基于第一性原理的Zr-H晶体结构稳定性及原子扩散行为研究

发布时间：2018-03-23 09:22

本文选题：锆-氢体系　切入点：第一性原理　出处：《哈尔滨工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：锆合金不仅是优异的核燃料包壳材料,还具有很好的储氢性能,核能的生产及氢能的储存都与锆合金紧密相关。锆合金作为包壳材料在服役中容易发生氢脆,造成巨大损失,解决其氢脆问题一直是科学家们的研究重点。深入研究氢与锆之间的相互作用,无论对于锆的氢脆问题的解决还是锆基储氢材料的发展都具有重要价值。本文基于第一性原理方法研究了锆-氢体系的晶体结构、能量性质、力学性质及原子扩散性质,并从电子层次对这些性质进行了解释,从微观上研究氢与锆作用的机理。确定锆-氢晶体结构模型是进行各类性质计算的基础,因此首先对氢在锆晶体中的占位进行了模拟研究。结果发现:无论在α-Zr晶体还是β-Zr晶体中,晶格畸变程度与氢含量正相关,氢含量相同时,氢原子在四面体间隙时的晶格畸变程度都大于八面体间隙;但是,氢原子在四面体间隙时的溶解热小于八面体间隙,因此,氢原子倾向于占据在四面体间隙位置。电子结构分析发现:氢原子的作用具有局域性,改变了近邻锆原子的态密度,氢近邻α-Zr原子的4p轨道及β-Zr原子4d轨道的部分电子会向氢的1s轨道转移,杂化成键;氢降低了α-Zr晶体中的锆原子间键强度,存在弱键效应,提高β-Zr晶体中的锆原子间键强度,存在强键效应。对锆-氢体系中氢原子扩散行为的研究发现:在α-Zr晶体中,氢的扩散具有各项异性,沿基面的扩散激活能小于沿c轴的扩散激活能,已有实验结果一致,在基面上沿T-T路径扩散,在不同原子层间扩散时则沿着T-O-T路径扩散;在β-Zr晶体中,氢原子会在近邻四面体间隙之间直接直线扩散,在次近邻四面体间隙间扩散时则需要经过中间的八面体间隙。在空位扩散机制基础上对锆原子自扩散行为研究发现:氢原子的加入使得α-Zr中空位形成能及锆原子自扩散激活能都降低,促进了锆原子的自扩散;β-Zr晶体中空位形成能提高、锆原子自扩散激活能降低,即虽然空位变的难以形成但最终还是促进了锆原子的自扩散。对锆-氢体系的表面能、弹性模量、拉伸与压缩力学性能进行了模拟。对表面能的研究发现:氢原子降低了α-Zr晶体基面及棱柱面的表面能,使表面稳定性增加。提高了β-Zr晶体{100}及{110}面的表面能,降低了表面稳定性。对弹性模量及应力-应变曲线的研究发现:氢降低了α-Zr晶体的杨氏模量、剪切模量、体模量,并且使塑性指标G/B减小,发生软化。降低了α-Zr晶体沿c轴方向的单向理论抗拉与抗压强度,反映了氢原子的弱键效应。氢提高了β-Zr晶体的杨氏模量、剪切模量、体模量,使G/B增大,发生硬化。提高了β-Zr晶体的力学稳定性,使其单向理论抗拉强度提高,抗压缩能力也提高,体现了氢原子对β-Zr晶体的强键效应。
[Abstract]:Zirconium alloy is not only an excellent nuclear fuel cladding material, but also has good hydrogen storage performance. The production of nuclear energy and the storage of hydrogen energy are closely related to zirconium alloy. Zirconium alloy as a cladding material is prone to hydrogen embrittlement in service, resulting in huge losses. Solving the hydrogen embrittlement problem has always been the focus of scientists. Both the hydrogen embrittlement problem of zirconium and the development of zirconium based hydrogen storage materials are of great value. In this paper, the crystal structure, energy properties, mechanical properties and atomic diffusion properties of zirconium hydrogen system are studied based on the first principle method. The mechanism of the interaction between hydrogen and zirconium is studied microscopically. The crystal structure model of zirconium and hydrogen is the basis for the calculation of all kinds of properties. The results show that the degree of lattice distortion in 伪 -Zr crystal and 尾 -Zr crystal is positively correlated with the hydrogen content, and the hydrogen content is the same as that in 伪 -Zr crystal and 尾 -Zr crystal. The lattice distortion of hydrogen atoms in tetrahedron gap is greater than that in octahedral gap, but the solution heat of hydrogen atom in tetrahedron gap is smaller than that in octahedral gap. Hydrogen atoms tend to occupy the position in tetrahedron gap. The electronic structure analysis shows that the action of hydrogen atoms is localized, which changes the density of states of the nearest zirconium atoms. The 4p orbital of 伪 -Zr atom and the 4d orbital of 尾 -Zr atom transfer to the 1s orbital of hydrogen, and hydrogen decreases the bond strength of zirconium atom in 伪 -Zr crystal, and there is a weak bond effect, which increases the bond strength of zirconium atom in 尾 -Zr crystal. There is a strong bond effect. The diffusion behavior of hydrogen atoms in zirconium hydrogen system is studied. It is found that in 伪 -Zr crystal, the diffusion activation energy along the base plane is smaller than that along the c axis, and the experimental results are consistent. It diffuses along T-T path on the base plane and along the T-O-T path when diffused between different atomic layers. In 尾 -Zr crystal, the hydrogen atom diffuses in a straight line between the near tetrahedron gap. On the basis of vacancy diffusion mechanism, the self-diffusion behavior of zirconium atoms is studied. It is found that the addition of hydrogen atoms makes the formation energy of vacancies and zirconium atoms in 伪 -Zr. The self-diffusion activation energy decreases, The vacancy formation energy in 尾 -Zr crystal is increased, and the self-diffusion activation energy of zirconium atom is decreased, that is, the self-diffusion of zirconium atom is promoted in the end, although the vacancy is difficult to form, the elastic modulus of zirconium hydrogen system is obtained. The mechanical properties of tensile and compression were simulated. The surface energy of 伪 -Zr crystal was decreased by hydrogen atom, and the surface stability of 伪 -Zr crystal was increased, and the surface energy of 尾 -Zr crystal {100} and {110} was improved. The study of elastic modulus and stress-strain curve shows that hydrogen decreases the Young's modulus, shear modulus and bulk modulus of 伪 -Zr crystal, and makes the plasticity index G / B decrease. Softening occurs. The unidirectional theoretical tensile and compressive strength of 伪 -Zr crystal along c axis is reduced, which reflects the weak bond effect of hydrogen atom. Hydrogen increases the Young's modulus, shear modulus and bulk modulus of 尾 -Zr crystal, and makes G / B increase. By hardening, the mechanical stability of 尾 -Zr crystal is improved, the unidirectional theoretical tensile strength is improved, and the compressive ability is improved, which reflects the strong bond effect of hydrogen atom on 尾 -Zr crystal.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.414

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