The effects of annealing atmosphere and intrinsic component on high temperature evolution behaviors of SiC fibers

In this work, the second (F1) and third (F2) generation SiC fibers were treated at different temperature under vacuum and Ar atmosphere to analyze the influence of fiber composition and atmosphere on the high temperature evolution of SiC fibers. The results reveal that SiC decomposition and graphene formation could occur in SiC fibers over 1600 °C under vacuum or 2000 °C under Ar atmosphere. The mechanical properties of both F1 and F2 fibers are remarkably degraded accompanied by the SiC decomposition. The formed graphene size is related to the SiC grain size before decomposition, while the increment of temperature will promote SiC grain growth and SiC decomposition simultaneously. Under Ar atmosphere, the Si sublimation rate is slow so that SiC grains can grow fully, therefore, the converted graphene crystallite size is much larger than that under vacuum. SiC decomposition rate is related to the excess carbon and pores in the fibers. The inhibition effect of carbon micro-coating around SiC grains formed by excess carbon and promotion effect of pores formed by SiCxOy decomposition co-exist in SiC fibers. This work reveals that effective inhibition of Si sublimation is of significance for the stability of SiC fibers under ultra-high temperature.