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Figure 1.  The GB1 model with a mean grain size of 10.86 nm contains 16 randomly oriented grains with 2814985 atoms. The atoms are color-coded by the grain ID. GI stands for grain interior.

Figure 2.  The compression behavior and failure process of the GB1 model. (a) The stress–strain relationship. I, II and III represent elastic deformation, quasi-plastic deformation and failure, respectively. (b) The average angle of three-atom chains and intra-icosahedra change with strain. (c) The structure at the compression strain ε = 0.030, which remains relatively unchanged. (d) The structure at ε = 0.076, where quasi-plastic deformation initiates. (e) The structure at ε = 0.164, where the von Mises stress reaches its maximum value. (f) The structure at ε = 0.200. (g) The structure at ε = 0.320 is completely damaged. A and B denote the two grains presented in Figs. 4 and 5.

Figure 3.  Equation of state (EOS) for the GB1 model. (a) Pressure–volume data from our simulations and the Murnaghan EOS function. (b) Temperature–pressure relationship compared with the results of previous studies. I, II and III represent the elastic deformation, quasi-plastic deformation and failure, respectively.

Figure 4.  The local structural evolution with structures including grain A and grain B, colored by the von Mises shear strain map at various strains. (a) The structure before the structural change. (b) The structure at 0.076 strain where GB sliding occurs. (c) The structure at 0.115 strain where intergranular amorphization occurs. (d) The structure at 0.164 where intragranular amorphization forms in grain A. The magenta balls represent the atoms B1–B4 in different icosahedra near the GB.

Figure 5.  The local structural evolution within the GB involving grain A and grain B, with structures colored by the axial stress map in white and black. (a) The structure at 0.076 strain, where the chains suffer greater stress in both grain A and grain B. (b) The structure at 0.115 strain, where the chains in grain A form new B–B bonds with neighboring icosahedra. (c) The structure at 0.150, where intragranular amorphization has formed in grain A. (d) The structure at 0.164, where the chains in grain B form new B–B bonds with neighboring icosahedra. The magenta balls represent the atoms B1–B4 in different icosahedra near the GB, and the green balls mark the C1–B5–C2, C3–B6–C4 chains.

Figure 6.  The radial distribution function of the initial and deformed nB₄C at various strains.

Figure 7.  The compression behavior for three nB₄C models. (a) Stress–strain relationships. (b) The Hall–Petch behavior. (c) P–V relationship for nB₄C and single-crystal B₄C. (d) T–P relationship for nB₄C and single-crystal B₄C.

Figure 8.  Strain rate dependence of nB₄C. (a) Von Mises stress versus strain. (b) Compressive strength versus strain rate.