DIFFUSIONAL CREEP OF FINE-GRAINED MAGNESIUM OXIDE - MAGNESIUM-CHROMITE CERAMICS (PERICLASE, SPINEL).

摘要

Dense, two-phase MgO-MgCr(,2)O(,4) ceramics with a range of phase proportions were prepared by hot pressing. Creep experiments were carried out at 1300(DEGREES)C on samples having mean grain sizes between 1 and 6 (mu)m. The observed stress dependence (n = 1.3) and grain size dependencies (m (GREATERTHEQ) 3) point to grain boundary diffusion as being the rate controlling deformation mechanism. Specimens crept to almost 50% true strain exhibited a distinct periclase elongation perpendicular to the compressive stress direction, but little to no preferred spinel orientation. The primary creep regime data showed a distinct break in its exponential decay, probably related to the two phase nature of the material. Cavitation and microcracking were not observed in any of the samples.;Comparing the creep data obtained in this study to that in the literature, it is seen that the addition of second phase spinel to a fine-grained periclase body causes a significant reduction in creep rates. The data also suggest the hypothesis that mixed phase MgO-MgCr(,2)O(,4) grain boundaries may have diffusive mass transport rates intermediate between those of the single phase MgO-MgO and MgCr(,2)O(,4)-MgCr(,2)O(,4) boundaries.