A crossover in the mechanical response of silicon carbide due to the accumulation of chemical disorder

Molecular dynamics simulations of nanoindentation of silicon carbide (SiC) with varying chemical disorder are carried out to investigate the variations in mechanical responses and mechanisms due to the accumulation of chemical disorder. A crossover of deformation mechanisms with increasing chemical disorder is revealed in light of the transition of indentation response (pressure-depth curves) changing from a series of equally spaced load drops to irregularly spaced and less pronounced fluctuations, then to numerous small oscillations. This crossover arises from the interplay between dislocation motions confined to ordered atomic layer fragments and atomic rearrangements localized in embedded chemical and/or topological disordered clusters. At the presence of chemical disorder, the outburst and complete propagation of dislocations dominating in 3C-SiC evolve into discontinuous motions of multiple branched dislocations which are likely to be prematurely trapped by chemical disordered clusters. The extension of amorphous network as a result of elevated chemical disorder significantly inactivates the dislocation activities, initiating increasingly compelling localized plastic flow in the form of atomic rearrangements. Likewise, the changes in hardness due to the accumulation of chemical disorder, which is observed to decreases about ∼50% in amorphous SiC with highest imposed level of chemical disorder, can also be attributed to the switch of deformation mechanisms.