Molecular Dynamics Study On Mechanical Properties Of Nickel Based Single Crystal Superalloys Containing Defects

Nickel（Ni）-based single-crystal superalloys are widely used in aerospace turbine blade materials due to their excellent mechanical properties.Nickel-based single-rystal high-temperature alloys are mainly composed ofγ′-Ni₃Al precipitation phase embeddingγ-Ni matrix phase composition.Due to different lattice parametersγ/γ′,a mismatch dislocation network is formed at the interface,and research has shown that the mismatch dislocation network can effectively hinder the movement of dislocations,which will have a significant impact on the deformation behavior and mechanical properties of nickel based single crystal high-temperature alloys.Voids and cracks,as inevitable defects in actual production and use,also have a serious impact on the mechanical properties of materials.Due to size limitations,traditional experiments cannot observe dislocation changes and the micro deformation process of alloys.However,molecular dynamics（MD）methods can observe atomic motion information in real-time,obtain detailed motion information,and obtain physical quantities that cannot be measured in traditional experiments.Therefore,this article adopts molecular dynamics simulation to study the deformation mechanism of Nickel-based single-crystal high-temperature alloys with defects under different loads,temperatures,and strain rates,aiming to provide a theoretical basis for the interpretation of experimental phenomena and material design applications.Based on the actual structure of Nickel-based single-crystals,theγ,γ′andγ/γ′models with central cracks were established.MD was used to explore the influence of matrix（γ,γ′andγ/γ′）,strain rate(1×10⁹s^-1～3×10⁹s^-1)and temperature（300 K～900 K）on crack propagation.It is observed that the dislocation and slip systems in theγ′model were concentrated near the crack,resulting in rapid expansion of the dislocation,resulting in the fastest crack growth rate and earliest occurrence of fracture.However,theγandγ/γ′models hinder the crack propagation due to the combined effects of Lomer-Cottrell lock and stacking fault tetrahedron structure and Stair-rod dislocation,resulting in relatively slow crack propagation rate.Increasing strain rate and/or decreasing temperature can lead to higher yield stress and Young’s modulus for models with central cracks.In addition,strain rate and temperature can change the direction of crack growth,and at higher strain rates and temperatures,the crack tip will slip intoγphase,leading to cracks in theγphase expansion.A Ni-based single-crystal superalloy model containing voids was established to simulate the stress strain curves and microstructure of the[100],[110],and[111]oriented models under uniaxial tensile and compressive loads at the same deformation temperature and strain rate,and to study the tension compression asymmetry.The Young’s modulus of the material exhibited obvious anisotropy under both tensile and compressive loads,but the yield strength of the material only showed obvious anisotropy under tensile loading.Under tensile and compressive loads,the influence of temperature and strain rate on the mechanical properties of the[100],[110]and[111]orientation models were consistent,and there was no obvious tensile-compression asymmetry,the temperature increases or the strain rate decreases,and the yield strength increases.Different orientation models have different asymmetry of tension and compression.Under compressive load,the[100]oriented model has relatively more slip planes and is more prone to slip.The tensile yield strength of the[100]oriented model is higher than that of compression;[110]The orientation model has significantly more slip surfaces under tensile load than under compression,making it easier for dislocations to slip under tensile load,resulting in lower model strength;The tensile yield strength of the[110]orientation model is lower than that of compression,and the distribution of slip planes is not significantly different under the tensile and compressive conditions of the[111]orientation model.Therefore,the yield strength of the model is also not significantly different.The tensile yield strength of the orientation model[111]is close to that of compression.Established different shape void models and conducted tensile simulations on them.It was found that the Young’s modulus of different shape void models is the same,but the yield strength is different.Among them,the yield strength of the circular void model is the largest,followed by the square void model,and the diamond void model is the smallest.Compared to the circular and square void models,the diamond void model has acute angles perpendicular to the tensile direction,with a large number of dislocations and severe stress concentration.Therefore,under the same strain rate,the diamond void model is more likely to be pulled and deformed,and the degree of deformation is greater.