晶体取向显微成像的应用

扼要介绍LINK OPAL电子背散射衍射技术中的一种全新的图像--晶体取向显微成像图,并讨论晶体取向显微成像技术在钢铁材料研究中的应用。     

基于EBSD技术构建弹性各向异性粗晶材料超声仿真模型的研究

针对弹性各向异性粗晶材料晶粒结构和取向定量描述困难,导致超声检测仿真结果与试验符合程度较差的问题,提出基于电子背散射衍射(Electron back-scatter diffraction,EBSD)技术确定晶粒形态及晶体取向的建模思路。利用EBSD技术实测得到了尺寸为96 mm×12 mm的离心铸造奥氏体不锈钢(Centrifugally cast austenitic stainless steel,CCASS)轴-径向截面的晶体取向图谱,选择15°取向相(差)角定义EBSD图谱的晶粒结构,并对晶体取向进行归一化处理。在此基础上借助Bond变换法赋以晶粒在对应晶体取向下的刚度矩阵,对模型中晶粒的弹性特征进行量化表征,建立CCASS超声检测模型。采用时域有限差分法进行数值计算,结果表明:利用该方法能够较好地重现CCASS超声检测特有的结构噪声和主频降低等现象,为揭示超声波在弹性各向异性粗晶结构中的散射机理提供了解决思路。     

采用电子背散射衍射技术研究变形温度对压缩后1235铝合金织构的影响

采用电子背散射衍射技术对经不同温度热压缩后1235铝合金的织构进行了研究,分析了在50%变形量、0.1s-1应变速率下,变形温度对该合金晶粒取向、晶界特征及织构组分的影响。结果表明:随着变形温度的升高,织构的取向聚集性弱化,织构相对体积总含量降低,晶粒内小角度晶界更稀疏,大角度晶界更加平直且连通性好,再结晶晶粒长大更充分。     

(TiB+La2O3)/IMI834钛基复合材料超塑性变形行为及显微组织演变

对(TiB+La_2O_3)/IMI834钛基复合材料进行超塑性变形,研究了不同温度(850,900,950,1 000℃)和初始应变速率(0.000 5,0.001 0,0.005 0s~(-1))对其超塑性变形行为及显微组织的影响。结果表明:该复合材料由α-Ti、TiB、La_2O_3相及弥散分布的(TiZr)_xSi颗粒组成;复合材料具有较好的超塑性,在900℃、0.001 0s~(-1)条件下,断后伸长率最大,为505%;复合材料的应变速率敏感系数高于0.30,随应变速率增加,流变应力和变形激活能增大;随变形程度增加,复合材料中片层α相逐渐等轴化,小角度晶界向大角度晶界转变,但孔洞缺陷增多;晶界滑动、晶粒转动和动态再结晶是(TiB+La_2O_3)/IMI834钛基复合材料超塑性变形的主要变形机制。     

电子背散射衍射技术在材料科学研究中的应用

介绍电子背散射衍射(EBSD)的工作原理、衍射花样包含的物理意义,通过典型实例,系统论述EBSD技术在材料研究领域中的应用,主要包括测定晶体取向、织构、取向关系、应变分布、晶格常数、物相鉴定及晶界性质研究等方面。     

X70管线钢残余塑性应变的背散射电子衍射表征方法研究

为了研究高钢级油气管线环焊缝脆性开裂失效与微小残余塑性应变之间的关系问题,采用背散射电子衍射对不同应变下的X70管线钢进行了表征研究。通过四点弯曲试验和拉伸试验制备带有残余塑性应变的样品,表征了衍射带对比度、核平均取向差与应变的关系。结果表明：X70钢,对于10%以内的塑性变形,金相和硬度等工程手段无法识别;在X70钢管四点弯曲的梯度塑性应变预制样品和系列拉伸样品中,材料EBSD衍射带对比度与微小塑性变形相关性较差,而核平均取向差与±2%以上的塑性变形有较好正相关性,有望用于实际管线残余塑性变形的定性或半定量评估。     

