Molecular Dynamics Study Of C/Cr Element Segregation At Bcc-Fe Grain Boundary

Early cracks occur along grain boundaries during deformation of metallic materials,resulting in material fracture,which reduces ductility and strength of materials.Segregation of alloying elements on grain boundary is an important factor to change grain boundary properties.The grain boundary segregation of alloying elements may strengthen or weaken grain boundary properties.The segregation of different alloying elements has different effects on grain boundary strength and material toughness.C/Cr is an important alloy element in metal materials.In previous studies,the effect of C/Cr element grain boundary segregation on the mechanical properties of BCC-Fe grain boundary has rarely been reported.In this paper,the tensile and shear deformation of ?3(111),?3(112),?3(111)/(11-5),?3(112)/(55-2)grain boundaries of Bcc-Fe have been studied by means of molecular dynamics.The effects of different vacancies(10%,20%,30%,40%,50%)on grain boundaries and the segregation content of different C/Cr elements at grain boundaries on grain boundaries were analyzed at different temperatures(10K,300 K,600K).The results are as follows.Tensile stress-strain curves of unbiased ?3(112)grain boundaries at 10 K and 300 K show that the tensile stress first increases with the increase of strain,then fluctuates in a small range with the increase of strain,and finally increases twice and then decreases abruptly(model fracture).The presence of vacancies or C significantly alters this property.The presence of vacancies or C causes the tensile stress of the ?3(112)grain boundary to increase as the strain increases,and then suddenly decreases(fracture),and there is no phenomenon of secondary stress increase.The presence of vacancies or the segregation of C(a certain number of Fe atoms on the C-exchange grain boundary)will significantly change the defect-free?3(111),?3(112),?3(111)/(11-5),?3(112)/(55-2)tensile strength,tensile elongation,shear strength,and ultimate shear strain at grain boundaries.For ?3(111)and ?3(111)/(11-5)grain boundaries,at 10 K,the reduction of the tensile and shear strength of the vacancies to the two grain boundaries(relative to the unbiased grain boundaries)decreases with theentry of C into the vacancies.For ?3(112),?3(112)/(55-2)grain boundaries,at 300 K and600K,the reduction of vacancy to grain boundary tensile and shear strength(relative to the unbiased polycrystalline boundary)will follow The C element is reduced by entering a vacancy.For the ?3(111),?3(111)/(11-5)grain boundaries,at 10 K and 300 K,the tensile and shear strength of the unbiased polycrystalline grain boundary is higher than that of the Cr-copolymerized grain boundary.For the ?3(112),?3(112)/(55-2)grain boundaries,at10 K,the tensile and shear strength of the unsegregated grain boundaries is higher than that of the Cr-copolymerized grain boundaries.Under the same temperature conditions.The increase or decrease of tensile strength,elongation,shear strength and shear limit strain(relative to unbiased grain boundaries)of Cr element grain boundary segregation are different.It varies with the change in Cr segregation content.