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Positron annihilation lifetime spectroscopy (PALS) was performed to characterize the interfacial nanostructure between the oxide particles and ferritic matrix in two types of oxide dispersion strengthened (ODS) alloys: FeCr dispersed with Y-Ti oxide nanoparticles and FeCrAl dispersed with Y-Al oxide nanoparticles. The spectra were precisely fitted and decomposed into three components with two trapping rates. Bulk lifetime approached the theoretical value of 107 ps by taking into account the positron trapping at two types of defects. Structural characterization was performed by coincidence Doppler broadening and high-resolution transmission electron microscopy (HRTEM), revealing that two-trapping defect clusters were closely associated with Y-Ti or Y-Al oxide particles. Trapping was not detected in the non-ODS alloys. Based on Kuramotos advanced theoretical work, the shorter annihilation lifetime (179–194 ps) could be ascribed to positron trapping at vacancies and divacancies localized under the misfit dislocations associated with Y-Ti or Y-Al oxide particles. The longer annihilation lifetime (301–323 ps) could be attributed to Ar-filled gas bubbles precipitated at the oxide particle-matrix interfaces. These results of PALS analyses were consistent with the HRTEM characterization. • PALS spectra were well fitted and decomposed into the bulk and two types of positron-trapping sites. • The bulk lifetime τb of the ODS alloys is close to the theoretical value of 107 ps. • One of the positron-trapping sites is vacancies and divacancies localized under the misfit dislocation associated with oxide particles. • The other site is the Ar-filled gas bubbles precipitated at the oxide particle-Fe matrix interfaces. [ABSTRACT FROM AUTHOR]

Static discontinuous recrystallization was studied during room temperature annealing of a newly designed 80% room temperature rolled oxide dispersion strengthened copper. At early stages of annealing, fine new oriented nanosized/submicron grains were recrystallized in the unique matrix of single brass-oriented deformed grain. Upon longer annealing time up to 14 months, the size, area fraction and number density of the recrystallized grains increased significantly along with changing the crystallographic textures. The analysis of misorientation angle distribution of boundaries indicated transformation of low angle boundaries to high angle boundaries results in nucleation of recrystallized grains by significant contribution of static recovery. Furthermore, the constant level of mechanical hardness after recrystallization was interpreted by the balance between grain size hardening, oxide particle hardening and strain hardening. • Recrystallization of ODS copper was studied during room temperature annealing. • The hardness remained constant by the balance of grain size, oxide particle and strain hardening. • Transformation of LABs to HABs results in nucleation of recrystallized grains. • Discontinuous recrystallization happened by significant contribution of static recovery. [ABSTRACT FROM AUTHOR]

To control the microstructure of FeCrAl-ODS (oxide dispersion strengthened) alloy using γ/α transformation, the austenite-stabilizing element cobalt was added to Fe-12Cr-(3,5)Al ODS alloys at 15 and 25 wt% in accordance with the phase diagram computed using the thermodynamic analysis software FactSage. Four designed alloys were fabricated using mechanical alloying, spark plasma sintering, and final annealing at 1150 °C. Three phases were identified: matrix with bcc structure, chromium carbide, and dispersed CoAl intermetallic compound. Nanosized oxide particles were also characterized by transmission electron microscopy. As the temperature increased to 1000 °C, the 3Al-alloys with 15 or 25 wt% Co and 5Al-alloy with 25 wt% Co took α to γ transformation, whilst α-phase remained in the 5Al-alloy with 15 wt% Co. Suppression of α to γ transformation in high Al and low Co alloy was successfully explained by the reduced driving force for α to γ transformation, compared with the pinning of α/γ interfaces by oxide particles. Continuous cooling transformation curves constructed by in-situ high temperature X-ray diffraction showed that microstructure control using the γ/α phase transformation is feasible. • The γ/α transformation in FeCrAl oxide dispersion strengthened alloys can be achieved by appropriate cobalt addition. • A several-tens-nanometer-sized dispersing CoAl phase was observed. • A comparison of chemical driving force and pinning force of oxide particles was performed. • Phase transformation retarding can be explained by considering the pinning force of oxide particles. [ABSTRACT FROM AUTHOR]

The reactive elements (Ti, Al and Zr) have been widely used for the improvement of the strength or the oxide resistance of ODS steels. In the present work, we studied the effect of the reactive elements on the precipitation of oxide particles, especially focusing upon the appropriate amount of the oxide composing elements, by addition of the large amounts of Y2O3 and reactive elements. The mechanically alloyed powders are annealed in a wide temperature range from 773 to 1423 K and then analysed by various analysis methods (small-angle X-ray scattering and X-ray diffraction by synchrotron radiation X-ray, scanning transmission electron microscope combined with energy dispersion X-ray spectroscopy, high-resolution transmission microscopy and 3D-atom probe). Ti, Al and Zr enhanced the growth of oxide particles, opposite to the many studies of Ti- and Zr-added ODS steels, as a result of the addition of Y2O3 and these elements ten times larger than those for usual use. The nucleation and growth of oxide particles are discussed by simulating the critical radius of nucleation and the growth based on the LSW theory. Y4Zr3O12 is stable and easy to precipitate even at lower annealing temperature. All reactive elements enhance the growth of oxide particles because of their big molar volume as compared to that of Y2O3. [ABSTRACT FROM AUTHOR]

