Diameter Of Dislocation Loops Research Articles

Hardening and ductility loss of RAFM steel CLF-1 irradiated with high-energy heavy ions

Irradiation induced hardening and ductility loss of a Chinese reduced-activation ferritic / martensitic steel CLF-1 is evaluated by utilizing the high-energy heavy ion irradiation and the subsequent miniature specimen test technique. Specimens were irradiated with high energy 14N6+ and 56Fe17+ ions supplied by a cyclotron to generate a quasi uniform atomic displacement damage plateau from surface to a depth about 25 μm. Three successively increasing damage levels (0.05, 0.1 and 0.2 dpa) were approached at a low temperature around 223 K. The small punch test at room temperature showed that the ductility loss can be observed at the lowest damage level and increases with the increasing damage level, similar to the variation trend of yield stress with irradiation dose. The TEM observation revealed that the average size and number density of irradiation-induced defect clusters also increased with displacement damage. Assuming that the hardening is caused by the self-interstitial-type dislocation loops, an estimation by combining the numerical calculation of the number density / mean diameter of dislocation loops with the dispersion barrier hardening model yields a similar dose dependence of the irradiation hardening.

The influence of nitrogen and nitrides on the structure and properties of proton irradiated ferritic/martensitic steel

The 12Cr1MoWV (wt%) ferritic/martensitic steel HT9 is a candidate material for fuel cladding in advanced nuclear reactors, such as the Versatile Test Reactor currently under development. As such, understanding the relationship between microstructure and mechanical properties in the context of irradiation environments for these steels is critical. N content, and more specifically interstitial N, has been hypothesized to be detrimental to irradiated properties at lower temperatures (less than 0.3Tm) to a total of 6 dpa; however, in this work at a dose of 1 dpa the irradiated microstructure was improved with added N, leading to less irradiation hardening. Three variants of HT9 were irradiated with 1.5 MeV protons to a dose of 1 dpa at 300 ˚C. The HT9 variants included Low (10 ppm), Mid (190 ppm), and High (440 ppm) N alloys that were otherwise nearly identical. Changing the N content had a variety of effects on the irradiated defect structures. As N content increased, the average dislocation loop diameter decreased, while the number density of loops increased. Additionally, extensive Ni clustering was observed on dislocations and interfaces. The Mid and High N specimens exhibited significantly less hardening (ΔHV≅100) relative to the Low N specimen (ΔHV≅160). The decrease in hardening is attributed to vanadium carbonitride acting as a sink for Ni clusters that would otherwise form on dislocations. Under the irradiation conditions used, these results suggest increasing the N content in HT9 may have a desirable effect on the irradiated structure and properties at the dose studied, as well as the swelling resistance at higher doses. In other words, N content appears to be a powerful tool for tailoring the self-interstitial atom cluster mobility in F/M steels for different temperature and dose applications.

“Contextualizing dispersoid evolution within the microstructure of MA956 using ion irradiation”

• MA956 was irradiated with 5 MeV Fe ++ up to 200 dpa from 400 to 500 °C. • Dispersoid evolution was attributed to Ostwald coarsening mechanism. • Rate theory was used to explain dislocation behavior as a function of temperature. • Voids nucleated on dispersoids only at 450 °C, 200 dpa. • The complex behavior of dispersoids is influenced by the evolution of the other microstructure features. Determining the microstructure evolution of oxide dispersion-strengthened (ODS) alloys is important for predicting the safety and structural integrity of fast reactors. In particular, understanding the co-evolution of dispersoids with the dislocation loops and network is critical for a comprehensive understanding of the microstructure response to radiation. Ion irradiations were performed on oxide dispersion strengthened MA956 with 5 MeV Fe ++ ions from 400 to 500 °C at doses ranging from 50 to 200 dpa. Characterization was performed primarily with scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy to investigate the Y-Al-O dispersoids, voids and dislocations. Regardless of temperature, the dispersoids increased in diameter and decreased in number density, which was attributed to an Ostwald coarsening mechanism supported by calculations of the radiation enhanced diffusion and ballistic dissolution. MA956 demonstrated excellent void swelling resistance and did not form voids except at 450 °C, 200 dpa where voids nucleated upon dispersoids. The dislocation loop diameter was highest at 500 °C followed by 400 °C then 450 °C while number density tended to decrease with dose. The dislocation behavior was explained as a function of the evolving defect kinetics, utilizing rate theory to calculate point defect concentrations and the increasing diffusivity of vacancies. At 400 °C, the interstitials had high enough diffusivity to nucleate new loops but vacancies remained relatively immobile. At 450 °C, vacancies are able to annihilate interstitials due to non-negligible mutual recombination causing the decreased number density of loops. At 500 °C, vacancy and interstitials are both mobile where the interstitials coalesce to form larger loops and vacancies provide a pathway for solutes diffusing to and from dispersoids.

