Creep and stress-rupture behavior of Y2O3–Nd2O3-doped silicon nitrides with different additive contents

Tensile creep tests were performed on two grades of gas-pressure sintered silicon nitride. Silicon nitride SN4 contained 2.0 mol% Nd2O3 and 2.0 mol% Y2O3 as sintering aids, and the additives for silicon nitride SN1 were 0.5 mol% Nd2O3 and 0.5 mol% Y2O3. The delayed failure of SN4 was thought to result from creep rupture because considerable creep deformation was found with a high stress exponent of n=10.7 in the stress range of 137 to 220 MPa at 1300°C, and the stress-rupture parameter was determined to be N=8.4. The delayed failure of SN1 was thought to result from subcritical crack growth since no significant creep deformation was found and a high stress-rupture parameter of N=20.7 was determined. The creep and stress-rupture mechanisms are discussed based on the creep test results and microstructure observation.