Abstract Effects of Zr and excessive oxygen addition on the oxidation behavior of FeCrAl-ODS alloys are evaluated by high-temperature air and steam oxidation tests together with analyses using the thermochemical multiphase computer software FactSage. Zr addition to improve the strength of FeCrAl-ODS alloys increases the oxidation rate, but the oxidation rate can be reduced by increasing the excessive oxygen content to the appropriate level. From thermochemical multiphase calculations, Zr activity becomes lower in the alloy matrix with increasing excessive oxygen, and preventing ZrO 2 formation within the alumina scale can decelerate oxygen inward diffusion through ZrO 2. Addition of Zr and excessive oxygen can also improve adhesion of the alumina scale at 1400 °C. Once the protective alumina scale is lost during oxidation at 1500 °C, Fe O direct reaction with exothermic heat takes place and an oxidation reaction with partial melting rapidly proceeds within 30 min. Highlights • Effects of zirconium and oxygen on the oxidation of FeCrAl-ODS alloys was studied. • Zr and O added FeCrAl-ODS alloys achieve excellent high-temperature strength and oxidation resistance. • Addition of Zr and excessive oxygen can also improve adhesion of alumina scale at 1400 °C. • Once the protective alumina scale is lost during oxidation at 1500 ℃ just beneath the melting point of alloys. [ABSTRACT FROM AUTHOR]

Abstract The high-temperature deformation mechanism of the FeCrAl-ODS ferritic steel was investigated at 1000 °C for the creep loading perpendicular to the elongated and aligned grains. The strain rate was varied in the range from the order of 10−2 to 10−7s−1. With decreasing strain rate from 10−2 to 10−5s−1, creep mechanism shifts from conventional dislocation creep pinned by oxide particles to grain boundary sliding (GBS) assisted concomitantly by diffusional creep. With further decreasing strain rate to 10−7s−1, deformation mechanism is drastically changed; group of three grains can move cooperatively, and cooperative GBS (CGBS) was originally recognized. The threshold stress for onset of CGBS was designated as σ t h I (C G B S). Rate limiting process of CGBS is dominated by dislocation movement over the oxide particles so as to relieve the stress accumulation due to CGBS. The σ t h I (C G B S) for CGBS corresponds to one third of the conventional threshold stress for dislocation creep. Highlights • Creep deformation mechanism was studied for FeCrAl-ODS ferritic steels. • At the strain rate of 10−7s−1, cooperative grain boundary sliding (GCGBS) was discovered. • CGBS is dominated by dislocation movement over the oxide particles. • The threshold stress for CGBS was found to be one third of the conventional threshold stress for dislocation creep. [ABSTRACT FROM AUTHOR]

Following the severe accident at the Fukushima Daiichi nuclear power plant in 2011, recrystallized FeCrAl-ODS claddings have been developed in Japan as an accident-tolerant fuel (ATF) to mitigate the extent of oxidation reactions with hot steam. This paper presents an overview of the alloy design and the process used to manufacture the recrystallized cladding, together with a analysis of the applicability of these alloys as BWR fuel cladding and a summary of the results of simulated severe accident performance. A synergistic effect of co-addition of 12 mass% Cr and 6 mass% Al was found to suppress steam oxidation by a stable Al 2 O 3 scale formation and to inhibit a brittle αʹ precipitate after aging. The incorporation of 0.4 mass% Zr greatly improved not only the high temperature strength by replacing coarse Y-Al oxide particles with finer Y-Zr particles, but also the oxidation resistance at temperatures above 1673 K. These excellent performances are associated with the excess oxygen content. It was verified that core excess reactivities affected by the increased neutron absorption by Fe, Cr, Al can be compensated by reducing the thickness to half that of Zircaloy cladding, while maintaining mechanical integrity. A simulated design basis Loss of Coolant Accident (LOCA) event with assessment of post-LOCA ductility confirmed that FeCrAl-ODS cladding provided a greater safety margin along with exceptional high temperature strength and a significantly higher integral LOCA burst temperature compared with wrought FeCrAl alloy (C26M) and Zircaloy. An analysis using the MAAP 5.05b SA code indicated that melting of the Zircaloy core could be slightly accelerated due to release of the huge amount of exothermic reaction heat in the case of small amount of coolant injection. In contrast, the water injection always acts toward cooling the FeCrAl-ODS core. [ABSTRACT FROM AUTHOR]

For new Ni-base ODS superalloy manufactured by mechanical alloying, zone annealing experiment was implemented with parameters of temperature and hot zone velocity in order to develop the directionally recrystallized columnar grains. The progressive growth front of the columnar grains is synchronized with the hot zone movement, and columnar grains in millimeter scale were accomplished by appropriate hot zone velocity. This is secondary recrystallization through preferentially abnormal grain growth of the primarily recrystallized grains with the texture of cube orientation (001)[0 1 ¯ 0] as well as Goss orientation (110)[001]. The growth rate of the columnar grains estimated by using the grain boundary energy (ΔG gb ) of the primarily recrystallized grains, pinning force by oxide particles (ΔG pin ) and mobility of the grain boundary is relatively comparable to the hot zone velocity. The steep temperature gradient ahead of hot zone is substantially critical to keep the small size of the primarily recrystallized grains that lead to higher driving force for columnar grain growth due to the large grain boundary stored energy. [ABSTRACT FROM AUTHOR]

Further improvement of high-temperature strength is required for the martensitic oxide-dispersion-strengthened (ODS) steels that are the promising structural materials for the advanced fission and fusion reactors, since they have better formability and isotropic mechanical property emphasized as the engineering structural materials. We conducted severe hot rolling at the elevated temperature and subsequent air-cooling for the martensitic 9CrODS steels, and their tensile and creep strength recorded the highest worldwide for the engineering class of ferritic-martensitic steels. Significant strength improvement is originated by replacing the martensitic structure with a transformed coarse ferrite during hot rolling and subsequent air-cooling. The formation of the transformed coarse ferrite doesn’t follow the widely accepted ultrafine grain formation by the similar processing in the ferrite-martensite steels. New structural control and improving high-temperature strength for the ODS steels are greatly important and opened the window for realizing high-performance fission and fusion reactor materials. [ABSTRACT FROM AUTHOR]

