外应力场下NiAl合金微裂纹动态扩展的分子动力学模拟

目的 对NiAl合金中不同晶体取向的裂纹扩展动力学行为进行原子尺度研究，明晰在塑性变形过程或实际应用过程中裂尖的脆性解理和塑性变形行为，为研究NiAl合金的塑性变形行为和评估服役寿命提供理论基础。方法 建立了4种不同取向的裂尖模型，其扩展取向分别为(010)001]、(0■1)100]、(010)101]、(01■)011]，用分子动力学方法对上述模型进行模拟，采用Gear算法计算原子在真实受力状态下的运动情况。结果 在NiAl合金中，微裂纹在外载作用下的裂尖反应强烈依赖于裂纹取向（裂纹面及裂纹前沿方向）。{110}裂纹面的裂纹构型易于脆性解理扩展；{100}裂纹面的裂纹构型具有一定的塑性，裂尖处可形成位错发射，位错的出现可以协调塑性变形，模拟结果与实验观察相一致。结论 裂纹的晶体取向对裂尖的马氏体相变行为有重要影响，当裂纹前沿为<100>方向时，原子在裂纹前端的{100}滑移面上运动，诱导B2相转变成L10相，产生马氏体相变，这种马氏体相变有利于相变增韧，能够促进裂尖处位错发射，可提升材料塑性和服役寿命。

Molecular Dynamics Simulation of Micro-crack Propagation in NiAl Alloy under External Stress Field

The work aims to study the crack propagation dynamics behavior in NiAl alloy with various crystal orientations at atomic scale, clarify the brittle cleavage and deformation behavior of crack tip during plastic deformation or practical engineering application and provide a theoretical basis for the study of plastic deformation behavior and service life evaluation of NiAl alloy. In this paper, four crack tip models with different orientations were established, which were (010)001], (01) 100], (010)101] and (01)011], respectively. The above models were simulated by molecular dynamics method. Gear algorithm was adopted to calculate the motion of atoms under real stress state. The results showed that the crack tip reaction of micro-cracks in NiAl alloy under external loading was strongly dependent on the crack orientation (crack surface and crack front direction). The crack model of {110} crack plane was prone to brittle cleavage propagation. The crack configuration of {100} crack surface had a certain plasticity. Dislocated emission and coordinated plastic deformation could be formed at the crack tip. The simulation results were consistent with the experimental observations in literature. The crystal orientation of the crack has an important effect on the martensite transformation behavior at the crack tip. When the crack front is <100>, the atoms move on the {100} slip plane at the crack front, inducing the transformation of B2 into L10, and thus producing martensite transformation, which is beneficial to the effect of phase transformation and toughness, and can promote the dislocated emission at the crack tip, and is beneficial to improve plasticity and service life of NiAl material.