Microstructure and creep behavior of an Y-α-β sialon composite

Impression and Compression Creep of SiAlON Ceramics

“…Activation energies and stress exponents were calculated using for compression creep and for impression creep, and are listed in Table III. The activation energies measured by both impression and compression creep are somewhat lower than those reported in the literature for Si 3 N 4 and SiAlONs 16,18–20,22,23,34–36 . The activation energies for Compositions A and B are not significantly different (within the standard error of the linear regressions), and are similar for both test methodologies.…”

“…Creep deformation of these materials in uniaxial tension is attributed to viscous flow of the intergranular phase and dilation of the structure so that rigid grains may slide past each other 18,21 . Unaccommodated strain in tension is the result of cavity formation, both at multi‐grain junctions and along the boundaries between grain pairs 17,18,22,23 . Cavities are nucleated to relieve the stresses that build up as a result of viscous flow and grain‐boundary sliding 23 .…”

“…They noted that some cavitation occurred in the specimens tested using the impression creep test, but no cavitation was seen in the specimens tested in uniaxial compression. However, the sharp angularity of the void space that was created between the grains during their impression creep testing appears to indicate that dilation of the structure occurred, rather than cavitation, which typically produces more rounded voids 17,18,22,23 …”

“…However, some studies of SiAlON materials showed that if cavitation occurs during compressive creep tests, the measured stress exponent increases from 1 to the range of 1.5–2.5 19,36 . In tension or bending, the stress exponent increases to the range of 2–7, as the cavitation mechanism is strongly related to the magnitude of the applied tensile stress 18,22,23,34,35 …”

Microstructure and Creep Behavior of Silicon Nitride and SiAlONs

“…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.…”