Shock wave fabricated ceramic-metal nozzles

Abstract

Shock compaction was used in the fabrication of high temperature ceramic-based materials. The materials' development was geared towards the fabrication of nozzles for rocket engines using solid propellants, for which the following metal-ceramic (cermet) materials were fabricated and tested: B4C-Ti (15 vol.-%). B4C-Al, and TiB2-Al, with an Al content typically between 15-20 vol.-%. Here, the B4C-Ti was only shock-compacted, while the other two cermets were shock compacted followed by melt infiltration with Al. The materials were subjected to gradually more severe testing conditions. Slabs of the materials were first tested for thermal shock resistance in an acetylene flame, followed by testing in the exhaust gas stream of a rocket propellant, and thereafter as a cylindrical insert in a nozzle of TZM alloy. The B4C-Ti composite showed erosion and cracking after the first test in the propellant flame, while the B4C-Al composite failed the insert tests. The TiB2-Al composite performed well under all conditions. A venturi nozzle of that material was formed during compaction. This real, shaped nozzle was shown to function well, even during repeated 3-6 s tests. This could be explained by the resistance of TiB2 to molten Al, the high thermal conductivity of the TiB2-Al cermet and the in situ formation of a protective layer, consisting mainly of Al2O3