扫描电镜电子背散射衍射系统的研制

本文介绍了扫描电镜电子背散射衍射接收系统,并将该系统成功地安装在JSM-840扫描电镜上。     

采用机械能助渗法制备渗锌层的显微组织与性能

采用机械能助渗法在Q235钢表面制备了渗锌层,研究了渗锌层的表面形貌、截面形貌、物相组成、显微硬度、抗高温氧化性以及耐蚀性能,并与常规粉末包埋法制备的渗锌层进行了对比。结果表明:采用机械能助渗法制备的渗锌层中主要含有FeZn15、FeZn11、FeZn9和FeZn7相,显微硬度与采用传统粉末包埋法制备的无明显差别,均为270~350HV;与Q235钢和采用常规粉末包埋法制备的渗锌层相比,采用机械能助渗法制备的渗锌层具有更高的抗高温氧化性,虽然其耐腐蚀性能有所降低,但其可作为阳极起到保护试样的作用。     

冷拔高碳钢丝在退火过程中再结晶织构的演变

利用扫描电镜和电子背散射衍射技术对冷拔高碳钢丝在600℃等温退火过程中再结晶织构的演变进行了研究,并且探究了织构强度与钢丝形变量及钢丝抗拉强度的关系。结果表明:再结晶织构继承了原来形变的〈110〉织构,并且随退火时间的延长,该织构强度先增加后减弱,并有〈112〉织构出现;形变量较大的钢丝其再结晶织构的强度也较高;钢丝的抗拉强度变化趋势与〈110〉织构强度的变化趋势有一定的对应关系。     

Crystallographic Characteristic of Intermetallic Compounds in Al-Si-Mg Casting Alloys Using Electron Backscatter Diffraction

The Al-Si-Mg alloy which can be strengthened by heat treatment is widely applied to the key components of aerospace and aeronautics. Iron-rich intermetallic compounds are well known to be strongly influential on mechanical properties in Al-Si-Mg alloys. But intermetallic compounds in cast Al-Si-Mg alloy intermetallics are often misidentified in previous metallurgical studies. It was described as many different compounds, such as AlFeSi, Al8Fe2Si, Al5(Fe, Mn)3Si2 and so on. For the purpose of solving this problem, the intermetallic compounds in cast Al-Si alloys containing 0.5% Mg were investigated in this study. The iron-rich compounds in Al-Si-Mg casting alloys were characterized by optical microscope(OM), scanning electron microscope(SEM), energy dispersive X-ray spectrometer(EDS), electron backscatter diffraction(EBSD) and X-ray powder diffraction(XRD). The electron backscatter diffraction patterns were used to assess the crystallographic characteristics of intermetallic compounds. The compound which contains Fe/Mg-rich particles with coarse morphologies was Al8FeMg3Si6 in the alloy by using EBSD. The compound belongs to hexagonal system, space group P2m, with the lattice parameter a=0.662 nm, c=0.792 nm. The β-phase is indexed as tetragonal Al3FeSi2, space group I4/mcm, a=0.607 nm and c=0.950 nm. The XRD data indicate that Al8FeMg3Si6 and Al3FeSi2 are present in the microstructure of Al-7Si-Mg alloy, which confirms the identification result of EBSD. The present study identified the iron-rich compound in Al-Si-Mg alloy, which provides a reliable method to identify the intermetallic compounds in short time in Al-Si-Mg alloy. Study results are helpful for identification of complex compounds in alloys.     

Crystallographic preferred orientation (CPO) of gypsum measured by electron backscatter diffraction (EBSD)

An investigation by electron backscatter diffraction on gypsum shows that this technique can be used to study the microstructures and crystallographic preferred orientation of gypsum. Presented here are the methods, verification tests and data obtained from a naturally deformed sample of gypsum‐rich rock. The electron backscatter diffraction data show the sample has a strong crystallographic preferred orientation.     

Reply to comment by Maurice et al. in response to “Bragg’s Law Diffraction Simulations for Electron Backscatter Diffraction Analysis”

A reply to Maurice et al.'s comment on "Bragg's Law Diffraction Simulations for Electron Backscatter Diffraction" is presented. A new method for microscope geometry calibration is briefly presented. Also, evidence that simple diffraction simulations can be profitable tools for absolute elastic strain measurements in crystalline materials is reiterated.     

Is fast mapping good mapping? A review of the benefits of high‐speed orientation mapping using electron backscatter diffraction

Orientation mapping using automated electron backscatter diffraction (EBSD) is now a common technique for characterizing microstructures. Improvements in software and hardware have resulted in high‐speed mapping capabilities above 80 000 points h^?1. For ‘routine’ microstructural analyses of materials such as steel and aluminium (e.g. texture and grain size measurements and high angle boundary characterization), high‐speed orientation mapping is an ideal approach with minimal penalty on the final statistics. However, for the accurate analysis of very low angle boundaries and for routine analyses of more difficult materials (e.g. most rock samples), we advocate a more patient approach to orientation mapping with an emphasis on data accuracy and reliability. It is important that the objectives of any EBSD analysis are carefully considered before starting – in this way the maximum potential of an EBSD system can be achieved.     

