Ni Zr Research Articles

The absolute entropy of Ni0.667Zr0.333 and Ni0.333Zr0.667 amorphous alloys

The heat capacities of amorphous and crystallineNi0.667Zr0.333 and Ni0.333Zr0.667 alloys were measured in the temperature range from K to the crystallization points for the former or to K for the latter. The results together with the data on the thermodynamic properties ofthe Ni–Zr melt were used for the calculation of the absolute entropy of the amorphousalloys on the assumption that the entropies of a substance in undercooled liquid and glassystates coincide at the glass-transition point. The entropy and heat capacity of theamorphous alloys was found to exceed those of the crystalline ones. The residual entropy ofNi0.333Zr0.667 andNi0.667Zr0.333 amorphous alloys at0 K is, respectively, 2.7 ± 2.1 and 0.2 ± 1.7 J mol−1 K−1, which is significantly below the residual entropy values typical for traditional oxide glasses(4–17 J mol−1 K−1). This points to a much higher degree of order in amorphous metallic alloys as comparedto glassy oxides.

Effect of liquid temperature on thermal stability and crystallization behavior of Ni-based amorphous alloys

The effect of liquid ejection temperature ( T liq ) during melt-spinning on the thermal stability and crystallization behavior of amorphous Ni 59 Zr 20 Ti 16 Si 5− x Sn x ( x =0,3) alloys has been studied. Glass transition temperature ( T g ) and crystallization onset temperature ( T x ) of the amorphous Ni 59 Zr 20 Ti 16 Si 5 alloy are not affected by the variation of T liq . On the other hand, the amorphous Ni 59 Zr 20 Ti 16 Si 2 Sn 3 alloy shows different behaviors. T g is not dependent on T liq but T x shifts towards the lower temperature side with decreasing T liq , resulting in a decrease of the supercooled liquid region (Δ T x = T x − T g ). The effect of T liq on the thermal properties can be understood by the presence of short-range order clusters, which is related to Ni–Zr atomic pairs in the liquid state.

Vacuum hot pressing of gas-atomized Ni–Zr–Ti–Si–Sn amorphous powder

Fully amorphous Ni 57 Zr 20 Ti 18 Si 3 Sn 2 powders without any crystallinity are successfully fabricated in the particle size range below 75 μm by gas-atomization method. Gas-atomized Ni 57 Zr 20 Ti 18 Si 3 Sn 2 amorphous powder exhibits the glass transition temperature ( T g ) of 828 K and the crystallization temperature ( T x ) of 886 K. The gas-atomized Ni 57 Zr 20 Ti 18 Si 3 Sn 2 amorphous powder posesses a supercooled liquid region (Δ T x ) of 58 K. Based on the determined consolidation condition, the gas-atomized Ni 57 Zr 20 Ti 18 Si 3 Sn 2 amorphous powder was consolidated by a vacuum hot pressing apparatus. The optimum consolidation conditions were determined by isothermal annealing of Ni 57 Zr 20 Ti 18 Si 3 Sn 2 amorphous powder. The consolidated bulk Ni 57 Zr 20 Ti 18 Si 3 Sn 2 samples show completely amorphous on processing after consolidation. The relative density and hardness of the consolidated bulk Ni 57 Zr 20 Ti 18 Si 3 Sn 2 compacts are greater than 99 % and 800 Hv, respectively.

Effects of Sn addition on the glass forming ability and crystallization behavior in Ni–Zr–Ti–Si alloys

The effect of Sn substitution for Si on the glass forming ability (GFA) and crystallization behavior has been studied in Ni 59Zr 20Ti 16Si 5 − x Sn x ( x=0, 3, 5) alloys. A bulk amorphous Ni 59Zr 20Ti 16Si 2Sn 3 alloy with diameter up to 3 mm can be fabricated by injection casting. Partial substitution of Si by Sn in Ni 59Zr 20Ti 6Si 5 − x Sn x alloys improves the glass forming ability. The improved GFA of the Ni 59Zr 20Ti 16Si 2Sn 3 alloy is can be explained based on the lowering of liquidus temperature. The crystallization sequence becomes completely different with addition of Sn. The amorphous Ni 59Zr 20Ti 16Si 5 alloy crystallizes via precipitation of only a cubic NiTi phase in the first crystallization step, whereas the amorphous Ni 59Zr 20Ti 16Si 2Sn 3 alloy crystallizes via simultaneous precipitation of orthorhombic Ni 10(Zr,Ti) 7 and cubic NiTi phases. Addition of Sn in the Ni 59Zr 20Ti 16Si 5 alloy suppresses the formation of the primary cubic NiTi phase. The bulk amorphous Ni 59Zr 20Ti 16Si 2Sn 3 alloy exhibits high compressive fracture strength of about 2.7 GPa with a plastic strain of about 2%.

