The high temperature creep deformation of Si3N4-6Y2O3-2Al2O3

Abstract

The creep properties of silicon nitride containing 6 wt% yttria and 2 wt% alumina have been determined in the temperature range 1573 to 1673 K. The stress exponent, n, in the equation e « a , was determined to be 2.00 +_0.15 and the true activation energy was found to be 692 +_ 25 kJ mol~. Transmission electron microscopy studies showed that deformation occurred in the grain boundary glassy phase accompanied by microcrack formation and cavitation. The steady state creep results are consistent with a diffusion controlled creep mechanism involving nitrogen diffusion through the grain boundary glassy phase.

Fabrication of Heat-Resistant and Plastic-Formable Silicon Nitride

“…It is obvious that the accommodation process here is the solution-precipitation process because of the slight grain growth and elongation of β-Si 3 N 4 grains. Furthermore, the present experimental activation energy of 571.8 kJ/mol, which corresponds to that for the diffusion of nitrogen ions through the grain boundary glassy phase [36], is similar to other values reported for the deformation of Y 2 O 3 /Al 2 O 3 -doped silicon nitride materials for the grain boundary sliding mechanism accommodated by a diffusion-controlled solution-precipitation process [36,37]. The solution-precipitation process in fine-grained ceramics can be controlled by either an interface reaction or by diffusion in the liquid.…”

Creep behavior of a carbon-derived Si3N4/SiC nanocomposite

“…Todd and Xu. 32 reported approximately 700 kJ/mol for the activation energy for the diffusion of nitrogen ion through the grain boundary.…”

Microstructure and Creep Behavior of Silicon Nitride and SiAlONs

“…It cannot tolerate the large deformation necessary to undergo tertiary creep without failure. However, a few studies of creep of Si 3 N 4 in four‐point bending have shown tertiary creep regions 68 . Secondary, or steady‐state creep is the most studied, because the other two regions are transient and depend on numerous factors.…”

“…Tensile Creep: Creep deformation in tension is attributed to viscous flow of the intergranular phase and dilation of the structure so that rigid grains may slide past each other 65,74 . Unaccommodated strain in tension is the result of cavity formation, both at multigrain junctions and along the boundaries between grain pairs 24,65,66,68,71,75,76 . Cavities are nucleated to relieve the stresses that build up as a result of viscous flow and grain boundary sliding, 76 and are most commonly found at multigrain junctions.…”