Room-Temperature Strength of Sintered Silicon Nitride Subjected to High-Temperature Creep Loading

Room-temperature strength was evaluated using sintered silicon nitride crept specimens. Creep tests were performed using 4-point bending loading at 1400°C in air. The bending creep tests applied stresses from 100 to 400 MPa for 10−1 to 3×103 hours. For applied stress over 200 MPa, the room-temperature strength of the crept specimen had two stages. In the first stage the strength degraded slowly, and in the second stage the strength degraded rapidly. In the first stage, oxidation caused the strength degradation, since the degradation was similar for the different applied stresses. In the second stage, large creep deformation mainly caused the strength degradation. Early in the stage, creep induced matrix and boundary damage under the oxidation layer caused the degradation. At the end of the stage, cracks induced by creep caused the degradation.Copyright © 1994 by ASME