【作者】 李雪；

【导师】 魏小平；

【作者基本信息】 兰州交通大学 ， 物理学， 2025， 硕士

【摘要】 当材料处于高剂量的粒子辐照和高温等恶劣环境中时,不可避免地会经历多种形式的损伤演化,进而有空位、间隙原子和位错环等缺陷结构的形成。这些缺陷会与材料的微观结构特征(晶界、析出相)发生相互作用,进而影响其宏观性能的变化。在核反应堆的极端服役环境中,材料(燃料包壳和结构部件)长期暴露于高能中子、离子等辐照场中,会引发一系列性能退化现象,包括辐照脆化、辐照肿胀以及辐照加速蠕变等。深入探究辐照损伤机制不仅能够揭示材料在极端辐照环境下缺陷的演化规律,还能够评估材料在辐照环境中宏观性能的变化。为开发新型抗辐照材料提供理论指导,从而提升核反应堆的安全性和服役寿命。Cu-Ni合金因其出色的抗腐蚀性能和高温稳定性而成为核工程领域的重要候选材料,被广泛应用于反应堆热交换元件、辐照屏蔽系统等场景。然而,在高温与强辐照耦合的极端条件下,该合金体系中会形成复杂的缺陷结构,导致其宏观性能的改变。本文以Cu-Ni合金为研究对象,采用分子动力学方法,系统研究了该合金在不同辐照条件(温度、初级碰撞原子(PKA)能量和方向)下的初级离位损伤演化过程,并深入分析了辐照诱导的缺陷对合金力学性能和晶格热导率的影响。研究主要分为以下两个方面:首先,系统研究了Cu-Ni合金在不同温度、PKA能量和方向条件下的位移级联演化行为。结果表明,随着辐照温度的升高,Cu-Ni合金中Frenkel缺陷对数目呈现一个小幅度的下降趋势,这可能是由于高温环境下原子迁移率增强,促进了空位和间隙原子的复合过程。在不同PKA能量下,Cu-Ni合金中Frenkel缺陷对的数目随着PKA能量的增加而增加,这归因于更高能量的PKA可引发更剧烈的级联碰撞过程,从而产生更多的缺陷。而不同的PKA方向对Frenkel缺陷对数目的影响较小,其主要作用体现在缺陷的空间分布上。值得注意的是,残余缺陷在晶体中不是单一分布的,而是会以团簇(空位团簇和间隙团簇)的形式分布。进而对缺陷团簇进行了分析。发现对于空位团簇和间隙团簇,都会随着体系中Ni含量的增加而减少。与空位团簇相比,间隙团簇更容易聚集并形成更大的团簇。接着,研究了辐照前后Cu-Ni合金的力学性能和晶格热导率的变化规律。在力学性能方面,结果表明Ni元素的添加提升了Cu基体的屈服强度。而与未经辐照的Cu-Ni合金相比,辐照处理会导致Cu-Ni合金的屈服强度降低,且这种降低程度与PKA能量呈正相关,使合金呈现出典型的辐照硬化脆化特征。通过微观结构表征发现,这种力学性能退化主要源于辐照诱导缺陷的演化行为。由前面研究可知,随着PKA能量的升高会产生更多的Frenkel缺陷对数目,这在拉伸应力作用下易于聚集并演化为位错或位错环,从而促进位错的增加,导致Cu-Ni合金会提前屈服。值得注意的是,Frenkel缺陷对的空间分布同样影响屈服行为,有利于位错成核的缺陷构型会进一步降低材料的屈服强度。在晶格热导率方面,研究发现,完美Cu-Ni合金的晶格热导率随温度的升高呈现显著变化,这主要归因于温度诱导的声子-声子散射效应增强,该效应破坏了声子动量守恒,降低了声子的平均自由程。经过辐照处理后,随着PKA能量的增加,晶体中空位和间隙原子等缺陷浓度显著上升,进一步增强了声子散射效应,导致Cu-Ni合金晶格热导率的降低。这种效应在较高Ni含量的合金中较为显著,表明Cu-Ni合金中的晶格无序和质量不匹配会进一步放大声子的散射作用。综上所述,研究辐照前后材料的力学性能(如屈服强度)和晶格热导率,不仅有助于评估材料在辐照环境中的性能变化,还可以为优化材料设计、提高其抗辐照性能提供科学依据。这对于保障核能安全、优化热管理设计以及应对未来极端环境挑战具有重要意义。同时,这些研究也推动了材料科学和相关学科的发展,具有深远的影响。更多还原