Dose dependence of ion irradiation effects on 12Cr–6Al-ODS steel with electron-beam weld line

Oxide dispersion strengthened (ODS) steels are promising accident tolerant fuel (ATF) cladding alternatives because of their excellent oxidation resistance and mechanical properties at high temperatures. Coupons of 12Cr–6Al-ODS steel with an electron-beam (EB) weld line were irradiated with 6.4 MeV Fe3+ ions at 300 °C to nominal doses of 2.6, 7.9 and 13.0 dpa at 600 nm depth below the irradiated surface. Transmission electron microscopy (TEM) and nano-indentation tests were performed after ion irradiation to investigate the post-irradiation microstructures including the stability of oxide nanoparticles and the irradiation induced hardening, respectively, with special attention paid to the comparison between base metal and EB weld line. Oxide nanoparticles in base metal were stable under present irradiation conditions as no significant change was observed with respect to the average diameter and number density. A similar trend was recognized for the oxides in EB weld line. As for irradiation-induced dislocation loops, EB weld line exhibited larger average diameter and higher number density than base metal. And the average diameter of dislocation loops increased with increasing irradiation dose, while the number density appeared to peak at an intermediate dose of 7.9 dpa, irrespective of in base metal or EB weld line. Irradiation hardening was estimated by two different methods, so called bulk hardness by Nix-Gao model and the reference depth hardness at an indentation depth of 225 nm. Both methods showed a higher irradiation hardening in EB weld line than in base metal irrespective of irradiation dose, and hardening saturation was noted in EB weld line. The estimated hardening by dispersed barrier hardening (DBH) model was consistent with the measured hardening, suggesting that the irradiation hardening could be mainly attributed to the formation of dislocation loops with different Burgers vector.

Microstructural evolution of CLAM steel under 3.5 MeV Fe13+ ion irradiation

The microstructural evolution of CLAM steel under 3.5MeV Fe13+ ion irradiation in the temperatures from 100 to 550°C with irradiation doses up to 2.79dpa was investigated using transmission electron microscope. Dislocation loops were always observed in the steel after irradiation at 100, 300 and 550°C to different irradiation doses. The density and average diameter of dislocation loops increased with increasing irradiation dose at different temperatures. While, with the increasing the irradiation temperatures, the density of dislocation loops in the irradiated steel decreased with the increase of its diameter. Irradiation-induced voids were observed in the steel after irradiation at 550°C, and the average diameter of voids increased with increasing irradiation dose, which was 3.57, 8.02 and 8.23nm corresponding to a dose of 0.38, 0.76 and 2.75dpa, respectively. In addition, black dots were also observed in the steel after irradiation at 550°C to 2.75dpa. The formation of voids produced by irradiation at 550°C in the steel may be caused by the variation of microstructure at high temperature, such as the density of dislocation loops and irradiation-induced defects, the number of precipitates and the width of martensite laths.

MeV–GeV ion induced dislocation loops in LiF crystals

Formation of prismatic dislocation loops and evolution of dislocation structure in LiF crystals irradiated with swift 238U and 36S ions of specific energy 11MeV/u at fluences up to 1013ionscm−2 has been investigated using chemical etching and AFM. It has been shown that prismatic dislocations are formed in the stage of track overlapping above threshold fluences Φ≈109Ucm−2 and Φ≈1010Scm−2. The diameter of dislocation loops reaches 600–1000nm for 238U ions and 200nm for 36S ions. The dislocations created by 238U ions are arranged in rows along the direction of ion beam, whereas 36S ions create freely distributed dislocation loops each of them being oriented along the ion beam. The role of dislocations in ion-induced nanostructuring and hardening is discussed.

