【摘要】：強(qiáng)流脈沖電子束輻照改性技術(shù)是近幾十年興起的一種材料表面改性方法,具有能量利用率高、清潔、處理后工件尺寸變形小等優(yōu)點(diǎn),在工業(yè)、航空航天等領(lǐng)域得到廣泛的應(yīng)用。電子束發(fā)射源作為電子的發(fā)生裝置,是電子束輻照設(shè)備中的關(guān)鍵部件。碳纖維材料具有發(fā)射閾值低、發(fā)射電流密度高、發(fā)射的電子束均勻性好、壽命長(zhǎng)等優(yōu)點(diǎn),是理想的陰極電子發(fā)射材料。本研究使用碳纖維作為陰極材料,研制了平面與環(huán)形兩種結(jié)構(gòu)形式的碳纖維強(qiáng)流脈沖電子束源。對(duì)電子束傳輸過程與輻照特性進(jìn)行了模擬與實(shí)驗(yàn)研究,對(duì)TiN涂層與9310鋼進(jìn)行了輻照處理。使用粒子網(wǎng)格及蒙特卡羅碰撞方法(PIC-MCC)研究了不同輻照參數(shù)對(duì)平面碳纖維強(qiáng)流脈沖電子束源發(fā)射出的電子束傳輸過程及輻照特性的影響規(guī)律。模擬結(jié)果表明:在電子束傳輸過程中,外部約束磁場(chǎng)、輻照距離、氣壓都會(huì)對(duì)電子的運(yùn)動(dòng)軌跡和輻照均勻性產(chǎn)生影響。外部約束磁場(chǎng)可以抑制電子在傳輸過程中由于自身庫倫斥力而導(dǎo)致的運(yùn)動(dòng)軌跡發(fā)散。施加15mT外部磁場(chǎng)后,陽極接收到的輻照電子束流可達(dá)8kA,電子束在陽極表面的輻照均勻性大于90%。由于電子在傳輸過程中與空間中性粒子發(fā)生碰撞,導(dǎo)致電子數(shù)量和能量的損失。輻照距離越長(zhǎng)、氣壓越高,電子數(shù)量和能量的損失越嚴(yán)重,到達(dá)陽極的電子束流越小。測(cè)試結(jié)果表明,平面碳纖維強(qiáng)流脈沖電子束源的最大發(fā)射電流可以達(dá)到8kA,輻照能量密度可以在1.8~10J/cm2之間調(diào)控。使用平面碳纖維強(qiáng)流脈沖電子束源發(fā)射的電子束對(duì)TiN涂層與9310鋼進(jìn)行輻照改性處理。TiN涂層經(jīng)過電子束輻照處理后,涂層的表面形貌與性能都發(fā)生明顯變化。經(jīng)過能量密度5J/cm2的電子束輻照后,Ti N涂層表面出現(xiàn)重熔層,涂層納米硬度略有下降,表面粗糙度增加。涂層與基體的結(jié)合力約為20N,與未輻照TiN涂層與基體的結(jié)合力相比,提高近1倍。當(dāng)電子束輻照能量密度達(dá)到8J/cm2時(shí),由于輻照應(yīng)力增大,導(dǎo)致TiN涂層表面出現(xiàn)裂紋甚至剝落,涂層硬度明顯下降,表明涂層已經(jīng)失效。TiN涂層電子束輻照處理后,表面出現(xiàn)孔洞�？锥吹男纬�,是由于電子束輻照導(dǎo)致的涂層次表層首先熔化及向外噴發(fā),以及電子束輻照過程中涂層內(nèi)部氣體向外逸出導(dǎo)致的。電子束輻照處理后,9310鋼表面出現(xiàn)熔坑與波浪狀起伏,截面出現(xiàn)重熔層,重熔層的厚度與電子束輻照能量密度有關(guān),電子束輻照能量密度越高,重熔層厚度越厚。電子束輻照后,9310鋼試樣表層相組成發(fā)生轉(zhuǎn)變,出現(xiàn)奧氏體。電子束輻照處理后,9310鋼的耐腐蝕性能得到提高。使用PIC-MCC方法研究了輻照參數(shù)對(duì)環(huán)形碳纖維強(qiáng)流脈沖電子束源發(fā)射出的電子束傳輸過程及輻照特性的影響規(guī)律。陰極電壓與輻照距離都會(huì)對(duì)環(huán)形碳纖維強(qiáng)流脈沖電子束源發(fā)射的電子束輻照均勻性產(chǎn)生影響。在傳輸過程中,環(huán)形碳纖維強(qiáng)流脈沖電子束源發(fā)射的電子與空間中性粒子發(fā)生碰撞,導(dǎo)致電子數(shù)量和能量的損失,輻照距離越長(zhǎng)、氣壓越高,電子數(shù)量和能量的損失越嚴(yán)重,到達(dá)陽極的電子束流越小。模擬與實(shí)驗(yàn)結(jié)果均表明,電子間的庫倫排斥作用有助于提高環(huán)形碳纖維強(qiáng)流脈沖電子束源發(fā)射的電子束的輻照均勻性。隨著陰極電壓和傳輸距離的增加,電子間的庫倫排斥作用增強(qiáng),電子束在陽極表面的分布更加均勻,環(huán)形碳纖維強(qiáng)流脈沖電子束源發(fā)射的電子束輻照均勻性得到改善。測(cè)試結(jié)果表明,環(huán)形碳纖維強(qiáng)流脈沖電子束源的最大發(fā)射電流可以達(dá)到8kA,輻照能量密度可以在1.4~8.3J/cm2之間調(diào)控。使用環(huán)形碳纖維強(qiáng)流脈沖電子束源發(fā)射的電子束對(duì)9310鋼進(jìn)行輻照處理。當(dāng)電子束輻照能量密度為5J/cm2時(shí),試樣截面頂部出現(xiàn)重熔層,放置在不同位置處試樣重熔層厚度的相對(duì)標(biāo)準(zhǔn)偏差為9.39%。結(jié)果表明,環(huán)形碳纖維強(qiáng)流脈沖電子束源發(fā)射的電子束具有良好的輻照均勻性,可以滿足圓形部件的電子束輻照改性應(yīng)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.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG174.4

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