ISSN:
1551-2916
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Internal friction experiments were conducted on a model SiC polycrystal prepared from preoxidized (high-purity) SiC powder. This material contained high-purity SiO2 glass at grain boundaries in addition to a free-carbon phase, which was completely removed upon powder preoxidation. Comparative tests were conducted on a SiC polycrystal, obtained from the as-received SiC powder with the addition of 2.5 vol% of high-purity SiO2. This latter SiC material was also investigated after annealing at 1900°C for 3 h in a nitrogen atmosphere. Electron microscopy observations revealed a glass-wetted interface structure in SiC polycrystals prepared from both as-received and preoxidized powders. However, the former material also showed a large fraction of interfaces coated by turbostratic graphite. Upon high-temperature annealing in nitrogen, partial glass dewetting occurred, and voids were systematically observed at multigrain junctions. The actual presence of nitrogen could only be detected in a limited number of wetted interfaces. A common feature in the internal friction behavior of the preoxidized, SiO2-added and nitrogen-annealed SiC was a relaxation peak that resulted from grain-boundary sliding. Frequency-shift analysis revealed markedly different characteristics for this peak: both the magnitude of the intergranular glass viscosity and the activation energy for grain-boundary viscous flow were much higher in the nitrogen-annealed material. Results of torsional creep tests were consistent with these findings, with nitrogen-annealed SiC being the most creep resistant among the tested materials.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1151-2916.2001.tb01017.x
