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The NERVA engine environment and material property requirements are discussed. Cryogenic radiation tests performed on structural alloys in support of the NERVA Program are presented. Eleven alloys were irradiated in liquid hydrogen to an average dose of 5 × 1016 nvt (E > 1.0 Mev). These alloys, which were tested in tensile and shear in the postirradiation condition prior to warmup, include the A356-T6, 6061-T6, and 7075-T6 aluminum alloys; Types 347 and A-286 stainless steels; Hastelloy C, Inconel X-750, and Inconel 713-C nickel-base alloys; and Ti-5Al-2.5Sn ELI titanium alloy. The D-979 nickel-base alloy and Type 410 stainless steel were tested in shear only. Most alloys showed small but significant changes in one or more properties, with the two cast alloys, Inconel 713-C and Type A356, being most affected. Notched tensile strengths were relatively insensitive to this dose level. Three alloys decreased in shear strength. Although aluminum alloys are quite insensitive to radiation damage at ambient and higher temperatures, their sensitivity to damage at cryogenic temperatures is comparable to that of the other alloys. Six alloys were irradiated in liquid nitrogen to neutron doses between 5 × 1017 and 1 × 1018 nvt (E > 1.0 Mev). These alloys were tension-tested without warmup in the postirradiation condition at 140 R. In addition, all alloys were annealed at room temperature for several days and later tested at 140 and 540 R. Selected alloys were annealed and tested at various temperatures up to 1750 R. The alloys tested in tension included the 2219-T6 aluminum alloy, Type 301 cold-worked, and Type 303 Se annealed-bar stainless steels, the nickel-base Inconel 718 and Inconel X-750 alloys, and Ti-5Al-2.5Sn ELI titanium alloy. Radiation effects were noted in all materials on testing without warmup. Partial or complete recovery of properties occurred at 540 R for all specimens. Marked differences were observed in the behavior of sheet and bar stock in 2219-T6 aluminum and Inconel 718. The influence of test temperature and test atmosphere is discussed, and recommendations are made regarding future radiation-testing variables for obtaining engineering design data.
radiation effects, low temperature, cryogenics, metals, nuclear propulsion, rocket engines, aluminum alloys, stainless steels, nickel alloys, titanium alloys
Lombardo, J. J.
Chief, Materials Branch, Space Nuclear Propulsion Office, Cleveland, Ohio
Dixon, C. E.
Manager, Advanced Materials Section, REON Division, Aerojet-General Corp., Sacramento, Calif.
Begley, J. A.
Metallurgical engineer, Westinghouse Astronuclear LaboratoryLehigh University, PittsburghBethlehem, Pa.Pa.