Atomistic simulations of the mechanical deformation of irradiation-amorphized silicon carbide

Irradiation-induced atomic-scale defects and lattice disorder in Silicon Carbide (SiC) can significantly affect the material's mechanical properties. Currently there lacks a unified physical model capable of describing the law in which the properties of SiC scale with the accumulation of defects, especially in terms of the underlying physical mechanism. To develop fundamental models that are capable of describing the various physical properties of SiC as a function of microstructural change, molecular dynamics simulations of uniaxial tension were performed on a series of irradiation-amorphized SiC (a-SiC) samples with a range of imposed chemical disorder, which is defined as the ratio between the number of homonuclear bonds and heteronuclear bonds (x≡N_C-C/N_Si-C). With increasing chemical disorder, significant alternation of mechanical response of a-SiC has been detected in terms of increasingly pronounced plastic flow. Meanwhile relevant mechanical properties, including Young's modulus, strength, yield stress and strain, as well as failure strain scale monotonically with chemical disorder while in distinct manners. Specifically slight chemical disorder (x=0.045) could induce substantial reduction of Young's modulus up to -2%, whereas strength basically linearly varies with chemical disorder until x≈0.5 upon which the variations in mechanical properties tend to saturate. Further examination of the evolution of atomic structure of a-SiC reveals a crossover of deformation mechanisms from homogeneous elastic deformation to localized plastic flow, which accounts for the strong chemical disorder dependence of the mechanical properties as well as mechanical responses of amorphous SiC. This crossover is also manifested in switching of fracture mode from brittle failure dominated by lattice instability in the ligaments between topological disordered clusters to nanoductile failure preceded by percolation of nanocavities. Employing chemical disorder to measure the defect concentration of a-SiC could contribute to the quantification of the correlation between mechanical properties and the corresponding defective a-SiC structure. Moreover the distinct scale laws shown by Young's modulus and strength with chemical disorder and the proposed critical chemical disorder threshold could benefit the quantitative evaluations of the mechanical performances of SiC components in different irradiation environments.