SEDL / STP / STP955-EB / STP33847S

Radiation-Induced Segregation in Light-Ion Bombarded Ni-8% Si

Packan, N
Research staff member, and research associate, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN

Heatherly, L
Research staff member, and research associate, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN

Kesternich, W
Research Scientists, Institute for Solid State Research, Jülich Nuclear Research Facility, Jülich,

Schroeder, H
Research Scientists, Institute for Solid State Research, Jülich Nuclear Research Facility, Jülich,

Pages: 11    Published: Jan 1987

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Abstract

Radiation-induced segregation (RIS) is an important area of current research because of potential detrimental effects including embrittlement. In this work, a quantitative assessment is made of radiation-induced silicon segregation to internal grain boundaries compared with that to the external surfaces. Tension specimens of Ni-8 atomic % Si have been irradiated at 750 K (475°C) with either 7-MeV protons or 28-MeV alpha particles to damage levels of 0.1 to 0.3 dpa. Postirradiation tension testing at 300, 720, or 975 K produces ductile failures with elongations > 15%. However specimens that had implantation of 250 to 1000 atomic ppm He at 975 K (700°C) before irradiation did fracture intergranularly when pulled at 975 K inside a scanning Auger microprobe, thereby exposing grain boundary surfaces for depth profile analysis. After correction for preferential sputtering effects, RIS of silicon to outer surfaces is found to give rise to a strongly enriched surface layer, 20 to 30 nm thick, followed by a shallow depletion zone for the next ∼200 nm, in agreement with previous studies in the literature. By contrast, silicon segregation to fracture-exposed grain faces varies considerably from face to face but generally declines more gradually with little or no depletion zone. Observations of silicon profiles and Ni³Si formation at grain boundaries obtained by analytical transmission electron microscopy (TEM) generally confirm the Auger results.