考虑相界效应的Ni基单晶合金纳米压痕模拟

Nanoindentation simulation of Ni-base single-crystal superalloy with the consideration of interface effect

利用分子动力学方法分别模拟金刚石压头压入Ni模型和Ni基单晶合金γ/γ′模型的纳米压痕过程,通过计算得到两种模型[001]晶向的弹性模量及硬度.采用中心对称参数分析不同压入深度时两种模型内部位错形核、长大过程以及Ni基单晶合金γ/γ′(001)相界面错配位错对纳米压痕过程的影响.结果显示:压入深度0.641 nm之前,两种模型的压入载荷-压入深度曲线相似,说明此时相界面处的错配位错对纳米压痕过程的影响很小;压入深度0.995 nm时,在错配位错处发生位错形核,晶体在γ相中沿着{111}面滑移,随即导致Ni基单晶合金γ/γ′模型压入载荷的下降,并在压入深度达到1.487 nm之前低于Ni模型相同压入深度时的压入载荷;压入深度从1.307 nm开始,由于相界面错配位错的阻碍作用,Ni基单晶合金γ/γ′模型压入载荷上升速度较快.

Nanoindentation made by diamond indenter on pure Ni and the γ/γ＇ -phase in a Ni-base single-crystal superalloy is simulated respectively with molecular dynamics method. Elasticity modulus and hardness of the two models are calculated. Initiation and growth of dislocations and the influence of misfit dislocations of γ/γ＇-phase in Ni-base singlecrystal superalloy at different indentation depths are analyzed with center symmetry parameter. Results show that the relationship between indentation load and depth for the two models is similar when the indentation depth below 0.641 nm, indicating that the misfit dislocation on interface little affects the indentation. When the indentation depth reaches 0.995 nm, the dislocation nucleation can be found in misfit dislocations and the crystals that have slipped along {111} -oriented crystal surface in γ-phase. As a result, the indentation load of the latter model decreases and is smaller than that in pure Ni model before the indentation depth reaches 1.487 nm. When the indentation depth reaches 1.307 nm, owing to the inhibition caused by misfit dislocations at the interface, the indentation load for the γ/γ＇-phase model in Ni-base single-crystal superalloy increases rapidly.