ZTC4钛合金铸件组织晶粒度测定及评估方法研究

目的 针对大型复杂精密钛合金铸件等飞机关键结构件组织和性能的评估,提出了一种ZTC4钛合金铸件组织晶粒度的评估及分析方法。方法 通过对各类钛合金典型铸件的结构复杂性、凝固过程等关键因素进行分析,对铸件组织随机取样、试样制备与试样显示、试样检验、图像自动拼接、晶界描绘、图像处理测量和数据统计分析的组织定量表征方法。结果 确定铸件在取样过程中需要关注的重要因素,如壁面厚度变化、筋板的交接状态、铸型的种类以及浇冒口位置等,建立了反映铸件上性能的取样原则,建立了基于像素统计的组织定量表征方法,涵盖了晶粒最大尺寸、最小尺寸、平均尺寸和晶粒不规则度等指标。结论 该方法可以真实、准确、定量地反映钛合金铸件的显微组织特征,为钛合金铸件的综合评估提供基础数据支撑。     

基于频谱能量的材料晶粒尺寸表征方法

研究了利用超声频谱能量对材料晶粒尺寸进行表征的方法。通过不同的热处理方式获得了不同晶粒尺寸的奥氏体不锈钢材料,再分别利用衰减系数法、声速法和频谱能量法对材料的晶粒尺寸进行表征。结果表明:频谱能量法得到的衰减系数与平均晶粒尺寸呈非线性关系,晶粒尺寸的预测误差在4%~15%以内,优于传统的分析方法,证明了新方法的有效性。     

IF钢再结晶晶粒尺寸、显微织构和晶界特征分布的EBSD研究

对IF钢板的罩式退火工艺和连续退火工艺进行了模拟，并运用电子背散射衍射(EBSD)技术研究了两种退火工艺处理的IF钢板的再结晶晶粒尺寸、显微织构和晶界特征分布及其与二次加工脆性间的关系。试验结果表明，两种退火工艺的IF钢板在再结晶晶粒尺寸、显微织构和晶界特征分布上存在很大的差异，这种差异导致了两种退火工艺的实验钢板在深冲性能和韧脆转变温度上的差异。     

无间隙原子钢晶界特性的电子背散射衍射研究

运用电子背散射衍射（EBSD）技术，对不同冷轧变形条件下再结晶IF钢板中的晶界特征分布和晶界连通性进行了研究。结果表明，增加冷轧变形量，有利于增加IF钢板中的小角度晶界（∑1），但对（∑3～∑29）重位点阵晶界的影响不大。低能特殊晶界（∑1～∑29）的增加有利于破碎IF钢板中的随机晶界网络，改善其晶界连通性。此外，IF钢板的晶界特征分布与其晶粒尺寸密切相关，小晶粒周围易出现低能特殊晶界，而大晶粒周围易出现高能随机晶界。     

用氢气/甲醇混合气体在微波等离子体CVD中合成纳米晶粒金刚石膜

用微波等离子体增强化学气相沉积方法(MPECVD),利用氢气和甲醇的混合气体,在硅片上沉积出纳米晶粒的金刚石薄膜.用扫描电子显微镜(SEM)、拉曼光谱(Raman)、原子力显微镜(AFM)及扫描隧道显微镜(STM)对薄膜的晶粒平面平整性及纯度进行了表征.通过SEM发现,提高甲醇浓度或降低沉积温度可以减小金刚石膜的晶粒尺寸.拉曼光谱显示薄膜中确实存在纳米晶粒的金刚石,并且薄膜的主要成分为金刚石.用AFM测得薄膜表面的粗糙度Rms＜80m,STM观测晶粒的平均尺寸在10～20m之间.研究结果表明,用MPECVD方法,利用氢气和甲醇的混合气体是制备纳米晶粒金刚石膜的一种理想方法.     