Amorphization of Ni60Nb20Zr20 by mechanical alloying

Abstract Elemental Ni, Nb and Zr powder mixtures with composition Ni 60 Nb 20 Zr 20 were mechanically alloyed in a ball mill. The evolution of structure of the powders was investigated with a combination of X-ray diffractometry and differential scanning calorimetry and was compared with corresponding melt spun samples. Mechanical alloying of Ni 60 Nb 20 Zr 20 alloy involves two consecutive amorphization reactions. Mechanical alloying first leads to the amorphization reaction between Ni and Zr layers with a strong thermodynamic driving force as well as fast kinetics for Ni–Zr amorphization compared with Ni–Nb amorphization. On further milling the kinetic requirements for a Ni–Nb amorphization reaction is fulfilled and consequently a Ni–Nb amorphous phase forms. The resulting two amorphous phases homogenize at longer milling times.

Heat Capacity and Absolute Entropy of the Ni–Zr Amorphous Alloys

In this work, we carried out comprehensive measurements of the heat capacity of the amorphous and crystalline alloys Ni 0.667 Zr 0.333 and Ni 0.333 Zr 0.667 in the temperature range from ~12 K to the crystallization points for the former and from ~12 to 900 K for the latter. The resulting data, along with data on the high-temperature thermodynamic properties of a liquid solution and crystalline phases [6], were used for calculating the absolute entropy of the amorphous state. The Ni 0.333 Zr 0.667 and Ni 0.667 Zr 0.333 amorphous alloys as bands 2.5‐3.0 mm wide and 0.02 mm thick were obtained by the spinning method on a copper disk in a vacuum setup under a purified helium atmosphere. The initial ingots were prepared from components with a purity of no less than 99.8 wt %. The composition of the first alloy corresponds to the intermetallic compound NiZr 2 , whereas the second alloy belongs to the twophase Ni 21 Zr 8 + Ni 10 Zr 7 region of the Ni‐Zr phase diagram. Preliminary studies of the heat behavior of the alloys at high temperatures by differential scanning calorimetry (SETARAM DSC 111) showed that the amorphous alloys Ni 0.667 Zr 0.333 and Ni 0.333 Zr 0.667 crystallize in the temperature ranges 817‐874 and 628‐686 K with maxima at 841 and 655 K, which is accompanied by exotherms equal to 3.58 and 2.91 kJ/mol, respectively. Thus, the alloys were converted into the crystalline state by heating of the samples under dynamic vacuum conditions to temperatures 100 K higher than those of the crystallization peak maxima. The conversion was monitored by repeat DSC analysis.

Preparation and thermal stability of mechanically alloyed amorphous Ni–Zr–Ti–Si composites

Abstract The feasibility of preparing amorphous Ni57Zr20Ti20Si3 composite powders by mechanical alloying of pure Ni, Zr, Ti, Si, and ceramic powder mixture after 5 h milling was investigated. The as-milled powders were examined by X-ray diffraction, scanning electron microscopy, and differential thermal analysis. Amorphous Ni57Zr20Ti20Si3 composite powders were prepared successfully at the end of milling for all the compositions studied. The thermal stability of the amorphous matrix is not significantly affected by the presence of the ceramic particles. It is suggested a partial dissolution of the atoms constituting the ceramic species in the amorphous phase can result change of matrix composition and lead to the variation of the glass transition and crystallization behaviors.

Host phases for actinides in simulated metallic waste forms

Argonne National Laboratory has developed an electrometallurgical process for conditioning spent sodium-bonded metallic reactor fuel prior to disposal. A waste stream from this process consists primarily of stainless steel cladding hulls containing undissolved metal fission products and a low concentration of actinide elements. This waste will be immobilized in a metallic waste form whose baseline composition is stainless steel alloyed with 15 wt% Zr (SS–15Zr). This paper presents transmission electron microscope, energy-dispersive X-ray spectroscopy, and electron diffraction observations of SS–15Zr alloys containing 2–11 wt% U, Np, or Pu. The major U- and Pu-bearing materials are Cr–Fe–Ni–Zr intermetallics with structures similar to that of the C15 polymorph of Fe 2Zr, significant variability in chemical compositions, and 0–20 at.% actinides. A U-bearing material similar to the C36 polymorph of Fe 2Zr had more restricted chemical variability and 0–5 at.% U. Uranium concentrations between 0 and 5 at.% were observed in materials with the Fe 23Zr 6 structure.

Comparison of high temperature shape memory behaviour for ZrCu-based, Ti–Ni–Zr and Ti–Ni–Hf alloys

New ZrCu-based high temperature shape memory alloys with M s close to 500 K are under development. The shape memory behaviour of this material is compared to those of Ti–Ni–Zr and Ti–Ni–Hf alloys. The optimal compositions show a shape recovery of not less than 3% at temperatures above 470 K.

