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Microstructure and tensile properties ranged from ambient temperature to 700 ℃ of the 12Cr ODS steel were investigated by scanning electron microscopy, electron backscatter diffraction technique, and tensile tests. Results show that microstructure is composed of elongated grains with <110> axis parallel to rolling direction. Ultimate tensile strength and 0.2% offset yield strength gradually decrease with increasing test temperature. Uniform elongation and total elongation reduce with the temperature rising up to 500 ℃, whereas increase at higher temperatures due to activation of slip systems. Moreover, ductility in rolling direction is better than that in transverse direction. Fracture surfaces suggest that a large number of small and uniform dimples, and predominant cleavage-like facets present in rolling direction, and transverse direction, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In this work, high-temperature mechanical properties and microstructure of a 9Cr-ODS steel were studied. The properties were compared with those of the current reduced activation ferritic/martensitic steels (RAFMs) of CLAM and JLF-1. The tensile strength of the 9Cr-ODS steel was almost twice the values of the RAFMs at all the test temperatures, and the strength level at 923–973K was comparable to those of the RAFMs at 823K. The 9Cr-ODS steel also exhibited superior creep strength. Prediction with Larson–Miller parameter for the typical blanket conditions suggested that the 9Cr-ODS steel can successfully extend the maximum operation temperature to ∼923–973K. The 9Cr-ODS steel has a tempered martensitic structure with uniform oxide particles in the matrix. After creep tests, the mean diameter and density of the oxide particles did not change significantly by different creep temperatures and stresses, suggesting the stability of the microstructure. [Copyright &y& Elsevier]

Abstract: Microstructural changed of JLF-1 steel induced by static tensile loading and tension/compression cyclic loading was investigated following tensile and low cycle fatigue tests in vacuum at elevated temperature. Secondary cracks in radial direction were observed on the fracture surface of the tensile specimen at RT. Initial cyclic hardening followed by cyclic softening was observed during fatigue at RT and 673K. In contrast, only cyclic softening was observed at 873K. Transmission electron microscopy images of specimens with a total strain range Δε t =1.8% at RT, 673K and 873K showed that cyclic softening is caused by the reduction of the dislocation density and increment of lath width resulted by partial annihilation of original lath boundaries and cyclic deformation. The peak stress and lath width imply qualitative relationships that correlate with the number of cycles. [Copyright &y& Elsevier]

Abstract The anisotropy in creep properties and its microstructural origins in two oxide dispersion strengthened (ODS) steels (i.e., 12Cr-ODS-IMR and 12Cr-ODS-NIFS) were systematically investigated. Both ODS steels exhibited the anisotropic creep properties. The creep strength in longitudinal directions (LD) or extrusion directions (ED) specimens was better than that in transverse directions (TD) specimens. The microstructural characterizations revealed that both steels had elongated grains along the ED and relatively equiaxed grains in other orientations. Both steels had a streak-like distribution of precipitates along the ED that was composed of Ti-enriched precipitates and nano-scale oxide particles in local area. The fractography of the crept TD and LD specimens suggested that both steels fractured by the mixed ductile and brittle fracture modes. The propagation of cracks and intergranular decohesion along the boundaries of elongated grains were more severe in the TD specimens than in the LD specimens. The combined effects of elongated grain morphology with low grain shape aspect ratio and segregation of precipitates along the ED can explain the anisotropy in creep properties. The anisotropy in 12Cr-ODS-IMR steel was relatively higher than that in 12Cr-ODS-NIFS steel, and the additional cold rolling and lower final heat treatment temperature in 12Cr-ODS-IMR steel were responsible for it. [ABSTRACT FROM AUTHOR]

