Showing papers on "Zirconium alloy published in 2004"

Crystallography of Zirconium Hydrides in Recrystallized Zircaloy-2 Fuel Cladding by Electron Backscatter Diffraction

Abstract: Precipitation morphology and habit planes of the delta-phase Zr hydrides, which were precipitated within the a-phase matrix grains and along the grain boundaries of recrystallized Zircaloy-2 cladding tube, have been examined by electron backscatter diffraction (EBSD). Radially-oriented hydrides, induced by residual tensile stress, precipitated in the outside region of the cladding, and circumferentially-oriented hydrides in the stress-free middle region of the cladding. The most common crystallographic relationship for both types of the hydrides precipitated at the inter- and intra-granular sites was identical at (0001)(alpha) // {111}(delta), with {1017}(alpha) // {111}(delta) being the occasional exception only for the inter-granular radial hydrides. When tensile stress was loaded, the intra-granular hydrides tended to preferentially precipitate in the grains with circumferential basal pole textures. The inter-granular hydrides tended to preferentially precipitate on the grain faces opposite to tensile axis. The change of prioritization in the precipitation sites for the hydrides due to tensile stress could be explained in terms of the relaxation effect of constrained elastic energy on the terminal solid solubility of hydrogen at hydride precipitation.

High-strength Cu-based crystal-glassy composite with enhanced ductility

Abstract: Low ductility of glassy alloys prevents their technical application as structural materials. In this work, we study the Cu-based crystal-glassy composite material with good mechanical properties. Formation of the Cu10Zr7 phase in the glassy matrix of a high-strength Cu50Zr30Ti10Nb10 bulk alloy upon solidification led to higher Young’s modulus and enhanced ductility of such a composite compared to Cu-based glassy alloys. The as-cast structure was studied by x-ray diffraction and scanning electron microscopy.

Zirconium alloys in nuclear power engineering

Abstract: Results of studies of zirconium alloys E110 and E635 that have served in parts of VVER-1000 reactors are presented. The influence of the composition on the properties of alloys E110 and E635 is studied and improved modifications are suggested. The effect of the total content of admixtures in alloy E110 on corrosion and embrittlement of pipes under conditions simulating LOCA is investigated.

Overheating threshold and its effect on time-temperature-transformation diagrams of zirconium based bulk metallic glasses

Abstract: A pronounced effect of overheating is observed on the crystallization behavior for the three zirconium-based bulk metallic glasses: Zr41.2Ti13.8Cu12.5Ni10Be22.5, Zr57Cu15.4Ni12.6Al10Nb5, and Zr52.5Cu17.9Ni14.6Al10Ti5. A threshold overheating temperature is found for each of the three alloys, above which there is a drastic increase in the undercooling level and the crystallization times. Time–temperature-transformation (TTT) diagrams were measured for the three alloys by overheating above their respective threshold temperatures. The TTT curves for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and Zr57Cu15.4Ni12.6Al10Nb5 are very similar in shape and scale with their respective glass transition temperatures, suggesting that system-specific properties do not play a crucial role in defining crystallization kinetics in these alloys. The critical cooling rates to vitrify the alloys as determined from the TTT curves are about 2 K/s for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and 10 K/s for Zr57Cu15.4Ni12.6Al10Nb5. The measurements were conducted in a high-vacuum electrostatic levitator.

Effect of Pre-Hydriding on Thermal Shock Resistance of Zircaloy-4 Cladding under Simulated Loss-of-Coolant Accident Conditions

Abstract: Experiments simulating loss-of-coolant accident (LOCA) conditions were performed to evaluate the effect of pre-hydriding on the thermal-shock resistance of oxidized Zircaloy-4 cladding. Test rods fabricated with 580-mm long claddings were isothermally oxidized at temperatures ranging from 1,220 to 1,530 K in steam and then were quenched with flooding water. Both artificially hydrided (400 to 600ppm) and non-hydrided claddings were subjected to these tests. Since cladding fracture on quenching primarily depends on the amount of oxidation, the fracture threshold was evaluated in terms of “equivalent cladding reacted (ECR).” Under an axially unrestrained condition, the fracture threshold is about 56% ECR, and the influence of pre-hydriding is not observed. The fracture threshold is decreased by restraining the test rods on quenching, and it is more remarkable in pre-hydrided claddings than in non-hydrided claddings. Consequently, the fracture threshold was about 20% ECR and 10% ECR for non-hydrided and pre-h...

Bulk glassy Ni(Co–)Nb–Ti–Zr alloys with high corrosion resistance and high strength

Abstract: Bulk glassy Ni 60− x Co x Nb 20 Ti 10 Zr 10 ( x =0–20 at.%) alloys with a large supercooled liquid region of more than 40 K were formed by copper-mold casting. The alloys with 5 and 10 at.% cobalt possess the highest glass-forming ability in the present alloy system and their critical diameter for glass formation is 1.5 mm. The bulk glassy alloys with different cobalt contents exhibit nearly the same corrosion behavior in HCl solutions. Their corrosion rates are less than 10 −3 mm per year in 1 N and 6 N HCl solutions. The bulk glassy alloys are spontaneously passivated with low passive current densities of around 10 −1 A m −2 in 1 N and 6 N HCl solutions. XPS analysis revealed the formation of a niobium-enriched passive film on the alloys by air-exposure or immersion in the acids, which could be responsible for the high corrosion resistance of the glassy Ni-based alloys. The Vickers hardness, Young’s modulus, compressive fracture strength and compressive fracture elongation of the 1.5 mm diameter bulk glassy alloys are 860, 160 GPa, 3050 MPa and 2% respectively. The facture surface exhibits a vein-like morphology.

