铸辗成形环坯热压缩过程中晶粒的取向和织构演变

在不同变形温度和应变速率为0.1 s-1条件下研究了砂型铸造和离心铸造Q235B环坯的热压缩变形行为,并使用电子背散射衍射(EBSD)技术分析其晶粒取向和织构的演化特点。结果表明:Q235B环坯的晶粒在1000℃尺寸较小,有少量仍保持铸造状态的晶粒,组织演变的机理为动态回复和大应变几何动态再结晶;离心铸造环坯中有22%集中在20°-50°的大角度晶界。在1100℃再结晶充分,晶粒趋于等轴状;晶界取向差分布仍呈现典型的双峰特征,大角度晶界的比例为60%-75%。在1000℃砂型铸造Q235B的织构组态,为少量沿着001//ND取向线分布的{001}100立方织构和{001}110织构;在1100℃主要是高斯织构{110}001和沿着110//ND向{110}001方向移动并聚集的旋转立方织构{110}110。在1000℃离心铸造环坯的织构组态为旋转立方织构{110}110和铜型织构{112}111,Copper织构沿着ε-取向线分布;在1100℃主要为{001}110织构和沿着γ取向线由黄铜R{111}112向{111}110转变的织构,再结晶的程度高,取向密度大。     

6082-T6铝合金搅拌摩擦过程中动态再结晶方式对焊核区织构类型的影响

采用电子背散射衍射技术,借助取向成像分析软件,分别研究了6082-T6铝合金搅拌摩擦焊焊核区后退侧、焊核区正中心、焊核区前进侧上表面晶粒形貌、晶界特征、织构组分的演化。结果表明,焊接过程中,焊核区后退侧金属产生热塑性变形、晶粒内位错塞积与重组,形成小角度晶界的亚晶粒,部分小角度晶界通过旋转转变为大角度晶界,发生"连续动态再结晶",母材粗大晶粒被细化。同时形成(111)[110]剪切织构,而在(111)[110]取向晶粒周围产生许多变形亚结构。(001)[100]立方取向亚结构在位错密度及位错组态上的优势,使其在焊接热循环作用下成为"非连续动态再结晶"的晶核,随后长大为(001)[100]立方取向晶粒。轴肩的旋转挤压作用,使焊核区晶粒沿ND方向旋转,故在焊核区正中心位置出现(001)[110]旋转立方织构,而在前进侧出现(111)[110]剪切织构和(001)[100]立方织构。     

CGO硅钢初次再结晶组织及织构演变规律

对3%(质量分数)Si CGO硅钢冷轧板进行初次再结晶退火实验,设置不同的退火保温时间,将退火后的样品分别使用OM,TEM及EBSD进行分析,观察其微观组织、位错及织构分布,研究CGO硅钢初次再结晶过程中组织及织构的演变规律。结果表明:随着退火保温时间的延长,回复再结晶的程度增加,当保温时间延长至300s时,再结晶基本完成且呈现等轴晶状态,随着保温时间的延长,组织中位错密度降低。初次再结晶退火保温时间对初次再结晶织构分布有影响:随着保温时间的延长,{111}〈112〉和{110}〈112〉织构含量不断下降,{111}〈110〉织构的含量先减少后增加,立方及旋转立方组分基本保持不变,Goss织构组分逐渐增多。当保温时间较短时,晶粒取向差主要为小角度晶界并存在大量亚晶,随着保温时间的延长,大角度晶界逐渐增多。     

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.     

薄规格取向硅钢二次再结晶过程中Goss织构演变的Monte Carlo模拟

通过EBSD实验获取了薄规格取向硅钢(0.18 mm厚)初次再结晶样品表面晶粒组织的取向数据,并以此构建模拟的初始组织.采用Potts模型Monte Carlo方法对薄规格取向硅钢初次再结晶样品的二次再结晶过程进行了模拟仿真,研究了表面能对Goss织构演变的影响.模拟结果表明:Goss取向晶粒与相邻晶粒的表面能差是Goss取向晶粒异常长大的重要驱动力;表面能差存在一个临界值(约12％),只有当表面能差大于此临界值时才会发生表面能驱动Goss取向晶粒的异常长大.     

