| 022Cr17Ni12Mo2 alloy steel is a kind of austenitic stainless steel,because the added Mo element leads to the corrosion resistance and high temperature strength,and makes it still keep its excellent physical properties at high temperature.022Cr17Ni12Mo2 alloy steel is also widely used in industrial instruments because of its good strength and corrosion resistance.However,in addition to high strength,engineering materials also need good plasticity and toughness to prevent hidden problems such as fracture accidents during maintenance.The low plasticity of 022Cr17Ni12Mo2 alloy steel limits its application in many advanced technologies to some extent.Therefore,this paper will study the plastic behavior dislocation dynamics of 022Cr17Ni12Mo2 alloy steel under impact loading.Firstly,the MD method is used to establish the polycrystalline model of022Cr17Ni12Mo2 alloy steel,the appropriate system synthesis and its potential function are selected for model relaxation,and the DDD method is used to establish the dislocation high strain model.Secondly,the dynamic mechanical response and microstructural evolution of022Cr17Ni12Mo2 alloy steel at different impact velocities are studied at the atomic scale by means of molecular dynamics simulations.The results show that plastic waves appear within the material when the impact velocity is greater than 0.5 km/s.The main reason for the plastic deformation is that the impact load exceeds the Hugoniot elastic limit of the material,and the deformation of the microstructure is controlled by the nucleation and slip of dislocations at this time.When the impact velocity is greater than 0.75km/s,there are both elastic and plastic waves,more dislocation junctions and LC locks begin to appear,dislocation motion is restricted,and plasticity is reduced.When the impact velocity is greater than 1.5km/s,more slip systems are activated due to the sharp increase of shear stress,which proliferates dislocations and enhances plasticity.The distribution of Mo elements makes the grain boundaries more stable and affects the plastic deformation of the material.This work is an important guide to the enhancement of the strength and toughness of 022Cr17Ni12Mo2 alloy steel under impact loading and the failure mechanism of the material.Finally,the plasticity of 022Cr17Ni12Mo2 alloy steel under the conditions of high strain and high temperature was investigated by dislocation dynamics on the medium and long scales.For the samples under dynamic impact experiments of SHPB,a high density of dislocation inhomogeneous distribution was observed inside the samples by TEM,HRTEM and EBSD characterization,along with more deformation twins and L-C locks.After the comparative analysis of simulation and experiment,from the cross-slip mechanism of dislocations,the 022Cr17Ni12Mo2 alloy steel is activated at high strain rate with high frequency of activated slip system,and the dislocation multiplication drives the strain hardening rate to increase.The plastic deformation at the same strain rate is mainly controlled by the activated initial dislocations.At high temperature,the shear stress and critical resolved shear stress change according to the dislocation multiplication.As the temperature increases into the second stage of strain hardening,the cross-slip is activated and starts to annihilate the absorbed dislocations,resulting in the initial temperature at this stage being inversely proportional to the rate of increase of the dislocation density,and the strain hardening rate increases with the increase of the initial temperature.Meanwhile,this paper analyzes the existence of yield stresses with irrelevant strain rates impeding the dislocation movement at ultra-high strain rates under the assumption of different initial dislocations.The predictions result of the model are in general agreement with experiments,which can provide a reference for the study of 022Cr17Ni12Mo2 alloy steel in extreme environments. |
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