Microstructural examination of neutron, proton and self-ion irradiation damage in a model Fe9Cr alloy

Abstract

Transmission electron microscopy (TEM) was used to compare the microstructural defects produced in an Fe9Cr model alloy during exposure to neutrons, protons, or self-ions. Samples from the same model alloy were irradiated using fission-neutrons, 2MeV Fe+ ions or 1.2MeV protons at similar temperatures (~300°C) and similar doses (~2.0dpa). The neutron-irradiated alloy contained visible interstitial dislocation loops with b=〈111〉, and on average ~5nm in size. The density varied from 2±1x10 20 m -3 (in the matrix far from dislocations and boundaries) to 1.2±0.3x10 23 m -3 (close to helical dislocation lines). Chromium α'-phase precipitates were also identified at a density of 7.4±0.4x10 23 m -3 . Self-ion irradiation produced mostly homogeneously distributed dislocation loops (6-7nm on average), and with a greater fraction of 〈100〉 loops (~40%) than was seen in the neutron-irradiated alloy, and at a density of 6.8±0.8 x10 22 m -3 . In contrast to the loops produced by neutron irradiation, the self-ion irradiated Fe9Cr contained only vacancy-type loops. Chromium also remained in solution. Proton-irradiated Fe9Cr contained interstitial dislocation loops close to helical-dislocation segments, similar to the neutron-irradiated sample. Chromium α'-phases were also identified in the proton-irradiated sample at a density of 2.5±0.3x10 23 m -3 , and large voids (up to 7nm) were found at a density over 10 22 m -3 . Like the neutron-irradiated sample, the density of dislocation loops was also heterogeneously distributed; far from grain boundaries and dislocation lines the density was 2.5±0.4 x10 22 m -3 , while close to helical dislocation lines the density was 8.1±1.3 x10 22 m -3 .

Atom probe characterisation of segregation driven Cu and Mn–Ni–Si co-precipitation in neutron irradiated T91 tempered-martensitic steel

“…It is well known, and the topic of a large amount of literature, that a smaller amount of hardening is contributed by dislocation loops, as illustrated in [24] for Fe-Cr binary alloys. Potential contributions from the evolution of network dislocations is rapidly emerging as an issue, but is not close to being well quantified [26,27,40,43,78]. However, discussion evolved dislocation loop and line hardening, including the effects of segregation and precipitation, is beyond the scope of this paper.…”

“…Neutron irradiation drives microstructural and microchemical evolutions in TMS, like T91, which have detrimental effects on the mechanical properties, thus limiting the lifetime and performance of reactor structural components. Reported microstructural features that result from neutron irradiation of 9-12 wt% Cr tempered-martensitic alloys, such as T91, HT9 and Eurofer97, include the Mn Ni Si precipitates (MNSPs) [13][14][15][16][17][18][19][20] (often described as 'G-phase' -Mn6Ni16Si7 [21]), Cr-rich alpha prime (⍺') precipitates [14,17,[22][23][24], voids, dislocation loops, evolved network dislocations, and solute segregation to, and precipitation at, dislocations [19,[25][26][27]. These microstructural changes are due to the excess radiation defect generation and clustering, dislocation climb, radiation-induced segregation (RIS) and radiation enhanced diffusion (RED).…”

Nanocluster evolution and mechanical properties of ion irradiated T91 ferritic-martensitic steel

“…Ion damage cascades form dislocation loops [14] at 300 o C. At the 'high' dose, Si segregated to the periphery of dislocations as shown in Figure 7(a). These Si-decorated dislocations have either a line or loop formation, and these loops have an average diameter of 13 nm ± 3 nm.…”

“…Microstructural and microchemical evolution is driven by neutron irradiation [2]. Characteristic microstructural features that result from neutron irradiation of T91 steel are the formation of Mn, Ni and Si -rich precipitates (MNSP) [3][4][5][6][7][8] (also known as G-phase Mn6Ni16Si7), Cr-rich alpha prime (α') formation [4,7,[9][10][11], voids [12] and solute segregation towards dislocations [13][14][15]. These features are a resultant of radiation-induced precipitation and radiation-enhanced diffusion mechanism [16].…”

Interface-Driven Strain in Heavy Ion-Irradiated Zr/Nb Nanoscale Metallic Multilayers: Validation of Distortion Modeling via Local Strain Mapping

“…Heavy ion irradiation is commonly used to mimic fusion neutron-induced irradiation damage for several reasons. First, ion fluxes are much higher, enabling the desired dpa level to be obtained in minutes or hours, rather than months or years. − Second, the defect clusters induced during heavy ion and neutron irradiations are quite similar, such as dislocation loops (size up to 10 nm) in the irradiated BCC metals . Third, the neutron spectrum of typical fission sources fails to replicate the high-energy neutrons (14.1 MeV) that will be produced by the DEMO fusion reactor. , Finally, neutron irradiation also results in radioactivity, often necessitating long storage of samples to reduce their activity.…”