Computational design of carbon enriched ceramics for improved strength and toughness

Silicon Carbide (SiC) is a strong and hard engineering material frequently considered for abrasives, rotating disks, bearing, high temperature coatings etc. Poor fracture toughness due to brittleness is one of the limitations that keeps SiC from applying in widespread structural applications. In this study mechanical properties of a new type SiC-based "C enriched" ceramics where certain Si atoms are substituted by C atoms have been studied using MD simulation. Five different systems with different fraction of "C" enrichments, namely 10%, 20%, 30%, 40% and 50% have been investigated. After equilibrating all types of enriched systems as well as the control SiC system, we studied their equilibrium densities, free energy profiles and internal morphologies as a function of "C" enrichment amount. The energy profiles suggest that all "C" systems should be thermodynamically viable because total configuration energies for all systems were minimized and remained stable over a long period of time. The densities of different "C" enriched system drop from 3.25 gm/cm³ to 3.05 gm/cm³ for "C" enrichment upto 20%. For higher than 20% "C" enrichments, densities then increase monotonically. We explore the microstructures by measuring the average coordination number and radial distribution functions of different systems. Both these studies confirm that the newly designed materials have local microstructure change. We then evaluated tensile and shear response of these newly developed materials and found the mechanical properties depend on amount of carbon enrichment. Our study suggests that "C" enrichment has strong influence on both tensile and shear properties of ceramics with optimum results attained at enrichment between 20% and 30%.