Advanced Tactical and Boost Nozzle Materials

A new generation of high temperature materials is required to meet the severe temperature, pressure and ablation requirements for future advanced solid propellant tactical and boost nozzles. The Integrated High Performance Rocket Propulsion Technology (IHPRPT) initiative phase III goals identify stringent weight and performance improvements for these motors. Existing refractory metal nozzles are heavy and suffer from increased erosion at elevated temperatures. In low oxygen partial pressures, TaC has been considered as a light-weight alternative to refractory metals due to its exceptionally high melting point. However pure TaC exhibits a lower hardness than many of the other refractory carbides and with aluminized propellants exhibits significant ablation/erosion rates similar to those of high purity graphite. In an effort to improve the performance of TaC for tactical and solid boost nozzle applications, the introduction of interstitial refractory carbides has been investigated in amounts between 5 and 50 mole percent to improve the hardness and strength. Additions of TiC, ZrC, HfC, VC, or NbC, were made to TaC and hot pressed at 2000°C or 2100°C and at a pressure of 6ksi. Following densification these different material combinations were characterized by X-ray diffraction, and electron microscopy of the polished sections was performed to reveal the microstructure and grain size. The material combinations were also characterized by density, indentation hardness and flexural strength. The individual material combinations were evaluated against comparable property data generated from TaC hot pressed at temperatures between 1900°C and 2400°C and pressures between 4ksi and 8ksi