"Inert" Strengths of Silicon Nitride Ceramics at Elevated Temperatures

An attempt to determine high temperature "inert" strengths of several silicon nitride ceramics was made by using dynamic fatigue testing at the very high stressing rate of 2 x 106 MPa/min. The fatigue strengths of all the silicon nitride materials exhibited a well-defined convergence to the corresponding room-temperature inert strengths as stressing rate was increased. The result showed that the high temperature Inert" strength of a ceramic material can be obtained by using sufficiently high stressing rates (greater or = 2 x 10(exp 6) MPa/min) at which fatigue strength converges to a specific value. The specific value can be close to the room-temperature strength of the material.