两步熔盐法制备片状BaTiO_3晶体及其表征

BaTiO_3薄片微晶通过两步熔盐法通过使用Ba4Ti13O30作为中间产物的离子交换制备。用XRD和SEM对熔融盐反应产物的晶体结构和微观结构进行了表征。研究结果表明,当使用NaCl熔盐时,熔盐与总反应物的质量比为1∶1,1 050℃下3h,可以制备纯的BaTiO_3微晶。其晶粒尺寸为16μm,厚度为1μm,且分散性较好。XRD图谱显示晶粒以纯的BaTiO_3相存在。用这种方法合成的片状颗粒可以用作织构陶瓷的模板。     

晶粒尺寸可控的纳米二氧化钛的制备

采用微乳法和溶胶-凝胶法相结合的方法制备纳米二氧化钛,通过改变制备参数可以将纳米二氧化钛的晶粒尺寸控制在6~30 nm之间。采用X射线衍射、透射电镜等表征手段,对不同的制备条件与晶粒尺寸的关系进行研究。通过在可见光下对亚甲基蓝水溶液的降解测试其光催化活性。结果表明:补充结论纳米二氧化钛具有良好的光催化性能。     

考虑晶粒尺寸影响的硬度预测模型

目的研究了晶粒尺寸对冷成形过程中材料硬度变化的影响。方法通过不同的退火处理,获得了具有不同晶粒尺寸的材料。采用压缩试验、压痕试验和有限元模拟相结合的方法,研究了不同初始晶粒尺寸条件下材料硬度与等效应变的关系。结果初始晶粒尺寸d对材料初始硬度HV0、硬化系数K、硬化指数n有较大影响,随着晶粒尺寸的增大,它们呈减小趋势。同时提出了一个考虑晶粒尺寸影响的硬度预测模型,并进行了实验验证,硬度的预测值与测量值吻合较好。结论该模型能准确预测具有不同初始晶粒尺寸的材料在冷成形过程中的硬度分布。     

合金化热镀锌IF钢板镀层显微组织的TEM观察

介绍了用聚焦离子束方法制备合金化热镀锌IF钢板镀层横截面TEM试样，应用透射电镜对其显微结构进行了观察。结果表明，商用合金化热镀锌IF钢板镀层显微结构由近界面的牙齿状Г相层和等轴Г1相及δ相组成，晶粒尺寸为0．5～1μm；δ相电子衍射斑点中存在明显的超点阵斑点。     

两种晶粒长大Monte Carlo方法的比较

比较了两种改进的晶粒生长的Monte Carlo方法。通过比较晶粒形貌演化图和晶粒尺寸随时间的变化，发现这两种方法不仅都能够给出比Metropolis抽样更加改进的晶粒生长指数，且明显加快了模拟速度，而且晶粒大小的分布更加合理。这与正常晶粒拓扑演化和理论分析的生长动力学相符合。最后给出了两种改进的方法和Metropolis方法得到的晶粒尺寸分布曲线。     

Austenite and ferrite grain sizes in interstitial free steel

Abstract

An oxidation method has been employed to reveal prior austenite grain boundaries in C–Mn and interstitial free (IF) steels. The ability of this technique to reveal prior austenite grain boundaries is assessed by comparing its results with those of an etching method applied on the C–Mn steel. Optimum conditions were established by trial and error. The conditions varied with different steels and with heat treatment temperature. In the IF steel rapid grain growth at high temperatures in the ferrite range made a significant contribution to the prevention of grain refinement through transformation. Attempts to obtain the smallest prior austenite grain size in the IF steel to assess the ability of the oxidation technique to reveal fine austenite grains led to an average austenite grain size of 80 μm in warm rolled samples after the shortest holding time at 950°C.

MST/3203     

The combined influence of grain size distribution and dislocation density on hardness of interstitial free steel

Understanding the relationship between microstructure features and mechanical properties is of great significance for the improvement and specific adjustment of steel properties. The relationship between mean grain size and yield strength is established by the well-known Hall-Petch equation. But due to the complexity of the grain configuration within materials, considering only the mean value is unlikely to give a complete representation of the mechanical behavior. The classical Taylor equation is often used to account for the effect of dislocation density, but not thoroughly tested in combination with grain size influence. In the present study, systematic heat treatment routes and cold rolling followed by annealing are designed for interstitial free(IF) steel to achieve ferritic microstructures that not only vary in mean grain size, but also in grain size distribution and in dislocation density, a combination that is rarely studied in the literature. Optical microscopy is applied to determine the grain size distribution. The dislocation density is determined through XRD measurements. The hardness is analyzed on its relation with the mean grain size, as well as with the grain size distribution and the dislocation density. With the help of the variable selection tool LASSO, it is shown that dislocation density, mean grain size and kurtosis of grain size distribution are the three features which most strongly affect hardness of IF steel.     