The oxide dispersion strengthened (ODS)-Cu alloys produced by the combined process of mechanical alloying and hot isothermal pressing (MA-HIP) process have high strength properties, although they have low ductility. In this study, the MA-HIP process was modified based on the yttrium addition and oxygen addition methods to improve the ductility by controlling the microstructure of the ODS-Cu alloys. Namely, we replaced pure Y and Cu 2 O powders with a Cu-Y intermetallic compound and pre-heated Cu powders as the starting materials. The final product showed considerable microstructural differences: on the macro-scale, the frequency of interconnection of large/small Cu grain colonies, which was a main factor in brittle fracture, was reduced; while on the nanoscale, yttrium remained as yttria (Y 2 O 3) particles within the large size Cu grains. These multiscale microstructural changes resulted in the improved mechanical property: the newly-developed ODS-Cu bulk did not fracture at bending strains of 18% or greater, which can be compared with the previous value of 5% or less in a three-point bending test. Furthermore, the conductivities of our ODS-Cu alloys are 94–96% of pure Cu. This improvement in properties, therefore sheds light to the future application of the ODS-Cu alloys in high-temperature environments. • A newly elemental addition method for ODS-Cu alloys was used to improve the microstructure and mechanical properties. • The new ODS-Cu had improved ductility due to microstructural changes and did not fracture at bending strains above 18%. • The electric conductivities of a new ODS-Cu alloys are 94–96% of pure Cu. • The Y 2 O 3 particles were dispersed within the coarse Cu grains, increasing the maximum strength. [ABSTRACT FROM AUTHOR]

• Recrystallization partially occurs at 1073 K, and is complete at 1273 K. • Higher Ti addition retards the recrystallization and leads to grain refinement. • Precipitates form after annealing at 973 K and above in V-4Cr-(1∼4)Ti alloys. • Recrystallization behavior is not obviously affected by further reducing the level of high-activation and interstitial impurities. The microstructural evolution and Vickers hardness variations upon annealing in the temperature range of 873 – 1273 K of cold rolled high-purity V-4Cr-(0∼4)Ti alloys are investigated. Results show that partial recrystallization occurs at 1073 K, recrystallization is complete at 1273 K, and Ti addition results in grain refinement. Grains become more isotropic after annealing at 1273 K. Besides, precipitates are observed after annealing at 973 K and above when Ti concentration is 1 wt% and higher. The size of precipitates increases with increasing Ti concentration and annealing temperature. Furthermore, Vickers hardness of cold rolled V-4Cr-xTi alloy drops to a minimum with increasing annealing temperature to 1173 K due to recovery of dislocations and recrystallization process. With annealing at 1273 K, hardness does not vary for V-4Cr-0Ti alloy, whereas it slightly increases for V-4Cr-(1∼4)Ti alloys, which is presumably attributed to partial dissolution of precipitates into the matrix. Additionally, purification by further reducing the high-activation impurities and interstitial impurities dose not evidently affect the recrystallization behavior and hardness of V-4Cr-4Ti alloy after recrystallization, however, the low-activation property is expected to be enhanced. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-purity vanadium alloys were developed for structural materials in fusion reactor. • Precipitates form when Ti concentration is about 1 wt% in high-purity V-4Cr-xTi alloys. • Solid solution strengthening is prominent and increases as Ti concentration rises. • 1 wt% Ti addition is presumably proper from the viewpoint of scavenging effect and precipitation strengthening. Effects of Ti concentration on microstructure and mechanical properties of high-purity V-4Cr-xTi alloys have been studied by means of scanning electron microscopy, transmission electron microscopy, Vickers hardness and tensile tests. Results show that precipitation occurs with 1 wt% Ti addition and above, whose diameter gradually increases as Ti concentration rises. Vickers hardness and tensile strength increase with increasing Ti concentration. Moreover, strengthening mechanisms consisting of solid solution strengthening (σ SS), grain boundary strengthening (σ GB), and precipitation strengthening (σ P) are theoretically estimated. The strength contribution sequence is σ SS > σ GB > σ P. Solid solution strengthening from Ti increases with increasing Ti concentration, and precipitation strengthening is not significantly dependent on Ti concentration. Additionally, 1 wt% Ti is probably sufficient to scavenge the interstitial impurities and provide comparable precipitation strengthening with V-4Cr-4Ti alloy. [ABSTRACT FROM AUTHOR]

