High temperature creep of ultrafine-grained Fe-doped MgO polycrystals

Abstract

Creep deformation in ultrafine-grained (0.1 to 1/~m) Fe-doped magnesia polycrystals is studied in compression, at temperatures of 700 to 1050 ~ C, and constant loads of 50 to 140 MPa. The stress exponent observed to be nearly unity and the strong grain size sensitivity (~ ~ d -2-*s ) suggest that diffusional creep mechanisms dominate the deformation. In the grain size range of the present study the grain boundary diffusion contribution is significantly more important than lattice diffusion. Magnesium is tentatively identified as the rate-controlling species along grain boundaries from an analysis of the diffusivities inferred from the present work and from other authors for Fe-doped magnesia.

Densification of nanocrystalline MgO ceramics by hot-pressing

“…17 Similar strain hardening behavior with stress exponent of unity was observed under lower stress of 140 MPa between 700 and 860 • C in MgO with submicron grain size. 18 These data support the relatively large plastic strains observed in the nanocrystalline grains (Fig. 11).…”