薄规格取向硅钢二次再结晶过程中Goss织构演变的Monte Carlo模拟

通过EBSD实验获取了薄规格取向硅钢(0.18mm厚)初次再结晶样品表面晶粒组织的取向数据,并以此构建模拟的初始组织。采用Potts模型Monte Carlo方法对薄规格取向硅钢初次再结晶样品的二次再结晶过程进行了模拟仿真,研究了表面能对Goss织构演变的影响。模拟结果表明:Goss取向晶粒与相邻晶粒的表面能差是Goss取向晶粒异常长大的重要驱动力;表面能差存在一个临界值(约12%),只有当表面能差大于此临界值时才会发生表面能驱动Goss取向晶粒的异常长大。     

升温速率对冷轧超薄取向硅钢再结晶行为的影响

利用EBSD技术对比分析了升温速率对冷轧超薄取向硅钢再结晶行为的影响.结果表明,冷轧超薄带中再结晶形核位置、再结晶织构类型受升温速率的影响不大,主要取决于形变组织;剪切带、{111}〈112〉取向晶粒晶界、形变带和形变不均匀区均为再结晶的形核位置,剪切带的再结晶形核优势更为明显;再结晶晶粒取向以Goss({110}〈001〉)取向为主,同时存在{210}〈001〉、{310}〈001〉以及一定比例的杂乱取向.然而,升温速率显著影响Goss织构的强度及退火样品的组织均匀性;慢速升温条件下,Goss织构比例和锋锐度降低,说明回复导致不同织构的形变组织储存能差异减小,降低了Goss取向的形核优势;快速升温条件下,剪切带内的Goss晶核具有更大的形核优势,吞并临近的形变组织完成再结晶,形成更强和锋锐的Goss织构.此外,快速升温可提高再结晶完成后的组织均匀性、降低平均晶粒尺寸.     

取向电工钢中Goss晶粒生长的取向环境

将以MnS为主要抑制剂的普通取向电工钢作为实验材料,检测并分析脱碳样品的宏观织构及脱碳和随后加热至925℃时样品的微观织构,统计分析了Goss与周围晶粒的取向差分布。根据取向差原理计算了脱碳样品主要织构组分内各取向晶粒的取向差环境。结果表明,取向电工钢脱碳退火后Goss晶粒与周围晶粒的取向差分布呈现大角度特征,主要取向差分布范围为30°-45°,而非Goss晶粒与周围晶粒的取向差分布则呈现更多小角度特征。二次再结晶后,Goss晶粒与周围晶粒的取向差分布仍然以大角度特征为主。     

镁合金搅拌摩擦焊接头晶粒取向和织构分析

利用背散射电子衍射分析技术(EBSD)和取像显微分析技术(OIM),通过定量测量变形镁合金AZ80A搅拌摩擦焊搭接接头的焊核区晶粒取向和织构,探讨了搅拌摩擦焊焊核区形成的微观过程.结果表明:AZ80A合金在搅拌摩擦焊过程中,存在塑性变形和动态再结晶两种微观过程,导致焊核区所形成的晶粒织构密度不强、取向呈多样化的趋势;晶粒为再结晶细晶粒;在焊核区,变形织构{1,-1,0,4}<1,0,-1,0>略偏离板法向20°,且随板厚方向向下越来越强,同时再结晶取向越来越多;焊核区晶粒继承了母材中的{1,-1,0,4}<1,0,-1,0>变形织构,在焊核区所发生的动态再结晶含有一定程度的原位再结晶.     

多道次喷涂对AZ80镁合金基体组织状态的影响

目的 为探究超音速火焰喷涂的高温高速射流对镁合金基体的影响,以形变后镁合金表面纯铜涂层的制备过程为研究对象,研究喷涂过程中镁合金基体的微观组织演化机理。方法 采用超音速火焰喷涂（HVAF）工艺在挤压态AZ80镁合金试样表面制备纯铜涂层,对不同喷涂道次下获得的试样进行微观组织观察与显微硬度测试,结合EBSD分析涂层结合面附近基体的晶粒尺寸分布、再结晶状态及织构取向等。结果 在高温高速射流作用下,涂层结合面附近的基体发生再结晶,平均晶粒尺寸由50μm细化至15.2μm;随着喷涂道次的增加,β相逐渐回溶,孪晶消失,基体硬度先降低至70HV0.2后恢复到80HV0.2,织构强度逐渐减小至10.042。结论 多道次超音速火焰喷涂过程中,由于第二相回溶与再结晶的共同作用,镁合金基体硬度呈现出先降低再升高的趋势;再结晶晶粒以晶界弓出形核与亚晶转变共同形成,并在涂层压应力作用下选择性偏转与长大,逐渐吞并原始变形晶粒;与此同时,亚晶界逐渐转变为大角度晶界,晶粒被再次细化,最终导致涂层结合面处基体产生明显的择优取向。     

