预处理工艺对双辊铸轧3003铝合金再结晶行为的影响

对双辊铸轧3003铝合金板材进行了3种预处理退火,研究不同预处理工艺下的冷轧板材在380～500℃退火时晶粒组织和再结晶织构的变化规律。结果表明:最优化预处理工艺为610℃/12h+460℃/12h,高温阶段第二相尺寸发生粗化,低温阶段基体中Mn的过饱和固溶度显著降低,两者均有利于提高后续退火时的再结晶形核率。500℃退火时,在粗大第二相的附近产生了粒子诱发形核机制,降低了再结晶织构强度;并且退火时几乎不存在析出,析出相对再结晶形核的抑制作用甚微,从而得到了晶粒细小、织构弱的再结晶组织。     

Recrystallization in internally oxidized Cu-Ag-Al alloys

The isothermal recrystallization kinetics of rolled Cu-Ag alloys containing up to 0.9 vol % alumina have been followed through hardness measurements; and nucleation rates have been obtained by X-ray back-reflection techniques. Electron microscopic studies have been carried out to characterize the as-deformed structures and the structural changes occurring during the annealing process. The recrystallization of the alloys was either accelerated or retarded as the alumina content increased. This effect has been found to depend both on the dispersion parameters and the degree of deformation. The recrystallization behaviour of these alloys is controlled primarily by the nucleation process. Nucleation occurred after an incubation period and involved the formation of subgrains from the cell structure and their subsequent growth to a viable size. The difficulty of the formation of viable nuclei has been attributed to the particle restraint on sub-boundary migration and to the lack of heavily distorted regions in the defect structure. The rate of nucleation was a function of time and found to depend on the dispersion, initial deformation and the temperature of anneal. The process of grain boundary migration during recrystallization was anisotropic.     

Effect of copper foil annealing process on large graphene domain growth by solid source-based chemical vapor deposition

Controlling the metal catalyst surface structure is a critical factor to achieve growth of large graphene domains. In this prospect, we explored the annealing process to create an oxide layer and subsequent recrystallization of Cu foil for growth of large graphene domain by the atmospheric pressure chemical vapor deposition (AP-CVD) technique. We revealed the transformation of Cu surface crystallographic structures in every step of annealing process by electron back-scattered diffraction analysis. Initially, electroless polished Cu foils are annealed in Ar and then in H₂ atmosphere to obtain a smoother surface with reduced graphene nucleation sites. The transformation of Cu grain structures at various annealing steps was confirmed, where the gas atmosphere and annealing duration have significant influence. Graphene domains with the size more than 560 µm are obtained on the processed Cu surface using polystyrene as solid precursor. It is obtained that the oxidation and recrystallization process of Cu foil surface significantly influence the nucleation density, which enable growth of larger graphene domain in the developed CVD process.     

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.     

Methods and mechanisms for uniformly refining deformed mixed and coarse grains inside a solution-treated Ni-based superalloy by two-stage heat treatment

The uniform refinement mechanisms and methods of deformed mixed and coarse grains inside a solution-treatment Ni-based superalloy during two-stage annealing treatment have been investigated.The two-stage heat treatment experiments include an aging annealing treatment(AT)and a subsequent recrystallization annealing treatment(RT).The object of AT is to precipitate some δ phases and consume part of storage energy to inhibit the grain growth during RT,while the RT is to refine mixed and coarse grains by recrystallization.It can be found that the recrystallization grains will quickly grow up to a large size when the AT time is too low or the RT temperature is too high,while the deformed coarse grains cannot be eliminated when the AT time is too long or the RT temperature is too low.In addition,the mixed microstructure composed of some abnormal coarse recrystallization grains(ACRGs)and a large number of fine grains can be observed in the annealed specimen when the AT time is 3 h and RT tem-perature is 980℃.The phenomenon attributes to the uneven distribution of δ phase resulted from the heterogeneous deformation energy when the AT time is too short.In the regions with a large number of δ phases,the recrystallization nucleation rate is promoted and the growth of grains is limited,which results in fine grains.However,in the regions with few δ phases,the recrystallization grains around grain boundaries can easily grow up,and the new recrystallization nucleus is difficult to form inside grain,which leads to ACRGs.Thus,in order to obtain uniform and fine annealed microstructure,it is a prereq-uisite to precipitate even-distributed δ phase by choosing a suitable AT time,such as 12 h.Moreover,a relative high RT temperature is also needed to promote the recrystallization nucleation around δ phase.The optimal annealing parameters range for uniformly refining mixed crystal can be summarized as:900℃×12 h+990℃×(40-60 min)and 900℃×12 h+1000℃×(10-15 min).     