【Abstract】 When the material is exposed to harsh environment such as high dose particle irradiation and high temperature,it will inevitably undergo various forms of damage evolution,and then have the formation of defect structures such as vacancy,interstitial atoms and dislocation rings.These defects will interact with the microstructure characteristics of the material(grain boundaries,precipitates),and then affect the change of its macro properties.In the extreme service environment of nuclear reactors,long-term exposure of materials(fuel cladding and structural components)to high-energy neutrons,ions and other radiation fields will lead to a series of degradation phenomena,including irradiation embrittlement,irradiation swelling and irradiation accelerated creep.In-depth investigation of the mechanism of radiation damage can not only reveal the evolution law of defects in the extreme irradiation environment,but also evaluate the change of macroscopic properties of materials in the irradiation environment.It provides theoretical guidance for the development of new anti-irradiation materials to enhance the safety and service life of nuclear reactors.Due to its excellent corrosion resistance and high temperature stability,Cu-Ni alloys has become an important candidate material in the field of nuclear engineering,and is widely used in reactor heat exchange components,radiation shielding systems and other scenarios.However,under the extreme conditions of high temperature and strong radiation coupling,complex defect structures will be formed in the alloy system,resulting in changes in its macro properties.In this dissertation,the evolution process of the primary out-of-place damage of Cu-Ni alloys under different irradiation conditions(temperature,primary colliding atom(PKA)energy and direction)was systematically studied by molecular dynamics method,and the effects of the irradiation-induced defects on the mechanical properties and lattice thermal conductivity of the alloy were deeply analyzed.The research is mainly divided into the following two aspects:Firstly,the displacement cascade evolution behavior of Cu-Ni alloys at different temperature,PKA energy and direction is systematically studied.The results show that with the increase of irradiation temperature,the number of Frenkel defect pairs in Cu-Ni alloys presents a small decreasing trend,which may be due to the enhancement of atomic mobility under high temperature environment,which promotes the recombination process of vacancy and gap atoms.At different PKA energies,the number of Frenkel defect pairs in Cu-Ni alloys increases with the increase of PKA energy,which is attributed to the fact that PKA with higher energy can cause more intense cascade collision process,resulting in more defects.However,different PKA directions have little effect on the logarithm of Frenkel defects,and their main effect is reflected in the spatial distribution of defects.It is worth noting that the residual defects are not distributed singly in the crystal,but will be distributed in the form of clusters(vacancy clusters and gap clusters).Then the defect clusters are analyzed.It is found that both vacancy clusters and gap clusters decrease with the increase of Ni content in the system.Compared with vacancy clusters,gap clusters cluster more easily and form larger clusters.Then,the mechanical properties and lattice thermal conductivity of Cu-Ni alloys before and after irradiation were studied.In terms of mechanical properties,the results show that the addition of Ni increases the yield strength of Cu matrix.Compared with the unirradiated Cu-Ni alloys,the yield strength of Cu-Ni alloys is reduced by radiation treatment,and the reduction degree is positively correlated with the PKA energy,so that the alloy presents typical irradiation hardening embrittlement characteristics.Through microstructure characterization,it is found that the degradation of mechanical properties is mainly due to the evolution behavior of irradiation-induced defects.It can be seen from the previous studies that with the increase of PKA energy,more Frenkel defect pairs will be generated,which are easy to aggregate and evolve into dislocation or dislocation ring under the action of tensile stress,thus promoting the increase of dislocation and leading to premature yield of Cu-Ni alloys.It is worth noting that the spatial distribution of Frenkel defect pairs also affects the yield behavior,and the defect configuration conducive to dislocation nucleation will further reduce the yield strength of the material.In terms of lattice thermal conductivity,it is found that the lattice thermal conductivity of perfect Cu-Ni alloys changes significantly with the increase of temperature,which is mainly due to the enhancement of the temperature-induced phonon-phonon scattering effect,which breaks the momentum conservation of phonons and reduces the mean free path of phonons.After irradiation,with the increase of PKA energy,the concentration of defects such as vacancy and gap atoms in the crystal increases significantly,which further enhances the phonon scattering effect and leads to the decrease of the thermal conductivity of the Cu-Ni alloys lattice.This effect is more significant in alloys with higher Ni content,indicating that lattice disorder and mass mismatch in Cu-Ni alloys further magnify phonon scattering.In summary,the study of mechanical properties(such as yield strength)and lattice thermal conductivity of materials before and after irradiation is not only helpful to evaluate the performance changes of materials in the irradiation environment,but also can provide a scientific basis for optimizing material design and improving its anti-irradiation performance.This is of great significance for ensuring nuclear energy safety,optimizing thermal management design,and addressing future extreme environmental challenges.At the same time,these studies have also promoted the development of materials science and related disciplines,with far-reaching influence.更多还原