NASA has led many efforts in developing and advancing novel metal alloys for applications such as liquid rocket engines. One such alloy that NASA has evolved and matured is GRCop-42, named after NASA’s Glenn Research Center, where it was developed.
This copper-chrome-niobium material is used in applications such as liquid rocket engine combustion chambers, where high conductivity, high strength, and good fatigue life is required at temperatures exceeding 750° C. This novel alloy, combined with the complexity of additive manufacturing (AM) laser-powder-bed fusion, has recently enabled new propulsion concepts that were not previously possible.
NASA engineers at the Marshall Space Flight Center in Huntsville, Ala., have successfully hot-fire tested two advanced rotating detonation rocket engines (RDREs). A new class of chemical rocket engines, RDREs show the potential to increase performance by over 20 percent compared to traditional constant-pressure rocket engines. This new engine system used L-PBF to create complex internal features, pushing the boundaries of AM to mitigate the high heat loads that otherwise would have melted the component.
To date, NASA has accumulated 18 starts and more than 800 seconds of total duration with the most extreme heat loads observed in combustion devices. Beyond RDREs, NASA has accumulated some 42,000 seconds and well over 1,000 starts on various GRCop-42 L-PBF combustion chambers. NASA has worked with the AM supply chain to make the GRCop-42 powder and components commercially available.
Realizing that a limited number of alloys for AM are available for extreme environments, NASA has focused its efforts to fill this gap. NASA HR-1, a hydrogen-resistant iron-nickel alloy, has also completed extensive characterization, material testing, and hot-fire testing to meet the needs of NASA and industry missions. High-pressure hydrogen can cause the embrittlement of many materials, and specialty alloys must be formulated to accommodate this environment. The NASA HR-1 alloy has been tested in gaseous hydrogen up to 345 bar with no degradation in properties.
NASA targeted the use of the additive process of laser-powder-directed-energy deposition to produce large-scale parts approaching 2 m in diameter and more than 3 m in height. Over 280 starts and 9,000 seconds have been accumulated during hot-fire testing of liquid rocket engine channel-cooled nozzles using the NASA HR-1 alloy.
As AM continues to revolutionize the manufacturing of propulsion applications, NASA has used integrated computational materials engineering (ICME) to develop other alloys specifically for AM processes. One example is GRX-810, an extreme-temperature alloy that uses oxide dispersion strengthening to achieve high performance. This alloy will be used in applications approaching 1,100° C and exhibits creep rupture over 6,000 hours with minimal oxidation.
GRX-810 has many use applications, including turbines, hot combustors, rocket engine injectors, and advanced heat exchangers. NASA is also using ICME to develop ultra-high temperature refractory alloys for use at temperatures over 2,000° C under the Refractory Alloy Additive Manufacturing Build Optimization project.
Additive manufacturing is enabling these high-performance alloys, which in turn will continue to improve efficiency, weight reduction, and higher temperatures in the aerospace propulsion applications—allowing for exploration of the Moon, Mars, and beyond.
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