No abstract

No abstract

Model FeCrAl alloys of Fe-10%Cr-5%Al, Fe-12%Cr-4.5%Al, Fe-15%Cr-4%Al, and Fe-18%Cr-3%Al (in wt %) were irradiated with 1 MeV Kr ++ ions in-situ with transmission electron microscopy to a dose of 2.5 displacements per atom (dpa) at 320C. In all cases, the microstructural damage consisted of dislocation loops with ½〈111〉 and 〈100〉 Burgers vectors. The proportion of ½〈111〉 dislocation loops varied from ~50% in the Fe-10%Cr-5%Al model alloy and the Fe-18Cr%-3%Al model alloy to a peak of ~80% in the model Fe-15%Cr-4.5%Al alloy. The dislocation loop volume density increased with dose for all alloys and showed signs of approaching an upper limit. The total loop populations at 2.5 dpa had a slight (and possibly insignificant) decline as the chromium content was increased from 10 to 15 wt %, but the Fe-18%Cr-3%Al alloy had a dislocation loop population ~50% smaller than the other model alloys. The largest dislocation loops in each alloy had image sizes of close to 20 nm in the micrographs, and the median diameters for all alloys ranged from 6 to 8 nm. Nature analysis by the insideoutside method indicated most dislocation loops were interstitial type.

The serration of grain boundaries in Inconel 600 caused by heat treatment is studied systematically. A new method based on Fourier transforms is used to analyse the multiple wave-like character of the serrated grain boundaries.A new metric -the serration index -is devised and utilised to quantify the degree of serration and more generally to distinguish objectively between serrated and non-serrated boundaries. By considering the variation of the serration index with processing parameters, a causal relationship between degree of serration and solution treatment/cooling rate is elucidated. Processing maps for the degree of serration are presented. Two distinct formation mechanisms arise which rely upon grain boundary interaction with carbides: (i) Zener-type dragging which hinders grain boundary migration and (ii) a faceted carbide growth-induced serration.

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 .

No abstract

No abstract

No abstract