【作者】 徐京城；

【导师】 赵纪军；

【作者基本信息】 大连理工大学 ， 凝聚态物理， 2011， 博士

【摘要】 核聚变能,是未来解决能源危机的终极方案。核聚变反应堆中复杂的工况环境,对材料提出了苛刻的要求。第一壁结构材料的辐照损伤是目前核聚变研究的一个重要方面。本论文简单地讨论了氢原子在第一壁材料中的行为,研究了铁磁体心立方Fe-Cr二元合金随着铬元素含量不同而引起的力学性质与平均磁矩的变化,针对低活化钢中重要的少量元素钨,系统地研究了铬、钨元素对Fe-Cr-W三元合金力学性质的影响。我们希望我们的计算结果对理解钨材料中的氢原子行为和低活化钢组分的设计能起到一定的指导作用。钨基材料已经被应用于国际热核聚变实验反应堆(ITER)中的第一壁材料设计中。氢原子等杂质将会通过反应等离子体的轰击而引入,对于面向等离子体钨基壁材料的性能和稳定性有很重要的影响。采用第一性原理密度泛函理论和平面波赝势技术,我们研究了氢原子在完美体心立方钨晶格中的行为。我们比较了氢原子在不同吸附间隙位的结合能以确定氢原子在钨晶格中的最佳吸附位为四面体间隙位。我们还计算了氢原子在钨晶格中扩散的迁移势垒,发现最优的迁移路线为四面体间隙位一对角线间隙位一四面体间隙位。我们同时还研究了两个孤立氢原子在钨晶格中的相互作用,我们的研究对氢原子的扩散以及钨基材料中氢泡的形成提供了一定的理论依据。由于优良的抗辐照肿胀、抗辐照脆性性能和很好的热力学性质,低活化铁素体/马氏体钢被认为是热核聚变实验反应堆的重要结构材料候选材料。低活化马氏体/铁素体钢主要以铁磁体一心立方Fe-Cr二元合金(其中Cr的质量含量为7-12%)为基础,同时含有钨、钒等微量元素。大量的实验、理论研究表明, Cr元素对于低活化钢力学性能、抗辐照效应有着重要的影响。由于低活化钢是聚变反应堆的主要结构材料,其力学性质对于聚变反应堆的安全而言非常重要,因此研究Cr元素对低活化钢力学性质的影响也具有重要的意义。论文以Fe-Cr二元合金(Cr的原子个数比为0-15.6%)体系的随机固溶体模型为研究对象,采用第一性原理方法研究了Cr元素对Fe-Cr二元合金体系力学性能的影响。计算结果表明,Fe-Cr二元合金的晶格常数均大于铁磁体心立方纯铁晶体的晶格常数；Fe-Cr二元合金的杨氏模量、剪切模量随着Cr元素含量的增加呈非单调增加的趋势。不同组分的Fe-Cr二元合金均表现为展性行为。Fe-Cr二元合金的平均原子磁矩随Cr元素含量的增加呈线性下降的趋势。低活化铁素体/马氏体钢的最丰要成分为Fe-Cr-W三元合金。采用基于密度泛函理论的精确松饼势轨道(EMTO)方法,结合相干势近似(CPA)和全电荷密度(FCD)技术,我们研究了一系列随机固溶体模型Fe-Cr-W三元合金的力学性能随组分变化的情况。计算了体模量B、剪切模量G、杨氏模量E、体模量与剪切模量比值(B/G)和泊松比(v)与三组元含量的相应关系。整体而言,Fe-Cr-W三元合金体系的弹性模量随着Cr元素的增加而增大,W元素对合金体系的弹性模量变化影响不大。更多还原

【Abstract】 Nuclear fusion energy is the future ultimate solution to the energy crisis. Nuclear fusion reactor works with the complicated environment, and that put forward stringent requirements for materials in fusion reactors. The irradiation effects of the first wall structural materials are important for the research of nuclear fusion. In this thesis, We briefly discussed the irradiation effects of hydrogen atoms in the first wall materials, investigated the changes in the mechanical properties and average magnetic moment caused by different chromium content in the ferromagnetic BCC Fe-Cr binary alloys. Considering the important elements tungsten with small amount in low activation steels, a systematic study of effect of chromium and tungsten element to mechanical properties of Fe-Cr-W ternary alloy was carried out. We hope these theoretical results help us to understand the irradiation effects in the relevant materials, and the calculations of the mechanical properties of steels are helpful for determining suitable compositions for the low activation steels.Tungsten-based materials are used as the first wall materials in ITER. Hydrogen impurities were introduced via bombarding with the reaction plasma, which are important for the behavior and stability of the tungsten wall. Using the first-principles density functional theory and planewave pseudopotential technique, we have simulated the behaviors of hydrogen atoms inside the perfect tungsten bcc lattice. The binding energies for different interstitial sites were compared to determine the optimal trapping site for the hydrogen atom inside the tungsten host lattice. The diffusion barriers for hydrogen atom migration between nearby trapping sites and the interaction between two interstitial hydrogen atoms were also calculated. The implication of our theoretical results on the hydrogen diffusion and accumulation behavior was also discussed.Because of the excellent resistance to swelling and embrittlement under irradiation and good thermal and mechanical properties, reduced activation ferritic/martensitic steels (RAFM steels) are considered as the primary structural materials of future fusion reactors. RAFM steels are composed of the body centered cubic (BCC) Fe-Cr alloys (7-12 wt.% Cr) with some trace elements (such as, W, V, etc.). Amount of experimental and theoretical results indicate that the Cr element play a significantly role in the mechanical properties and irradiation effect of RAFM steels. As the primary structure materials in ITER fusion reactors, the mechanical properties of RAFM steels are important to the safety. Thus, it is necessary to investigate the fundemental mechanical properties of Fe-Cr alloys with different Cr content. Modelling Fe-Cr alloys as a random solid solution model, we employed the first-principles method to inverstigate the effect of Cr element to the lattice constants and the elastic properties of ferromagnetic bcc Fe1-xCrx (0=x=0.156) alloys. We found that the lattice parameters of Fe-Cr alloys are all larger than that of BCC pure Fe solid. The Young’s modulus and shear modulus of Fe-Cr alloys rise non-monotonically with increasing Cr composition. All Fe-Cr alloys with diferent compositions exhibit the ductile behavior.The average magnetic moment per atom of Fe-Cr alloys decrease linearly with increasing Cr concentration.The basic composition of RAFM steels is Fe-Cr-W alloy. Using the exact muffin-tin orbitals (EMTO) method, combined with coherent potential approximation (CPA) and full charge density (FCD) technology, we investigated composition dependence of mechanical properties for Fe-Cr-W random alloys within the composition range of 7.8-10.0 wt.% of Cr and 1.0-2.0 wt.% of W. Bulk modulus B, shear modulus G, Young’s modulus E, BIG ratio, and Poisson ratio v were discussed as functions of ternary composition. On the whole, the elastic moduli of Fe-Cr-W alloys increase with chromium content; the influence of tungsten is relatively weak.更多还原