Mechanical properties and elastic constants due to damage accumulation and amorphization in SiC

Damage accumulation due to cascade overlap, which was simulated previously, has been used to study the changes in elastic constants and the bulk and elastic moduli as a function of dose in SiC. These mechanical properties generally decrease with increasing dose, and the rapid decrease at low-dose levels indicates that point defects and small clusters play a more important role in the change in elastic constants than the topological disorder. The internal strain relaxations, which have no effect on the elastic constants, C-11 and C-12, in a perfect SiC crystal, have a significant influence on the elastic constants calculated in damaged SiC. The elastic constants, C-11, C-12, and C-44, in the cascade-amorphized (CA) SiC decrease about 19%, 29%, and 46%, respectively. The bulk modulus decreases 23%, and the elastic modulus decreases 29%, which is consistent with experimental results. The stability of both the perfect SiC and CA-SiC under hydrostatic tension has been also investigated. The mechanical properties in the CA-SiC exhibit behavior similar to that in perfect SiC, but the critical stress at which the CA-SiC becomes structurally unstable is one order of magnitude smaller than that for perfect SiC.