Evolution Of Radiation Defects And The Interaction Between Stacking Fault Tetrahedron And Grain Boundaries In Metal

The structural materials of spacecraft tend to be affected by the high-energy particle because of the use of nuclear power and the space irradiation environment when the spacecraft in the deep space exploration.This may produce a large number of micro-defects in the spacecraft structure material,which may not only reduce its material performance,the service life and structure reliability,may also affect the spacecraft ability of detection efficiency.Therefore,it is of great theoretical significance and application value of engineering to understand the irradiation defects evolution mechanism and the basic structural properties of irradiation defects,and to clarify the reaction mechanism between irradiation defects and the correlation between mechanical behavior of materials by means of micro-scale simulation.In this paper,the radiation defect evolution mechanism of nanotwinned copper in the process of multiple cascade collision is studied.The shear stability of stacking fault tetrahedron(SFT) near different grain boundaries is analyzed.Furthermore,the influence of the SFT size,SFT structure and stacking fault energy(SFE)on the shear deformation mechanism of SFT is also discussed.sand energy of the laminated tetrahedron on the shear deformation mechanism of the laminated tetrahedron are discussed.The main research contents and conclusions are as follows:1)Multiple collision cascades(MCC)of nanotwinned(nt)Cu with different twin spacings are performed to model the response of nt Cu upon a radiation dose of 1 displacement per atom(dpa).The microstructural radiation defect evolution and the some average properties of defect clusters at the different radiation doses are analyzed.The formation and elimination mechanism of SF during radiation is discussed.The research results show that the interaction of coherent twin boundaries(CTBs)with point defects,dislocation and SFT may decrease the radiation defects density greatly.Besides,the decrease of the twin spacings may hinder the formation and growth of SFT.In addiation,the interactions of CTB and radiation defects may induce the migration of CTBs.Moreover,the potential formation and elimination mechanisms of stacking fault are found to be due to the climb of Frank partial dislocation and glide of Shockley partial dislocations.2)We present mechanism studies of SFT in CTB bicrystal copper under shear.The shear stability of SFT is investigated.Detailed analysis of atomistic structures involved in CTB migration and SFT configuration evolutions during the shear are made.A complete transformation mechanism analysis of SFT is assisted by dislocation motions and atomic diffusions in SFT area.It is found that CTB bicrystal embedded with a larger size of SFT have a smaller critical stress at their incipient plasticity.Dislocation motion begins with the dissociation of two stair-rod dislocations on the SFT basal plane while the CTB migration direction with respect to SFT,resulting in the atomic diffusions,determines the final configuration of SFT.The continuous migrations of CTB towards and away SFT respectively lead to the collapse and flip over of SFT.3)Molecular dynamics simulations are performed to investigate the size-dependent stability of SFT in four different metal CTB bicrystals under shear.The influence of SFE on the SFT transformation is analysed.It is found that different size-dependent SFT stability stems from the competition between CTB migration and SFT dissociation at the incipient plasticity of CTB bicrystal.For SFT of any sizes in Cu and Ag,and larger size SFT in Ni,initial CTB always keeps still and SFT dissociates at the incipient plasticity.For SFT of any sizes in Al and smaller size SFT in Ni,SFT always keeps stable so that CTB migrates instead.SFT size effect transforms the deformation mechanism at the incipient plasticity from CTB migration to SFT dissociation in Ni.4)We present the transformation of SFT near four Cu symmetric tilt grain boundaries(GBs)under shear.Atomistic structures involved in GB deformation and SFT configuration evolutions during the shear are analyzed.Our results show that the presence of SFT has small influence on critical stress corresponding to the incipient plasticity of GB bicrystal.Because GB deformation such as migration,sliding and structure evolvement occur at a smaller external shear stress not large enough to activate the destroy of SFT,and SFT near four GBs transforms only when interacting with partial dislocation or GB.Besides,the presence of an SFT does not substantially change the deformation modes of these four GBs.For GB deforming in the complex mechanism due to atom-shuffling,partial dislocation nucleation and local GB dissociations,GB or dislocation may interact with SFT and induce the destory of SFT.5)The formation mechanism of three kinds of SFTs is analyzed.The structural stability and shear deformation evolution mechanism of SFT are discussed.The result shows that no-apex SFT,one-apex SFT,and two-apex SFT can evolute from the trapezoid,triangle,parallelogram,respectively.The larger the height of the trapezoid,the less the stability of the no-apex SFT.The structural stability of a complete one-apex SFT.The closer the adjacent side length is the lower the structural stability of two-apex SFT is.When the number of identical vacancies is contained in three different structural SFT,the shear stability of no-apex SFT is the lowest,while the shear stability of two-apex SFT is the highest.