Elastic constants and tensile properties of Al₂OC by density functional calculations

Al₂OC is a compound that forms as a nanoscale grain-boundary crystalline film in silicon carbide ceramics, and is responsible for imparting high low-temperature toughness and high-temperature creep strength in these materials. The elastic properties and ultimate strengths properties of Al₂OC are determined from first-principles calculations. The crystal structure of Al₂OC was approximated by an optimized model based on the wurtzite structure. The full set of single-crystal elastic stiffness c_ij was calculated, from which the polycrystalline elastic constants were obtained by using the Voigt-Reuss-Hill averaging scheme. The tensile properties and the ideal strength in [001] direction of Al₂OC were also computed and compared to those of SiC, where it was found that indeed, Al₂OC is the weaker and more brittle phase, supporting fracture mechanics expectations for SiC containing Al₂OC-type intergranular films.