【作者】 吴尉；

【导师】 杨启法；

【作者基本信息】 中国原子能科学研究院 ， 核燃料循环与材料， 2003， 硕士

【摘要】 合金化钼单晶基体表面气相沉积钨{110}择优取向钨单晶涂层是一种性能优越的热离子转换器的发射极材料。钨{110}晶面占发射极表面的份额对整个热离子转换器的功率输出及寿命都有决定性的影响。 本文采用扫描电镜、透射电镜、电子探针、电子衍射、高分辨晶格像等多种实验试样手段，对俄罗斯LUTCH研究院提供的材料——合金化钼单晶基体表面气相沉积钨{110}择优取向单晶涂层的微观结构进行了较为深入的研究。 首先，研制了单晶试样的化学深侵蚀法、恒电位电化学深侵蚀法和氩离子腐蚀等方法，并采用这些方法成功地显示了钨单晶涂层及其与合金化钼单晶基体之间的微观组织结构。研究发现，对单晶试样，要把合金化Mo单晶基体组织、互扩散层和W涂层的显微组织同时显示出来是很不容易的，不同的实验的参数显示出不同的显微组织。TEM试样采用银铜钎焊方法及离子减薄等技术手段来制备，成功地制备出用于透射电镜观察的涂层界面试样。 通过SEM、TEM分析发现，俄罗斯LUTCH研究院提供样品的基体材料和钨涂层均为单晶；不但基体和涂层有相同的晶体取向<111>，而且它们的晶格常数也接近一致，约为3.14(?)；从样品的SEM形貌像和EDS分析可以发现，在Mo合金基体材料和W涂层之间有一互扩散层，互扩散层的主要成分为Mo和W。互扩散层的厚度在10μm左右，其中重扩散层为3μm左右。在重互扩散区内含有C、O等杂质成分；从成分分析还可以观察到高温真空退火过程中，基体材料Mo向W涂层中的扩散深度要大于涂层中W向基体材料中的扩散深度。 合金化Mo合金基体材料、互扩散层和W涂层均有一系列亚晶组织组成，亚晶呈一定的晶粒取向。W涂层的亚晶粒尺寸大于互扩散层的亚晶粒尺寸；样品涂层呈现多层结构，推测涂层的各个部分存在一定的密度、成分、取向、应力状态的差异，在W涂层中可以观察到微空洞。在互扩散层部位(原始界面附近)由于应力较大，容易发生开裂。 样品的TEM分析发现，W涂层由一系列尺寸更小的亚晶组成，亚晶的尺度在几百钠米左右，这些亚晶的取向差很小。在W涂层中存在氧化物或碳化物的夹杂物，夹杂出物的尺度在几百钠米左右。中国原子能科学研究院硕士学位论文 管型发射极外表面经电解蚀刻后，钨{11叫晶面呈现规律性分布，由相互成120度角的六组{110}平面组成，相邻的(110)晶面呈现台阶结构。蚀刻出的台阶面的形貌与所处的位置有关。台阶面的分布是不均匀的，呈现明显的分区特征，台阶的分布依次表现为:在亮带区，台阶面最宽，离开亮带区，台阶面宽度逐渐变窄，在两个亮带交替过渡区，台阶面最窄，然后又由窄变宽，进入第二个亮带。 在轴向为<111>晶向的圆柱型合金化铝单晶基体表面气相沉积相同取向的钨单晶涂层，经电解蚀刻后可得到具有高份额的钨{110}晶面。 蚀刻出{110}晶面质量的好坏不仅与蚀刻的电压、蚀刻电流密度有关，而且与钨单晶涂层的表面加工状态、阴极电极的形状有关。1伏特电压是一个较理想的蚀刻电位。 研究工作得到的结论对国内用CVD方法制备热离子能量转换器发射极W涂层材料、发射极表面用电解蚀刻工艺制备高分额的{1 10}晶面等都具有重要的参考价值。更多还原

【Abstract】 The material of 110-oriented monocrystal tungsten which was achieved by the technique of chemical vapor deposition on the substrate of monocrystal molybdenum alloy is one of the most promising materials which have been currently utilized for the emitter of thermionic energy converter. The proportion of {110} plane to the emitter surface has a significant effect both on the power and the work time of the thermionic energy converter.This kind of material, which was provided by Lutch Academe of Russia, was studied in this paper. And the SEM, TEM, EDS and Electron diffraction techniques were applied to reveal the microstructure of it.The SEM samples were prepared by the methods of the chemical and electrochemical deep corrosive which were developed in this paper, and the argon ion corrosive method was also used to prepare the SEM samples. The TEM samples were prepared by the method of welding and ion-beam thinning. Low melting point Ag-Cu alloy were used as solder.The results show: not only the substrate and its layer are single crystals, but also the axial crystal orientation of the layer and its substrate are [111] orientation; the lattice constant of tungsten layer is almost same as that of molybdenum alloy, both are about 3.14 A; the atom of tungsten layer was located at the epitaxial lattice of its substrate; the thickness of the inter-diffused layer is about 10 m and the heavy inter-diffused layer is about 3 m; Additionally, it is found that carbon and oxygen are enriched in inter-diffused layer. And the diffusivity of molybdenum in its layer is deeper than that of tungsten in its substrate.The structure of substrate, layer and their inter-diffused layer are all composed of sub grain; and the sub grain’s dimension of tungsten layer is larger than that of the inter-diffused layer; the cross section of monocrystal tungsten layer takes on sandwich structure, that is probably due to the differences of their density, component, orientation and state of stress, and there are a lot of micro cavity in the monocrystal tungsten layer after corroded; it’s very easy to crack about on the original interface between substrate and its layer.The sub grain’s dimension of tungsten layer that is about hundreds of nanometre observed by the method of TEM is smaller than that of observed by the method of SEM,the orientation of those sub grains is same as each others; and there are a few oxide or carbide whose dimension is also about hundreds of nanometer in the CVD tungsten layer.The cylindrical surface of CVD monocrystal tungsten coating that its axial direction is [111] orientation can be gained high proportion {110} planes after etched; the morphology of {110} planes on the cylindrical surface is very regularly, that it can be equally divided into six area by six {110} planes; the angle between each {110} plans is 120 ; In each area, the neighbor’s {110} planes take on steps form, and the width of {110} steps in each area appear a recurrent change: the width of {110} steps is the widest in first that is the bright area , than become narrower gradually, after get across a transitional area, the width of {110} steps become wider and wider again.The quality of etching is not only related to the voltages and the electrical currents, but also related to the surface state of machining and the shape of cathode. The 1 etching voltage is a idea etching voltage.The results gained in this paper are useful to the fabrications of CVD thermionic energy converter’s tungsten emitter and the processing of etching {110} plans.更多还原