The growth of oxide particles in FeCrAl- oxide dispersion strengthened steel (ODSS) considering an accident condition of the light-water reactor at above 1500 K was studied by using a high-temperature annealing. Oxide particles grew from 9 nm to more than 50 nm as maximum at 1623 K for 27 h, with decreasing their number density in two orders of magnitude. Most of the oxide particles in 15Cr-7Al were identified as YAM or YAP, while the oxide particles in 15Cr-7Al-0.4Zr were identified trigonal Y 4 Zr 3 O 12 . Zr addition to 15Cr-7Al ODSS accelerated the growth of the oxide particles, which is quite contrary to the effect of Zr addition during sintering as suggested in the literature. The kinetics of coarsening was characterized by an equation of Ostwald ripening. The diffusion activation energies obtained in the present materials were quite larger than the conventional diffusion activation energy of Y in alpha-iron. Gibbs free energy of oxides should be considered to discuss the coarsening. [ABSTRACT FROM AUTHOR]

Increasing Cr content from 9 to 12 mass% leads to superior corrosion and high-temperature oxidation resistances, and usually changes microstructure from martensite to a ferrite. To make transformable martensitic type of 12CrODS steels that have superior processing capability by using α/γ phase transformation, alloy design was conducted through varying nickel content. The structure of 12CrODS steels was successfully modified from full ferrite to a transformable martensite-base matrix containing ferrite. This ferrite consists of both equilibrium ferrite and a metastable residual ferrite. It was shown that the fraction of the equilibrium ferrite is predictable by computed phase diagram and formation of the residual ferrite was successfully evaluated through pinning of α/γ interfacial boundaries by oxide particles. [ABSTRACT FROM AUTHOR]

Abstract: The 9CrODS steel specimens were prepared by different processing with hot-rolling and different cooling rate. The hardness and high-temperature tensile properties were measured. Microstructure was analyzed by means of EBSD inverse pole figure and kernel average miss-orientation angles. The hot-rolled and then air-cooled specimen has the highest tensile strength. The furnace-cooled specimen also has better tensile strength at 700°C than air-cooled specimen at normalized condition. The high-temperature strength of 9CrODS steel is significantly improved with increasing grain size that can be induced by hot-rolling or furnace-slow cooling, where the localized grain boundary deformation can be suppressed. [Copyright &y& Elsevier]

Abstract: Out-of-pile FCCI tests for 9CrODS steel were performed at 973K by using simulated fission products Cs and Te under the oxygen potential in equilibrium with Fe/FeO and Cr/Cr2O3. Al2O3 powder were inserted to reduce a concentration of the Cs and Te in the system; its molar fraction is Cs:Te:Al2O3 =1:1:1000. From EPMA and XRD analyses, Cr2O3 was formed at the most outer layer, which significantly suppressed the fission product corrosion. Cr2Te3 was also produced at the outer layer and interior of 9CrODS steel through liquid Te migration along grain boundaries. It was demonstrated the corrosion depth of 9CrODS steel is between PNC-FMS and PNC316, which were tested as reference. The Cs and Te assisted corrosion of 9CrODS steel was thermodynamically analyzed through the formation of Cs2O, Cs3CrO4, Cr2O3 and Cr2Te3. [Copyright &y& Elsevier]

Brain vasculature forms the blood-brain barrier ( BBB) that restricts the movement of molecules between the brain and blood, but the capillary of the median eminence ( ME) lacks the BBB for secretion of adenohypophysial hormone-releasing peptides. In the present study, we aimed to elucidate whether continuous angiogenesis occurs in the ME of adult mice. By using a mitotic marker, bromodeoxyuridine ( Br dU), we demonstrated that new endothelial cells were born continuously in the ME of adults. Prominent expression of NG2, platelet-derived growth factor receptor B ( PDGFRB), and delta-like ligand 4 was observed at pericytes of adults, although the expression of these angiogenesis-associated proteins has been shown to be at low or trace levels in adult mature capillary. In addition, vascular endothelial growth factor ( VEGF), a key regulator of angiogenesis, was expressed highly in the nervous parenchyma of the ME. Expression of VEGF receptor 2 ( VEGFR2) was observed at endothelial cells in the external zone and at somatodendrites in the internal zone. Finally, a VEGFR- and PDGFR-associated tyrosine kinase inhibitor, SU11248, significantly decreased the number of Br dU-positive proliferating endothelial cells and parenchyma cells. In conclusion, the present study demonstrates VEGF-dependent continuous angiogenesis in the ME of adult mouse brains under normal conditions, which provides new insight into our understanding of neurosecretion in the ME. [ABSTRACT FROM AUTHOR]

The single- and multi-mode Richtmyer-Meshkov instabilities (RMI) with reshock are numerically analyzed in two- and three-dimensional domains. Four different types of air/ SF interface shapes are investigated in a shock tube configuration, and the predicted post-reshock growth rates are compared with available empirical models of Mikaelian's (Physica D 36(3):343-347, ) and Charakhch'an's (J Appl Mech Tech Phys 41(1):23-31, ). The simulation of 3D multi-mode RMI shows good agreement with a past experimental study, but other interface types (2D single-mode, 2D multi-mode and 3D single-mode) result in different growth rates after reshock. Parametric studies are therefore performed to investigate the sensitivities of the post-reshock growth rates to model the empirical parameters. For single-mode RMI configurations, the interface shape is found to be only a weak function of the post-reshock growth rate, as also predicted by previous reshock models. The post-reshock growth rate shows a linear correlation to the velocity jump due to reshock; however, it is only about a half of the prediction of Charakhch'an's model even though the growth before reshock compares well with pre-reshock models. The 3D single-mode post-reshock RMI growth rate is nearly 1.6 times larger than the 2D single-mode RMI. The parametric studies of multi-mode RMI show two distinctly different growth rates depending on the mixing conditions at reshock. If the interface remains sharp at the time of reshock, the post-reshock growth rate is as large as the single-mode cases. However, if the interface is mixed due to non-linear interactions of bubbles and spikes, the growth rates becomes slow and independent of the interface shapes. Overall, this study provides new insights into the flow features of reshocked RMI for different initial perturbation types. [ABSTRACT FROM AUTHOR]

