Showing papers on "Zirconium alloy published in 1999"

Efficient dopants for ZrNiSn-based thermoelectric materials

Abstract: Four efficient n-type dopants have been found for ZrNiSn-based thermoelectric materials. These are Nb or Ta at the zirconium sites, and Sb or Bi at the tin sites. No suitable dopant was found for the nickel sites. In a alloy, a power factor of and a thermal conductivity of were measured at 300 K, resulting in a dimensionless figure of merit ZT = 0.12. These values are increased to and at 700 K.

Magnetic properties of HITPERM (Fe, Co)88Zr7B4Cu1 magnets

Abstract: A new class of nanocrystalline alloys with composition Fe44Co44Zr7B4Cu1 has been developed. This and similar alloys of general composition (Fe, Co)–M–B–Cu (where M=Zr, Hf, Nb, etc.) have been named HITPERM. They offer large magnetic inductions and excellent soft magnetic properties at elevated temperatures. Thermomagnetic properties, permeability, and frequency dependent losses are described in this report. These alloys exhibit high magnetization that persists to the α→γ phase transformation at 980 °C. Alternating current permeability experiments reveal a high permeability at 2 kHz with a loss value of 1 W/g at Bs=10 kG and f=10 kHz.

Nanocrystalline composites with high strength obtained in Zr–Ti–Ni–Cu–Al bulk amorphous alloys

Abstract: Nanocrystalline composites with the grain size less than 10 nm were produced by annealing of Cu-mold cast Zr70−x−yTixNi10Cu20Aly (X=5–7.5 and Y=10–15 at %) bulk amorphous alloys. The nanostructured alloys show increased tensile strength at the volume fraction of nanoparticles less than 30%. The microstructure of the amorphous alloys was found to contain medium range order (MRO) domains, which uniformly distributed in the amorphous matrix. We suggest that MRO domains provide nucleation sites for precipitation of the primary crystals and lead to the formation of nanocrystalline composites.

The intermetallic zirconium compounds zrnial, zrrhsn, and zrptga : structural distortions and metal-metal bonding in fe2p related compounds

Abstract: ZrNiAl, ZrPtGa, and ZrRhSn have been prepared by reacting the elements in an arc-melting furnace and subsequent annealing at 970 K. These compounds have previously been investigated only by use of X-ray powder data for ZrPtGa and ZrRhSn and single crystal film data for ZrNiAl. Precise single crystal diffractometer data are reported in the present paper. The structure of ZrNiAl is confirmed. It adopts a substitution variant of the Fe2P type: P6̄2m, a = 691.5(2), c = 346.6(1) pm, Z = 3, wR2 = 0.0538, 320 F2 values, 14 parameters. The structure refinement reveals a large displacement parameter U33 for one nickel position, indicative of a slight nickel dislocation. Weak superstructure reflections could be found on Guinier powder patterns for ZrPtGa and ZrRhSn. These compounds crystallize with the HfRhSn type structure (Z = 6 , space group P6̄2c), a superstructure of the Fe2P type: a = 714.5(1), c = 706.3(2) pm, wR2 = 0.0651, 594 F2 values, 18 parameters for ZrPtGa and a = 734.2(2), c = 721.8(2) pm, wR2 = 0.0349, 355 F2 values, 18 parameters for ZrRhSn. Structural motifs of these compounds are transition metal centered trigonal prisms formed by the zirconium, aluminium, gallium, and tin atoms. While these trigonal prisms are regular in ZrNiAl, significant distortions occur in the structures of ZrPtGa and ZrRhSn. Due to the distortions of the trigonal prisms in the superstructures, some platinum and rhodium atoms are dislocated from the subcell mirror planes towards Pt-Pt and Rh-Rh pairs with distances of 310 and 313 pm, respectively. The formation of the superstructure is most likely due to packing reasons. Chemical bonding in ZrRhSn was investigated on the basis of an extended Hückel calculation.

Microstructure and mechanical properties of two-phase Cr–Cr2Nb, Cr–Cr2Zr and Cr–Cr2(Nb,Zr) alloys

Abstract: The microstructures and mechanical properties of binary and ternary Cr-based alloys containing Nb, Zr, or both Nb and Zr, have been studied in both the as-cast and annealed conditions. The level of alloying in each instance was targeted to lie below. or approximately at, the maximum solubility in chromium. The as-cast microstructures of these alloys consisted of Cr-rich solid solution surrounded by small amounts of interdendritic Cr-Cr 2 X eutectic structure. Annealing at 1473 K resulted in solid-state precipitation of the Cr 2 X Laves phase in the Cr-Nb and Cr-Nb-Zr alloys, but not in the Cr-Zr alloys. The binary Cr 2 Nb phase consisted of an extensively twinned ({111} twins) C15 structure whereas the presence of Zr modifies its appearance substantially; the twinned C15 structure persists. Oxides were occasionally present and their compositions were qualitatively determined. Vickers hardness primarily depended upon the volume fraction of the Cr 2 X Laves phase present. Age hardening due to solid-state precipitation of Cr 2 X Laves phase within the Cr-rich matrix was observed in the Nb-containing alloys. The room temperature bend strength of the alloys was strongly affected by the presence of grain-boundary Cr 2 X phase. It is considered that porosity as well as oxides in the alloys also lowers their bend strength.

