Influence of SiC/Silica and Carbon/Silica Interfaces on the High‐Temperature Creep of Silicon Oxycarbide‐Based Glass Ceramics: A Case Study

In the present study, the high-temperature creep behavior of three SiOC glass ceramics with different phase compositions are compared by the authors. All three SiOC glass ceramics have a vitreous silica matrix in common, but comprise different homogeneously dispersed phases 1) only spherical beta-SiC nanoparticles (sample denoted hereafter SiC/SiO2), 2) only high-aspect ratio sp(2)-hybridized carbon (i.e., C/SiO2), and 3) both phases (SiC and segregated carbon, i.e., C/SiC/SiO2). Compression creep experiments are performed at temperatures in the range between 1100 and 1300 degrees C and true stresses of 50 to 200 MPa. The determined activation energy for creep of the SiOC glass ceramics of around 700 kJ mol(-1) is independent of the phase composition. A stress exponent value of approximately 2 indicates an interface-controlled deformation mechanism. All SiOC glass ceramics exhibit significantly higher creep viscosities than that of vitreous silica. Surprisingly, the spherical beta-SiC nanoparticles have a higher impact on the effective creep viscosities of SiOC as compared to that of the high-aspect ratio segregated carbon phase. It is concluded that this originates from the beta-SiC/silica and C/silica interfaces, which have different effects on the creep behavior of silicon oxycarbide-based glass ceramics.