Abstract: The use of transient liquid-phase bonding of 9CrODS steels using Fe–3B–2Si–0.5C filler was investigated for bonding temperature of 1180°C and hold times of 0.5–4.0h. The sequential process, consisting of isothermal melting, solidification and homogenization, was confirmed for bonding the 9CrODS steel. The precipitation of chromium boride found in 19CrODS steel is avoided in 9CrODS steel due to the lower Cr content. Silicon tends to be slightly enriched inside the bonding zone. Agglomeration and coarsening of Y2O3 particles in 9CrODS steel lead to softening inside the bonding zone formed by incipient melting of the foil bonding alloy, and in a diffusion affected zone (DAZ) adjacent to the bonding zone. [Copyright &y& Elsevier]

Abstract: Tungsten is an effective element for solid-solution strengthening and is a ferrite former in 9CrODS ferritic steel, however excessive tungsten leads to Laves phase formation. Appropriate tungsten concentration in 9CrODS ferritic steel was found to be around 2mass%, which produces high temperature strength without Laves phase precipitation. The stress increment due to solid-solution strengthening by tungsten was characterized as relatively small, compared to enhanced ferrite formation, the so called residual α-ferrite. [Copyright &y& Elsevier]

Abstract: It is recognized that the high-temperature strength of 9Cr-ODS ferritic steels is maintained by the presence of a ferrite phase. In order to clarify the formation process of the ferrite phase, 9Cr-ODS ferritic steels containing various contents of Y2O3, i.e., 0mass%, 0.1mass%, 0.35mass%, and 0.7mass%, are prepared by means of mechanical alloying and hot-pressing. The ferrite phase is formed by the addition of 0.35mass% and 0.7mass% Y2O3; however, it is not formed for steels without and with 0.1mass% Y2O3 normalized for 1h at 1050°C. It is considered from the thermodynamic analyses that the pinning of the α–γ interface motion by the dispersed Y–Ti complex oxide particles can be attributed to the retention of the ferrite phase normalized at 1050°C, and this ferrite phase cannot be δ-ferrite that is in equilibrium with the γ-phase. [Copyright &y& Elsevier]

Abstract: Oxide dispersion strengthened (ODS) ferritic steels, which are the most promising candidate materials for advanced fast reactor fuel elements, have exceptional creep strength at 973K. The superior creep property of 9Cr-ODS ferritic steels is ascribed to the formation of a nonequilibrium phase, designated as the residual ferrite. The yield strength of the residual ferrite itself has been determined to be as high as 1360MPa at room temperature from nanoindentation measurements. The creep strength is also enhanced by minimizing the number of packet boundaries induced by the martensitic phase transformation. The creep strain occurs at a lower stress than that necessary for the deformation of the intragrain regions, which are strengthened by an interaction between nanosize oxide particles and dislocations; this occurs by sliding at weaker regions such as at the grain boundaries and packet boundaries. It is found that 9Cr-ODS ferritic steels behave as fiber composite materials comprising the harder residual ferrite and the softer tempered martensite. [Copyright &y& Elsevier]

Abstract: Strain-controlled low cycle fatigue tests were conduced for 9Cr–ODS and 12Cr–ODS steels at 873, 923, 973 and 1023K. The total strain ranges were controlled from 0.5% to 1.5% with strain rate of 0.1%/s. Corresponding plastic strain ranged from 0.01% to 1%. The ODS steels exhibit relatively low level of plastic strain and thus have longer fatigue life in the low total strain region compared to conventional ferritic steels such as Mod. 9Cr–1Mo steel. Neither noticeable cyclic hardening nor softening was observed in ODS steels, whilst Mod. 9Cr–1Mo steel shows an apparent cyclic softening at 873 and 923K. This is attributable to the excellent microstructure stability due to the presence of nano-sized oxide particles dispersed in ODS steels. [Copyright &y& Elsevier]

Abstract: This paper describes the effect on creep strength and microstructure of 9Cr-oxide dispersion strengthened martensitic steel (9Cr-ODS steel) produced by differences in titanium concentration and consolidation temperature. The increase of titanium concentration to 0.30–0.35wt% was shown to provide considerable improvement of creep strength accompanied by the increase of residual-α ferrite. The elevation of hot-extrusion temperature degraded the creep strength, however, it appeared to increase the volume fraction of residual-α ferrite. The creep deformation process of 9Cr-ODS steel was discussed to explain these results based on microstructure observations. [Copyright &y& Elsevier]

Abstract: We have studied the electrical conduction of tetrakis(alkylthio)–tetrathiafulvalene (TTC n –TTF) on thin-film field-effect transistors (FET). The field-effect mobility of 10−6–10−5 cm2/Vs was obtained for TTC n –TTF with n =8, 14, and 18. The mobility increased with increase in the length of alkyl chains. The origin of the increase in mobility is attributed to the reduction in intermolecular distance between adjacent TTF moieties caused by the intermolecular interaction through alkyl chains. Consistently, the X-ray diffraction (XRD) experiments showed that the longer alkyl chain gives the shorter distance between the adjacent TTF moieties. The temperature dependence of the mobility for TTC n –TTF shows a change in activation energy at around 220K, which is attributable to the phase transition of TTC n –TTF. [Copyright &y& Elsevier]

