The combustion chamber is the hottest part of a rocket engine and the higher the temperature the more efficiently the engine can perform. This means that there is an ongoing desire to increase the heat that a chamber can operate at by using highly heat-resistant materials. Currently, C103, which is an alloy of niobium with hafnium is used with R512E di-silicide coating for chamber temperature up to ~1350°C.
Ceramic material such as silicon nitride (Si3N4) is able to withstand heats of up to around 1500˚C and even higher, making it particularly suitable for rocket combustion chambers, but ESA wanted to join this ceramic with C103 alloy material due to the difficultly of manufacturing monolithic ceramic combustion chambers.
Early hot fire tests had demonstrated the usefulness of combining these two materials, however these tests had used bolts to join them together, which increases the risk of failure on the combustion engine, making it unsuitable for astrospace use. The ESA sought TWI’s assistance in joining the two challenging materials for the first time.
Following research, TWI found a solution and was able to successfully join C103 alloy with silicon nitride for the first time in our history, using diffusion bonding and brazing processes with the aid of interlayers. The joining of these dissimilar materials was demonstrated in the form of rings, which is representative of thruster combustion chamber joint geometry.
This pioneering work means that ESA’s rocket combustion chamber can now operate at the desired higher heats, improving efficiency without jeopardising safety.
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