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。     

Yielding behavior and its effect on uniform elongation in IF steel with various grain sizes

In the present study, IF steel specimens with different grain sizes ranging from 12 to 0.45 μm were fabricated by accumulative roll-bonding process and subsequent annealing. Tensile tests revealed that by decreasing the mean grain size down to an ultrafine range smaller than approximately 1.5 μm, yielding behavior of the IF steel gradually changed from continuous yielding to discontinuous yielding. An abrupt loss in the uniform elongation occurred, when the average grain size was smaller than about 1 μm. Hall–Petch analysis on the yield stress and uniform elongation implied that the abrupt loss in the uniform elongation in the UFG grain size range corresponded to the appearance of the discontinuous yielding behavior. As it has been found in many UFG materials, discontinuous yielding is believed to be a unique mechanical behavior of UFG materials, and it has significant importance on the uniform elongation of UFG materials.     

罩式退火无间隙原子钢的最优冷轧压下率的确定

以工业生产的含钛、铌和含钛的两种无间隙原子(IF)钢热轧钢板为试验材料,在实验室研究了冷轧压下率对两种IF钢的显微组织、力学性能和再结晶织构的影响。结果表明:在试验条件下,两种试验钢经不同冷轧压下率冷轧和720℃×5 h罩式退火后,再结晶完成,随着冷轧压下率的增加,晶粒变得细小均匀,退火后得到的织构也增强,并且织构类型有转向{111}织构的趋势;塑性应变比r90在压下率为70%时达到最大值,随着冷轧压下率的进一步增大,r90值减小;应变硬化指数n90值逐渐降低。最后提出工业生产中冷轧压下率最佳范围为70%~80%,可获得良好的深冲性能。     

氧化法显示钢的奥氏体晶粒度的准确性

选用不同钢种在不同加热温度条件下,采用比较法和截点法对两种常用的奥氏体晶粒度显示方法,即氧化法和晶粒边界腐蚀法进行了对比性研究。结果表明：氧化法显示钢的奥氏体晶粒度的准确性能够满足生产检验的要求,氧化法与晶粒边界腐蚀法所显示的奥氏体晶粒平均弦长的差值会受钢种及加热温度的影响。     

Individual Grain Orientation and Heterogeneous Deformation in Cold-deformed Interstitial-Free Sheet Steel

The cold rolling deformation textural evolution of an interstitial-free （IF） steel sheet is investigated by experiment and simulation. The microstructure of the IF steel is observed by transmission electron microscopy （TEM）. The relationship between the deformation behavior of individual grain and the grain orientation are connected by Taylor factor M. The results show that the grains with higher Taylor factor are deformed slighter than those with lower ones. By considering the heterogeneous deformation, the texture simulation result can be greatly improved.     

X射线衍射分析高能喷丸后45钢的表层晶粒尺寸

首先对45钢试样表层进行了高能喷丸处理,然后采用X射线衍射仪(XRD)对喷丸后试样表层的组织结构进行了分析,给出了实测XRD谱和降噪后的XRD谱,通过半高宽分析了试样表层晶粒的大小,并计算了平均晶粒尺寸。结果表明:高能喷丸处理30 min后,45钢表层平均晶粒尺寸为64.847 8 nm,达到了纳米量级,说明采用高能喷丸方法可在45钢表层形成纳米层。     

Fractal based correlations for Nb microalloyed steel undergoing static recrystallization

A new elliptical function for predicting the area fraction of the nucleated sub-grains during static recrystallization has been proposed which considers the fractal based correlation between the sub-grain size and the prior austenite grain size for Nb microalloyed steel. To derive the correlation, fractal analysis of microstructural images of Nb microalloyed steel was performed. The proposed elliptical model in conjunction with the fractal based grain size model improves the prediction of the final grain size distribution for the Nb microalloyed steel and gives excellent correlation with experimental results.