Abstract: Effects of varying oxygen concentration and final heat treatment on high-temperature strength and microstructure in 9Cr-oxide dispersion strengthened steel (9CrODS) were investigated. It was shown that appropriate control of excess oxygen concentration remarkably improves creep strength of 9CrODS. This creep strength improvement is ascribed to ultra-fine oxide particle dispersion in a part of the grains and increasing austenite (γ) to ferrite (α) diffusional transformation. Enhancement of austenite (γ) to ferrite (α) diffusional transformation leads to suppression of grain boundary sliding. Creep strength of 9CrODS can be remarkably improved by controlling excess oxygen concentration and performing a furnace-cooling heat treatment for austenite (γ) to ferrite (α) diffusional transformation. [Copyright &y& Elsevier]

Abstract: The effects of mechanical alloying (MA) conditions on oxygen contamination were investigated to establish the manufacturing technology of oxygen-controlled oxide dispersion strengthened (ODS) martensitic steel. High-temperature mechanical tests and microstructure observations were performed in oxygen-and-titanium-controlled steels in order to demonstrate high-temperature strength improvement using oxygen control. Oxygen content was drastically reduced by the purification of MA atmosphere, Ar gas. It was shown that the lower speed agitation at the beginning of MA was effective for the reduction of oxygen contamination because oxygen was mixed mainly at the beginning of mechanical alloying due to the imperfect replacement of Ar gas. Dense distribution of oxide particle and significant improvement in high-temperature strength were achieved by applying 99.9999wt% Ar in MA atmosphere and reducing oxygen contents. It was revealed that the merely increasing Y2O3 and titanium addition cannot improve the high-temperature strength. The excess oxygen is an important parameter for making oxide particles finely and densely distributed as well as improving high-temperature strength. [Copyright &y& Elsevier]

The effects of different percentages of oxygen and titanium on the mechanical properties and microstructure of 9Cr-ODS steel were investigated. It was shown that the high-temperature strength was drastically improved by controlling the atomic ratio between excess oxygen and titanium (x in TiOx) around 1.0. When x is around 1.0, the elongated alpha-grains containing the ultra-fine and close oxide particle dispersion were generated in addition to equiaxed martensite grains. Furthermore, the number density of oxide particle in the martensite grains increased. The control of phase transformation and oxide particle dispersion by adjusting oxygen and titanium contents should be a key technology to achieve superior high-temperature strength. [Copyright &y& Elsevier]

In the collaboration work between JNC and CEA-Saclay, JNC and CEA independently manufactured ODS martensitic cladding tubes by their own fabrication routes. Manufacturing started from the same hollow shape mother tubes with a composition of 9Cr–2W–0.1Ti–0.24Y2O3. The HPTR cold-rolling process was used by both JNC and CEA, but the applied fabrication routes included different cross-section reduction ratios, number of passes and intermediate heat treatments. The manufactured claddings exhibited an isotropic grain structure and equivalent tensile strength in the longitudinal and transverse directions. Even though different cross-section reduction ratios and intermediate annealing treatments were used, both cladding tubes manufactured by JNC and CEA showed similar levels of tensile and internal creep rupture strength. [Copyright &y& Elsevier]

A quantitative correlation of the swelling rate versus swelling is presented. Swelling data of 20% cold-worked 316 stainless steels were analyzed using the power law swelling equation. The prolonged transient region with keeping the suppressed swelling rate was clearly demonstrated for the improved 316 stainless steels like PNC316 and 316Ti. Rate theory analyses lead to the role of precipitates as point defect sinks for retardation of the void growth. [Copyright &y& Elsevier]

The FeCrAl-oxide dispersion strengthened (ODS) alloy is the promising cladding material for the accident-tolerant fuel (ATF) of the light water reactors (LWR) to suppress the oxidation reaction with hot steam by Al 2 O 3 formation. Ring-creep tests for FeCrAl-ODS alloy cladding were carried out at 973 K and 1273 K to evaluate the deformation mechanism at the sever accident. The temperature-compensated strain rate by Fe-diffusion coefficient versus the normalized stress by shear modulus was constructed. The dislocation detachment stress from the dispersoid was derived by considering the dislocation-dispersoid elastic interaction and the dislocation relaxation effect by climb motion. When the applied stress exceeds the dislocation detachment stress, dislocations overcome the dispersoids with the reduced values of the stress exponent, which is attributed to the dislocation climb motion. When the stress is lower than the dislocation detachment stress, large size of cavities exists at the grain boundaries. Grain boundary sliding (GBS) is dominant factor for the low strain rate creep deformation at 1273 K, where dislocation climb also plays a critical role for release of the stress concentration induced by GBS. Based on those findings, new constitutive equations for creep deformation were constructed, which is applicable to low stress, low strain rate and high temperature conditions encountered at the reactor sever accident. [ABSTRACT FROM AUTHOR]

Abstract This study describes the effect of microstructural development on high tensile properties of a newly developed He/H 2 milled oxide dispersion strengthened copper in a large centimeter sized spherical morphology. Electron back scattered diffraction showed development of a strong texture of (110) plane in micron sized (1.2 μm) grains on the surface of milled spheres. A combination of microstructural features of inhomogeneous grain size, nanoscale lenticular/rectangular deformation twins, high dislocation density and fine oxide particles distribution induced a very high ultimate tensile strength (688 MPa)-ductility (8.6% elongation). Highlights • Large centimeter sized spherical morphology was obtained in He/H 2 milled ODS copper. • A (110) texture in micron sized grains was developed on the surface of spheres. • Complex microstructural features induced a very high UTS-ductility. [ABSTRACT FROM AUTHOR]

