含孔洞缺陷的单晶镍拉伸行为:孔洞生长和聚集机理

Tensile Behavior of Single-Crystal Nickel Containing Void Defects:Void Growth and Coalescence Mechanisms

利用分子动力学模拟研究了孔洞中心形成平面与加载方向的夹角(θ)对单晶镍在单轴拉伸下孔洞生长和聚集行为的影响及机理。结果表明:单晶镍的屈服应力和平均流动应力随着夹角θ的增加而下降,应力下降速率随着夹角θ的增加而加快。当夹角θ=90°时(加载方向垂直于孔洞中心平面时),单晶镍中孔洞独立生长时间最短且孔洞之间最先发生聚集,导致其最易进入软化阶段,这是由于夹角θ=90°时,单晶镍中最快的孔洞体积分数增长速率和损伤演化速率。当夹角θ=90°时,单晶镍中1/6<112>(Shockley)位错长度的显著降低,以及fcc晶体结构的原子数目向Other和hcp晶体结构的最大转变速率,导致θ=90°时单晶镍的损伤演化速率最快且损伤程度最剧烈。值得注意的是,当θ=90°时单晶镍中孔洞最易聚集是由于该条件下孔洞表面受到更大的拉应力作用。通过该工作,旨在揭示金属材料在高应变率下的孔洞聚集行为及机理,并对揭示其软化行为和断裂机理提供了理论指导。

Molecular dynamics simulations were used to investigate the effect and mechanism of the angle(θ)between the plane of void center formation and the loading direction on void growth and coalescence behavior in single-crystal nickel under uniaxial tension.The results show that the yield stress and average flow stress of single-crystal nickel decrease with increasingθ,and the rate of stress decrease accelerates with increasingθ.Whenθ=90°(loading direction perpendicular to the plane of void center),the independent growth time of voids in single-crystal nickel is the shortest and void coalescence occurs first,leading to the easiest way to entering the softening stage.This is due to the fastest growth rate of void volume fraction and damage evolution rate in single-crystal nickel whenθ=90°.Whenθ=90°,the significant reduction of 1/6<112>(Shockley)dislocation length and the maximum transformation rate of atomic number from fcc crystal structure to Other and hcp crystal structures in single-crystal nickel lead to the fastest damage evolution rate and the most severe damage level.It is worth noting that voids in single-crystal nickel are most likely to coalesce whenθ=90°,due to the larger tensile stress on the void surface under this condition.