TENSILE CREEP OF A SILICON-NITRIDE CERAMIC

The tensile creep behavior of a hot isostatically pressed silicon nitride ceramic containing 6 percent yttria was characterized at temperatures between 1250 and 1400 degrees C and applied stresses between 72 and 250 MPa. Creep extension of specimens with nominal 10 mm gauge length was measured by laser extensometry, showing final extensions between 20 and 200 mu m. Secondary creep strain rates varied from 0.3 to 3000 Gs(-1). Some tests ended with specimen failure between 1 and 500 h, but other tests were discontinued after 1000 up to 2500 h without failure. A least-squares fit of the Norton and Arrhenius functions to 31 strain-rate tests yielded a stress exponent of 8.4 +/- 0.9 and an activation energy of 1310 +/- 140 kJ/mol. A Monkman-Grant function was fitted to represent strain rate versus failure time.