Application of small-scale testing for investigation of ion-beam-irradiated materials
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Andrew M. Minor Department of Materials Science, University of California Berkeley, Berkeley, California 94720; and National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California 94720
Osman Anderoglu, Yongqiang Wang, and Stuart A. Maloy Los Alamos National Laboratory, Materials Science and Technology Division, Los Alamos, New Mexico 87545
Peter Hosemann Department of Nuclear Engineering, University of California Berkeley, Berkeley, California 94720 (Received 25 June 2012; accepted 28 August 2012)
Small-scale testing techniques such as nanoindentation and micro-/nanocompression are promising methods for addressing mechanical properties of ion-beam-irradiated materials. We performed different proton irradiations and critically evaluated the results obtained from nanoindentation and pillar compression, both performed parallel and perpendicular to the irradiation direction. Experiments parallel to beam direction suffer from variation of material properties with penetration depth. This is improved by cross-sectional experiments, thereby probing the effect of different doses along the beam penetration depth on mechanical properties. Finally, we demonstrate that, compared with nanoindentation, miniaturized uniaxial compression experiments offer a more reliable and straightforward interpretation of the mechanical data, as they impose a nominally uniaxial stress on a well-defined volume at a specific position. Moreover, the exposed pillar geometry is not influenced by surface contamination and enables in situ observation of the governing mechanical processes, which is typically not possible during indentation experiments in a half-space geometry.
I. INTRODUCTION
Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2012.303
mechanical changes. Depending on the material, irradiation dose, and radiation condition, a wide range of extended defects can be created. Those caused by atomic displacements at a given temperature are mainly responsible for an increase in hardening,9 yield strength (YS),10 ultimate tensile strength (UTS),5 and ductile-to-brittle transition temperature (DBTT).11 Moreover, a reduction of total and uniform elongation, upper shelf energy, and fracture toughness is commonly observed. Most early radiation damage studies were conducted in an actual reactor environment, where the dose a material receives is measured in neutron flux [n/(cm2 s)]. This, however, makes it difficult to compare different neutron spectra and assorted radiation sources to be evaluated on a common basis. Therefore, the dose unit of displacements per atom (dpa), initially based on the Kinchin–Pease model1 was found to be more useful and is widely accepted today for facilitating cross comparison among various radiation sources. However, electrical resistivity measurements performed during post irradiation annealing clearly showed a defect evolution,12 which leads to extended defects influencing the m
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