Armed Services Technical Information Agency Arlington Hall Station Arlington 12, Virginia

The objective of this contract was the study of rocket faikire mechanisms in conjunction with the development of nozzle materials for solid propellant motors. Study of graphite comprised the major part of the program, with emphasis on erosion mechanisms. Commercial and experimental graphite grades were tested in an oxy-acetylene torch and the effects of graphite purity, density, orientation and microstructure on erosion-resistance were evaluated. The effect of graphite purity appeared to overshadow all other features in the dynamic tests; erosion decreased with greater purity. Similar trends were not observed in oxidation studies conducted at temperatures up to 1900°C in static air or flowing atmospheres. Graphite density had the greatest influence on resistance to ablation in the arc plasma experiments. New graphite materials were developed and evaluated on the program, including hot pressed compositions and several impregnated bodies. Subsidiary effort was directed toward evaluating the suitability of zirconium carbide as a nozzle material. The poor thermal shock-rt aistance of this material is a major obstacle to its use in nozzle applications. Incorporation of tantalum and tungsten fibers in ZrC results in considerable improvement in resistance to thermal spalling, although still not sufficient to prevent cracking. Minor effort was directed toward the study of thoria-base bodies reinforced with tungsten fibers. Ten promising materials were fabricated into rocket nozzles and tested in static motor stands. Erosion performance is presented along with analysis of failure mechanisms.