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.

• Received 24 October 2003

DOI:https://doi.org/10.1103/PhysRevB.69.224108