A document describes the low-cost manufacturing of C103 niobium alloy combustion chambers, and the use of a high-temperature, oxidation-resistant coating that is superior to the standard silicide coating. The manufacturing process involved low-temperature spray deposition of C103 on removable plastic mandrels produced by rapid prototyping. Thin, vapor-deposited platinumindium coatings were shown to substantially improve oxidation resistance relative to the standard silicide coating.Development of different low-cost plastic thrust chamber mandrel materials and prototyping processes (selective laser sintering and stereolithography) yielded mandrels with good dimensional accuracy (within a couple of mils) for this stage of development.
The feasibility of using the kinetic metallization cold-spray process for fabrication of free-standing C103 thrusters on removable plastic mandrels was also demonstrated. The ambient and elevated temperature mechanical properties of the material were shown to be reasonably good relative to conventionally processed C103, but the greatest potential benefit is that cold-sprayed chambers require minimal post-process machining, resulting in substantially lower machining and material costs.
The platinum-iridium coating was shown to provide greatly increased oxidation resistance over the silicide when evaluated through oxyacetylene torch testing to as high as 300 ºF (≈150 ºC). The iridium component minimizes reaction with the niobium alloy chamber at high temperatures, and provides the high-temperature oxidation resistance needed at the throat.
This work was done by Brian E. Williams and Victor M. Arrieta of Ultramet for Johnson Space Center. MSC-24495-1