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.     

The simultaneous growth of monocrystalline and polycrystalline silicon films with controlled parameters

The influence of the temperature of deposition of nucleation layers on the structure of polycrystalline silicon films which grow locally during the epitaxial growth of monocrystalline films was investigated.The structure of polycrystalline films grown in the high temperature chloride process has been found to depend on the deposition mode of the nucleation layer. For temperature changes in the range 800–860°C, the grain sizes in polycrystalline silicon increase by more than one order of magnitude.It was shown that heat treatment of films of small grain size in an atmosphere of oxygen leads to a decrease in their resistance owing to recrystallization of the grains, whereas during the annealing of films of large grain size the oxidation of intergrain boundaries is the dominant process resulting in an increase in the resistance.The possibility of using polycrystalline films fabricated under specific technological conditions for the isolation of integrated circuit elements was demonstrated.     

Influence of intermediate annealing on final Goss texture formation in low temperature reheated Fe-3%Si steel

The precipitation behavior of inhibitors and their influence on final Goss texture formation in grain-oriented electrical steels produced by compact strip processing technology with a reheating temperature lower than 1200 °C were investigated under two distinct intermediate annealing methods: conventional intermediate recrystallization annealing and a new intermediate decarburizing and recrystallization annealing method without final decarburizing after the second cold rolling. The initiation of secondary recrystallization, the distributions of second phase particles, the final Goss texture, and the grain structure were observed. The new technology could maintain higher inhibitor densities because the deformed matrix could provide higher site densities for inhibitor nucleation before secondary recrystallization, resulting in a relatively higher inhibition effect of the second phase particles. The new technology could also compensate for the disadvantages of fewer inhibitors induced by fewer dissolved Mn and S elements in the matrix during lower reheating temperature for hot rolling. The final sheet produced after the secondary recrystallization annealing obtained stronger Goss texture, larger grain size, and better magnetic properties.     

Static recrystallization simulations by coupling cellular automata and crystal plasticity finite element method using a physically based model for nucleation

This study presents a 2D cellular automata simulation of static recrystallization (SRX) arising from the subgrain growth in single-phase material following cold deformation by coupling with a crystal plasticity finite element (CPFE) method. The spatial distribution of the stored deformation energy was obtained by CPFE simulation, based on which the initial deformed microstructure consisting of nonuniformly distributed subgrains was predicted. To simulate grain/subgrain growth during annealing, a curvature-driven mechanism was used, in which the grain/subgrain boundary energy and mobility were misorientation-dependent. On the SRX nucleation, a physically based model using critical subgrain size as criterion was adopted, which could provide better insight into the recrystallization nucleation mechanism involving grain boundary bulging. Simulations under different pre-deformation conditions were performed, and the influence of strain rate and strain on the SRX microstructure evolution and the transformation kinetics were investigated. Results show that deformation at higher strain rate can accelerate the SRX kinetics, and the SRX behavior depends more on the deformation state of individual grain than the nominal strain due to the relatively small computational domain.     

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.     

脉冲电流处理对冷轧态GH3030合金再结晶组织性能的影响

目的 探究不同工艺参数下脉冲电流处理对冷轧态GH3030合金静态再结晶组织的影响.方法 利用电子背散射衍射(EBSD),探究脉冲电流处理(EPT)和常规退火处理(CHT)对GH3030合金静态再结晶的影响.探究了两种热处理方式下不同退火温度和时间对冷轧态GH3030合金静态再结晶体积分数、晶粒尺寸以及硬度的影响,计算两种热处理方式下不同工艺参数的静态再结晶动力学方程与激活能.结果 与常规退火处理相比,脉冲电流处理可以快速提高冷轧态GH3030合金的静态再结晶体积分数,并且得到了尺寸更加均匀的晶粒,而脉冲电流处理的合金其硬度值均小于相同条件下常规退火处理的合金.根据静态再结晶动力学方程的结果可知,脉冲电流处理的合金再结晶激活能低于常规退火处理的合金,脉冲电流处理下发生完全再结晶所需时间远远少于常规退火处理下所需时间.结论 脉冲电流处理促进了冷轧GH3030合金静态再结晶行为,并且加速了再结晶晶粒的成核和长大,但脉冲电流处理对改善GH3030合金的硬度效果不明显.     

