Crystalline Zr Research Articles

Structure and crystallization of the partially crystalline Zr76Ni24 metallic glass

Abstract The partially crystalline Zr 76 Ni 24 (numbers indicate at.%) metallic glass was prepared by melt spinning. The structure and crystallization of the partially crystalline Zr 76 Ni 24 metallic glass during heat treatment at different heating rates have been investigated by means of differential scanning calorimetry in the temperature interval from 300 to 823 K and by X-ray powder diffraction (XRD) at room temperature. According to the XRD results, it was found that two sides of the quenched ribbons showed different structures. The XRD pattern of the side of the ribbon which was in contact with the wheel of the quenching apparatus shows a broad maximum corresponding to an amorphous phase. On the other hand, the XRD pattern of the side of the ribbon which was in contact with the inert atmosphere consists of a set of sharp lines. These lines were indexed and found that they belong to the orthorhombic Zr 3 Ni metastable crystalline phase. Crystallization studies showed that the existence of the orthorhombic Zr 3 Ni metastable crystalline phase does not change the thermal stability of the amorphous phase against further crystallization and remains unchanged during the annealing up to 823 K.

Influence of hydrogen dopant on the structure and crystallization of the partially crystalline Zr 76Ni 24 metallic glass

The influence of hydrogen dopant on the structure and crystallization of partially crystalline Zr 76Ni 24 metallic glass during heat treatment at different heating rates has been investigated by means of differential scanning calorimetry (DSC) in the temperature interval from 300 to 823 K and by X-ray powder diffraction (XRD) at room temperature. According to the XRD results, the as quenched Zr 76Ni 24 samples were mostly glassy (about 90%) with about 10% orthorhombic metastable Zr 3Ni crystalline phase. A systematic DSC analysis shows that adding hydrogen to these Zr 76Ni 24 samples raises the temperature of crystallization, T x1 for the hydrogen content up to x=0.054 ( x indicate at.%). Also, the hydrogen absorption causes an increase of the lattice parameter a and a decrease of the lattice parameter b of the orthorhombic metastable Zr 3Ni crystalline phase. The as quenched Zr 76Ni 24 samples showed to be oxidation resistant, whereas the oxidation rate of the hydrogen doped sample increases with increasing hydrogen content during heat treatment up to 823 K. The scales formed on the surface of the annealed hydrogen doped samples during the oxidation have a nanocrystalline microstructure consisting mainly of monoclinic ZrO 2.

Formation of Cu–Zr–Ni amorphous powders with significant supercooled liquid region by mechanical alloying technique

The amorphous Cu–Ni–Zr alloys were successfully synthesized by mechanical alloying mixtures of pure crystalline Cu, Ni and Zr powders with SPEX high-energy ball mill. These ranges are similar to those for amorphous alloys produced by melt-spinning techniques. The structure and thermal stability of these alloys were analyzed by X-ray diffraction and differential scanning calorimeter. Several amorphous alloy samples were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between T g and T x, i.e. Δ T x (= T g− T x), is 34 K for Cu 10Zr 60Ni 30, 48 K for Cu 20Zr 60Ni 20, 78 K for Cu 40Zr 55Ni 5, 81 K for Cu 50Zr 35Ni 15, 61 K for Cu 50Zr 40Ni 10 and 64 K for Cu 50Zr 45Ni 5.

Pseudo Float Melting State in Ladle Arc-Melt-Type Furnace for Preparing Crystalline Inclusion-Free Bulk Amorphous Alloy

A homogeneous melting state without any crystalline inclusions was achieved in an arc melt furnace by using a ladle arc-melting-type furnace. Molten alloy for pouring can be melted completely by arc heating just above the mold in a pseudo float melting (PFM) state. We combined a ladle arc-melt-type furnace and the squeeze cast method to produce bulk amorphous alloy sheet with a single amorphous phase structure, thereby successfully producing crystalline inclusion-free Zr 50Cu30Ni10Al10 bulk amorphous alloy sheets. The tensile strengths of the Zr50Cu30Ni10Al10 bulk amorphous alloys exceeded 1800 MPa, and the bending deflection of the alloys was improved by a factor of 10 using the PFM process.