Bulk metallic glass formation in Ni–Zr–Nb–Al alloy systems

Ni-based metallic glasses containing no metalloids are developed in Ni–Zr–Nb–Al alloy system. A partial replacement of Zr with Nb in Ni–Zr–Al alloys significantly enhances the glass-forming ability (GFA) and enlarges the undercooled liquid region during continuous heating of glassy ribbons. A quaternary Ni–Zr–Nb–Al metallic glasses exhibit large undercooled liquid region (>50 K), indicating high glass-forming ability of the alloy. The glass transition and crystallization temperatures of a quaternary Ni 61Zr 28Nb 7Al 4 alloy are 848 and 898 K, respectively, exhibiting a wide undercooled liquid region of 50 K. A complete Ni 61Zr 28Nb 7Al 4 glassy rod (φ1 mm) can be prepared by copper mold injection casting.

A molecular dynamics study on the role of localised lattice distortions in the formation of Ni–Zr metallic glasses

The formation of Ni–Zr binary metallic glasses resulting from the introduction of localised crystalline lattice distortions is investigated by means of constant-temperature, constant-pressure molecular dynamics simulations. Substitutional solid solutions of various composition were created by inserting substitutional atoms into a pure lattice. The insertion of Zr atoms into the regular Ni lattice determined its volume expansion, while the insertion of Ni atoms into the Zr lattice induced a volume contraction. Local lattice distortions are associated with substitutional atoms due to the size mismatch between Ni and Zr. The radial distribution functions, the rms atomic displacement and the static order parameter are used to characterise the response of the system to the insertion of substitutional atoms. The gradual loss of crystalline long-range order is accompanied by a large elastic softening. It appears that the static order parameter represents the fundamental quantity to characterise the elastic behaviour of both Ni- and Zr-based solid solutions.

Studies of Dissociation of Diatomic Molecules with Isotope Spectroscopy

AbstractFor Abstract see ChemInform Abstract in Full Text.

Local structure in hydrogenated Ti–Zr–Ni quasicrystals and approximants

We have investigated the influence of hydrogen on the local structure of Ti–Zr–Ni alloys, icosahedral quasicrystals or crystalline approximants, using extended X-ray absorption fine structure (EXAFS). With an increasing hydrogen-to-metal ratio from 0 to 1.7, a general increase of all the mean first distances was found except for the Zr–Ni (Ni–Zr) ones. The perturbation of the (quasi)lattice, induced by hydrogenation, is a maximum around the Ti and Zr atoms, which suggests that hydrogen atoms sit preferentially near titanium and zirconium atoms.

Thermodynamic Properties and Phase Equilibria in the Nickel—Zirconium System. The Liquid to Amorphous State Transition.

The vapour composition and the thermodynamic properties of Ni–Zr alloys in the liquid and solid states were studied by Knudsen-cell mass spectrometry over wide ranges of temperature (971–1896 K) and composition (0–99.8 mol% Zr). The accessible temperature range was enhanced by chemically generating volatile substances directly in the cell. For this purpose, the samples were mixed with powdered fluorides of magnesium, calcium, or sodium. Reduction reactions occurring in the cell produced zirconium fluorides, which were examined with the mass spectrometer. The thermodynamic functions of formation of all crystalline phases in the Ni–Zr system were determined. A representative file of experimental data was obtained for the Ni–Zr melt. It comprises about 900 values of the activities of both components at various concentrations and temperatures. The concentration and temperature dependences of the thermodynamic functions of liquid Ni–Zr alloy were described by the associated-solutions model under the assumption that NiZr, Ni2Zr and Ni3Zr associates exist in the melt. The phase equilibria computed on the basis of the obtained thermodynamic properties and the developed model are shown to agree with available experimental information. The nature of the interparticle interaction in the Ni–Zr system was analysed and the behaviour of the thermodynamic functions accompanying the process of transition of the Ni–Zr melt into the amorphous state was considered. Quantitative agreement with the independent experimental results was obtained.

Hydrogen absorption of C14 Laves NiTiZr-NiVNb pseudo-binary alloys

ABSTRACTHydrogen absorption and desorption properties of C14 Laves NiTiZr-NiVNb and NiTiZr-NiVZr pseudo-binary alloys were investigated by using the Sieverts' apparatus, XRD and the hydrogen analyzer. The hydrogen capacity and the 50% hydrogen desorption temperature, Td, of the C14 Laves NiTiZr alloy is 1.5 (H/M) and 850 K, respectively. On the other hand, the hydrogen capacity of the C14 NiVNb alloy is 0.2 H/M. In the Ni(TiZr)1−x(VNb)x pseudo-binary system, the hydrogen capacity of the alloys is decreased with increasing x, but the 50% hydrogen desorption temperature is almost constant. The substitution of VNb reduces the hydrogen absorption capacity of the C14 Laves NiTiZr alloy. The hydrogen desorption temperature of Ni(Ti1−xVx)Zr alloy is reduced to 580 K without serious decrease of the hydrogen capacity with increasing x.

