Ammrc Tr 68-17 Titanium Carbide Content Effect on Erosion in Cermet Rocket Nozzles

Analyses were carried out on subscale cermet nozzles fired in the AMMRC solid propellant engine at a designated maximum chamber pressure of 1100 psi for nominal burning times of 15 jeconds in order to determine mechanisms of erosion and the effect of the carbide constituent on erosion. The cermet class investigated consisted of an AISI Type 316 stainless steel matrix incorporating a hard phase of titanium carbide ranging in content from 20% to 55% by volume. The results of the study indicated that under the test conditions, increases in the titanium carbide constituents did increase the erosion resistance of the material. However, this was accomplished at the expense of thermal shock resistance. In addition, the mechanisms of erosion were determined to be thermal-chemical and mechanical in nature, manifested by both surface oxidation and thermal degradation of hardness and strength properties followed by the removal of discrete particles by the shearing action of the hot flowing gases. Erosion of the cermet nozzles was both asymmetrical and severe. Their erosion resistance was inferior to that of a lower density, commercial-grade graphite control nozzle tested under the same general conditions.