Preparation and characterization of Au/ZrO 2 nanoparticles obtained by oxidation of Zr XAu Y alloy

Recently, we have shown that powders containing both gold and ZrO 2 nanosized particles could be prepared by low temperature ( T<100 °C) oxidation of cast crystalline Zr–Au alloys. In this report, we present the preliminary results of a study aiming at preparing the mixed nanosized particles from thin films. In a first step, pure Zr and Au layers are alternatively deposited by RF sputtering on Si and W substrates under vacuum. Then, the intermetallic compounds are formed at high temperature under an inert atmosphere or in vacuum. The resulting samples are characterised by X-ray diffraction and by scanning electron microscopy (SEM).

Re-passivation current of amorphous Zr 65Al 7.5Ni 10Cu 17.5 alloy in a Hanks’ balanced solution

To evaluate the repassivation behavior of amorphous phase with chemical and structural homogeneity, time transient of re-passivation current density was measured on amorphous Zr 65Al 7.5Ni 10Cu 17.5 alloy and crystalline pure Zr with a momentary fracture of a ribbon shaped specimen in an artificial body fluid. Current density abruptly increased to a peak, J peak, and exponentially decreased to the constant value, J ∞, J peak and J ∞ on the amorphous specimen were smaller than those on the crystalline specimen, indicating that the amorphous phase would show the smaller dissolution rate from bare metal surface and from a re-passive film than the crystalline specimen, respectively. On the other hand, decrease rate of the current density on the amorphous specimen was smaller than that on the crystalline specimen, indicating the regeneration of passive film on the amorphous specimen was delayed probably because the amount of metal ions dissolved at the initial stage, i.e. the source of re-passive film, was smaller on the amorphous specimen. Consequently, the total charge for the re-passivation of the amorphous specimen was smaller than that of the crystalline specimen, supposing that the amount of dissolved metal ions during re-passivation was smaller on the amorphous specimen than the crystalline specimen.

“Big cube” phase formation in Zr-based metallic glasses

The formation of a metastable fcc NiTi 2-type intermetallic compound (big cube phase) from Zr-based metallic glasses have been studied in this work. This phase was found in partially crystalline Zr 52.5Cu 17.9Ni 14.6Al 10Ti 5 amorphous ribbons. Its nucleation could be avoided by adding 2% of Y, which acts as an oxygen scavenger. After annealing a fully amorphous ribbon, nanocrystals of the big cube phase have been observed. The Zr 55Cu 30Ni 5Al 10 alloy has been partially amorphised by copper moulding and arc melting. Large agglomerates of crystals of the big cube phase have been found embedded in the amorphous matrix. Also for this alloy, nanocrystal of the same phase has been found after crystallisation. From the results, it appears clear that the big cube phase nucleates first from the undercooled liquid. Its formation is hindered if the oxygen content in the undercooled liquid alloy is significantly reduced. After solidification, coarse grains were found, whereas nanocrystals were produced by crystallisation. The role of nucleation on the crystallisation process is briefly discussed.

Electron Beam Welding of Zr-Based Bulk Metallic Glass to Crystalline Zr Metal

We have tried an electron-beam welding of a Zr-based bulk metallic glass plate to a polycrystalline Zr metal one for a Zr41Ti14Cu12Ni10Be23 (at%) bulk metallic glass having an excellent glass forming ability. We have succeeded in butt-welding the bulk metallic glass and pure Zr metal plates with a thickness of 3 mm. Invisible defect or clack was detected around the bead and heat-affected zone. The bulk metallic glass around the interface kept the amorphous state. Formation of any crystalline phases except for hcp-Zr was not detected in the interface. The interface of the successfully welded sample exhibited enough toughness and joining strength to endure the bending through 90 degrees by hammering.

Hydrogen storage properties of nano-composites of Mg and Zr–Ni–Cr alloys

Mg and Zr–Ni–Cr alloy nano-composite hydrogen storage materials have been prepared by high energy mechanical milling (MM) of Mg powders with either crystalline ZrNiCr and ZrNi 1.6Cr 0.4 powders or mechanically milled amorphous ZrNiCr and ZrNi 1.6Cr 0.4 powders. Nano-composites of amorphous Zr–Ni–Cr alloy and Mg have better desorption kinetics compared to crystalline Zr–Ni–Cr alloy and Mg nano-composites. Amorphous ZrNi 1.6Cr 0.4 and Mg nano-composites desorb larger amount of H 2 much faster than amorphous ZrNiCr and Mg nano-composites. The nano-composite of 35 wt.% amorphous ZrNi 1.6Cr 0.4 and Mg releases 4.3 wt.% H 2 at 300°C in 30 min. X-ray diffraction revealed that there are no reactions between Mg and Zr–Ni–Cr alloys in the milling, activation, and subsequent cycling processes, proving that amorphous ZrNi 1.6Cr 0.4 is an effective hydrogen absorption and desorption catalyst.

