dependent on crystallography, i.e. misorientation of the adjacent grains and orientation (inclination) of the GB in a crystal. Boundary mobility is rate-controlling in recrystallization and grain growth and thus, affects microstructure evolution and texture formation. This paper deals with recent advances in our understanding of misorientation and inclination dependence of grain boundary migration.     

Effect of initial texture on dynamic recrystallization of AZ31 Mg alloy during hot rolling

Wedge-shaped AZ31 plates with two kinds of initial textures were rolled at 573 K to investigate the effect of initial texture on dynamic recrystallization (DRX). The results indicated that the initiation and nucleation of DRX were closely related to the initial texture. The initiation and completion of DRX in the TD-plate were significantly retarded compared with that in the ND-plate. Twin related DRX nucleation was mainly observed in the ND-plate samples; while gain boundary related DRX nucleation was mainly observed in the TD-plate samples. The different DRX behavior between the TD- and ND-plates was attributed to the different deformation mechanism occurring before DRX initiation. For the ND-plate, dislocation glide was considered as the main deformation mechanism accompanied with {1 0 −1 1}-{1 0 −1 2} double twin, which led to the increment of a faster increasing stored energy within the grains. And {1 0 −1 1}-{1 0 −1 2} double twin was mainly found to be DRX nucleation site for the ND-plate. For the TD-plate, {1 0 −1 2} extension twin was the dominant deformation mechanism which resulted in a basal texture with the c-axis nearly parallel to ND. The stored energy caused by dislocation motion was relatively small in the TD-plate before a basal texture was formed, which was considered as the main reason of that DRX was retarded in the TD-plate compared with that in the ND-plate. Based on the difference in deformation mechanism and DRX mechanism caused by the different initial texture, the variation in grain size, micro-texture and misorientation angle distribution in the ND and TD plates were discussed.     

Microstructure characterization based on the type of deformed grains in cold-rolled,Cu-added,bake-hardenable steel

The electron backscatter diffraction technique has been used to characterize the microstructure of deformed grains in cold-rolled, Cu-added, bake-hardenable steel. A new scheme based on the kind and number of average orientations, as determined from a unique grain map of the deformed grains, was developed in order to classify deformed grains by type. The α-fiber components, γ-fiber components and random orientations, those which could not be assigned to either γ-fiber or α-fiber components, were used to define the average orientation of unique grains within individual deformed grains. The microstructures of deformed grains in as-rolled specimens were analyzed based on the Taylor factor, stored energy, and misorientation. The relative levels and distributions of the Taylor factor, the stored energy and the misorientation were examined in terms of the types of deformed grains.     

Orientation dependent mechanical properties of commercially pure (cp) titanium

The present investigation is an attempt at correlating the crystallographic orientation and mechanical properties of hexagonal commercially pure titanium (cp-titanium). Annealed cp-titanium sheets are subjected to tensile deformation along the rolling direction, along 45° to the rolling direction and along 90° to the rolling direction respectively. Crystallographic textures and mechanical properties of these cp-titanium samples are investigated in the present study. The hardness of different grains/orientations is estimated through nanoindentation, grain average misorientation, orientation estimated elastic stiffness and Taylor factor measurements. It is observed that the hardness of the grains close to basal orientation is higher compared to non-basal orientations. It is further observed that the estimated bulk mechanical properties of cp-titanium have a direct relationship with the volume fraction of basal grains/orientations.     

Recrystallization of copper under hydrostatic pressure up to 15 kbar

Hydrostatic pressure (up to 15 kbar) during annealing results in retardation of recrystallization during initial recrystallization of copper; the rate of nucleation and growth of new grains are both retarded. The effect of pressure on the nucleation rate is extremely high and a finer crystalline structure results during annealing under pressure.The difference in the rate of formation of recrystallization nuclei and their growth under uniform pressure is connected with the considerable role of volume diffusion in nucleation of the recrystallized structure.     

Microstructure and microtextural studies of friction stir welded aluminium alloy 5052

The present investigation presents a composite picture of the microstructural developments in a friction stir welded (FSW) AA5052. Optimized, defect free and chemically homogeneous, FS weld was generalized in four regions – base material (BM), nugget, advancing side (AS) and retreating side (RS), using standard nomenclatures. Each region had its signature of microstructural features. AS had clear indications of shear and of grain fragmentation. The nugget region, on the other hand, had nearly equiaxed grains, with strong in-grain misorientation and presence of grain-interior dislocation structure ruling out contributions from static recrystallization. Equiaxed grains of the nugget region had typical onion ring structure – each ring did approximately correspond to one dominant family of orientation. Microstructural developments, as obtained from relative grain refinement, in-grain misorientation development, relative banding, etc., were most significant in nugget followed by AS and then by RS. Heterogeneous plastic deformation and thermal activation through localized heating/friction were the apparent causes. Most of the friction stir welded specimen fractured away from the nugget and showed ductile mode of failure.     