High-strength high-toughness amorphous zirconium alloy

Abstract: An amorphous zirconium alloy which has a composition represented by the formula Zr-Ala-Nib-Cuc-Md (wherein M is at least one element selected from the group consisting of Ti, Nb, and Pd; a, b, c, and d respectively are numbers in at.% satisfying the relationships 5 a 10, 30 b+c 50, b/c 1/3, and 0 or higher, and the fracture toughness is 50 MPa•m or higher.

Ultrasonic measurement of the kearns texture factors in zircaloy, zirconium, and titanium

Abstract: Texture, developed during the processing of zirconium and zirconium alloys, e.g., ZIRCALOY, plays an important role in determining the properties and performance of the resultant structural components. Extending the work done on cubic metals, ultrasonic velocity measurements were used to nondestructively characterize the texture in hexagonal sheet metals. A theory is developed relating the texture coefficients W LMN (L≤4, found in an expansion of the crystallite orientation distribution function (ODF) in terms of generalized spherical harmonics) to industrially measured Kearns factors, which predict the fraction of basal poles aligned in a particular sample reference direction. Ultrasonic characterization of texture has been performed on three sheets of zirconium (one pure, two ZIRCALOY) and on one sheet of titanium. These results are compared to the Kearns factors, measured by X-ray diffraction (for the two ZIRCALOY sheets) and to the W LMN value measured by neutron diffraction (for the pure zirconium and the titanium). Results show that ultrasonics predict both the orientation distribution coefficients (ODCs) and the Kearns factors very well.

Effects of compositional and structural change on the corrosion behaviour of nitrogen implanted Zircaloy-4

Abstract: The influence of nitrogen implantation on the corrosion behaviour of Zircaloy-4 was examined by potentiodynamic polarization tests in a chloride and an acid solution, and the results were discussed with structural and compositional variations of implanted layer that was determined by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). The resistance to localized corrosion of Zircaloy-4 was very sensitive to the ion dose and the substrate temperature during the implantation. At substrate temperatures above 200°C, the pitting potential of the nitrogen implanted alloy in deaerated 4 M NaCl at 80°C increased gradually with the ion dose from 350 mVSCE for the unimplanted sample to 990 mVSCE for the alloy implanted with an ion dose of 6×1017 ions cm−2, and then the alloy was immune to pitting when implanted with ion doses greater than about 1×1018 ions cm−2. In contrast to this, the alloy implanted at 100°C exhibited an inferior corrosion resistance to the unimplanted sample irrespective of the ion dose. A drastic increase in the resistance to pitting corrosion in chlorides as well as a significant reduction in the passive current density in acid solution of the implanted alloy, were found to be associated with the formation of ZrN layer with a stoichiometric ratio of N to Zr. The low resistance to localized and general corrosion of the alloy implanted at 100°C was attributed to the increase in structural defects produced by ion bombardment, and to low atomic mobility in the implanted layer.

Electrochemical Properties of Zr‐V‐Ni System Hydrogen Storage Alloys

Abstract: The Zr-V-Ni system multicomponent alloys were investigated by electrochemical measurements, X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive spectroscopy. At room temperature, the discharge capacity of ZrV{sub x}Mn{sub 0.9{minus}x}Ni{sub 1.1} (x = 0.1--0.8) alloys remains at a high level when x = 0.3--0.5. A C15 main phase alloy has good capacity. ZrV{sub 0.5}Mn{sub 0.3}T{sub 0.1}Ni{sub 1.1} (T = Ni, Co, Fe, or Al) alloys exhibit lower discharge ability at room temperature because higher contents of V and Mn (i.e., (V + Mn)/AB{sub 2} = 0.8) form more stable hydrides. Al substitution also stabilizes the hydrides effectively. All these alloys have discharge capacities of about 350 mAh/g on heating to 328 K. Further investigation showed that the substitution of Ti for Zr decreases markedly the thermodynamic stability of the hydrides and promotes a promising discharge capacity at room temperature. During cycling, the preferential anodic oxidation of some components, such as Ti and V, degrades the reversible storage ability. An electrochemical method was adopted to evaluate the PcT isotherm for Zr-based alloys. This method is suitable for all hydride electrodes as well.