Effect of composition and high-temperature annealing on the local deformation behavior of silicon oxycarbides

Abstract Silicon oxycarbides with varying compositions were investigated concerning their elastic and plastic properties. Additionally, the impact of thermal annealing on their elastic properties was assessed. Phase separation of SiOC seems to have no significant impact on Young’s modulus (high values of β-SiC compensate the low values of the vitreous silica matrix) and hardness. However, it leads to an increase in Poisson’s ratio, indicating an increase in the atomic packing density. The phase composition of SiOC significantly influences Young’s modulus, hardness, brittleness and strain-rate sensitivity: the amount of both β-SiC and segregated carbon governs Young’s modulus and hardness, whereas the fraction of free carbon determines brittleness and strain-rate sensitivity. Thermal annealing of SiOC glass-ceramics leads to an increase in Young’s modulus. However, the temperature sensitivity of Young’s modulus and Poisson’s ratio is not affected, indicating the glassy matrix being stable during thermal annealing. A slightly improved ordering of the segregated carbon and the β-SiC nanoparticles upon thermal annealing was observed. It is suggested that this is responsible for the increase in Young’s modulus.