Showing papers on "Zirconium alloy published in 2009"

Effect of microstructure on the high-temperature deformation behavior of Nb-Si alloys

Abstract: Deformation behavior of Nb–Si–Zr alloys is investigated at various temperatures ranging from RT to 1670 K The master alloy ingots composed of Nb–181 at% Si–15 at% Zr doped with Mg are Ar-arc-melted The ingots contain Nb rods (radius: 1 μm) in Nb 3 Si matrix formed by eutectic reaction Alloys are subjected to heat treatments at 1923 K for 4–100 h to obtain a large Nb network structure with small silicide (α-Nb 5 Si 3 ) particles by decomposing Nb 3 Si matrix into Nb and Nb 5 Si 3 through a eutectoid reaction Compression tests are conducted at room temperature in air and at elevated temperatures in Ar atmosphere At 1471 K the maximum strength is 500 MPa and compressive ductility is higher than 10% with a strain rate of 10 × 10 −4 s −1 , while at room temperature the maximum strength is over 1500 MPa and compressive ductility is about 15% The high-temperature deformation obeys a power-law type equation The stress exponent n is evaluated to be 48 and the apparent activation energy is 350 kJ/mol The Vickers indentation at room temperature revealed that the crack propagation at room temperature is suppressed effectively by ductile Nb This suggests that the Nb aggregate in the network structure acts as a large Nb grain containing fine Nb 5 Si 3 particles, which might be beneficial for ductility at low temperatures

Behavior of High Burn-up Fuel Cladding under LOCA Conditions

Abstract: LOCA-simulated experiments were performed with MDA, ZIRLO™, M5®, NDA, and Zircaloy-2 cladding specimens with local burn-ups ranging from 66 to 76 MWd/kg. Short test rods fabricated with the cladding specimens were heated, isothermally oxidized at 1,459 to 1,480K in steam flow, and finally quenched in flooding water. Rod rupture and subsequent double-sided oxidation of the cladding were also simulated in the experiments. Neither split-fracture nor fragmentation occurred during the quench in the cladding specimens which were oxidized to about 18–27% of the metallic thickness. Accordingly, the fracture boundary, a most important safety issue, is not reduced significantly by the high burn-up and use of the new alloys within the examined scope, although it may be somewhat reduced with pre-hydriding during the reactor operation as observed in unirradiated specimens.

Direct and low energy electrolytic co-reduction of mixed oxides to zirconium-based multi-phase hydrogen storage alloys in molten salts

Abstract: Direct synthesis of Zr-based AB2-type hydrogen storage alloys (HSAs) from mixed oxide precursors has been achieved by electrolysis in molten CaCl2 at 900 °C and a cell voltage below 3.2 V. The process resembled direct oxide-to-metal conversion in solid state, and the target alloys, namely ZrCr2, ZrCr0.7Ni1.3 and Zr0.5Ti0.5V0.5Cr0.2Ni1.3, were formed in situ during electrolysis without going through any melting step. Electrolysis energy consumption could be as low as 9.59 kWh (kg-HSA)−1 and the metal recovery yield was generally higher than 90%. The electrolytic products were readily obtained as powders with the designated compositions and crystal structures (e.g. the C14 and C15 Laves phases). More importantly, these Zr-based electrolytic HSA powders were composed of nodular micro-particles which are very desirable for fabrication of electrodes with micro-porosity to facilitate electrolyte ex- and ingression. Galvanostatic discharge-charge tests of the as-prepared electrolytic HSA powders resulted in similar or higher hydrogen storage capacities (up to 280 mAh g−1) in comparison with the same HSAs prepared by e.g. arc-melting the individual metals as reported in literature. Particularly, the electrolytic Zr-based HSAs were unique for their high initial capacities without any pre-treatment for activation, and they also exhibited highly satisfactory discharge rate capability with less than 20% capacity loss when the discharge current increased from 50 to 600 mA g−1.

Catalyst and manufacturing method and use therefor

Abstract: Provided is a catalyst which has excellent durability and high oxygen reducing ability, and which is not corroded in an acidic electrolyte or at high electric potential. The catalyst is characterized by comprising a metal carbonitride oxide which contains zirconium and/or titanium, and also contains two metallic elements (M) selected from the group comprising tin, indium, platinum, tantalum, zirconium, titanium, copper, iron, tungsten, chromium, molybdenum, hafnium, vanadium, cobalt, cerium, aluminum, and nickel.

