【作者】 张力；

【导师】 马欣新；

【作者基本信息】 哈尔滨工业大学 ， 材料科学与工程， 2011， 博士

【摘要】 非线性科学的迅速发展使其成为众多学科的前沿课题之一,孤子作为非线性科学的一个分支,在许多工程领域有着重要应用。晶体点阵中,由于非线性原子间作用力和点阵离散性之间的耦合,在一定条件下,使得晶格振动发生局域化,振动模式能量的传输呈现长程传播而不衰减的孤子特性,这种振动模式称为晶格振动孤子。可以预测这一效应对材料的诸多行为如扩散、相变等产生影响。离子辐照损伤缺陷和晶格振动孤子效应都可能对扩散产生影响,其中辐照损伤缺陷只能在辐照损伤区影响扩散行为,而晶格振动孤子效应可以长程传播而能量不发生衰减,进而可能对辐照损伤区以外的扩散行为产生影响,据此本文设计了在远离辐照损伤区引入扩散偶这一试验方案,分离了辐照损伤缺陷与晶格振动孤子效应。本文研究了离子辐照诱发晶格振动孤子对材料间隙扩散、置换扩散和表面偏聚行为的长程作用,以及离子能量、束流密度、孤子传播距离、晶界在晶格振动孤子效应分别与间隙扩散、置换扩散和表面偏聚耦合过程中起到的作用。针对离子辐照诱发晶格振动孤子与材料间隙扩散行为的长程耦合效应,设计了Fe-C在铁素体—奥氏体双相区的反应扩散过程。预制200?m厚度脱碳层的45钢,在铁素体/奥氏体双相温度区保温,碳从基体向脱碳层中迁移,并诱发铁素体向奥氏体的转变。该过程由碳在远离表面的奥氏体中扩散所决定,因而分离了辐照损伤效应与晶格振动孤子效应。用定量金相法分析奥氏体含量的深度分布,进而评价碳的扩散。在这一过程中对材料表面施加离子辐照,研究离子辐照对碳在铁中间隙扩散的影响规律。试验结果表明,预制柱状晶脱碳层的45钢,在双相区温度保温时,碳沿晶界优先向表面扩散,使铁素体柱状晶晶界处碳含量升高,发生奥氏体转变,奥氏体从晶界向晶内长大;在保温过程中对表面施加氩离子辐照,会使碳向表面的扩散受到抑制;随着离子能量的升高和离子束流密度的增大,碳的扩散受到更加显著的抑制;碳的扩散发生在距辐照表面200?m深度内,由此可知离子辐照对辐照损伤区以外的碳扩散产生了抑制作用。预制等轴晶脱碳层的45钢,表面100?m内碳的扩散受到抑制,而100²00?m内碳的扩散未受影响,说明晶界对离子辐照诱发长程效应的衰减作用。碳在奥氏体中扩散的微观过程是碳在奥氏体晶格相邻八面体间隙之间的迁移;离子辐照诱发晶格振动孤子,导致奥氏体中八面体间隙畸变,因此碳的扩散激活能升高,扩散系数降低,碳向表面的扩散受到抑制。针对离子辐照诱发晶格振动孤子与材料置换扩散行为的长程耦合效应,设计了Cu-Ni互扩散体系。利用铜-镍体系无限固溶的特性,在定向凝固单晶和柱状晶铜,以及多晶铜片状样品正面,用磁控溅射方法沉积镍镀层,扩散时在远离样品扩散偶的一端即样品背面施加离子辐照,即分离了辐照损伤效应与晶格振动孤子效应。研究了样品厚度、离子能量和离子束流密度对铜-镍扩散行为的影响。试验中使用辉光放电光谱方法分析了镍的浓度分布;使用扫描电子显微分析了基体和镀层的组织结构;使用正电子寿命谱和慢正电子湮没多普勒展宽谱方法分析了单晶铜经过离子辐照后未辐照面的缺陷状态。试验结果表明,在以单晶或柱状晶铜为基体的铜-镍扩散偶中,离子辐照对铜镍之间的扩散产生了长程的加速作用,随着样品厚度的降低和离子能量的升高,扩散系数有所增加;而离子束流密度的增大对扩散系数不产生显著影响。离子辐照使镍在单晶铜中的扩散激活能由1.01eV降为0.94eV,频率因子由3.48×10^-7cm²/s降为2.34×10-7cm²/s。在以柱晶铜为基体的扩散偶中,离子辐照对铜的再结晶行为产生了显著的加速作用。在以多晶铜为基体扩散偶中,离子辐照对铜镍界面的扩散无显著影响,显示晶界对长程效应的阻碍特性。正电子分析显示,离子辐照导致未辐照次表面空位类缺陷含量降低。提出了离子辐照长程加速置换扩散的机制:扩散的长程加速不是由辐照损伤缺陷扩散至铜镍扩散偶位置所导致,而是由于离子辐照诱发的晶格振动孤子效应降低了扩散偶附近晶体的空位迁移能,使扩散系数增大。铜-镍扩散试验中发现,铜元素在镍镀层表面发生偏聚,离子辐照导致表面偏聚效应显著增强,偏聚深度达到约500nm,随样品厚度的降低,表面偏聚效应更加显著。结合离子辐照对单晶铜缺陷状态长程影响的试验结果,提出了离子辐照长程加速表面偏聚的机制。离子辐照诱发晶格振动孤子效应导致空位迁移能的降低,及空位迁移向表面方向的概率增大,导致空位向表面空位闾的流量增大;在铜-镍体系中,空位迁移与铜原子迁移耦合且方向相反,因而空位向表面的加速迁移,导致平衡偏聚在极表面的铜向次表面加速迁移。更多还原