The effect of SiC nanoparticles on deformation texture of ARB-processed steel-based nanocomposite

In this study, the influence of SiC nanoparticles on deformation texture of steel-based nanocomposite fabricated by accumulative roll bonding process was investigated. It was found that there was a texture transition from the rolling texture to the shear texture for both pure interstitial free steel and steel-based nanocomposite. However, the texture transition occurred in different cycles for the pure steel (the third cycle) and steel-based nanocomposite (the first cycle). It was realized that the fraction of low misorientation angle grain boundaries was decreased and the fraction of high misorientation angle grain boundaries was increased by the number of cycles. Also, recrystallization occurred in the pure steel and steel-based nanocomposite samples after the third and first cycles, respectively. In addition, the occurrence of recrystallization in steel-based nanocomposite was sooner than that of pure steel. At the early stage of dynamic recrystallization in processed steels, the {011}< 100 >-oriented grains were evolved and the fraction of grains with α-fiber and γ-fiber orientations was slightly decreased. The formation of the rolling texture in the steel-based nanocomposite samples was different from the typical rolling texture for the pure steel samples, due to the presence of the SiC nanoparticles in the nanocomposite. The weak rolling texture was attributed to the high stored energy of deformation, which was, in turn, due to low deformation temperature.     

Promotion of texture weakening in magnesium by alloying and thermomechanical processing: (I) alloying

The recrystallization and texture evolution of four Mg–Zn–Ce sheets with a warm-rolled microstructure obtained through two stages that can be characterised as rough rolling and finish rolling were investigated at different stages of post-rolling annealing. On annealing, the same regions of the microstructure, located by hardness indentations, were examined and tracked by electron backscatter diffraction (EBSD). Furthermore, intragranular misorientation axes (IGMA) analysis was used to investigate the associated deformation mechanisms in the as-deformed material. By combining these two methods, the development of the recrystallization microstructure was investigated and important aspects, such as preferential nucleation sites, correlation between activated deformation mechanism and initial orientation of the recrystallized grains, were studied. The results showed that the Mg–1Zn–1Ce alloy, which had the highest Ce/Zn ratio, showed the weakest as-rolled texture and the most homogenous distribution of shear banding/twinning. The IGMA analysis also showed that in Mg–1Zn–1Ce, other types of dislocations rather than basal 〈a〉 were activated; in particular, prismatic 〈a〉 type was activated during deformation. Therefore, the weakening of recrystallization texture during rolling resulting from the addition of RE elements was linked with a change in dynamic recrystallization (DRX) behaviour. Since the Mg–1Zn–1Ce alloy corresponds to the highest level of Ce in solid solution, the observed texture weakening was possibly due to decreasing grain boundary mobility as a result of solute partitioning of RE elements to dislocations and grain boundaries.     

A study of precipitation and recrystallization behaviour of aluminium alloy AA1235

The recrystallization behaviour of 92% cold rolled commercial pure aluminium has been studied. Annealing was done at different conditions to evaluate the effect of recrystallization temperature and time on the microstructure and texture of the alloy along with a study of subsequent precipitation. Variation of orientation between grains has been studied by the orientation imaging microscopy (OIM). During precipitation, cube component {001}<100> has dropped and rolling texture component has increased comparatively. Recrystallization texture is the combination of cube, rolling and random texture. However, during grain growth strong cube grains have formed. A significant number of dislocations are present during grain growth owing to the pinning effect of Al₃Fe particles.     