一种新型铁素体不锈钢的深冲性能研究

为探究一种新型铁素体不锈钢的深冲性能,在840~920℃不同温度下对新型铁素体不锈钢的冷轧板做再结晶退火处理,通过XRD、SEM和EBSD等分析方法研究了退火2 min或4 min后,材料微观组织、宏观织构的变化规律对深冲性能的影响及其内在机理.研究表明:保持退火时间2 min,退火温度900℃时,试验钢拥有较多的有利γ纤维织构,主要为{111}112取向,并有少量α纤维织构,此时平均塑性应变比r-=1.77,高于其他退火温度下的值;延长退火时间,在900℃下保温4 min,不同取向晶粒获得了长大机会,晶粒尺寸均匀性显著改善,r-值提高至1.82,试验钢有望取得理想深冲性能.     

Phase-field model during static recrystallization based on crystal-plasticity theory

A numerical model and computational procedure for static recrystallization are developed using a phase-field method coupled with crystal-plasticity theory. In this model, first, the microstructure and dislocation density during the deformation process of a polycrystalline metal are simulated using a finite element method based on strain-gradient crystal-plasticity theory. Second, the calculated data are mapped onto the regular grids used in the phase-field simulation. The stored energy is calculated from the dislocation density and is smoothed to avoid computational difficulty. Furthermore, the misorientation required for nucleation criteria is calculated at all grid points. Finally, phase-field simulation of the nucleation and growth of recrystallization is performed using the mapped data. By performing a series of numerical simulations based on the proposed numerical procedure, it has been confirmed that the recrystallization microstructure can be reproduced from the deformation microstructure.     

Effects of initial texture on deformation behavior during cold rolling and static recrystallization during subsequent annealing of AZ31 alloy

This study demonstrates that the initial texture of Mg alloy significantly affects the microstructure developed during cold rolling and the recrystallization behavior during subsequent annealing. In a sample with a texture oriented toward the normal direction(ND sample), thick and large-sized shear bands are intensively formed during cold rolling and the deformation is strongly localized along these bands. In contrast,in a sample with a texture oriented toward the transverse direction(TD sample), many {10-12} twins are formed at the early stage of cold rolling, and then, numerous small-sized shear bands are formed in these twins. Results of nanoindentation tests reveal that the cold-rolled ND sample has internal strain energy that is substantially concentrated along the shear bands, whereas the cold-rolled TD sample has a large amount of internal strain energy that is homogeneously distributed throughout the material;this latter behavior is strongly related to the extensive {10-12} twinning and the resultant microstructural variations in the TD sample. During subsequent annealing, recrystallization occurs locally along the shear bands in the ND sample, which leads to the formation of a bimodal grain structure comprising fine recrystallized grains and coarse unrecrystallized grains. In contrast, during subsequent annealing of the TD sample, static recrystallization occurs homogeneously throughout the material, which results in the formation of a uniform grain structure that mostly comprises equiaxed recrystallized grains.     

Identification of Particle Stimulated Nucleation during Recrystallization of AA 7050

Mechanical properties of polycrystalline metals are dependent upon the arrangement of microstructural features in the metal. Recrystallization is an important phenomenon that often occurs during thermo-mechanical processing of metals. This work focuses upon aluminum alloy 7050 and uses crystallographic texture and pair correlation functions of recrystallized grains to characterize the dominance of particle stimulated nucleation in the recrystallization process. The randomization of the recrystallization texture and similar pair correlation functions for the particle distribution and the recrystallization nuclei distribution indicate that particle stimulated nucleation controls the recrystallization behavior in this alloy.     

Microtexture of chloride treated CdTe thin films deposited by CSS technique

This work investigates the microstructural changes—especially in grain boundary structure and grain orientation distribution—in CdTe thin films deposited by close spaced sublimation at low (LT) and high temperatures (HT) and submitted to a CdCl₂ heat treatment. These changes are quantitatively described by microtexture analysis, a spatial distribution of the orientation of the grains. The analysis is performed in a scanning electron microscope by means of identification of the electron back-scattered diffraction patterns from individual grains. The texture of each grain, the misorientation between grains, and coincident site lattice boundary maps are obtained. The results show that the CdCl₂ treatment did not promote significant microstructural changes in HT-CdTe films, which grow with large and randomly oriented grains, and with a predominance of high-angle boundaries. On the other hand, for LT-CdTe films, this treatment promotes a substantial increase in grain size, a decreasing of preferential orientation, and an increase in the number of CSL and high-angle boundaries. These changes are considered to be a strong evidence for recrystallization.