ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Si-Al-O-N ceramics have been prepared by hot-pressing mixtures of Si3N4, AIN and SiO2 (with an addition of 1% MgO) having varying ratios of AIN/SiO2. Microstructural analysis by transmission electron microscopy and Auger electron spectroscopy has demonstrated the progressive increase in grain-boundary silicate glass in pressings prepared from compositions with excess SiO2 to compositions given by the formula Si6−zAlzOzN8−z. This formula represents the simple substitution of Al for Si atoms and O for N atoms in the hexagonalβSi3N4 crystal. Microstructures for this “balanced” composition are essentially single phase, consiting of non-faceted, sub-micron,β′ grains with a grain-boundary segregate layer of glass-forming silicate composition, containing impurity and additive metal ions, which may be detected only by Auger spectroscopy. This microstructure is in contrast with “unbalanced” compositions which contain facetedβ′ grains joined by a glassy silicate phase which is easily detected by electron microscopy. Final microstructural analysis combined with observations of density and phase content with progress of hot-pressing has confirmed the important role of liquid silicate formation and a “solution-reprecipitation” mechanism for densification. The presence of a 1% MgO additive is shown to accelerate this process, forming a low melting point silicate by reaction with SiO2, assisting the early solution of AIN and the reprecipitation ofβ′ substituted crystals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00738472
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