Molecular Dynamics Study On Fatigue Shear Deformation Of Nickel Metal Under Hyper-gravity Condition

There is a big difference between the mechanical properties of materials under dynamic loading and static mechanical properties.Dynamic mechanical properties play a crucial role in the fatigue behavior of superalloys.In order to study the effect of hyper-gravity loading on the dynamic mechanical properties of metallic nickel,the molecular dynamics method was used to systematically study the cyclic shear deformation and the fatigue propagation behavior of metallic nickel cracks under hypergravity conditions.In this paper,the fatigue shearing behavior of the[001]（010）single crystal nickel crack model at 10 K temperature and different supergravity intensities is investigated.It was found that the hypergravity load would produce a gradient of tensile stress along the hypergravity direction,leading to anisotropy in crack propagation,but not changing the deformation mechanism of the crack.With the increase of the supergravity,the crack propagation time under fatigue loading continues to advance.The critical stress intensity factor and fatigue crack life are inversely proportional to the supergravity strength.With the increase of supergravity strength,the crack length reaches the maximum value at 4?10¹²g,and the crack propagation is inhibited at5?10¹²g.This paper discusses the effect of temperature and the interaction of loading direction and supergravity on shear fatigue cracks in[001]（010）single crystal nickel.The results show that the[001]（010）crack propagation undergoes a brittle-to-ductile transition when the temperature increases from 10 K to 300 K.When the temperature reaches 600 K and above,crack propagation is inhibited at high temperature.The dislocation emission time of cracks decreased with the increase of temperature.At the same time,shear fatigue loading along the[110]（1?10）and[101]（010）directions was carried out on the single-crystal nickel crack model,and it was found that the deformation mechanism of the crack model was changed due to supergravity loading.The[110]（1?10）crack model is transformed from the slip plane deformation mechanism dominated by dislocation loops in a non-gravity environment to a deformation mechanism dominated by dislocation lines in a hypergravity environment.In the[101]（010）crack model,the size of the hyper-gravity affects the uneven distribution of the slip zone along the direction of the hyper-gravity.In order to explore the effect of grain boundaries in the shear deformation process of the crack model,theΣ3<110>{11?1}、Σ5<001>{120}andΣ11<110>{11?3}twin crystal models were constructed in this paper.The shear deformation process of the crack model under zero gravity and 5?10¹²g supergravity loads is simulated.In theΣ3<110>{11?1}twin crystal model,the plastic deformation mechanism during shear loading is dominated by crack-emitting dislocations.In theΣ5<001>{120}model,the main plastic deformation mechanism is the nucleation of grain boundary dislocations.In theΣ11<110>{11?3}model,in the zero gravity environment,dislocations first nucleate at the grain boundaries,while in the hypergravity environment of 5?10¹²g,the cracks preferentially emit dislocations.In this paper,a hypergravity field is constructed by virtual simulation,and the shear fatigue behavior of metallic nickel is studied by setting different hypergravity magnitudes.The interaction between the temperature effect and the loading direction and the hypergravity is discussed separately.The interaction between the crack and the grain boundary is studied by simulating the shear crack propagation behavior of the grain boundary and the crack model under different hypergravity environments.The above work realizes the characterization of the fatigue performance of metallic nickel under hypergravity conditions,and provides theoretical support for formulating the design and service strategy of turbine blades.