Wear of Nanocrystalline SiC: Massively Parallel Molecular Dynamics Simulations

Maneesh Mishra, Izabela Szlufarska, Materials Science Program

Silicon Carbide is an excellent material for MEMS and NEMS devices under extreme conditions. SiC has a lower oxidation rate than Si-based MEMS and has a higher band gap making it a choice for high temperature electronics. Although mechanical properties (hardness, fracture toughness) of SiC have shown to be largely superior to those of polycrystalline or bulk SiC, tribological properties of nanocrystalline SiC (nc-SiC) are not yet known.

Multi-scale computer simulations of tribological properties of nc-SiC will be performed with the goal of understanding fundamental nature of wear at these interfaces and its relation to micro and nano-structure. Nc-SiC structures with different grain sizes (d=5-15nm) will be generated by Voronoi construction (as shown in figure 1). A spherical amorphous SiC (a-SiC) tip with tip radius R = 10 nm will be used to perform sliding simulations on nc-SiC. The results will be compared with the sliding simulations conducted on single crystal SiC to understand the role of dislocation and grain boundary interaction during wear in nc-SiC.

To further understand the wear processes in nc-SiC as a function of grain size, we will conduct separate simulations of crack propagation in nc-SiC with columnar grains and different pre-existing crack length (critical flaw size). We will study fracture toughness as a function of grain size and crack length (R curve, inter-granular vs. intra-granular fracture). Again, the results will be compared to simulations performed with pre-existing cracks modeled in single crystal SiC as shown in figure 2.

The effect of oxide layer (a-SiO₂ on SiC surface) on the tribological properties will be investigated later on in the project. We will also determine the effect of dopant atoms on tribological properties of SiC surface.

This project will help unravel the dependence of wear on microstructure of a technologically relevant material and extract general rules that can be transferred to a broader class of materials.

Previous project:

Possibility of High Pressure Transformation during Nanoindentation of SiC