Various alloys with face-centered cubic structures were irradiated to fast fluences of 1.5 × 1021 n/cm2 (E > I MeV) and tested in tension at elevated temperatures. The alloys that were investigated included pure nickel (99.999%), Nickel 200, a non-nickel manganese stabilized stainless steel (Tenelon), and two cobalt alloys. One of the cobalt alloys contained 10% nickel (Haynes Stellite-25) while the other was nickel free (UMCo-50). It was found that irradiation caused embrittlement in all of these alloys when they were tested in tension at elevated temperatures.