Creep cavitation in a siliconized silicon carbide tested in tension and flexure

Cavity formation was quantified in a grade of siliconized silicon carbide containing 33 vol% silicon, The type, size, and density of cavities were determined for smooth-bar specimens tested in both tension and bending, and for indented specimens tested in tension, In both tension and bending, the volume fraction of cavities was found to be proportional to the tensile creep strain, Cavities nucleated at random locations throughout the test specimen, eventually coalescing into cracks that were the source of failure at high temperatures, In tension, the strain to failure was about 1%, In flexure, stress relaxation at the tensile surface of test specimens helped stabilize cracks that formed during creep, As a consequence, strains to failure were about twice as large in bending as in tension, In tensile specimens containing large, >300 mu m, indentation cracks, cavitation was profuse near the crack tips, At a volume fraction of about 3%, cavities coalesced to form secondary cracks near the tip of the indentation crack, Cracks advanced by linkage of cavitation cracks with the indentation crack, Crack growth was intermittent, requiring the buildup of cavities in front of the crack tip before crack advance could occur, If the indentation crack length was less than about 200 mu m, cavity formation at the tip of the crack was not sufficient for crack advance, In such case, failure would have to occur by cavity coalescence and crack formation at some other location in the test specimen.