CREEP CAVITATION IN A SILICONIZED SILICON-CARBIDE TESTED IN TENSION AND FLEXURE

Cavity formation was quantified in a grade of siliconized silicon carb ide containing 33 vol% silicon, The type, size, and density of cavitie s 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 proporti onal to the tensile creep strain, Cavities nucleated at random locatio ns throughout the test specimen, eventually coalescing into cracks tha t were the source of failure at high temperatures, In tension, the str ain to failure was about 1%, In flexure, stress relaxation at the tens ile surface of test specimens helped stabilize cracks that formed duri ng creep, As a consequence, strains to failure were about twice as lar ge in bending as in tension, In tensile specimens containing large, >3 00 mu m, indentation cracks, cavitation was profuse near the crack tip s, At a volume fraction of about 3%, cavities coalesced to form second ary cracks near the tip of the indentation crack, Cracks advanced by l inkage of cavitation cracks with the indentation crack, Crack growth w as intermittent, requiring the buildup of cavities in front of the cra ck tip before crack advance could occur, If the indentation crack leng th was less than about 200 mu m, cavity formation at the tip of the cr ack 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.