Grain size measurement by EBSD in complex hot deformed metal alloy microstructures

The measurement of grain size by EBSD has been studied to enable representative quantification of the microstructure of hot deformed metal alloys with a wide grain size distributions. Variation in measured grain size as a function of EBSD step size and noise reduction techniques has been assessed. Increasing the EBSD step size from 5% to 20% of the approximate mean grain size results in a change in calculated arithmetic mean grain size of approximately 15% and standard noise reduction techniques can produce a further change in reported size of up to 20%. The distribution of measured grain size is found not to be log‐normal, with a long tail of very small sizes in agreement with a computer simulation of linear intercept and areal grain size measurements through randomly oriented grains. Comparison of EBSD with optical measurements of grain size on the same samples shows that, because of the ability of EBSD to distinguish twins and resolve much smaller grains a difference of up to 50% in measured grain size results.     

Comparison of quartz crystallographic preferred orientations identified with optical fabric analysis,electron backscatter and neutron diffraction techniques

Three techniques are used to measure crystallographic preferred orientations (CPO) in a naturally deformed quartz mylonite: transmitted light cross‐polarized microscopy using an automated fabric analyser, electron backscatter diffraction (EBSD) and neutron diffraction. Pole figure densities attributable to crystal‐plastic deformation are variably recognizable across the techniques, particularly between fabric analyser and diffraction instruments. Although fabric analyser techniques offer rapid acquisition with minimal sample preparation, difficulties may exist when gathering orientation data parallel with the incident beam. Overall, we have found that EBSD and fabric analyser techniques are best suited for studying CPO distributions at the grain scale, where individual orientations can be linked to their source grain or nearest neighbours. Neutron diffraction serves as the best qualitative and quantitative means of estimating the bulk CPO, due to its three‐dimensional data acquisition, greater sample area coverage, and larger sample size. However, a number of sampling methods can be applied to FA and EBSD data to make similar approximations.     

电弧喷涂铝涂层工艺参数优化和涂层结构分析

采用电弧喷涂方法在Q235钢基体上喷涂铝涂层，并用正交设计的方法对工艺参数进行了优化。确定优化后的最优工艺参数为：喷涂电流150A，喷涂电压32V，雾化空气压力0．6MPa，喷涂距离150mm。试验结果表明：采用优化后的最优工艺参数进行喷涂，所得孔隙率比优化前降低了9．88％，而结合强度比优化前提高了2．30％，其主要原因是采用了较大的电弧功率为粒子重新融合创造了条件。喷涂电压和喷涂电流对提高电弧功率所起的作用不同，提高喷涂电流比提高喷涂电压对改善涂层质量更有效。     

Low angle boundary migration of shot‐peened pure nickel investigated by electron channeling contrast imaging and electron backscatter diffraction

Study on recrystallization of deformed metal is important for practical industrial applications. Most of studies about recrystallization behavior focused on the migration of the high‐angle grain boundaries, resulting in lack of information of the kinetics of the low angle grain boundary migration. In this study, we focused on the migration of the low angle grain boundaries during recrystallization process. Pure nickel deformed by shot peening which induced plastic deformation at the surface was investigated. The surface of the specimen was prepared by mechanical polishing using diamond slurry and colloidal silica down to 0.02 μm. Sequential heat treatment under a moderate annealing temperature facilitates to observe the migration of low angle grain boundaries. The threshold energy for low angle boundary migration during recrystallization as a function of misorientation angle was evaluated using scanning electron microscopy techniques. A combination of electron channeling contrast imaging and electron backscatter diffraction was used to measure the average dislocation density and a quantitative estimation of the stored energy near the boundary. It was observed that the migration of the low angle grain boundaries during recrystallization was strongly affected by both the stored energy of the deformed matrix and the misorientation angle of the boundary. Through the combination of electron channeling contrast imaging and electron backscatter diffraction, the threshold stored energy for the migration of the low angle grain boundaries was estimated as a function of the boundary misorientation.