Premium
Newtonian Viscosity of Amorphous Silicon Carbonitride at High Temperature
Author(s) -
An Linan,
Riedel Ralf,
Konetschny Christoph,
Kleebe H.Joachim,
Raj Rishi
Publication year - 1998
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1998.tb02489.x
Subject(s) - creep , materials science , amorphous solid , newtonian fluid , composite material , viscosity , atmospheric temperature range , volume fraction , hardening (computing) , silicon , silicon nitride , mineralogy , metallurgy , crystallography , thermodynamics , chemistry , physics , layer (electronics)
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/cm 3 . The shear viscosity in stage II was nearly Newtonian and was measured to be 1.3 × 10 13 ‐5.0 10 13 Pa·s at 1280°C, which is approximately 10 3 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.