Effect of the shell thickness on the mechanical properties of arrays composed of hybrid core-shell Si/SiC nanoparticles with overlapped shells

Atomistic simulations of quasi-static compression and tension of linear arrays consisting of hybrid spherical nanoparticles (NPs) with Si cores and 6H-SiC partially overlapped shells are performed to reveal the effect of the shell thickness on the deformation mechanism and mechanical properties of such NP arrays. The overlapped shells are considered as a model of a continuous coating that promotes the mechanical integrity of a nano-powder and transforms it into a porous composite material. At compression, the transition from ductile to brittle deformation behavior with increasing shell thickness is observed. The compression of a NP array with thick shells induces the formation of a quasi-conical slip surface. The fracture of a NP array at compression involves the fracture of both shell and core materials and can induce the formation of a new & beta;-Sn phase in the Si core. At tension, the deformation process is characterized by a relatively large proportional limit, and the fracture occurs in the weak cross sections at the necks between NPs, so that the NP cores remain intact after fracture. Before fracture, the largest microscopic stresses are observed in the shell material near the core-shell interface. The simulations predict a strong increase of modulus and strength at tension and compression with an increase in the relative shell thickness, the ratio of the shell thickness to the NP diameter, while the effect of the NP size on mechanical properties is relatively weak. This suggests that the relative shell thickness is the major similarity parameter that dominates the mechanical properties of the NP arrays. Interestingly, the simulations predict a larger modulus for NPs with thick shells compared to single-material SiC NPs. This points at a non-trivial role of the core-shell interface and the degree of the shell overlap in the load transfer in the arrays of NPs with overlapped shells.