Effects of preinjected helium in heavy-ion irradiated nickel and nickel-copper alloys
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INTRODUCTION
RADIATION-induced void swelling is one of the serious material problems to be solved for proposed fusion reactors, m To better understand the mechanisms controlling the void formation process, pure metals and simple alloys are often chosen for radiation damage studies, although they are unlikely to be used as fusion reactor materials. Ni-Cu alloys have been shown to be very resistant to void swelling under neutron, t2] ion, t3-61 and electron tT] irradiations in the past decade. Such an observation is significant because the alloy system forms a complete solid solution over the entire composition range and voids can easily be produced in both pure nickel and copper in the presence of certain gas atoms. Helium is a transmutation product in fusion reactor materials due to (n, o~) reactions and is also known as a void nucleation agent. Zinkle et al.[8] injected 200 appm helium into nickel, copper, and three Ni-Cu alloys at a homologous temperature of 0.65 Tm and found nothing anomalous concerning helium bubble growth in the alloys which would explain the suppression of void swelling. Other than the above study, the effect of helium in Ni-Cu alloys has not been carefully investigated, even though some of the previously irradiated samples contain a certain amount of helium, t2,3j The objective of this study is to determine whether preinjected helium would promote void formation in Ni-Cu alloys during heavy ion irradiation. A heavy-ion irradiated pure nickel specimen with helium L.M. WANG, formerly Research Assistant, Materials Science Program, University of Wisconsin-Madison, is Post-Doctoral Appointee with the Materials Science Division, Argonne National Laboratory, Argonne, IL 60439. S.J. ZINKLE, Research Staff Member, is with the Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6376. R.A. DODD, Professor, Department of Materials Science and Engineering, and G.L. KULCINSKI, Professor, Department of Nuclear Engineering and Engineering Physics, are with the University of Wisconsin-Madison, Madison, WI 53706. This paper is based on a presentation made in the symposium "Irradiation-Enhanced Materials Science and Engineering" presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, Illinois, September 25-29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD. METALLURGICAL TRANSACTIONS A
preinjection is included in the study for the purpose of comparison. II.
EXPERIMENTAL
The pure nickel specimen used in this study came from a degassed Marz grade sheet which contained 75 appm oxygen. Our previous results showed that at this residual oxygen level, the effect of preinjected helium on void formation is more pronounced than in the as-received foil which contains 180 appm oxygen.[9] This is because oxygen is also found to be a void stabilizer, t9,I~ Two Ni-Cu alloys, Ni-10 at. pct Cu and Ni-50 at. pct Cu, were fabricated from Marz grade Ni (99.995 wt pet pure) and Cu (99.999 wt pct pu
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