Diffusion‐Accommodated Grain Boundary Sliding and Dislocation Glide in the Creep of Sintered Alpha Silicon Carbide

Constant compressive stress creep experiments in the temperature and stress ranges of 1770 to 2020 K and 35 to 373 MPa have been performed on polycrystalline alpha SiC. Specimens having average grain sizes of 3.5, 4.9, and 7.5 μm have been studied in order to determine the grain size dependence of steady‐state creep in this material and to distinguish the relative contributions of diffusion‐accommodated grain boundary sliding and dislocation glide. Analysis of steady‐state creep rate data revealed different kinetics of creep below and above 1920 K as follows: activation energies of 387–541 and 838–877 kJ/mol, stress exponents of 1.0–1.4 and 1.4–2.5, and inverse grain size exponents of 2.5 and 4. The m value of 2.5 indicated Coble‐controlled creep with a contribution of Nabarro–Herring creep in the low‐temperature range. The m value was less reliable for the high‐temperature range because of the large differences in the microstructures of the three materials. The large number of high aspect ratio grains with increasing average grain size resulted in different contributions of diffusion‐accommodated grain boundary sliding and dislocation glide between thsee materials.