Abstract Currently, advanced ODS copper alloy is under study as a potential fusion material providing good mechanical properties. In this work, in order to develop a high performance ODS copper containing 0.5 wt% Y 2 O 3 oxide particles, the effect of room temperature rolling and subsequent annealing on the grain structure evolution, texture development and tensile properties are studied using EBSD, TEM and tensile tests. Microstructure evolution studies show the grain structure coarsens by enhancing the Brass texture during increase of rolling reduction and a unique single crystal-like brass-texture deformed structure is achieved after 80% rolling reduction. We found the deformation mechanism of partial slip by a 6 〈 211 〉 dislocations facilitated by the pinning of a 2 〈 101 〉 perfect dislocations through fine oxide particles is responsible for formation of Brass texture during room temperature rolling. Furthermore, the recrystallization of ODS copper retards to high temperature of ~700 °C and shows a fine-grained microstructure with different orientations of Goss, Brass, S and Copper. Evaluation of microstructure-mechanical properties of the recrystallized samples expresses that the bimodal grain size distribution at 800 °C for 30 min offers a good tensile strength-duc t ility (UTS: 491 MPa, el t : 19%) at ambient temperature. [ABSTRACT FROM AUTHOR]

Abstract: The 15wt% CrODS steels (15CrODS steels) were manufactured as the high-temperature fusion reactor materials and their tensile properties at 1273K were correlated with the oxide dispersion strengthening before and after aging. Fine dispersion of the oxide particles at initial condition in 15CrODS steels gives significantly higher strength compared with commercial MA956. The strength decrease in 15CrODS steels after aging at 1473K for 100h is attributed to coarsening of oxide particles, thus weakening of dispersion strength. [Copyright &y& Elsevier]

Abstract: The microstructure and tensile properties at 973K in 9CrODS steels were investigated with respect to various fractions of the residual ferrite from zero to 47vol.%. The formation of the residual ferrite was discussed from a balance between a chemical driving force for α to γ reverse transformation and the oxide particle pinning force, while 0.04mass% carbon sample could contain an equilibrium δ-ferrite. With increasing volume fraction of the residual ferrite, strength at 973K increases but ductility decreases, which is attributed to the fact that the residual ferrite is harder than the tempered martensite. [Copyright &y& Elsevier]

The interaction between oxide particles and dislocations in a 9Cr-ODS ferritic steel is investigated by both static andin situTEM observation under dynamic straining conditions and room temperature. The measured obstacle strength () of the oxide particles was no greater than 0.80 and the average was 0.63. The dislocation loops around some coarsened particles were also observed. The calculated obstacle strength by a stress formula of the Orowan interaction is nearly equaled to the average experimental value. Not only cross-slip system but also the Orowan interaction should be considered as the main interaction mechanism between oxide particles and dislocation in 9CrODS ferritic steel. [ABSTRACT FROM AUTHOR]

Two microstructural phenomena have been studied in a newly designed Ni-based ODS superalloy with a high solvus temperature. For the first time, a nanoscale lamellar γ/γ′ structure was obtained along the elastically soft [100] direction by a eutectoid-like reaction from a severely deformed matrix. In addition, the preferred distribution of semi-coherent Y 2 Hf 2 O 7 oxide particles was observed only in the γ phase due to the prior partitioning of Y and O to this phase. The microstructure development during the processing route is discussed based on the solvus temperature of this new ODS superalloy in comparison to commercial ODS superalloys. [ABSTRACT FROM AUTHOR]

• Spontaneous passivation exhibited for both 10Cr and 17Cr Al-ODS steel in HNO 3. • The ennoblement of corrosion potential is larger in low Cr Al-ODS steel. • Low Cr Al-ODS steel revealed a higher anodic and cathodic reaction rate in HNO 3. • Enrichment of Al 2 O 3 due to a synergistic effect of low Cr in 10Cr Al-ODS steel. • The higher corrosion resistance of 17Cr Al-ODS steel is attributed to higher Cr and Cr 2 O 3 formation. It is imperative to comprehend the corrosion behavior of different Cr containing Al-added ODS steel reactor clad materials in nuclear reprocessing simulating conditions, as high dissolution of clad material is not desirable. In this present work, the effect of varying HNO 3 concentrations (3, 6, 11.5 M HNO 3) and with oxidizing (Cr6+, Ce3+) and non-oxidizing (Fe3+) ions in 6 M HNO 3 on 10Cr (10Cr-5Al-0.5Ti-0.5Y 2 O 3 -Fe) and 17Cr (16.78Cr-4.46Al-0.5Ti-0.45Y 2 O 3 -Fe) Al-ODS steels are investigated. The potentiodynamic anodic polarization studies revealed an ennoblement of corrosion potential by elevated cathodic current resulting from increased oxidizing conditions in HNO 3 by concentration and oxidizing ions. Through various electrochemical techniques like open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), the 17Cr Al-ODS steel exhibited improved corrosion resistance with lower E corr , increased passivation range (E pass range), lower corrosion current density (i corr) and increased charge transfer resistance (R ct). The SEM studies revealed variation in corrosion morphology as shallow corrosion cavities and deeper corrosion pits in 17Cr Al-ODS and 10Cr Al-ODS steel, respectively, at high oxidizing environment. The enhanced corrosion resistance of 17Cr Al-ODS is associated to the improved passivation with the high Cr level in the steel compared to 10Cr-ODS steel, which is corroborated by XPS analysis. New knowledge on nitric acid corrosion mechanism on the Cr in Al-ODS steels and the influences of oxidizing ions in reprocessing environments are described. [Display omitted] [ABSTRACT FROM AUTHOR]