Effects of stress on radiation hardening and microstructural evolution in A533B steel

Bent specimens of A533B steel (0.16 wt% Cu) were irradiated at 290 °C to 1 dpa with 6.4 MeV Fe 3+ ions. Calculated tensile stresses at the irradiated surface were set to 0, 250, 500 and 750 MPa. The specimens were subjected to hardness measurements, transmission electron microscopy (TEM) observations and three-dimensional atom probe (3DAP) analysis. The radiation-induced hardening decreased with increasing stress to 500 MPa which was near the yield strength. TEM and 3DAP results showed that well-defined dislocation loops and solute clusters were formed. The diameter of dislocation loops increased and the number density decreased when the stress was applied, whereas the diameter and number density of solute clusters decreased. The hardening was mainly attributed to solute cluster formation. Application of tensile stress would control hardening by suppressing the solute cluster nucleation and growth.

Positron annihilation spectroscopy of proton irradiated single crystal BCC iron

Positron annihilation spectroscopy was used to analyze the open-volume defects created in single crystal, body-centered cubic iron irradiated with 1.0 MeV protons. The effects of irradiation dose and temperature were investigated. A novel technique utilizing a Bremsstrahlung beam to activate and induce positron decay in the bulk specimens, followed by Doppler broadening spectroscopy, was employed. No open-volume defects were detected in the 0.03 dpa irradiated specimens. However, the 0.3 dpa specimens exhibited an increase in the S parameter when compared to the 0.03 dpa specimens at 723 K. The 0.3 dpa specimen at 723 K indicated an increase in open-volume defects, as the radiation temperature increased compared to the 573 K, 0.3 dpa specimen. This was thought to be a consequence of the void and dislocation loop density decreasing while the void and dislocation loop diameter was increasing.

Elastic Stress Relaxation at Nanoscale: A Comprehensive Theoretical and Experimental Investigation of the Dislocation Loops Associated with As-Sb Nanoclusters in GaAs

AbstractA comprehensive experimental and theoretical investigation was performed for the system of As-Sb nanoclusters and nanoscale dislocation loops in GaAs:Sb films grown by molecular beam epitaxy at low temperature and subsequently annealed. A model was developed for the elastic stress relaxation, self-energies and interactions in such cluster-loop nanosystems. The model was based on the experimental investigation of the microstructure of the As-Sb nanoclusters by transmission electron microscopy. The atomic structures of the As-Sb nanoclusters and dislocation loops, as well as their orientation relationships were determined. A strong anisotropic mismatch between the As-Sb nanoclusters and GaAs matrix has been revealed. This mismatch was proven to be a reason for the formation of the prismatic nanoscale dislocation loops nearby the nanoclusters. Our theoretical model explores the elastic properties of an inclusion with uniaxial dilatation. For such inclusions, the elastic stresses and stored energy are determined in a closed analytical form. The theoretical analysis predicts a specific non-linear dependence of the dislocation loop diameter on the cluster diameter, which fits well the experimentally observed one. It is demonstrated that both the change in the inclusion self energy due to diminishing dilatation and the interaction between the dislocation loop and inclusion are important in the relaxation phenomena at stressed nanoscale inclusions in semiconductors.

Investigation of dislocation loops associated with As–Sb nanoclusters in GaAs

A model is developed for the elastic stress relaxation via formation of prismatic dislocation loops in a vicinity of the As–Sb nanoclusters built in GaAs matrix. The model is based on the experimental investigation of the microstructure of the As–Sb nanoclusters, which can be produced in Sb-doped GaAs films by the molecular-beam epitaxy at low temperature and subsequent anneal. A strong anisotropic mismatch between the As–Sb nanoclusters and GaAs matrix has been revealed by transmission electron microscopy. This mismatch was proven to be a reason for the formation of nanoscale dislocation loops near the nanoclusters. Our theoretical model explores the elastic properties of an inclusion with uniaxial dilatation. For such inclusions, the elastic stresses and stored energy are determined in a closed analytical form. The theoretical analysis predicts a specific nonlinear dependence of the dislocation loop diameter on the cluster diameter, which fits well the experimentally observed one. It is demonstrated that both the change in the inclusion self-energy due to diminishing dilatation and the interaction between the dislocation loop and inclusion are important in the relaxation phenomena in precipitated semiconductors.

