[en] Out-of-pile FCCI tests for 9CrODS steel were performed at 973 K 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

[en] 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.

[en] This study describes the effect of microstructural development on high tensile properties of a newly developed He/H₂ 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).

[en] A preliminary performance evaluation has been performed under accident conditions to compare advantages and disadvantages of application of FeCrAl-ODS steel for the current zirconium-based alloys. Some key material properties of the alloy were also measured for the quantitative evaluations. Under the LOCA condition the FeCrAl-ODS fuel cladding can maintain its mechanical properties beyond the LOCA criteria for the current (zirconium-based alloys) fuel cladding owing to excellent resistances to steam oxidation and thermal shock by water quenching. Moreover, the FeCrAl-ODS fuel cladding can give an additional margin for the fission product release. Under the BDBA condition the FeCrAl-ODS fuel cladding can dramatically reduce the recession rate by both the steam oxidation and the reaction with UO₂. (author)

[en] 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% Y₂O₃ 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 $\frac{a}{6}〈211〉$ dislocations facilitated by the pinning of $\frac{a}{2}〈101〉$ 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_tility (UTS: 491 MPa, el_t: 19%) at ambient temperature.

[en] Highlights: • A new ODS copper alloy including 0.42wt%Y₂O₃ particles was developed successfully by MA method. • MA resulted in decrease of crystallite size and increment of dislocation density and hardness. • Fine semicoherent Y₂O₃ particles were distributed with an average size of 10.8 nm and spacing of 152 nm. • The annealed ODS copper alloy showed a yield strength of 272 MPa and total elongation of 12%. - Abstract: Advanced oxide dispersion strengthened copper alloys are promising structural materials for application in divertor system of future fusion reactors due to high irradiation resistance, high thermal conductivity, and good mechanical properties. In this study, a new ODS copper including 0.42wt%Y₂O₃ nanosized oxide particles was developed successfully by mechanical alloying method using addition of 1 wt% Stearic acid in Ar atmosphere. Mechanical alloying resulted in decrease of crystallite size to 28 nm in concurrent with increment of dislocation density and hardness to the saturated level of $1.7\times {10}^{15}{\mathrm{m}}^{-2}$ and 226HV_0.1 after 48 h milling, respectively. Consolidated ODS copper by SPS and then hot roll-annealing at 900°C/60 min showed an average grain size of 1.1 µm with a near random texture. Furthermore, TEM observations demonstrated fine semicoherent Y₂O₃ oxide particles distributed with a misfit parameter (δ) of 0.17 in copper matrix with an average size of 10.8 nm and interparticle spacing of 152 nm. Finally, tensile test evaluation determined comparable mechanical properties of the annealed ODS copper (Cu-0.42wt%Y₂O₃) with Glidcop-Al25 including a yield strength of 272 MPa and total elongation of 12%, by two mechanisms of grain boundary strengthening and oxide particle strengthening.

[en] A Ce-type FeCrAl-ODS ferritic steel has been examined as a candidate Fe-Cr-Al alloy for the fuel cladding in BWRs. The properties examined in this study were the corrosion resistance to coolant water, the resistance to the high temperature steam and the interactions with neighboring materials (UO₂ and B₄C). For the corrosion test, the specimens were corroded in an autoclave with circulating pure water at 633 K and a pressure of approximately 20 MPa. In addition to the Ce-ODS, MA956 and SS316L alloys were also corroded as reference materials. For the steam oxidation test, the specimens were oxidized in an electric furnace at 1473 K for 100 h and 1573 K for 25 h under wet Ar gas flow. The materials reaction test with B₄C was carried out at 1573 K and 1673 K for 1 h. The test with UO₂ was performed in a high purity He gas at 1573 K and 1673 K for 1 h. A disk of UO₂ pellet was set on the Ce-ODS specimen and the reaction couple was held in the pure Zr box to prevent a surface oxidation by residual oxidizing gases. The cross sections of reaction couples were observed by an optical microscope (OM) and a secondary electron microscope (SEM) with energy-dispersive spectroscope (EDS) after the materials interaction tests. The results show that the Ce-type FeCrAl-ODS steel has demonstrated a good corrosion resistance to coolant water and high accident tolerances in the oxidation with high temperature steam and in the interactions with neighboring materials. Those favorable properties would imply that the oxide dispersion strengthened (ODS) technology can be a candidate option for further development of accident-tolerant fuels

[en] 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: 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 ZrO₂ formation within the alumina scale can decelerate oxygen inward diffusion through ZrO₂. 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, FeO direct reaction with exothermic heat takes place and an oxidation reaction with partial melting rapidly proceeds within 30 min.

[en] Highlights: • Cu-Y₂O₃ alloys were fabricated by an in-situ process based on MA-HIP. • Effects of Y amounts on the MA process and HIP process were investigated. • Cu-Y₂O₃ alloys show hardness-conductivity trade-off performance. - Abstract: Yttria (Y₂O₃) dispersed copper alloys were fabricated by an in-situ process combining Mechanical Alloying (MA) and Hot Isostatic Pressing (HIP). In this process, CuO powder was added into Cu(Y) alloy powders halfway during mechanical alloying (MA). To investigate the effects of Y + CuO amount on the MA process and HIP process respectively, four kinds of samples (Cu-0/1/3/5wt%Y₂O₃) were studied in this research. For powders after MA, it was confirmed by an X-ray diffraction system (XRD) that more Y + CuO addition can refine the grain size. By calculating the lattice parameters from the XRD data, and analyzing the thermal dynamics data that were obtained from the TG-DTA tests, it can be concluded that the Cu, Y were alloyed successfully at first, and then after the CuO addition, reaction between Cu(Y) and CuO occurred, extracting part of Y solute from the Cu(Y) solution. Consequently, the alloying and grain refinement effect together enhance the microhardness of the powders. After consolidation by HIP, the formation of Y₂O₃ particles were confirmed by XRD. The relative density and the Vickers hardness of the HIP samples increased with the increasing Y₂O₃ amounts, whereas the electrical conductivity showed an opposite change tendency.

[en] 9CrODS steel, a candidate fission and fusion structural material, was subjected to hot-rolling with varying parameters of surface temperature and cooling rate just after hot-rolling. The deformation-induced dynamic ferrite transformation was confirmed at the rolling temperature 805 °C above Ar₃ (780 °C). This transformation exhibits three characteristic features: transformation for extremely short duration (0.044 second), retaining carbon content equal to the original without long-distance carbon diffusion, and elongated coarse ferrite grains (10 μm). The massive transformation was proposed for the dynamic ferrite transformation from the hot-rolled austenite. The driving force for massive transformation was quantitatively estimated considering dislocations accumulated by hot-rolling. It was also shown that the oxide particles in 9CrODS steel play a critical role for dynamic ferrite transformation by suppressing the dynamic recrystallization at hot-rolling.