Recrystallization studies in solid-solution alloys of Cu-Ag-Al

The isothermal recrystallization kinetics of rolled Cu-Ag alloys containing up to 1.2 at.% Al have been followed metallographically and by hardness measurements and the nucleation rates measured by X-ray back-reflection techniques. Electron-microscopic studies have been carried out to characterize the as-deformed structures and the structural changes occurring during the annealing process. The recrystallization of the alloys was retarded as the aluminium content increased. Nucleation occurred both in the bulk and along the existing grain boundaries and the rates of nucleation varied with time. These effects have been found to be dependent on the deformation structure, alloy composition and the temperature of anneal. The process of grain-boundary migration during recrystallization was very anisotropic and this has been shown to be caused primarily by the nature of the deformation structure.     

Recrystallization behaviour during annealing of cold-rolled Cu–5Fe–2Sn alloy

The recrystallization behaviour during annealing of cold-rolled Cu–5Fe–2Sn alloy was clarified in this paper. The effects of annealing temperature and time on the microstructure and properties of the Cu–5Fe–2Sn alloy were investigated. The equations of electrical conductivity and recrystallization kinetics during annealing were obtained with Martition's rule and Avrami empirical formula. The variations of recrystallization volume fraction and the growth of recrystallization grain for Cu–5Fe–2Sn alloy after 40% cold rolling were discussed. The calculated conductivity and volume fraction of recrystallization have a good match with experimental results. The variations of the properties of annealed Cu–5Fe–2Sn alloy are attributed to the growth rate of recrystallization phase and the size of recrystallization grains.     

Effect of homogenization on recrystallization in a twin-roll cast Al–Fe–Si alloy

The effect of homogenization treatment on the recrystallization process in a twin-roll cast AlFeSi alloy was investigated by means of calorimetry, microstructural analysis, electrical conductivity, and hardness measurements and cupping tests. The response to annealing of cold-rolled AlFeSi sheet processed with a homogenization treatment at the cast gauge is a typical two-stage, recovery and recrystallization process, while that processed without homogenization softens without recovery. The rather limited precipitation capacity in the former allows recrystallization to occur largely discontinously, favoring the annealing texture. The nucleation rate and the volume fraction of the discontinously recrystallized grains are largely reduced in the sheet processed without homogenization, owing to extensive dynamic precipitation. This reduces the strength of the annealing texture components and gives a more or less random crystallographic texture after annealing. With a relatively finer-grain structure and a nearly random crystallographic texture, AlFeSi sheet processed to soft temper at 1 mm without a homogenization treatment is an attractive foil stock material.     

Microstructural Evolution in Cold-Rolled Squeeze-Cast SiCw/Al Composites during Annealing

A 15 vol. pct SiC_w/Al composite was fabricated by a squeeze cast route followed by hot extrusion in the extrusion ratioof 18:1 and cold rolling to 50%. Microstructural evolution in the cold rolled composite during annealing was studied usingmacrohardness measurement and transmission electron microscopy (TEM). It was found that, during cold rolling the plastic flowof the matrix was restricted by the whiskers around them along the rolling direction, which resulted in different microstructurefrom near whiskers to far away. The cold rolled composite exhibited different microstructural development on 1 h annealingat different temperatures. Under annealing at about 100℃, recovery reaction occurred obviously and the introduction ofSiC whiskers resulted in enhanced recovery reaction. Under annealing above about 200℃, recrystallization (growth of nucleiby high-angle grain boundary migration) and extended recovery took place simultaneously. When annealing temperaturewas increased up to 500℃, recrystallization     

Effect of the size and dispersion of precipitates formed in hot rolling on recrystallization texture in ferritic stainless steels

