THE CONSEQUENCES OF HELIUM PRODUCTION ON MICROSTRUCTURAL DEVELOPMENT AND DEFORMATION RESPONSE IN ISOTOPICALLY TAILORED FERRITIC ALLOYS

A series of alloys have been made adding various isotopes of nickel to a ferritic/martensitic steel in order to vary the production of heliu m during irradiation. 1.5% nickel mas added to Fe-12Cr either in the f orm oi Ni-60 which produces no helium, Ni-59 which produces helium at a rate of about 10 appm He/dpa, or natural nickel which provides an in termediate level of helium due to delayed development of Ni-59. Specim ens were irradiated in the HFIR to 7 dpa at 300, 100, 500, and 600 deg rees C. This paper reports on microstructural differences and differen ces in deformation response, measured by shear punch testing, found be tween these specimens irradiated under identical conditions but with t he different nickel isotopes. Little microstructural difference was fo und between specimens with Ni-59 and Ni-Nat. Helium bubble development for high helium generation conditions appeared to be very different a t 300 and 400 degrees C. At 300 degrees C, it appeared that high densi ties of bubble-like features formed whereas at 400 degrees C, only voi ds could be found. The addition of nickel at tiny isotopic balance tn the Fe-12Cr base alloy significantly increased the shear yield and max imum strengths of the alloys with the strength of the alloys decreasin g with increasing irradiation temperature. However, helium itself. up to 75 appm at over 7 dpa, appears to have little effect on the mechani cal properties of the alloys. (C) 1997 Elsevier Science B.V.