Hot deformation behavior and microstructural evolution of a modified 310 austenitic steel

To study the hot deformation behavior and microstructural evolution of a new modified 310 austenitic steel, hot compression tests were conducted at the temperature range from 800 to 1100 °C with strain rate of 0.1–10 s⁻¹ and strain of 30–70% using Gleeble 3500 thermal–mechanical simulator. The results showed that the serrated flow curves were caused by the competitive interaction between solute atoms and mobile dislocations. There were some coarsened precipitates on the high angle grain boundaries (HAGBs), which facilitated the nucleation of dynamic recrystallization grains. But these precipitates inhibited the growth of the recrystallization grains, and changed the deformation texture in the matrix. Low angle grain boundaries (LAGBs) decreased, while twin GBs and random HAGBs and increased as dynamic recrystallization occurred. Dynamic recrystallization occurred more readily at evaluated temperature or high strain rate. The true stress decreased with the reduction of LAGBs percent. The internal connections between mechanics and microstructures were also discussed.     

Diffusion behavior of aluminum in the surface layer of iron processed by shot peening

An ultrafine-grained surface layer was fabricated on a pure Fe plate by the shot peening process. The average grain size within the surface layer of 10 μm thick is about 28 nm. The diffusion kinetics of Al was measured by secondary ion mass spectrometry within a temperature range of 300-380 °C. The diffusion coefficient of Al in the nanocrystalline layer is about 4 orders of magnitude higher than that in coarse-grained Fe. The activation energy of Al diffusion in nanocrystalline layer is 1.38 eV, which is much smaller than that reported for Al diffusion in the conventional Fe. The enhanced diffusivity of Al may originate from a considerable amount of nonequilibrium grain boundaries and a high density of dislocations in the surface layer processed by shot peening.     

Annealing twinning and the nucleation of recrystallization at grain boundaries

Experimental evidence is presented which shows that, in three different low stacking fault energy materials, annealing twins form at grain boundaries during the very early stages of recovery following deformation. These observations provide the basis for the suggestion that twinning at grain boundaries during recovery might stimulate nucleation of recrystallization in low stacking fault energy materials. The experimental observations also lead to the implication that the density of recrystallization nuclei formed in such materials may be directly related to the strength of the deformation texture.     

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。     

CSP冷轧深冲薄板组织、性能的研究进展

CSP流程提供冷轧薄板基材具有独特的经济优势,总结近年来关于CSP冷轧深冲薄板组织和织构演变过程的研究,以及生产和实验研究得出的热轧等轴晶粒、冷轧退火后饼形晶粒、再结晶后有利织枸的影响因素及与最终成品板性能的相互关系,总结控制整个流程析出物（AlN、Fe3C）析出对“饼形晶粒”的形成及提高深冲性能起到关键作用。     

Effect of grain-boundary diffusion acceleration during recrystallization in submicrocrystalline metals and alloys prepared by severe plastic deformation

The results of studying the effect of grain-boundary diffusion acceleration during the annealing of submicrocrystalline (SMC) materials prepared by severe plastic deformation techniques are described. It is shown that the grain-boundary diffusion coefficient during recrystallization of SMC materials depends on the density of lattice dislocations and the pattern and rate of migration of the grain boundaries. It is found that, in SMC metals that undergo anomalous grain growth during annealing, the grain-boundary diffusion coefficient increases and its activation energy decreases. In SMC materials in which the recrystallization process exhibits conventional behavior, the diffusion properties of grain boundaries hardly differ from the equilibrium properties. Expressions describing the dependence of the grain-boundary diffusion coefficient on the migration rate of grain boundaries, as well as the thermodynamic and crystallographic parameters of the material, are derived. The calculation results are compared with the experimental data.     

高强IF钢板沿厚度方向的织构和显微组织

利用X射线三维取向分布函数(ODF)方法和金相方法分别对加磷强化的高强IF钢沿厚度方向织构和显微组织的不均匀性及其变化规律进行了研究。结果表明:该高强IF钢板厚度中心层的γ纤维织构强度及体积分数最高,其次为1/4厚度层,最弱为表层;钢板的显微组织则由表层大小不均匀的晶粒逐渐转变为中心层大小非常均匀的等轴晶粒;这种织构和显微组织沿厚度方向的不均匀现象是由于在轧制过程中钢板的变形不均匀性所造成的。