In the present paper, the size and dispersion of precipitates in ferritic stainless steels have been varied by applying different hot rolling processes, the effect of which on the evolution of recrystallization textures was investigated. The precipitate characterization was observed and studied by transmission electron microscopy and the texture evolution processes were characterized by X-ray diffraction and electron backscattering diffraction. The results show that low temperature finish rolling can promote the formation of a large number of fine and dense TiC precipitates in hot band. These fine and dense precipitates can be inherited in the final sheet, and are beneficial to facilitating the nucleation of randomly oriented grains by promoting the formation of inhomogeneous cold rolled microstructure, strongly suppressing the growth of recrystallized grains by pinning grain boundary migration, thereby weakening the formation of γ-fiber recrystallization texture and deteriorating the formability of final sheet. By contrast, strong γ-fiber recrystallization texture is developed in the sample with sparsely distributed coarse precipitates. Therefore, the size and dispersion of precipitates formed in hot rolling have significant effects on the nucleation of randomly oriented grains and the growth of recrystallized grains during recrystallization annealing, which play important roles in controlling the γ-fiber recrystallization texture in ferritic stainless steels.     

中间退火及成品退火速率对高压阳极铝箔微观组织的影响

采用不同中间退火温度及成品退火速率对高压阳极铝箔进行处理,并利用EBSD及XRD技术分析其微观组织结构,尤其是织构的变化规律。结果表明,中间退火温度对后续成品退火中形成立方织构起到了关键作用,这可能是由于低温中间退火保留了大量的形变储能,为成品退火时立方织构的形成增加了形核核心。同时,低的中间退火温度造成立方织构较理想位置偏转程度更大。随着成品退火加热速率的增大,铝箔再结晶分数及再结晶晶粒尺寸逐渐减小,这是由于退火加热速率的增大(低于临界加热速率),缩短了晶界迁移的时间,减缓了再结晶的发生。     

冷压缩和冷锻AZ31镁合金的组织演变和静态再结晶动力学研究

对AZ31镁合金进行了冷锻和冷压缩变形,并研究了其在此过程中的组织演变和再结晶动力学.实验结果表明,再结晶分数与退火时间之间的关系可以用JMAK等式采描述.根据动力学分析,可以计算出冷锻和冷压缩的再结晶激活能分别为53.5kJ/mol和85.1kJ/mol.冷压缩处理后的AZ31镁合金的再结晶激活能高于冷锻变形的,这主要与冷锻变形提供了更多的形核点有关.     

Solid-phase crystallization kinetics and grain structure during thermal annealing of a-Si:H grown by chemical vapor deposition

Solid-phase crystallization kinetics are examined during thermal annealing of as-deposited hydrogenated amorphous silicon (a-Si:H) thin films deposited by hot-wire chemical vapor deposition (HWCVD) and plasma-enhanced chemical vapor deposition (PECVD). The influence of deposition temperature of HWCVD material on crystallization is also considered. Real-time observation of the crystallization process using in situ transmission electron microscope heating allowed tracking of the crystalline volume fraction and grain number density by image-processing methods. Beyond an initial incubation period, roughly constant grain nucleation rate and growth velocity are observed. Extrapolation from early stages of crystallization allows estimation of the final average grain sizes. PECVD material shows a much lower nucleation rate than does HWCVD material under the same annealing conditions, whereas the grain growth velocities are comparable, leading to dramatically larger grain sizes in PECVD material. X-ray diffraction line widths from PECVD material are broader compared to HWCVD material. The diffraction line broadening is primarily determined by intragranular defect structure, rather than grain size. Low-temperature preannealing reduced the final XRD line widths of HWCVD material, indicating an influence on defect structure or density. Lattice contraction during crystallization of HWCVD material is observed to be independent of the initial hydrogen content.     

Effects of external electric field on recrystallization texture and microstructure of 08Al killed steel sheet

The effects of electric field annealing on recovery and recrystallization in a cold-rolled 08Al killed steel sheet were investigated. Results show that, with the application of a DC electric field, the recovery and recrystallization processes are retarded and the recrystallization -fiber texture is strengthened. Those retardation effects are attributed to a decrease of the driving force for recrystallization caused by electric field, which would hinder grain nucleation and growth on the whole. Possible reason for the intensification of the recrystallization -fiber texture through electrical annealing is briefly discussed.