COMPARATIVE QUANTITATIVE ANALYSIS OF [[beta]]-Si3N4 / [[beta]]-SiC MIXTURES. Jeffrey P. Nicolich, Zoltan Lences, Wolfgang Dressler and Ralf Riedel. Dept. of Materials Science, Dispersive Solids Group, Technical Universtity, Hilpertstraße 31/D, 60295 Darmstadt, Germany
Mean-normalized-intensity (MNI), reference-intensity-ratio (RIR) and full-pattern-fitting (Rietveld) methods of phase quantification are presented on mixtures of [[beta]]-Si3N4 and [[beta]]-SiC. Various experimental conditions are compared: Measurements were performed on reflection (Siemens D5000) as well as transmission (STOE) geometry diffractometers. Furthermore, runs were made with routine (fast, no sample rotation) and high-quality (slow, sample rotation) data collection.
Silicon carbide - silicon nitride composite materials are investigated by materials scientists for their improved mechanical properties over the single phases. Exceptionally good creep resistance due to pinning of the [[beta]]-Si3N4 grain boundries by [[beta]]-SiC particles is expected. Two types of additive free [[beta]]-Si3N4 materials were used: "SHS" is produced by self-propagation high-temperature synthesis, "Denka" is recrystallized from [[alpha]]-Si3N4 which in turn is produced by direct nitridation of silicon. The [[beta]]-SiC is commercial Superior Graphite type.
Both [[beta]]-SiC and "Denka" silicon nitride are equiaxed, with mean grain sizes of approximately 1 micron. "SHS" silicon nitride crystals are elongated up to 10 - 20 microns in length.