【Abstract】 The rapid development of non linear science make it one frontier field of many subjects. Soliton, an important branch of non linear science, pioneered the new ways of mathematical physics and is applicable in many fields of engineering. In crystal lattice, because of the coupling between non linear atomic force and the discreteness of the lattice, the vibrational mode may be localized and the energy transmission became soliton like. It can be predicted this effect will influence barious kinds of material behavior such as diffusion, phase transition and etc..Ion irradiation was employed in this work to excite the crystal lattice vibrational soliton, and the ion energy and current density were adjusted to control the strength of the crystal lattice vibrational soliton. The long range effect of crystal lattice vibrational soliton on the interstitial diffusion, substitutional diffusion and surface segregation were studied. The effects of temperature and grain boundaries in the irradiation-diffusion process were studied, too. The irradiation induced defects and crystal lattice vibrational soliton was separated by diffusion far away from the irradiated surface since crystal lattice vibrational soliton is long range effect while defect is short range effect.45 steel with 200?m columnar decarburized layer was heated at duplex zone with and without ion irradiation. The experiment result revealed carbon diffusion preferentially along the grain boundaries to the surface when the decarburized 45 steel was annealed at duplex temperature, which led to higher carbon concentration at the grain boundaries between columnar Ferrite crystals and then the nucleation of Austenite and their growth into the grain inner. The carbon diffusion was inhibited when ion irradiation was performed. Higher ion energy or ion current density led to stronger inhibition. The longer affected zone than that in classical theory of ion irradiation was explained by non linear crystal lattice excitation, which led to the stronger atomic force. The crystal lattice soliton deformed the shape of the octahedron interstitial in austenite, which led to the increasement of the diffusion activation energy, then the inhibition of carbon diffusion.Polycrystalline copper and directional solidificated single crystal and columnar crystal copper disks were employed as one side of the diffusion couple, the other side was nickel film by magnetron sputtering for its infinite solubility in copper. The diffusion couples were annealed with ion irradiation at the rare face of nickel films. Glow Discharge Optical Emission Spectroscope, Scanning Electron Microscope and Positron Annihilation were employed to analysis the element concentration depth distribution, the microstructure and the defect state of the diffusion couples, respectively. The experiment result revealed an acceleration of Ni diffusion in copper by ion irradiation in single and columnar copper substrate couples. The diffusion coefficient increased while the sample thickness decreased or the ion energy increased. There was no effect of ion current density on the diffusion coefficient. The diffusion activation energy was decreased from 1.01eV to 0.94eV and the frequency factor was decreased from 3.48×10^-7cm²/s to 2.34×10^-7cm²/s in single crystal copper substrate couples. Recrystallization acceleration of columnar crystal copper by ion irradiation led to the abnormal increasement of diffusion coefficient. No effect of ion irradiation on diffusion was found in polycrystalline copper substrate couples. Diffusion led to the disappearance of the interface between copper and nickel, and the appearance of holes in copper substrate, indicating faster copper diffusion into nickel. Slow positron Doppler Broadening Spectroscopy showed the decrease of vacancy like defects at the subsurface of the non irradiated surface. The mechanisms of acceleration of substitutional diffusion were proposed. The long range effect is due to the decrease of vacancy migration energy because of the non linear lattice excitation, but not the diffusion of irradiation damage induced defect to the backside of the samples.Copper segregation at the surface of nickel film were found in the copper-nickel diffusion experiments. Based on the changed surface defect state of single crystal copper after ion irradiation, the mechanism of copper surface segregation was proposed as, the lower vacancy migration energy and the higher probability of vacancy migrating to the surface led to the higher flux of vacancy to the surface vacancy sink. Particularly in copper-nickel system, there is coupling between vacancy flux and copper flux. The copper flux is opposite to the vacancy flux. As a result, the accelerated migration of vacancy to the surface led to the equilibrium segregated surface copper migrated to the subsurface layer.更多还原