聚焦离子束在金属研究中的应用

摘要

由于聚焦离子束(Focused Ion Beam,简称FIB)显微镜的最新运用,材料科学得以迅速发展.钢铁行业中,聚焦离子束技术不仅可以不断将涂料和钝化层变薄,而且特别适用于多相或成分混杂的和/或多孔材料的透射电子显微镜(Transmission Electron Microscope,简称TEM)薄片制备.四年前,在ArcelorMittal Gent设备上安装了三重束聚焦离子束仪器.随后利用该仪器对大量的各种各样的材料进行筛选和/或处理,以进一步进行TEM分析.FIB技术成功运用于图层、基体和界面研究领域.比如:1)图层应用:厚度均匀性、缺损性及腐蚀研究；2)衬底分析:裂纹扩展、晶界及晶粒取向；3)界面分析:金属间(化合的)相、扩散和偏聚,外延研究.由于FIB仪器的高成本性以及配套需要的专业操作技能,毫无疑问局限了其在钢铁研究中的日常应用.不过,仍然可以从聚焦离子束制备样品的独特方式中获得许多经济效益,比如更短的样品制备时间、对抽样区域的选择性,当然还有人为因素的影响极其有限.因此,通常情况下,FIB样品制备成为唯一一种可以用于制备透射电子显微镜薄片的途径.FIB同TEM的联用分析技术开启了一个化学的、微结构和晶体信息的新世界,这种新领域将在以下研究中得以体现:1)锌-铝-镁涂层的共晶相表征；2)富铬钝化层的缺损学研究；3)耐候钢的结构组成；4)无锌涂层的微结构:铝/镁显示为纳米晶体状的铝镁多相结构.%The recent use of the Focused Ion Beam (FIB) microscopes has allowed fast developments in materials science. The interest from the steel industry for the FIB technique is not only related to the ever decreasing thickness of coatings and passivation layers. Indeed, the FIB technique is particularly adapted for the preparation of TEM lamellae of multiphase or very heterogeneous and/or porous materials. Four years ago, a triple beam FIB instrument was installed at ArcelorMittal Gent and since then, a wide variety of materials have been screened and/or processed for further TEM analysis. FIB was successfully applied in the field of coating, substrate and interface studies e. g. 1) Coating applications: thickness-homogeneity, defectology, corrosion studies; 2) Substrate analysis: crack propagation, grain boundaries, grain orientations; 3) Interface analysis: intermetallic phases, diffusion and segregation, epitaxial studies. The high cost of a FIB instrument and the dedicated operator skills are certainly drawbacks for its routine applications in steel research. Nevertheless, a lot of economical benefit can be gained from the its unique way of sample preparation such as the shorter sample preparation time, the choice or selectivity of the sampling area, and of course, the extremely limited effect of artefacts. Very often, FIB sample preparation is the only way to produce TEM lamellae that cannot be obtained by other preparation techniques. FIB in combination with TEM analysis opens a new world of chemical, microstructural and crystallographic information as will be highlighted in the following topics. Deutectic phase characterization of Zn-Al-Mg coatings; 2) Defectology studies of Cr-rich passivation layers; 3) Structural composition of weathering steels; 4) Microctructure of Zn-free coatings: Aluminium/Magnesium showing nano crystalline Al-Mg rich phases.