The effects of Cu, Nb and Zr additions on the permanent magnetic properties of melt-spun Sm–Fe–Si–C ribbons

The effects of Cu, Nb and Zr additions on the permanent magnetic properties of melt-spun Sm–Fe–Si–C ribbons with Th 2Zn 17 structure were extensively studied. The additions of Cu, Nb and Zr limit the crystalline grain growth, and Nb and Zr are helpful in forming the amorphous. The coercivity enhancement was found only in the Cu-doped 2 : 17 type Sm–Fe–Si–C ribbons and the value of maximum intrinsic coercivity μ 0i H c is about 1.28 T for Sm 2Fe 13.5Cu 1.5Si 2C.

Bulk and surface properties of crystalline and amorphous Zr 36(V 0.33Ni 0.66) 64 alloy as active electrode material

The electrochemical hydrogen absorption/desorption behavior of a crystalline and an amorphous Zr 36(V 0.33Ni 0.67) 64 alloy sample was investigated. Electrodes made of the crystalline sample show a much lower resistance and consequently a higher discharge capacity compared to the electrodes made of the amorphous alloy. The XPS surface analysis did not explain the difference, we observed almost exactly the same depth profile on both samples. However the surface of the activated alloy compared to the non-activated was drastically changed. The oxide layer on an amorphous alloy seems to grow in a much more compact and stable structure than the oxide layer on a crystalline sample.

Structural changes in Co/Zr multilayers during annealing below the crystallisation temperature

The local structure of two multilayer systems Co/Zr of different layer thickness during annealing well below the crystallisation temperature was determined by means of extended X-ray absorption fine structure (EXAFS), performed at Co K edge as well as at Zr K edge. By taking additionally wide angle X-ray scattering (WAXS) measurements into consideration, the averaged EXAFS signal summing up contributions of all exited atoms in the sample could be separated into parts belonging to the crystalline and amorphous phases which occurred in the intermediate states of the system Co/Zr simultaneously. The existence and conservation of fibre textures within the crystalline layers and the conservation of periodicity in chemical composition perpendicular to the layer plane could be proved. Moreover, intensities of the 0002 and 10–11 reflections of Zr provided reasonable starting models for fitting crystalline Zr to a subshell model of close lying shells. Coordination numbers obtained for the crystalline phases of Co and Zr agreed well with the bulk data. Looking from the position of either absorbing species the atomic radial distribution was evaluated. Zr neighbours dominated for Zr as well as for Co central atoms. Around Co atoms we found Co at typical distances of 2.45, 2.78 and 3.06 Å; around Zr the Zr neighbours occupied neighbour shells at 3.07 and 3.30 Å. Distances between unlike atoms were found to be 2.65 and 2.81Å. These values describe single symmetric contributions of asymmetric pair distributions derived on the basis of multiple Gauss analysis. From EXAFS and WAXS we concluded that the amorphous part of the layer system is initially dominated by a Zr-rich phase which competes with a second amorphous phase of an approximate composition Co 50Zr 50 during the the subsequent stages. As the reaction proceeds the latter grows while the Zr-rich phase is reduced.

Thermodynamics of zirconium and hafnium orthophosphates (arsenates)

The enthalpies of solution of M IV [HP(As)O 4 ] 2 (where M IV is zirconium or hafnium) compounds and their monohydrates have been measured calorimetrically and the standard enthalpies of formation derived. The results obtained have been used for the calculation of dehydration enthalpies of M IV [HP(As)O 4 ] 2 .H 2 O. The standard enthalpies of formation of Zr(MAsO 4 ) 2 .nH 2 O (where M is lithium, sodium or potassium) compounds have also been determined and enthalpies of M + -H + exchange on crystalline Zr(HAsO 4 ) 2 .H 2 O have been obtained. Qualitative explanations for the observed ion exchange results are presented.