The microstructure of a new Ni-base oxide dispersion strengthened superalloy powder was studied for high temperature gas turbine applications after the mechanical alloying process. In this study, an atomized powder with a composition similar to the CMSX-10 superalloy was mechanically alloyed with yttria and Hf powders. The mechanically alloyed powder included only the supersaturated solid solution γ phase without γ′ and yttria provided by severe plastic deformation, while after the 3-step aging, the γ′ phase was precipitated due to the partitioning of Al and Ta to the γ′ and Co, Cr, Re, W, and Mo to the γ phase. Mechanical alloying modified the morphology of γ′ to the new coherent γ–γ′ nanoscale lamellar structure to minimize the elastic strain energy of the precipitation, which yielded a low lattice misfit of 0.16% at high temperature. The γ′ lamellae aligned preferentially along the elastically soft [100] direction. Also, the precipitated oxide particles were refined in the γ phase by adding Hf from large incoherent YAlO 3 to fine semi-coherent Y 2 Hf 2 O 7 oxide particles with the average size of 7 nm and low interparticle spacing of 76 nm. [ABSTRACT FROM AUTHOR]

Fourteen Fe–Cr–Al alloys with systematically varied Cr and Al compositions were irradiated at 350 ∘ C to 0.24 dpa by 10.5 MeV self-ions as model alloys for the Fe–Cr–Al (oxide dispersion strengthened: ODS) alloys being developed as accident tolerant fuel (ATF) cladding for light water reactors. Three dose rates (8 × 10 − 6 , 8 × 10 − 5 , and 8 × 10 − 4 dpa/s) were selected to predict the formation behavior of Cr-rich precipitates (CrRP) under neutron irradiation conditions. The effects of Cr, Al composition, and dose rate on the CrRP formation behavior were evaluated using a three-dimensional atom probe (3DAP) analysis. The results showed that the CrRP number density, volume fraction, and Cr concentration increase with increasing Cr composition, decreasing Al composition, and decreasing dose rate. Multiple regression analysis showed that in addition to these primary effects, there was an interaction between them on the CrRP volume fraction: (1) the higher the Al composition, the smaller the increase in the CrRP volume fraction with increasing Cr composition, and (2) the lower the Cr composition, the smaller the increase in the CrRP volume fraction with the decreasing Al composition and dose rate. It was also highlighted that to understand the dose rate effect on the CrRP formation behavior under neutron irradiation, it is useful to examine the irradiation time dependence, including the effective use of thermal aging data as a limit to the zero dose rate, in addition to the dose-dependency perspective. In addition to the systematic database of CrRP-related quantities established in this study, these considerations should contribute to further developing and validating numerical prediction models. [ABSTRACT FROM AUTHOR]

Highlights: [•] Aluminum addition to ODS steel improves compatibility between U-Zr fuel and the ODS steels. [•] It increases the threshold temperature for reaction layer formation by 50K. [•] The compatibility improvement mechanism was discussed using general thermodynamic data. [ABSTRACT FROM AUTHOR]

Abstract: It is known that the singularity in the non-cutoff cross-section of the Boltzmann equation leads to the gain of regularity and a possible gain of weight in the velocity variable. By defining and analyzing a non-isotropic norm which precisely captures the dissipation in the linearized collision operator, we first give a new and precise coercivity estimate for the non-cutoff Boltzmann equation for general physical cross-sections. Then the Cauchy problem for the Boltzmann equation is considered in the framework of small perturbation of an equilibrium state. In this part, for the soft potential case in the sense that there is no positive power gain of weight in the coercivity estimate on the linearized operator, we derive some new functional estimates on the nonlinear collision operator. Together with the coercivity estimates, we prove the global existence of classical solutions for the Boltzmann equation in weighted Sobolev spaces. [Copyright &y& Elsevier]

This is a continuation of our series of works for the inhomogeneous Boltzmann equation. We study qualitative properties of classical solutions; the full regularization in all variables, uniqueness, non-negativity and convergence rate to the equilibrium, to be precise. Together with the results of Parts I and II about the well-posedness of the Cauchy problem around the Maxwellian, we conclude this series with a satisfactory mathematical theory for the Boltzmann equation without angular cutoff. [ABSTRACT FROM AUTHOR]

We prove the global existence and uniqueness of classical solutions around an equilibrium to the Boltzmann equation without angular cutoff in some Sobolev spaces. In addition, the solutions thus obtained are shown to be non-negative and C in all variables for any positive time. In this paper, we study the Maxwellian molecule type collision operator with mild singularity. One of the key observations is the introduction of a new important norm related to the singular behavior of the cross section in the collision operator. This norm captures the essential properties of the singularity and yields precisely the dissipation of the linearized collision operator through the celebrated H-theorem. [ABSTRACT FROM AUTHOR]

As a continuation of our series works on the Boltzmann equation without angular cutoff assumption, in this part, the global existence of solution to the Cauchy problem in the whole space is proved in some suitable weighted Sobolev spaces for hard potential when the solution is a small perturbation of a global equilibrium. [ABSTRACT FROM AUTHOR]

Abstract: A monolithic-type flow sensor was developed to simplify the packaging process for microelectro mechanical system (MEMS) fluidic devices. In our design, a heater element for sensing flows as part of a thermal flow sensor was formed on the outside surface of a thin film in a tube, enabling us to connect electrical wiring from it to the outside of the tube directly. The monolithic-type flow sensor was produced by applying photolithography on a cylinder surface and transferring a cylindrical parylene film structure to the outside of the skeleton tube by using an adhesive heat-shrinkable tube. The relationship between the input power of the sensor and the flow rate obeyed King''s equation under the flow conditions for 0–2000sccm. The response time of 116ms, which is comparable to that of commercially available mass flow controllers, was obtained. [Copyright &y& Elsevier]

