单晶铜中的类层错四面体稳定性

Stability of Stacking-fault-tetrahedron-like Structures in Single Copper Crystal

层错四面体作为受核辐照作用金属材料中一类常见的三维缺陷,会极大的改变材料塑性变形行为.论文借助分子静力学和分子动力学方法,针对不同构型、不同尺寸的类层错四面体,考察了不同形状空位团簇演化为类层错四面体的位错反应机理和形成能变化趋势,研究了类层错四面体附近空位形成能分布特征和最小空位形成能随类层错四面体尺寸增大的变化规律,分析了含不同构型、不同尺寸的类层错四面体铜单晶体的微观变形机理和单晶体屈服应力随类层错四面体尺寸增大的变化规律.研究发现:类层错四面体通过Silcox-Hirsch机制形成,且经历了空位团簇坍塌、Frank位错环分解和Shockley位错交汇形成层错四面体棱边三个过程;类层错四面体附近最小空位形成能随着类层错四面体尺寸变化而变化,且变化趋势与类层错四面体构型在稳态、亚稳态和非稳态之间过渡相关,稳态无尖端类层错四面体的最小空位形成能变化趋势表现出明显的尺寸效应;剪切会导致含类层错四面体铜单晶体产生两类层错四面体位错开动模式,即:斜面Shockley偏位错滑移和层错四面体底面压杆位错分解,且含类层错四面体的单晶体屈服应力基本上随着类层错四面体尺寸增大而逐渐减小.

Stacking fault tetrahedron(SFT)is the most common type of vacancy-clustered 3Ddefects in irradiated face-centered-cubic(FCC)metals and alloys,which can play an important role in the mechanical properties of metallic materials.In this study,molecular statics(MS)and molecular dynamics(MD)simulations are carried out to investigate the stability of stacking-fault-tetrahedron-like structures(SFTLSs)when they interact with vacancies and are under shear.Firstly,different sizes and SFTLSs are created in a single copper crystal by considering different sizes and shapes of vacancy clusters on the(111)plane.We analyze the dislocation evolution mechanisms and variations of formation energies of SFTLS with different shapes during their formation processes.Then,we discuss the vacancy formation energy distribution in the vicinity of an SFTLS as well as the variation of the lowest vacancy formation energy vs the size of SFTLS.Finally,the deformation mechanism and yield stress variation of single copper crystal embedded with an SFTLS of different sizes are analyzed.It is found that SFTLS forms through the process of vacancy cluster collapse,Frank loop dissociation and formation of SFTLS edge due to the intersection of Shockley partial dislocations,namely the Silcox-Hirsch mechanism.The site at which the vacancy formation energy is lowest in an SFTLS changes as the size of SFTLS increases,and the lowest vacancy formation magnitudes are strongly connected to the transition between stable,metastable and unstable states of SFTLS.Moreover,remarkable size effect in the variation of lowest vacancy formation is seen in the stable state of no-apex SFTLS.Furthermore,there are two dislocation nucleation mechanisms corresponding to the incipient plasticity of single crystal with an SFTLS under shear,i.e.glide of Shockley partials on the tilt(111)planes and dissociation of stair-rod dislocations on the basal plane of an SFTLS.The yield stress of single crystal with an SFTLS basically decreases as increasing the size of SFTLS.The findings of this work may be helpful in revealing the mechanical properties of irradiated FCC metals.