Consolidation of amorphous Ni–Zr–Ti–Si powders by vacuum hot-pressing method

In the current study, we investigated the feasibility of fabricating amorphous Ni57Zr20Ti20Si3 powders by mechanical alloying, and consolidating them into bulk metallic glasses by a vacuum hot pressing technique. The as-milled and hot-pressed samples were examined by X-ray diffraction, scanning electron microscope, and differential thermal analysis. According to the results, amorphous Ni57Zr20Ti20Si3 powders were prepared after milling elemental powder mixtures for 5 h. The amorphous powders were found to exhibit a wide supercooled liquid region of 88 K before crystallization. Bulk metallic glasses were prepared successfully by consolidating the as-milled Ni57Zr20Ti20Si3 amorphous powders using vacuum hot pressing in the supercooled liquid region. Vickers microhardnesses of the as-pressed samples are in the range of 788–830 kg/mm2.

Investigations of mechanically alloyed Ni–Zr–Ti–Si amorphous alloys with significant supercooled regions

This study examined the amorphization behavior of Ni57Zr20Ti23−xSix (x=0, 1, 3) alloy powders synthesized by mechanical alloying technique. According to the results, after 5 h of milling, the mechanically alloyed powders were amorphous at compositions of Ni57Zr20Ti23−xSix (x=0, 1, 3). The amorphization behavior of Ni57Zr20Ti20Si3 was examined in details. The conventional X-ray diffraction and synchrotron EXAFS results confirm that the fully amorphous powders formed after 5 h of milling. The thermal stability of the Ni57Zr20Ti23−xSix amorphous powders was investigated by differential scanning calorimeter (DSC). As the results demonstrated, the amorphous powders were found to exhibit a large supercooled liquid region before crystallization. The supercooled liquid regions, defined by the difference between Tg and Tx, (i.e. ΔT=Tg−Tx), are 95 K, 66 K, and 88 K, for Ni57Zr20Ti23, Ni57Zr20Ti22Si1, and Ni57Zr20Ti20Si3, respectively.

Studies of dissociation of diatomic molecules with isotope spectroscopy

Abstract A method for studying dissociation of diatomic molecules by isotope spectroscopy is presented both theoretically and practically. A theory based on combinatorial analysis is presented for molecules of the form B 2 and BC. Molecular dissociation rates can be calculated from measurements of isotope exchange provided the isotopes in the molecules can be considered as chemically equivalent. Dissociation measurements of O 2 on Pt, RuO 2 , Ir and Ni–Zr–Sm as well as CO on Pt and Al are presented in the temperature range 400–900 °C.

Effects of Pd addition on the glass forming ability and crystallization behavior in the Ni–Zr–Ti alloys

The effect of Pd substitution for Ti on the glass forming ability and crystallization behavior has been studied in Ni 57Zr 20Ti 23− x Pd x ( x=0, 3, 5, 7, 10) alloys. Partial substitution of Ti by Pd in Ni 57Zr 20Ti 23− x Pd x improves the glass forming ability. With increasing Pd content x, from 0 to 7, Δ T x and T rg increase from 15 to 43 K and from 0.59 to 0.64, respectively. Crystallization sequence becomes completely different with addition of Pd. The amorphous Ni 57Zr 20Ti 23 alloy crystallizes via precipitation of only cubic Ni(Ti,Zr) phase in the first crystallization step, whereas the amorphous Ni 57Zr 20Ti 16Pd 7 alloy crystallizes via simultaneous precipitation of orthorhombic Ni 10(Zr,Ti) 7 and cubic NiTi phase. Addition of Pd in the Ni 57Zr 20Ti 23 alloy suppresses the formation of the primary cubic Ni(Ti,Zr) phase, leading to the improvement of glass forming ability.

Microstructure and crystallization of melt-spun Ti–Ni–Zr–Y alloys

Microstructure and crystallization behavior of melt-spun Ti 65Ni 25Zr 10− x Y x ( x=0, 2.5, 5, 7.5 and 10) alloys have been studied. The alloys show different microstructure with the cooling rate. Icosahedral quasicrystalline phase (I-phase) was obtained directly in alloys with x=0, 2.5, 5 and 7.5 prepared at a wheel surface velocity of 30 m/s and in x=0 alloy corresponding to a velocity of 55 m/s. Ribbons with x=2.5, 5 and 7.5 prepared at the wheel surface velocity of 55 m/s are in amorphous state. The primary precipitates for these amorphous alloys are I-phase. It is concluded that the proper addition of Y improves the glass forming ability of the Ti–Ni–Zr system.