In Situ TEM Observation of Growth Process of Zirconium Hydride in Zircaloy-4 during Hydrogen Ion Implantation

Abstract: In situ observation during hydrogen ion implantation was performed with a transmission electron microscope installed in an ion accelerator to investigate the growth process of Zr hydride in Zircaloy-4. To clarify the effect of radiation damage, some samples were irradiated with 4 MeV Ni3+ ions prior to hydrogen implantation. Growth processes of Zr hydrides accompanying the formation of dislocations were observed. The crystallographic relationship between the Zr matrix and Zr hydrides was identical with that found in previous studies: inter- and intragranular hydrides exhibiting a tendency to grow in the (112-0) direction. This growth can be attributed to a shear mechanism in which there are partial dislocations along basal planes. In specimens preirradiated with Ni ions, the growth rate of hydrides was suppressed, but the growth direction was not affected by radiation defects. It was also confirmed that the black spots induced by Ni3+ ion irradiation grew during hydrogen ion implantation, suggesting the f...

Local atomic structure around Ni, Nb, and Zr atoms in Ni–Nb–Zr–H glassy alloys studied by x-ray absorption fine structure method

Abstract: To elucidate hydrogen effects on the atomic configuration of Ni–Nb–Zr–H glassy alloys exhibiting proton-tunneling-induced Coulomb oscillation, we investigated the local atomic configuration around the Ni, Nb, and Zr atoms by x-ray absorption fine structure (XAFS) method. The analysis of the XAFS spectra indicates that there is the significant difference in structural response between the Zr 30 and the Zr 40 at. % alloys when hydrogen atoms are charged; charging the hydrogen atoms basically does not alter the local structures around the three atoms for the Zr 30 at. % alloy but induces the elongation of the Zr–Zr, Zr–Nb, and Nb–Ni distances for the Zr 40 at. % alloy. The distorted icosahedral Zr5Ni5Nb3 clusters assembled in randomly packed manners for the possible models in the Ni–Nb–Zr glassy alloy are proposed. The sites where hydrogen atoms occupy are also inferred.

Optimized Ring Tensile Test Method and Hydrogen Effect on Mechanical Properties of Zircaloy Cladding in Hoop Direction

Abstract: Data pertaining to the mechanical properties of the fuel cladding in the hoop direction are required for the analysis of high burn-up fuel behavior under reactivity-initiated accident (RIA) conditions. In the present study, by minimizing undesirable effects of friction and bending, the ring tensile test method was optimized to obtain precise data pertaining to the mechanical properties of the fuel cladding in the hoop direction. The optimized specimen has a single gauge section and is stretched using the tooling consisting of two half-mandrels. The gauge section is set on top of a half-mandrel; this arrangement is unique in comparison with other methods. Using the optimized test method, the mechanical properties of the prehydrided Zircaloy-4 cladding in the hoop direction were evaluated as functions of hydrogen concentration and test temperature. When the hydrogen concentration is below 500 ppm, the decrease in ductility due to hydriding is relatively small at all test temperatures. When the hydrogen conc...

Effect of microalloying of Nb on corrosion resistance and thermal stability of ZrCu-based bulk metallic glasses

Abstract: Bulk metallic glasses (BMGs) of Zr 46− x Nb x Cu 37.6 Ag 8.4 Al 8 with x = 0, 0.5, 1, 2 and 4 at.% were prepared by copper mould casting. The corrosion resistance of the ZrCu-based BMGs with different Nb contents was carefully examined by weight loss measurements and potentiodynamic polarization tests in 3 mass% NaCl, 1 N HCl and 1 N H 2 SO 4 solutions, respectively. Nb addition improves the newly developed BMGs’ corrosion resistance in chloride-containing solutions and the alloys all exhibit excellent corrosion resistance in 1 N H 2 SO 4 . The corrosion behavior of the alloy containing 0 and 4 at.% Nb in phosphate-buffered solution was examined by electrochemical polarization tests. The influence of Nb addition on glass forming ability (GFA), thermal stability and mechanical property was investigated by X-ray diffraction, differential scanning calorimetry and compression tests, respectively. It is found that the addition of Nb can deteriorate the GFA and thermal stability of the base system, but little effect is observed on the mechanical properties, e.g., yielding strength and plasticity, of the ZrCu-based BMG alloys.

In situ observation of dynamic recrystallization in the bulk of zirconium alloy

Abstract: Dynamic recrystallization and related effects have been followed in situ and in real time while a metal undergoes rapid thermo-mechanical processing. Statistics and orientation correlations of embedded/bulk material grains were deduced from two-dimensional X-ray diffraction patterns and give deep insight into the formation of the microstructure. Applications are relevant in materials design, simulation, and in geological systems.