X-Ray Microanalysis of Al/Zr Multilayers in the Transmission Electron Microscope

ABSTRACTA one-nanometer scale transmission electron microscope electron probe X-ray microanalysis characterization of as-deposited and annealed aluminum - 11.5 at.% zirconium multilayer samples in cross-section synthesized by magnetron sputtering is reported on here. Composition line profiles were acquired across Zr layers in as-deposited material and samples isochronnally annealed in a differential scanning calorimeter to temperatures of 290°C and 485°C. A spatial resolution of approximaty 1.5 to 2.0 nm was achieved in these experiments and will be improved by deconvoluti on of the instrumental electron probe function from the data. The as-deposited structure consisted of crystalline Al and Zr layers with thin amorphous layers at the Al/Zr interfaces. The amorphous interface layers increased in thickness upon annealing to 290°C. Additionally, at 290”C a metastable cubic alloy forms at the Zr deposited on Al interface. Upon heating to 485°C a multilayer of Al and metastable cubic AlxZr1-xphase is formed. The electron microscopic experimental technique, observations and data analysis will be discussed as applied to these multilayered materials.

Liquid Precursor Infiltration Processing of Powder Compacts: I, Kinetic Studies and Microstructure Development

The kinetics of infiltrating a solution precursor into Si3N4 powder compacts were studied using either water or an aqueous solution of Zr‐nitrate and Y‐nitrate that formed a crystalline Zr(Y)O2 (3 mol% Y2O3) solid solution during pyrolysis. When the powder compact contained air, the infiltration involved two steps: (1) relatively rapid intrusion of liquid via flow due to capillary pressure and (2) diffusion of entrapped gas to the surface as its pressure became equal to the capillary pressure. The kinetics of both processes are described with different parabolic rate laws–Darcy's law and Fick's law, respectively. When the intruded precursor is converted to an inorganic during heat treatment, the void space is partially filled with pyrolyzed precursor without shrinkage of the Si3N4 powder. The kinetics of subsequent cycles depend on the permeability of the pyrolyzed precursor, which depends on its microstructural development during heat treatment subsequent to pyrolysis. Surface cracks can form within the powder compact during either precursor drying or pyrolysis; they can be avoided by strengthening the powder compact by forming small necks between touching particles via evaporation–condensation. Precursor molecules were found to concentrate near the surface as the precursor solvent was removed by drying. The movement of precursor molecules was prevented by gelling prior to drying, viz., by soaking the infiltrated bodies in an aqueous NH4OH solution. Microstructures developed during cyclic precursor infiltration and pyrolysis were characterized to show that cracklike voids are produced within the pyrolyzed precursor due to its large volume change during pyrolysis and densification; the size distribution of the cracklike voids is proportional to the size distribution of the voids within the initial powder compact.

Synthesis of ultra-fine crystalline Zr xTi 1 − xO 4 powder by polymeric precursor method

Reactive Zr x Ti 1 − x O 4 ( x = 0.65, 0.50 and 0.35) powder was prepared by the polymeric precursor method. Studies by X-ray diffraction (XRD), nitrogen adsorption/desorption, and thermogravimetric analysis (TG) showed that powders with high crystallinity (> 90%) and high surface areas (> 40 m 2/g) are obtained after calcination at 700 °C for 3 h. Infrared spectroscopy and XRD results showed that these titanates nucleate from the amorphous phase with no intermediate phases, at low temperature (450 °C).

Formation of YBa2Cu3O7 films on silicon/silicide/oxide structures formed via amorphous CoZr alloys

Thin films of the superconductor YBa2Cu3O7 have been grown on Si(111)/CoSi2/ZrO2 structures by inverted cylindrical magnetron sputter deposition at 700 degrees C. The CoSi2/ZrO2 bilayer structure was formed simultaneously by annealing an amorphous CoZr alloy layer in O2 at 650 degrees C. The amorphous alloy was formed by solid state reaction of crystalline Co and Zr under long anneals at a temperature below the crystallization temperature of the CoZr alloy. The bilayer formation gave a polycrystalline ZrO2 and an epitaxial CoSi2 layer aligned with the Si(111) substrate, with a channelling yield of 40%. YBa2Cu3O7 films grown on this multilayered structure had a Tc of 81 K and a transition width, Delta T, of 3 K as measured by resistivity readings.