Terminal Solid Solubility of Hydrogen in Unalloyed Zirconium by Differential Scanning Calorimetry

Abstract: (2004). Terminal Solid Solubility of Hydrogen in Unalloyed Zirconium by Differential Scanning Calorimetry. Journal of Nuclear Science and Technology: Vol. 41, No. 9, pp. 949-952.

Analysis of zirconium oxide formed during oxidation at 623 K on Zr–2.5Nb and Zircaloy-4

Abstract: The corrosion kinetics of Zr–2.5Nb and Zircaloy-4 were studied at a temperature of 623 K in lithiated heavy water. The oxide films grown on both alloys during this exposure were strongly textured. The orientation distribution functions (ODF), calculated from the pole figures, showed that the major orientation components of the oxide formed on Zr–2.5Nb were (1 0 3 )[0 1 0] and (1 0 4 )[4 0 1] while a (1 0 4 ) fiber texture was formed on Zircaloy-4. The transformation of the structure of the oxide films from the tetragonal to monoclinic phase was followed and the volume fraction changes of these two phases were estimated. The volume fraction of the tetragonal oxide phase decreased with an increasing exposure time in the oxide films of both materials and at the same time, a significant difference in oxidation kinetics of Zr–2.5Nb and Zircaloy-4 was recorded. The results suggest that Zircaloy-4 has a greater fraction of tetragonal phase and a better corrosion resistance than Zr–2.5Nb.

Formation, thermal and mechanical properties of bulk glassy alloys in Zr–Al–Co and Zr–Al–Co–Cu systems

Abstract: New Zr-based bulk glassy alloys in Zr-Al-Co and Zr-Al-Co-Cu systems were developed The largest supercooled liquid region is upto 64 for the Zr 55 Al 20 Co 25 alloy and 80 K for the Zr 55 Al 20 Co 20 Cu 5 alloy, respectively Glassy rods with a diameter of 3 mm for the Zr 55 Al 20 Co 25 alloy and 5 mm for the Zr 55 Al 20 Co 20 Cu 5 alloy can he prepared by copper-mold casting Glassy Zr 55 Al 20 Co 20 Cu 5 sheet with a thickness of 2 mm was also formed by squeeze copper-mold casting The bulk glassy Zr 55 Al 20 Co 20 Cu 5 alloy exhibits Young's modulus of 92 GPa, elastic limit of 21%, tensile strength of 1960 MPa, compressive fracture strength of 2200 MPa, and compressive plastic strain of 06% The tensile strength value is considerably higher than those for the other Zr-based bulk glassy alloys reported upto date The synthesis of the new Zr-based bulk glassy alloys with high glass-forming ability and high tensile strength approaching 2000 MPa is expected to result in a future extension of application fields as a high strength material

High coercivity of melt-spun (Fe0.55Pt0.45)78Zr2–4B18–20 nanocrystalline alloys with L10 structure

Abstract: The structure and the coercivity (Hc) of rapidly quenched (Fe0.55Pt0.45)bal.Zr0–8B0–24 alloys prepared by the melt-spinning technique have been investigated. Ordered L10 Fe–Pt phase of 20–100 nm was obtained by rapidly quenching the melt for (Fe0.55Pt0.45)78Zr2B20 and (Fe0.55Pt0.45)78Zr4B18 alloys with high Hc of 341 and 649 kA/m in an as-quenched state, respectively. On the other hand, the (Fe0.55Pt0.45)78Zr4B18 alloy produced by Cu mold casting at a lower cooling rate than melt spinning is found to be composed of a mixed structure of Fe–Pt L10, ZrB12, PtZr and Fe3B phases and the alloy has much lower Hc of 74 kA/m than that of the melt-spun (Fe0.55Pt0.45)78Zr4B18 alloy. The lattice parameters (a and c) of the L10 phase in the melt-spun alloys suggest that Zr and B elements are contained in the L10 phase for the melt-spun alloys, which is possibly related to direct formation of the L10 structure by rapidly quenching the melt.

Hydrogen Generation in Reflooding Experiments with LWR-Type Rod Bundles (QUENCH Program)

Abstract: The QUENCH bundle experiments together with pertinent separate-effects tests are run to investigate the hydrogen source term resulting from water injection into an uncovered core of a light water reactor for emergency cooling. The test bundle consists of 21 fuel rod simulators, 20 of which are heated electrically over a length of 1024 mm. The center rod is either an unheated fuel rod simulator or a control rod containing B{sub 4}C absorber material. The Zircaloy-4 rod cladding and the grid spacers are identical to those used in pressurized water reactors, whereas the fuel is represented by ZrO{sub 2} pellets. After transient heating to 2000 K and above, cooling of the test bundle is accomplished by injecting water or steam into the bottom of the test section. Hydrogen generation during cooling was found either to stop almost immediately or to increase for a certain time. Increased hydrogen generation was found in those tests in which local melting occurred, probably as a result of oxidation of the melt containing zirconium. Hydrogen release in the flooding/cooling phase of all QUENCH experiments performed so far seems to be insensitive to the coolant (water or steam) under similar test conditions.