Effects of composition and helium injection on dislocation loop development in pure FeNiCr alloys under Ni ion irradiation

Pure Fe35Ni7Cr, Fe45Ni7Cr, Fe40Ni13Cr and Fe45Ni15Cr alloys were irradiated by 4MeV Ni 2+ ions at 948 K to doses of about 0.05, 0.3 and 1.0 dpa without helium injection or with simultaneous helium injection. With increasing Ni content and decreasing Cr content, the diameter of radiation-induced dislocation loops increased, and the dose at which the dislocation loops disappeared to develop into dislocation networks decreased. The diameter of dislocation loops induced by Ni 2+ ions irradiation with simultaneous helium injection was larger than that without helium injection for the Fe35Ni7Cr and Fe45Ni7Cr alloys.

Compositional dependence of dislocation loop development and microstructures in austenitic Fe-Ni-Cr alloys under proton irradiation

In order to examine the compositional dependence of dislocation loops and other microstructural changes under irradiation in austenitic Fe-Ni-Cr alloys, eight solution-annealed ternary Fe-Ni-Cr alloys whose Ni content varies from 25 to 45 wt% and Cr content from 5 to 15 wt% were irradiated by 200 keV protons at 873 K to 0.4, 1.6 and 15 dpa after helium pre-injection to 10 appm. Dislocation loop diameter increased but loop number density decreased with increasing Ni content and decreasing Cr content. A discernible compositional change of dislocation density was not detected. With increasing Ni content and decreasing Cr content, swelling decreased because of the drastic decrease of void number density. The attachment of dislocation lines to the voids, tiny voids smaller than 3 nm in diameter, and black contrast, which could be the contrast from void embryos smaller than 10 nm in diameter, were observed in the alloys irradiated to 1.6 dpa.

Residual defects in high-energy B-, P- and As-implanted Si by rapid thermal annealing

The annealing behavior of secondary defects generated in 2 MeV B- and P-, and 1 MeV As-implanted (100) Si with a dose of 5×1014 ions/cm2 has been investigated after rapid thermal annealing (RTA) treatment using cross-sectional TEM observations. The results are compared with ones obtained by furnace annealing (FA) treatment. RTA is more effective than FA for the defect density reduction of deep defects existing beyond 2 μm depths from the surface in B- and P-implanted layers. However, when a dislocation loop diameter is close to the substrate surface, as in the case of As implantation, the loops climb up to the surface by 1250 °C RTA. Moreover, repeated RTA is effective for the suppression of secondary defect growth in B- and P-implanted layers, while there is no difference in defect density or configuration for As implantation between repeated and simple RTA.

Flux pinning by radiation damage in oxygen-doped niobium

Abstract Niobium foils, doped with 10, 250, 480 or 904 wt. p.p.m. of oxygen, were irradiated with fast neutrons (E>0·1 MeV) to a total fluence of 9×1019 cm−2 at ∼50°C. The radiation damage as characterized by transmission electron microscopy consists of dislocation loops and ‘black spot’ damage (probably small, unresolved dislocation loops). The density of dislocation loops increases by about a factor of 20 with increasing oxygen content whereas the root mean square dislocation loop diameter decreases so as to maintain the total area of dislocation loop approximately constant. Despite the great increase in dislocation loop density ρ with oxygen content, the pinning force density F p at low reduced magnetic induction decreases by more than a factor of 20 from the 10 to the 904 p.p.m. oxygen sample. These results show that the decrease in loop size through its effect on the elementary pinning force f p of the loop far outweighs the increase in loop density. Tests of summation models are made using calculated values of the f p(D) for a loop of diameter D and the experimentally determined loop density distribution ρ(D). The linear summation of Dew-Hughes [F p ∝ ρ(D)f p(D)], which neglects the rigidity of the flux line lattice (FLL), is found to be inconsistent with the large decrease observed in F p with oxygen content whereas the quadratic sum of Labusch [F p∝ (D)f p 2(D)] and others who take the FLL rigidity into account is found to produce results in reasonable agreement with the observed decrease.