Helium embrittlement in Fe-Ni-Cr austenitic alloys and ferritic MA 956 alloy

The helium embrittlement with helium injection by cyclotron and the irradiation embrittlement with neutrons by JMTR were compared in Fe-25% Ni-15% Cr alloys and Fe-40% Ni-15% Cr alloys with and without intermetallic compound strengthening, and in the MA 956 alloy. The results are summarized as follows: 1.(1) For helium-injected austenitic alloys precipitation-hardened by γ′ or γ″ to their highest strength, the total elongation almost becomes zero even for a very low helium level of 5–10 at ppm.2.(2) For neutron-irradiation specimens, the embrittlement is also prominent for the specimens with highest tensile strength. The embrittlement may be caused primarily by helium from 10B(n, α) reactions.3.(3) Addition of 0.25% Ti to the Fe-25Ni-15Cr alloy slightly suppresses the helium embrittlement in the case of neutron irradiation, but not in the He-injected case.4.(4) The MA 956 alloy is found quite resistant to helium embrittlement even for high helium levels of 670 atppm.