Effect of BN content on the deformation mechanism of amorphous SiBN ceramics: A molecular dynamics study

The effects of BN content on the deformation mechanism of amorphous SiBN ceramics are investigated using molecular dynamics simulations. Simplex analysis shows that NB simplexes correlate with increased porosity. Average local entropy provides insight into atomic behavior that liquid-like regions are less dense than the others, with the existence of large simplexes (LS) with R _S ≥ 2.6 Å. Our calculations on elastic properties are consistent with ab initio and experimental results. Uniaxial tensile tests were performed to understand deformation, which predominantly occurs in the liquid-like region. The formation and development of high strain spots, STZs, and SBs are explained by the combination of quadrupolar rotational fields and local entropy. Liquid-like atoms have higher local entropy and strain, which induces surrounding rotation, then develop into SBs along the direction of regions with high rotational angle. LS aggregate and form tunnels within the liquid-like regions, which also leads to other regions around more dense. These tunnel formations along the SBs contribute to crack propagation. Si ₃ BN ₅ shows higher stability even with more pores due to the presence of the SiN phase, while Si ₃ B ₂ N ₆ and Si ₃ B ₅ N ₉ exhibit mixed SiN, BN, and NSiB phases.