An, Linan ; Riedel, Ralf ; Konetschny, Christoph ; Kleebe, Hans-Joachim ; Raj, Rishi (1998):
Newtonian Viscosity of Amorphous Silicon Carbonitride at High Temperature.
In: Journal of the American Ceramic Society, 81 (5), pp. 1349-1352. Wiley, ISSN 0002-7820,
DOI: 10.1111/j.1151-2916.1998.tb02489.x,
[Article]

Abstract

The creep viscosity of chemical-precursor-derived silicon carbonitride (SiCN), which is known to remain predominantly amorphous at temperatures below 1400°C, was measured in the temperature range 1090-1280°C. Experiments were done in uniaxial compression at constant loads in pure nitrogen atmosphere. The creep behavior exhibited three stages. In stage I the strain rate decreased rapidly with time and deformation was accompanied by densification. In stage II the samples exhibited a steady-state creep rate. In stage III, which commenced after long-term deformation, creep gradually declined to rates that were below the sensitivity of our apparatus. The relative density of the specimens during stage II and stage III remained constant at ≅2.3 g/cm3. The shear viscosity in stage II was nearly Newtonian and was measured to be 1.3 × 1013-5.0 1013 Pa·s at 1280°C, which is approximately 103 times the value for fused silica. The creep-hardened as well as uncrept specimens contained silicon nitride crystallites. The volume fraction of these crystals was variable but always less than 5%. Such a small volume fraction of crystals does not explain the dramatic creep-hardening behavior in stage III, even if it is assumed that the crystals formed during creep deformation in stage II.

Send an inquiry

Show editorial Details