初始压入位置对Ni基单晶合金纳米压痕影响研究

摘要

针对Ni基单晶合金建立初始压入γ相的γ/γ′模型和初始压入γ′相的γ′/γ模型，采用分子动力学方法模拟金刚石压头压入两种模型的纳米压痕过程，计算两种模型[001]晶向硬度.采用中心对称参数分析两种模型(001)相界面错配位错对纳米压痕过程的影响.结果显示：弛豫后，两种模型(001)相界面错配位错形式不同，其中γ′/γ模型(001)相界面错配位错以面角位错形式存在；压入深度在0.930 nm 之前，两种模型(001)相界面错配位错变化不大，压入载荷-压入深度及硬度-压入深度曲线较符合；压入深度在0.930 nm之后，γ′/γ模型(001)相界面错配位错长大很多，导致相同压入深度时γ′/γ模型比γ/γ′模型压入载荷和硬度计算结果小；压入深度在2.055 nm之后，γ/γ′模型(001)相界面错配位错对γ相中位错进入γ′相有阻碍作用，但仍有部分位错越过(001)相界面进入γ′相中，γ′/γ模型(001)相界面处面角位错对γ′相中位错进入γ相有更明显的阻碍作用，几乎无位错越过(001)相界面进入γ相中，面角位错的强化作用更明显，所以γ′/γ模型比γ/γ′模型压入载荷上升速度快.%Ni-based single crystal line alloy is constituted with γ phase and γ′ phase in the form of coherency. Since an indenter for two-phase coherent structure is bigger than the usual nano-scale indenter, the press location of indenter may be unclear in nanoindentation simulation. Bothγphase andγ′ phase may be pressed initially, and the mechanical properties shown are different because of the initial press locations. The nanoindentation of Ni-based single crystal line alloys is simulated by molecular dynamics method. Two models are used to study about the hardness in [001] crystal orientation, one is the modelγ/γ′with the initial indentation onγphase, and the other is the modelγ′/γwith the initial indentation on γ′ phase. The influence of misfit dislocation at (001) interface on nanoindentation of the two models is analyzed using a center-symmetry parameter. Results show that the misfit dislocation shape of the two models are different after relaxation. Lomer-Cottrell dislocation occurs on (001) interface in theγ′/γmodel. Before 0.930 nm press depth is reached, there is little change in the (001) interface misfit dislocation of the two models. Relationship between press load and press depth is similar for the two models, and it is the same in the relationship between hardness and press depth. After press depth reaches 0.930 nm, the misfit dislocation at (001) interface for modelγ′/γgrows big, which results in a smaller press load and a smaller hardness computation in the model γ′/γ than that in model γ/γ′. When the press depth reach 2.055 nm, we find only a small amount of dislocations in γ phase that can go into γ′ phase since the misfit dislocation at (001) interface in model γ/γ′ hinders the process. However, none of dislocations can go intoγ phase because of the prevention caused by Lomer-Cottrell dislocation at the (001) interface in the model γ′/γ. That means the Lomer-Cottrell dislocation reinforces the material obviously. So the press load in model γ′/γ grows faster than that in modelγ/γ′.