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 s ilicon nitride. Silicon nitride SN4 contained 2.0 mol Nd2O3 and 2.0 mol%. Y 2O3 as sintering aids, and the additives for silicon nitride SN1 were 0.5 m ol% Nd2O3 and 0.5 mol%. Y2O3. The delayed failure of SN4 was thought to res ult from creep rupture because considerable creep deformation was found wit h a high stress exponent of n = 10.7 in the stress range of 137 to 220 MPa at 1300 degreesC. and the stress-rupture parameter was determined to be N = 8.4. The delayed failure of SN I was thought to result from subcritical cr ack growth since no significant creep deformation was found and a high stre ss-rupture parameter of N = 20.7 was determined. The creep and stress-ruptu re mechanisms are discussed based on the creep test results and microstruct ure observation. (C) 2001 Elsevier Science Ltd. All rights reserved.