Progress in understanding radiation damage in structural materials is hampered by the lack of test reactors, long irradiations and high cost. Here we show that through strict control of experimental ...parameters and accounting for He production and damage-rate differences, the microstructure of ion-irradiated ferritic–martensitic steel closely resembles that created in-reactor across the full range of microstructure features. The level of agreement establishes for the first time the capability to tailor ion irradiation to emulate in-reactor radiation damage.
In the present study, the polarization characteristics of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) - Gd0.1Ce0.9O1.95 (GDC) composite cathodes with different volume ratios were investigated. Samples with volume ...ratios of 20:80, 30:70, 50:50, 70:30 and 100:0 vol % were tested. The electrochemical impedance spectroscopy tests and current voltage curve measurements were carried out for the current densities from 0 to 0.2 Acm−2 with an interval of 0.05 Acm−2. The results showed that a volume ratio of LSCF:GDC = 30:70 composite cathode led to the lowest overpotential, and the overpotential increased in the order of 30:70, 50:50, 70:30, 100:0, 20:80 vol %. Three dimensional microstructures of composite cathodes were reconstructed and quantified by dual beam focused ion beam-scanning electron microscope (FIB-SEM). The results showed that neither LSCF surface area nor triple phase boundary (TPB) alone could explain the dependence of polarization characteristics on volume ratios. Current and electrochemical potential distributions were simulated by the Lattice Boltzmann method, in which both surface and TPB reactions were considered. Prediction considering both surface and TPB reactions could predict qualitatively the dependence of overpotentials on LSCF - GDC cathode composition.
•LSCF-GDC composite cathode with different volume ratios of components are fabricated.•Polarization characteristics are evaluated.•Microstructures are reconstructed by FIB-SEM technique.•Cathode overpotential is correlated to the microstructural characteristics.•Performance of LSCF-GDC cannot be explained only by the surface reaction.
To simultaneously obtain superior superelasticity and biological properties, single- and multi-layer Ti–23Nb coatings were deposited on a cold-rolled NiTi substrate using laser metal deposition ...(LMD). The microstructure of the single-layer coating consisted of a cellular structure with a grid size of ∼300 μm in the eutectic layer, strip structures and prior β-(Ti, Nb) phases surrounded by the Ti2Ni(Nb) phase in the Ni diffusion zone. In contrast, the microstructure of the multi-layer coating consisted of α′, α′′, and prior β phases, which arise from the partition of Nb. Compared with the NiTi substrate, the Ni ion release concentration of the single-layer coating is reduced by 45% with similar nano-mechanical behavior, i.e. a nanohardness, H, of ∼4.0 GPa, a reduced Young's modulus, Er, of ∼65 GPa, an elastic strain to failure, H/Er, of ∼0.06, a yield stress, H3/Er2, of ∼0.016 GPa, and a superelastic strain recovery, ηsr, of ∼0.3. The reduction of Ni ion concentration for multi-layer coating after 35 days is even better at up to 62%, but at the cost of a degradation in the mechanical properties. The LMD coatings have a high dislocation density, and their creep is controlled by dislocation movement.
•The diffusion of Ni during laser melting leads to the formation of cellular and strip subgrains.•α″ martensite is critical for the properties of the TiNb binary alloys produced by LMD.•The single-layer coating can suppress the release of Ni ions while preserving the superelasticity of substrate.
Post-irradiation annealing was performed on a 304L SS that was irradiated to 5.9 dpa in the Barsebäck 1 BWR reactor. Evolution of dislocation loops, radiation-induced solute clusters and ...radiation-induced segregation at the grain boundary was investigated following thermal annealing at 500 °C and 550 °C up to 20 h. Dislocation loops, Ni-Si and Al-Cu clusters, and enrichment of Ni, Si and depletion of Cr at the grain boundary were observed in the as-irradiated condition. Dislocation loop size did not change significantly after annealing at 550 °C for 5 h but the loop number density decreased considerably and loops mostly disappeared after annealing at 550 °C for 20 h. The average size of Ni-Si and Al-Cu clusters increased while the number density decreased with annealing. The increase in cluster size was due to diffusion of solutes rather than cluster coarsening. Significant volume fractions of Ni-Si and Al-Cu clusters still remained after annealing at 550 °C for 20 h. Substantial recovery of Cr and Ni at the grain boundary was observed after annealing at 550 °C for 5 h but neither Cr nor Ni was fully recovered after 20 h. Annihilation of dislocation loops, driven by the thermal vacancy concentration gradient caused by the strain field and stacking fault associated with the loops appeared to be faster than annihilation of solute clusters and recovery of Ni and Si at the grain boundary, both of which are driven by the solute concentration gradients.