Abstract: We present the first global well-posedness result for the Boltzmann equation without angular cutoff in the framework of weighted Sobolev spaces, in a close to equilibrium framework, and for Maxwellian molecules. These solutions become smooth for any positive time. An important ingredient of the proof rests on the introduction of a new norm, encoding both the singularity and the dissipation properties of the linearized collision operator. [ABSTRACT FROM AUTHOR]

The FeCrAl-oxide dispersion strengthened (ODS) alloy is a promising candidate alloy for the accident tolerant fuel (ATF) cladding of light water reactors (LWRs) and has been recently developed in Japan. This paper reports on the progress of the development of accident tolerant FeCrAl-ODS fuel claddings for boiling water reactors (BWRs) in Japan. Both experimental and analytical studies were conducted to evaluate the influence of implementation of the FeCrAl-ODS fuel cladding to the current BWRs. In the experimental study, key material properties of FeCrAl-ODS fuel cladding have been obtained and accumulated using bar, sheet and tube-shaped materials to support the evaluations in the analytical study. In the evaluation at normal operating conditions, strength and ductility, corrosion property, tritium permeability, wear property, resistance to iodine stress corrosion cracking (SCC) and weldability were examined. A preliminary assessment of compatibility of the FeCrAl-ODS fuel cladding with the current recycling system in Japan was also conducted. In the evaluation of the design basis accident and the beyond design basis accident, strength, steam oxidation property, resistance to water quenching during a loss-of-coolant accident (LOCA) and the LOCA burst property were examined. In order to evaluate the influence of implementation of the FeCrAl-ODS cladding to the current BWRs, the core characteristics and the fuel behavior were evaluated in the analysis study at the normal operating condition. The analysis for the 9 × 9-type and the 10 × 10-type fuel assemblies and the reactor type of the Advanced BWR (ABWR) revealed a good applicability of FeCrAl-ODS fuel cladding. Finally, the challenges and perspectives found in the program are highlighted to enhance international collaborations to promote the development of the FeCrAl-ODS fuel cladding. [ABSTRACT FROM AUTHOR]

Abstract: A large number of mathematical studies on the Boltzmann equation are based on the Grad''s angular cutoff assumption. However, for particle interaction with inverse power law potentials, the associated cross-sections have a non-integrable singularity corresponding to the grazing collisions. Smoothing properties of solutions are then expected. On the other hand, the uncertainty principle, established by Heisenberg in 1927, has been developed so far in various situations, and it has been applied to the study of the existence and smoothness of solutions to partial differential equations. This paper is the first one to apply this celebrated principle to the study of the singularity in the cross-sections for kinetic equations. Precisely, we will first prove a generalized version of the uncertainty principle and then apply it to justify rigorously the smoothing properties of solutions to some kinetic equations. In particular, we give some estimates on the regularity of solutions in Sobolev spaces w.r.t. all variables for both linearized and nonlinear space inhomogeneous Boltzmann equations without angular cutoff, as well as the linearized space inhomogeneous Landau equation. [Copyright &y& Elsevier]

Abstract: Microstructural observation was performed on a neutron-irradiated oxide dispersion strengthened (ODS) ferritic steel with emphasis on oxide behavior, including phase stability under irradiation at elevated temperature (∼973K). Transmission electron microscopy observation of the Y–Ti complex oxide particles showed they were fine (∼40nm) whereas the Ti-oxide particles were relatively coarse (∼300nm). Dispersion parameters of oxide particles, such as mean size and number density, changed due to irradiation. This implies recoil resolution of the oxide particles. When irradiated at 973K, some Y–Ti complex oxides survived and interacted with the dislocation structures, which delayed the dislocation recovery and stabilized the elongated grain structure. It is considered that oxide particles could be effective pinning points of dislocations in motion under irradiation to a dose of ∼100dpa. [Copyright &y& Elsevier]

Abstract: The superior creep properties of 9Cr ODS (Oxide Dispersion Strengthened) steels result from small oxide particles dispersed in the matrix. Thus many investigations have studied the creep properties by focusing on the oxide particle distribution, but these results are not sufficient to clarify the creep mechanism and to develop material processing procedures for mass production. Potential microstructural features affecting the creep properties should be studied. The 9Cr ODS steel has many potential microstructural features, for example, PPB (Prior Particle Boundary) pores, precipitates, and two matrix phases. In particular, PPB pores link up and develop into large creep cavities. Therefore, particle size classification of mechanically alloying (MA) produced powders was performed to control PPB. Contrary to our expectations, the particle size classification did not only affect PPB creep cavities, but also other microstructural features. MA powder particle size effects on microstructural features and the creep properties were studied. [Copyright &y& Elsevier]

Abstract: 9Cr-ODS (oxide dispersion strengthened) steels are being developed for structural materials of fast breeder reactors and fusion reactors. The steels can be characterized by small Y–Ti–O complex oxide particles dispersed in the matrix. Thus, many researches have studied creep properties by focusing on oxide particles and dislocations with transmission electron microscopy (TEM) observations, but such studies are still insufficient to clarify the creep mechanism. In this work, a potential microstructural feature affecting creep properties, prior particle boundary (PPB) cavities formed during creep and aligned along the extrusion direction, was studied. Field emission gun-scanning electron microscopy (FE-SEM) observations on the crept specimens indicated PPB cavities enhanced creep crack propagation. The effect of PPB cavities on creep properties were quantitatively studied by consolidating two different sizes mechanical alloying (MA) powders (>90 and <45μm). PPB cavities decreased when using the larger MA powder and creep properties parallel to the extrusion direction were improved. It is concluded that PPB is one of the important microstructural features affecting creep properties, where a reduction in PPB cavities signifies an improvement. [Copyright &y& Elsevier]