Solidification Analyses of Bulky Zr&lt;SUB&gt;60&lt;/SUB&gt;Al&lt;SUB&gt;10&lt;/SUB&gt;Ni&lt;SUB&gt;10&lt;/SUB&gt;Cu&lt;SUB&gt;15&lt;/SUB&gt;Pd&lt;SUB&gt;5&lt;/SUB&gt; Glass Produced by Casting into Wedge-Shape Copper Mold

The liquid-crystalline transformation behavior during continuous cooling and the transformation-induced structure were examined for a Zr 60 Al 10 Ni 10 Cu 15 Pd 5 molten alloy which was ejected into a wedge-shape cavity in a copper mold. The wedge-shape cavity has a constant depth of 50 mm and different vertical angles (θ) ranging from 5 to 15 degrees. The ejection temperature of the molten alloy was also changed in the range of 1273 to 1573 K. The cast structure consists only of a glassy phase in the θ range smaller than 10 degrees and changes to a mixed structure consisting of glassy and nonequilibrium crystalline Zr 2 Ni and Zr 2 Cu phases in the higher θ range. The glass transition temperature and crystallization temperature of the cast metal glass are 683 and 778 K, respectively, which agree with those for the melt-spun glassy ribbon. The start (Cs) and termination (Ct) points for the transformation from the supercooled liquid to crystalline phases during continuous cooling were determined from the thermal analytical data obtained at different sites in the wedge-shape cavity and the continuous-cooling-transformation (C.C.T.) curves were constructed. The nose temperature (T n ) and the time (t n ) up to the nose point in the C.C.T. curves were 1018 K and 0.93 s respectively. The critical cooling rate for glass formation defined by (T m - T n )/t n is evaluated to be 110 K/s. Further, the time interval between Cs and Ct is as short as 0.2 s and the fast growth reaction is attributed to the easy formation of the nonequilibrium crystalline phases and the increase in temperature caused by the precipitation-induced recalescence.

Mechanical Stresses During Solid State Amorphization of Zr/Co Multilayers

AbstractThin film structures of crystalline Zr and Co, deposited in UHV, are investigated by bending beam technique and by X-ray diffraction. During isothermal annealing and interdiffusion reaction of the thin film double layer and multilayer packages large compressive stresses are generated while an amorphous ZrCo-phase is formed. This can, at first hand, be understood in terms of the Kirkendall effect where Co atoms, as the main moving species, lead to a volume increase of the film beyond the Co interface. The observed change in Zr lattice spacing in accordance with the evolution of mechanical stress indicates that the compressive stress is built up particularly within the Zr layer due to the solution of Co in Zr grains during the initial amorphization reaction. Film structures, having Co already present in the crystalline Zr layer after film deposition, show a decrease in reaction kinetics combined with a lower stress level, indicating that the interdiffusion reaction is depending on the stress state in the Zr grains. At late stages of annealing in high vacuum a sudden increase of additional compressive stress is observed, which could be attributed to the oxidation of Zr, very likely due to the formation of diffusion paths for oxygen through the Co (cap-) layer (Kirkendall voids). Such oxidation behavior was not observed with samples measured in situ in UHV directly after film deposition.

Stability of the Passive State of Ni-Zr Glassy Alloys

Abstract Electrochemical and microscopic investigations provided an insight into the anodic behavior of nickel-zirconium (Ni-Zr) glasses with 25 at% to 70 at% Zr in borate buffer solution containing up to 1 M sodium chloride (NaCl). Stability of the passive state of the glasses was high in the absence of Cl−. Oxygen evolution was observed at sufficiently noble potentials in contrast to the corresponding behavior of crystalline Zr, which formed an insulating film during anodization. Measurements of pit nucleation potential showed Ni-Zr glasses were less resistant to pitting than crystalline Zr at any Cl− concentration. Glasses of > 50% Zr were less resistant than of crystalline Ni. Pit nucleation potential decreased at ≈ 80 mV/dec of Cl− concentration, suggesting chemical breakdown of passivity. However, the short induction period of pitting for Zr-rich alloys was compatible with another mechanism of pit initiation involving structural effects within the passive film at high concentrations of Zr.