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Structure and Viscosity of Grain Boundary in High‐Purity SiAlON Ceramics
Author(s) -
Pezzotti Giuseppe,
Kleebe HansJoachim,
Okamoto Kazuhiro,
Ota Ken'ichi
Publication year - 2000
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.1151-2916.2000.tb01589.x
Subject(s) - materials science , grain boundary , sialon , grain boundary sliding , intergranular corrosion , composite material , ceramic , relaxation (psychology) , phase (matter) , viscosity , grain boundary diffusion coefficient , mullite , microstructure , mineralogy , metallurgy , chemistry , psychology , social psychology , organic chemistry
Three high‐purity SiAlON materials (Si 6− z Al z O z N 8− z , z = 1, 2, 3) were characterized with respect to both structure and viscous behavior of internal grain boundaries. Internal friction experiments provided a direct measure of the intrinsic viscosity of grain boundaries and concurrently revealed the occurrence of a grain‐boundary interlocking mechanism that suppressed sliding. A residual glass phase (consisting of aluminum‐rich SiO 2 ) and nanometer‐sized mullite residues were found at glassy triple‐grain junctions of the z = 1 SiAlON. A low‐melting intergranular phase dominated the high‐temperature behavior of this material and caused grain‐boundary sliding at temperatures as low as 1100°C. A quantitative analysis of the grain‐boundary internal friction peak as a function of oscillation frequency indicated an intergranular film viscosity of log η∼ 7.5 Pa · s at 1100°C. Glass‐free grain boundaries were a characteristic of SiAlON materials with z ≥ 2, which yielded a significant improvement in refractoriness as compared to the z = 1 SiAlON material. In these materials, relaxation resulting from grain‐boundary sliding was suppressed, and the internal friction curve simply experienced an exponential‐like increase.