Two types of oxide dispersion strengthening (ODS) steels (i.e. 12Cr-ODS-NIFS and 12Cr-ODS-IMR) with similar chemical compositions were produced through different fabrication processing. A systematic comparison was performed to investigate the effects of different fabrication processing on microstructure and mechanical properties of ODS steels. Compared to 12Cr-ODS-NIFS, the 12Cr-ODS-IMR steel exhibited significantly enhanced mechanical properties, such as higher Vickers hardness, tensile strength and creep strength. To understand the microstructural reasons for the excellent mechanical properties of ODS steels, systematic microstructure characterizations were carried out through a combined study of X-ray diffraction, electron backscattered diffraction, and transmission electron microscopy. It was found that both steels had similar grain structures comprising fine and heavily deformed grains smaller than ~1 μm and elongated coarse grains larger than ~10 μm, both of which possessed similar precipitates including coarse TiC x O 1− x particles and homogenously distributed Y 2 TiO 5 nanoparticles with diameters of several nanometers. 12Cr-ODS-IMR had a finer grain size, larger aspect ratio of grain length to width, and higher density of dislocations, which should be derived from the additional cold rolling and responsible for its better mechanical properties compared with 12Cr-ODS-NIFS. [ABSTRACT FROM AUTHOR]

Abstract: Deuterium permeation measurements and microstructure analyses on erbium oxide coating deposited by filtered arc deposition have been investigated. It is found that the permeation suppression efficiency is proportional to the coating thickness in case of the coating without pores and cracks reaching to the substrate. A phase transformation of the coating during the permeation measurements at 773–973K has been identified. A grain growth of the coating has occurred during the measurements and permeation suppression efficiency have enhanced according to the grain size. It is suggested that deuterium permeation through the coating is mainly dominated by the crystal grain diffusion. [Copyright &y& Elsevier]

• The powders after MA consisted of large- and small-Cu grain layers due to inhomogeneous distribution of yttrium atoms. • Areal fraction of small Cu grain layer increases with increasing MA duration. • The powders after ball-milled have exothermic reaction at around 310°C, which may be recrystallization and grain growth of Cu grains. • During heat treatment above 300°C after MA, yttrium atoms are diffused into the outer peripheral region and forms a new small-Cu grain area. Oxide dispersion strengthened Cu alloys (ODS-Cu) having dispersed yttria (Y 2 O 3) fabricated using hot isostatic pressing (HIP) of mechanically alloyed (MA) Cu-Y powders. They exhibited a heterogeneous mixed grain structure, which were composed of a large and small Cu grain area. In the small Cu grain regions, Y₂O₃ particles were segregated along the grain boundaries, and acted as a crack propagation path, leading to brittle fracture. Therefore, we investigated the microstructural changes by the MA and heat treatment processes for the microstructure optimization. The powders of 4 to 32 MA hours formed a nested crust-like layered structure with large and small Cu grains. The layers were destroyed by heat treatment at 500°C, because recrystallization and grain growth of Cu occurred in the temperature range of 310 - 330°C. It was considered that Y 2 O 3 was moved out to the circumferential area of the powders. Based on these results, it was suggested that the structural changes inside MA powders during HIP are the essential factor of the Y 2 O 3 distribution within the Y 2 O 3 -added ODS-Cu alloys. [ABSTRACT FROM AUTHOR]

Er 2 O 3 and Y 2 O 3 are promising materials for advanced breeding blanket system of nuclear fusion reactor because they have high electrical resistivity and effective tritium permeation suppression. In this report, Er 2 O 3 thin films were fabricated by metal organic chemical vapor deposition (MO-CVD) process with changing oxygen flow rates on the stainless steel 316 (SUS316) substrate with Y 2 O 3 layer fabricated via radio frequency (RF)-sputtering. Samples were prepared with four conditions of oxygen rate, 0.08, 0.13, 0.25, 0.42 Pa∙m3/s (50, 75, 150 and 250 sccm, respectively) and only on Er 2 O 3 / Y 2 O 3 –0.42 Pa∙m3/s sample was added thermal cycles. Four samples were observed with using X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Increasing oxygen flow rate during MO-CVD process increased the thickness of Er 2 O 3 thin film and decreased columnar width and succeeded in fabricating Er 2 O 3 thin film and dense microstructure on the SUS 316 substrate with Y 2 O 3 layer. • Effect of oxygen flow rate on erbia growth by metal organic chemical vapor deposition (MO-CVD) method was examined. • Effect of thermal cycling tests on fabricated Er 2 O 3 - Y 2 O 3 double layered film was examined. • Microstructure observation with X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM) revealed the growth direction of erbia film. [ABSTRACT FROM AUTHOR]