Creep and creep rupture behavior of an advanced silicon nitride ceramic were systematically characterized in the temperature range 1150" to 1300°C using uniaxial tensile creep tests. Absence of tertiary creep and the order-ofmagnitude breaks in both creep rate and rupture lifetime at certain threshold combinations of stress and temperature were two characteristic features of the creep behavior observed. Thermal annealing was found to have enhanced both subsequent creep resistance and creep rupture life. The stress exponent ( n ) and the activation energy ( Q ) defined in the Norton relation were found to be 12.6 and 1645 kJ/mol for the material investigated. Both values appear to fall in the general range of those reported for other but similar types of Si,N, ceramic materials. The stress exponent, m, equivalent to the slope of the LarsonMiller equation was found to be in the range 13 to 14.4, and that defined asp in the Monkman-Grant relation to be 0.91, based on the available experimental data. The values of m, n, and p obtained above approximately support the interrelationship of the three exponents given byp = mln.
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