碳纤维强流脉冲电子束源传输与辐照特性研究

发布时间：2018-08-17 15:50

【摘要】：强流脉冲电子束辐照改性技术是近几十年兴起的一种材料表面改性方法,具有能量利用率高、清洁、处理后工件尺寸变形小等优点,在工业、航空航天等领域得到广泛的应用。电子束发射源作为电子的发生装置,是电子束辐照设备中的关键部件。碳纤维材料具有发射阈值低、发射电流密度高、发射的电子束均匀性好、寿命长等优点,是理想的阴极电子发射材料。本研究使用碳纤维作为阴极材料,研制了平面与环形两种结构形式的碳纤维强流脉冲电子束源。对电子束传输过程与辐照特性进行了模拟与实验研究,对TiN涂层与9310钢进行了辐照处理。使用粒子网格及蒙特卡罗碰撞方法(PIC-MCC)研究了不同辐照参数对平面碳纤维强流脉冲电子束源发射出的电子束传输过程及辐照特性的影响规律。模拟结果表明:在电子束传输过程中,外部约束磁场、辐照距离、气压都会对电子的运动轨迹和辐照均匀性产生影响。外部约束磁场可以抑制电子在传输过程中由于自身库伦斥力而导致的运动轨迹发散。施加15mT外部磁场后,阳极接收到的辐照电子束流可达8kA,电子束在阳极表面的辐照均匀性大于90%。由于电子在传输过程中与空间中性粒子发生碰撞,导致电子数量和能量的损失。辐照距离越长、气压越高,电子数量和能量的损失越严重,到达阳极的电子束流越小。测试结果表明,平面碳纤维强流脉冲电子束源的最大发射电流可以达到8kA,辐照能量密度可以在1.8~10J/cm2之间调控。使用平面碳纤维强流脉冲电子束源发射的电子束对TiN涂层与9310钢进行辐照改性处理。TiN涂层经过电子束辐照处理后,涂层的表面形貌与性能都发生明显变化。经过能量密度5J/cm2的电子束辐照后,Ti N涂层表面出现重熔层,涂层纳米硬度略有下降,表面粗糙度增加。涂层与基体的结合力约为20N,与未辐照TiN涂层与基体的结合力相比,提高近1倍。当电子束辐照能量密度达到8J/cm2时,由于辐照应力增大,导致TiN涂层表面出现裂纹甚至剥落,涂层硬度明显下降,表明涂层已经失效。TiN涂层电子束辐照处理后,表面出现孔洞。孔洞的形成,是由于电子束辐照导致的涂层次表层首先熔化及向外喷发,以及电子束辐照过程中涂层内部气体向外逸出导致的。电子束辐照处理后,9310钢表面出现熔坑与波浪状起伏,截面出现重熔层,重熔层的厚度与电子束辐照能量密度有关,电子束辐照能量密度越高,重熔层厚度越厚。电子束辐照后,9310钢试样表层相组成发生转变,出现奥氏体。电子束辐照处理后,9310钢的耐腐蚀性能得到提高。使用PIC-MCC方法研究了辐照参数对环形碳纤维强流脉冲电子束源发射出的电子束传输过程及辐照特性的影响规律。阴极电压与辐照距离都会对环形碳纤维强流脉冲电子束源发射的电子束辐照均匀性产生影响。在传输过程中,环形碳纤维强流脉冲电子束源发射的电子与空间中性粒子发生碰撞,导致电子数量和能量的损失,辐照距离越长、气压越高,电子数量和能量的损失越严重,到达阳极的电子束流越小。模拟与实验结果均表明,电子间的库伦排斥作用有助于提高环形碳纤维强流脉冲电子束源发射的电子束的辐照均匀性。随着阴极电压和传输距离的增加,电子间的库伦排斥作用增强,电子束在阳极表面的分布更加均匀,环形碳纤维强流脉冲电子束源发射的电子束辐照均匀性得到改善。测试结果表明,环形碳纤维强流脉冲电子束源的最大发射电流可以达到8kA,辐照能量密度可以在1.4~8.3J/cm2之间调控。使用环形碳纤维强流脉冲电子束源发射的电子束对9310钢进行辐照处理。当电子束辐照能量密度为5J/cm2时,试样截面顶部出现重熔层,放置在不同位置处试样重熔层厚度的相对标准偏差为9.39%。结果表明,环形碳纤维强流脉冲电子束源发射的电子束具有良好的辐照均匀性,可以满足圆形部件的电子束辐照改性应用的要求。
[Abstract]:High-current pulsed electron beam irradiation is a new surface modification method for materials in recent decades. It has many advantages, such as high energy efficiency, cleanliness, small deformation of workpiece size, and so on. It has been widely used in industry, aerospace and other fields. Carbon fiber is an ideal cathode material for electron emission because of its low emission threshold, high emission current density, good uniformity and long lifetime. In this study, carbon fiber is used as cathode material, and two kinds of carbon fiber intense pulsed electron beam sources with planar and annular structures are developed. The process and irradiation characteristics of TiN coating and 9310 steel were simulated and experimentally studied. The effects of different irradiation parameters on electron beam propagation and irradiation characteristics of intense pulsed electron beam source of planar carbon fiber were studied by particle grid and Monte Carlo collision method (PIC-MCC). In the process of electron beam propagation, the external confined magnetic field, irradiation distance and pressure will affect the trajectory and irradiation uniformity of electrons. The electron beam irradiation uniformity on the anode surface is more than 90%. As the electron collides with the space neutral particles in the process of transmission, the loss of electron quantity and energy is caused. The longer the irradiation distance, the higher the pressure, the more