Void evolution in Fe++-irradiated ferritic-martensitic alloy HT9 was characterized in the temperature range of 400–480°C between doses of 25 and 375 displacements per atom (dpa) with pre-implanted ...helium levels of 0–100appm. A systematic study using depth profiling in cross-section samples was conducted to determine a valid region of analysis between 300 and 700nm from the surface, which excluded effects due to the injected interstitial and the surface. Pre-implanted helium was found to promote void swelling at low doses by shortening the nucleation regime and to retard void growth at doses in the transient regime by enhancement of nucleation of small voids. Swelling was found to peak at a temperature of 460°C. The primary effect of temperature was on the nucleation regime; nucleation regime was the shortest at 460°C compared to that at 440 and 480°C. The growth rate of voids was temperature-invariant. Steady state swelling was reached at 460°C between 188 and 375dpa at a rate of 0.02%/dpa.
Solution-annealed 304L stainless steel (SS) was irradiated to 130 dpa at 380 °C, and to 15 dpa at 500 °C and 600 °C, and cold-worked 316 SS (CW 316 SS) was irradiated to 130 dpa at 380 °C using 5 MeV ...Fe++/Ni++ to produce microstructures and radiation-induced segregation (RIS) for comparison with that from neutron irradiation at 320 °C to 46 dpa in the BOR60 reactor. For the 304L SS alloy, self-ion irradiation at 380 °C produced a dislocation loop microstructure that was comparable to that by neutron irradiation. No voids were observed in either the 380 °C self-ion irradiation or the neutron irradiation conditions. Irradiation at 600 °C produced the best match to radiation-induced segregation of Cr and Ni with the neutron irradiation, consistent with the prediction of a large temperature shift by Mansur's invariant relations for RIS. For the CW 316 SS alloy irradiated to 130 dpa at 380 °C, both the irradiated microstructure (dislocation loops, precipitates and voids) and RIS reasonably matched the neutron-irradiated sample. The smaller temperature shift for RIS in CW 316 SS was likely due to the high sink (dislocation) density induced by the cold work. A single self-ion irradiation condition at a dose rate ∼1000× that in reactor does not match both dislocation loops and RIS in solution-annealed 304L SS. However, a single irradiation temperature produced a reasonable match with both the dislocation/precipitate microstructure and RIS in CW 316 SS, indicating that sink density is a critical factor in determining the temperature shift for self-ion irradiations.
Localized deformation has emerged as a potential factor in irradiation-assisted stress corrosion cracking of austenitic stainless steels in LWR environments and the irradiated microstructure may be a ...critical factor in controlling the degree of localized deformation. Seven austenitic alloys with various compositions were irradiated using 2–3
MeV protons to doses of 1 and 5
dpa at 360
°C. The irradiated microstructure consisting of dislocation loops and voids was characterized using transmission electron microscopy. The degree of localized deformation was characterized using atomic force microscopy on the deformed samples after conducting constant extension rate tension tests to 1% and 3% strain in argon. Localized deformation was found to be dependent on the irradiated microstructure and to correlate with hardening originating from dislocation loops. Dislocation loops enhance the formation of dislocation channels and localize deformation into existing channels. On the contrast, voids mitigate the degree of localized deformation. The degree of localized deformation decreases with SFE with the exception of alloy B. Localized deformation was found to have similar dependence on SFE as loop density suggesting that SFE affects localized deformation by altering irradiated microstructure.
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