Mechanical properties, phase transitions, and fragmentation mechanisms of 6H, 3C, and amorphous SiC nanoparticles under compression

The molecular dynamics simulations of quasi-static compression of SiC nanoparticles (NPs) with diameters from 5 to 40 nm are performed in the temperature range from 0.1 to 3500 K. The crystalline NPs with hexagonal, 6H-SiC, and cubic, 3C-SiC, lattices, as well as amorphous NPs, are compressed along [001], [110], and [111] crystallographic directions with either plane indenters or periodic boundary conditions. The dominant mechanism of deformation depends on the type of the SiC polymorph, NP size, temperature, and lattice orientation with respect to the compression direction. For small NPs at low temperature, the compression mostly induces amorphization of 6H-SiC NPs and formation of rock-salt phase core in 3C-SiC NPs, while the compressive stress only marginally depends on the lattice orientation. For large NPs, the deformation induces formation of multiple dislocations and slip planes that result in the material fragmentation. The morphology and number of fragments strongly depend on the SiC polymorph and lattice orientation. The fragmentation of large 6H-SiC NPs preferentially occurs along {0001} plane independently on the compression direction. An increase in temperature promotes the dislocation nucleation with subsequent fragmentation and relative motion of large fragments. As a result, the average stress at large deformation tends to increase with the NP size at small temperatures and to decrease at elevated temperatures. On average, 6H-SiC NPs compressed along [001] direction demonstrate stronger resistance to compression in the regime of plastic deformation compared to 3C-SiC NPs and other lattice orientations.