serious the loss of electron quantity and energy, and the smaller the electron beam current reaching the anode. The maximum emission current of the fiber intense pulsed electron beam source can reach 8 kA and the irradiation energy density can be regulated between 1.8 and 10 J/cm 2. The TiN coating and 9310 steel were irradiated by the intense pulsed electron beam source of planar carbon fiber. The surface morphology and properties of the TiN coating were studied after electron beam irradiation. After electron beam irradiation with energy density 5J/cm2, a remelting layer appeared on the surface of TiN coatings, the nano-hardness of the coatings decreased slightly, and the surface roughness increased. The adhesion between the coatings and the substrate was about 20N, which was nearly twice as high as that between the non-irradiated TiN coatings and the substrate. The surface of TiN coating was cracked or even peeled off because of the increase of irradiation stress, which indicated that the coating was invalid. The surface of TiN coating appeared holes after electron beam irradiation. The thickness of the remelted layer is related to the energy density of the electron beam irradiation. The higher the energy density of the electron beam irradiation is, the thicker the remelted layer is. Austenite appeared. The corrosion resistance of 9310 steel was improved after electron beam irradiation. The influence of irradiation parameters on electron beam propagation and irradiation characteristics of annular carbon fiber intense pulsed electron beam source was studied by PIC-MCC method. In the process of transmission, the electron emitted by the intense pulsed electron beam source of annular carbon fiber collides with the neutral particles in space, resulting in the loss of electron quantity and energy. The longer the irradiation distance, the higher the pressure, the more serious the loss of electron quantity and energy, and the smaller the electron beam current reaching the anode. The results of simulation and experiment show that the Coulomb repulsion between electrons is helpful to improve the irradiation uniformity of electron beams emitted from annular carbon fiber intense pulsed electron beam source. The radiation uniformity of the pulsed electron beam source is improved. The results show that the maximum emission current of the pulsed electron beam source can reach 8 kA, and the irradiation energy density can be controlled between 1.4 J/cm 2 and 8.3 J/cm 2. When the energy density of electron beam irradiation is 5J/cm2, a remelting layer appears at the top of the sample section, and the relative standard deviation of the thickness of the remelting layer is 9.39% at different positions. The results show that the electron beam emitted by the intense pulsed electron beam source of annular carbon fiber has good irradiation uniformity and can satisfy the electron beam irradiation of circular parts. Requirements for modified applications.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG174.4

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