Nucleation and early-stage growth of creep cavities in hot-pressed silicon carbide

Abstract

Fine-grained silicon carbide with a continuous second phase grain boundary film was crept under compressive loading at 1600°C. The resultant nucleation and growth of creep cavities was characterized using small-angle neutron scattering. It was found that nucleation occurred within approximately the first 5% of the lifetime, so that the modeling of failure essentially involves the treatment of cavity growth and ultimate coalescence. The results suggested that cavity nucleation and growth occurred entirely within the viscous grain boundary film. However, the cavities do not grow, crack-like, across the grain boundary facets, but rather nucleate as lens-shaped pores which gradually transform, as the film thickens, to very slowly growing spheroidal cavities. The results are shown to contrast with similar experiments on an alumina with clean grain boundaries, in which pore nucleation, rather than pore growth, controlled creep life.