Computer Simulation Of Radiation Resistance Of Tungsten Under Strain Field

Tungsten(W)and its alloys have important application prospects in future advanced nuclear energy systems.In the extreme environment of nuclear energy systems,W would be exposed to energetic particle bombardment,high temperature and stress field,etc.,which would change its microstructure and properties,and hence affect the long-term safety of systems.Therefore,it is important to study the defect evolution mechanism and evaluate the radiation resistance of tungsten under stress/strain field.In this thesis,the radiation resistance of tungsten in different strain fields and the effects of void and dislocation loop on its mechanical properties were studied using molecular dynamics(MD)simulations.The primary contents and results are as follows:1.The formation energies of point defects(self-interstitial atom(SIA),He interstitial and vacancy),the binding energy of divacancy and the threshold displacement energy((9)in tungsten under hydrostatic strain fields have been calculated.With strain varying from-2%(compressive)to 2%(tensile),the formation energies of SIA and He intersititial decreased rapidly,while the formation energy of vacancy increased slightly.Divacancy prefers to bind at 1st nearest-neighbor in tensile strains,and at 2nd nearest-neighbor in compressive strains.The minimum (9 lay in <100> or <111> directions,and (9 decreased with the hydrostatic strain from-2% to 2%.2.The displacement cascade behaviors of tungsten in hydrostatic strains and uniaxial strains parallel/perpendicular to the primary knock-on atom(PKA)direction have been investigated at 100,300,500 and 1000 K.The hydrostatic strain has a larger influence on the displacement cascade in tungsten than the uniaxial strain.When the uniaxial strain was perpendicular to the PKA direction,the displacement cascade was not affected by the strain.With hydrostatic strains or the uniaxial strain parallel to the PKA direction varying from-2% to 2%,the number of Frenkel pairs,the clustered SIA fraction and the average size of defect clusters increased,while the clustered vacancy fraction didn’t change.Uniaxial strains led to the preferential orientation formation of SIAs and their clusters.The fractions of SIAs and their clusters oriented along the strain direction increased with the increasing tensile strain,while the fractions decreased with the increasing compressive strain.The influence of the strain on radiation damage decreased with the increasing temperature.3.The stress-strain responses of W in <100>,<110> and <111> directions at 300 K and the effects of dislocation loops and voids have been studied.<111> was found to be the strongest direction,whereas <100> to be the weakest.The presence of loops and voids degraded the tensile strength of W.As the radius of the SIA loop increased,the tensile strength decreased.As the void radius increased,both tensile strength and elastic modulus decreased.