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The operative and controlling mechanisms of steady-state creep in sintered a-Sic have been determined both from kinetic data within the ranges of temperature and constant compressive stress of 1670 to 2073 K and l38 to 414 MPa, respectively, and from the results of extensive TEM and other analytical analyses. Dislocations in glide bands, B4C precipitates, and the interaction of these two entities were the dominant microstructural features of the crept material. The stress exponent increased from 1.44 to 1.71 with temperature; it was not a function of stress at a given temperature. The curves of In E vs 1/T showed a change in slope at 1920 2 20 K. The respective activation energies below and above this temperature interval were 338 to 434 and 802 to 914 kJ/mol. A synthesis of all this information leads to the conclusion that the controlling creep mechanism at low temperatures is grainboundary sliding accommodated by grain-boundary selfdiffusion; at high temperatures, the controlling mechanism becomes grain-boundary sliding accommodated by lattice diffusion. The parallel mechanism of dislocation glide contributes increasingly to the total strain as the number/volume of precipitates declines as a result of progressive coalescence with increasing temperature.

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