Nanoindentation investigation of ion-irradiated Fe–Cr alloys using spherical indenters

Bushby, A. J.; Roberts, Steve; Hardie, Christopher D.

doi:10.1557/jmr.2011.304

Cited by 25 publications

(18 citation statements)

References 22 publications

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“…The model uniquely captures the four-fold pile-up increase in the <001> grain in the implanted samples, affirming the strain-softening hypothesis. Strain-softening and consequent slip channel formation in irradiated materials, both fcc and bcc, has been experimentally observed in numerous studies [39]- [41]. This is of particular concern as it may lead to untimely failure due to loss of ductility.…”

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confidence: 95%

Orientation-dependent indentation response of helium-implanted tungsten

Das

Tarleton

et al. 2019

Applied Physics Letters

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A literature review of studies investigating the topography of nano-indents in ion-implanted materials reveals seemingly inconsistent observations, with report of both pile-up and sink-in. This may be due to the crystallographic orientation of the measured sample point, which is often not considered when evaluating implantation-induced changes in the deformation response. Here we explore the orientation dependence of spherical nano-indentation in pure and helium-implanted tungsten, considering grains with <001>, <110> and <111> out-of-plane orientations. Atomic force microscopy (AFM) of indents in unimplanted tungsten shows little orientation dependence. However, in the implanted material a much larger, more localised pileup is observed for <001> grains than for <110> and <111> orientations. Based on the observations for <001> grains, we hypothesise that a large initial hardening due to heliuminduced defects is followed by localised defect removal and subsequent strain softening. A crystal plasticity finite element model of the indentation process, formulated based on this hypothesis, accurately reproduces the experimentally-observed orientation-dependence of indent morphology. The results suggest that the mechanism governing the interaction of helium-induced defects with glide dislocations is orientation independent. Rather, differences in pile-up morphology are due to the relative orientations of the crystal slip systems, sample surface and spherical indenter. This highlights the importance of accounting for crystallographic orientation when probing the deformation behaviour of ion-implanted materials using nano-indentation. Main textIon-implantation is commonly used to mimic irradiation damage in materials. This costeffective technique allows examination of specific irradiation factors. For example heliumimplantation introduces irradiation-like defects, while enabling examination of the interaction of these defects with the implanted helium [1]- [3]. Similarly self-ion implantation has been extensively employed to emulate the cascade damage caused by neutron irradiation [4], [5]. Nano-indentation is often used to gain insight into the mechanical properties of the few-micronthick ion damaged layers. Marked changes in pile-up morphology around nano-indents have been observed in irradiated materials, even for low damage levels. A review of several studies reveals seemingly contradictory observations. For example, large pile-up around 250 nm deep Berkovich nano-indents was observed in 0.3 at.% helium-implanted W-1 at. % Re [6]. But for HT9 ferritic/martensitic steel, implanted with both helium and protons, there was no noticeable difference in indent surface profile [7]. A suppression of pile-up was noticed around indents in 2 MeV W + ion implanted W-5 wt%Ta (0.04 dpa) [8]. On the other hand Fe + implantation of Fe-12 wt%Cr lead to a distinct increase in pile-up [9]. This raises the question why implantation with helium or self-ions causes pile-up increase in some materials and suppression in others. Generally, pi...

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confidence: 95%

Orientation-dependent indentation response of helium-implanted tungsten

Das

Tarleton

et al. 2019

Applied Physics Letters

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“…In contrast, there are few methods available for the characterisation of mechanical properties from such small volumes of material, and analyses regarding best practise and validity of using these techniques for irradiated materials are scarce. There have been several investigations which have used nanoindentation as a means to measure the effects of ion irradiation on mechanical properties [1][2][3][4][5][6][7][8][9][10][11][12]. The majority of investigations have been conducted using a Berkovich tip geometry and include various methods such as load-unload [1,2] and continuous stiffness measurement (CSM) [8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Understanding the effects of ion irradiation using nanoindentation techniques

Hardie

Roberts

Bushby

2015

Journal of Nuclear Materials

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101

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The effects of ion irradiation in materials for research are usually limited to a shallow surface layer of the order of one micrometre in depth. Determining the mechanical properties of such irradiated materials requires techniques with high spatial resolution. Nanoindentation is a relatively simple method for investigating these shallow layers with the advantage that statistically rich data sets for elastic and plastic property values can be generated. However, interpretation of the results requires and understanding of the material response, including the extent of the plastic zone with respect to the irradiated layer, pile-up or sink-in of material around the indentation site that affect the calculated contact area and hence derived mechanical property values. An Fe + self-irradiated Fe12%Cr alloy was investigated with three different indenter tip geometries, a Cube corner, Berkovich and 10 micron radius indenter. Sharp indenters provide sufficiently small plastic zones to be contained within the irradiated layer but pop-in events and pile-up need to be taken into account for correct interpretation of the mechanical properties of the irradiated material.

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“…The compressive yield stresses in the implanted and unimplanted materials are similar, which is different from the nanohardness results which show a clear hardening effect from implantation, as is commonly found [25]. Using the well known relation that hardness % 3Â flow stress [28] the flow stress of unimplanted pure iron would be predicted from the indentation data to be % 1 GPa and that of the implanted material % 1.8 GPa.…”

Section: Resultsmentioning

confidence: 65%

“…Electropolished 3 mm discs of the same material were also implanted at the same time to allow TEM studies of the damage structure in material with an identical thermal cycle. The predicted damage profile (using SRIM with an Fe displacement energy of 40 eV) is shown in Bushby et al [25]; there are two overlapping peaks due to the two beam energies used, giving a fairly uniform damage profile with an average dose of 6 dpa over the first 0.75 lm depth, decreasing to zero at 1 lm depth.…”

Section: Methodsmentioning

confidence: 99%

“…The implantation time was 124 min for the 2.0 MeV ions and 75 min for the 0.5 MeV ions. The bulk samples were mounted on stainless steel holders in a similar manner to that described by Armstrong et al [6] and Bushby et al [25] The temperature monitored by a thermocouple mounted alongside the samples; this gave a reading of 275°C ± 10°C throughout the experiment. Electropolished 3 mm discs of the same material were also implanted at the same time to allow TEM studies of the damage structure in material with an identical thermal cycle.…”

Section: Methodsmentioning

confidence: 99%

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