Amorphous Zr Research Articles

Evolution of microstructure in Zr 55Cu 30Al 10Ni 5 bulk amorphous alloy by high power pulsed Nd:YAG laser

In this work surface modification of Zr-based bulk amorphous alloy Zr 55Cu 30Al 10Ni 5 was carried out with pulsed Nd:YAG laser. The as-cast and modified surface of amorphous alloys at different conditions were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. Phases like Cu 10Zr 7, CuZr 2 and NiZr 2 were identified which result in the enhancement of hardness of the modified alloys surface. It was observed that low laser power and prolonged irradiation time provides large nucleation frequency and limited growth rate which intern produces small spherical particle dispersion homogeneously distributed in an amorphous matrix resulting significant increase in surface hardness.

Investigation of precipitation phases in as-cast wedge ingot of bulk amorphous Zr 56.6Cu 17.3Ni 12.5Al 9.6Ti 4 alloy

In order to clarify the competing relationships among the intermetallic precipitation phases during the cooling of a bulk amorphous Zr 56.6Cu 17.3Ni 12.5Al 9.6Ti 4 alloy, the wedge-shaped ingots of this alloy were made by casting the melt into a wedge-shaped copper mould, and then the zones with different cross-sections were studied by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that these phases are very different in both the morphology and sizes, and they are dependent on the thickness of wedge ingot, i.e., the cooling rates. It is therefore concluded that the Zr 2Ni phase is the strongest competing rival to the amorphous matrix in this alloy. These findings support that compared to Zr–Ni pair, Zr–Cu pair has a larger glass forming tendency. The glass forming ability can be improved by inhibiting the precipitation of Zr 2Ni phase by, for example, decreasing the Ni content in this alloy.

Impact of interface variations on J– V and C– V polarity asymmetry of MIM capacitors with amorphous and crystalline Zr (1−x)Al xO 2 films

Polarity asymmetries in J– V and C– V characteristics of symmetrical MIM capacitors with amorphous and crystalline Zr (1− x )Al x O 2 films and TiN electrodes are evaluated. Physical analysis of the interface between the TiN bottom electrode and the ZrO 2 layer reveals that the TiN bottom electrode undergoes enhanced oxidation during crystallization of ZrO 2. Simultaneously, nitrogen is incorporated into ZrO 2 near the TiN interface, and an intermixing of ZrO 2 and TiO 2 was identified by AR-XPS and SIMS. This asymmetry results in significant band offset differences for top and bottom electrodes of the crystalline MIM capacitor. Conduction mechanisms are correlated to amorphous vs. crystalline film properties. In addition, asymmetrical charge trapping and a higher trap density is found for crystalline Zr (1− x )Al x O 2 compared to amorphous films, leading to a polarity dependence in the leakage currents.

Electron-irradiation-induced nano-crystallization in quasicrystal-forming Zr-based metallic glass

Phase selection in electron-irradiation-induced crystallization and crystal-to-amorphous-to-crystal (C–A–C) transition at 298 K in quasicrystal-forming Zr–Pt metallic glass alloys were investigated. Two types of f.c.c. nano-crystalline precipitates were formed in amorphous Zr 80Pt 20 and Zr 66.7Pt 33.3 alloys under electron irradiation; such unique nano-crystalline structures were not observed during thermal annealing. It was inferred that unique phase selection in electron-irradiation-induced crystallization and thermal crystallization can be explained by the large negative chemical mixing enthalpy (Δ H chem) in Zr–Pd and Zr–Pt alloys.

Diffusion barrier capability of Zr–Si films for copper metallization with different substrate bias voltage

Efficiency of Zr–Si diffusion barriers in Cu metallization has been investigated. Amorphous Zr–Si diffusion barriers were deposited on the Si substrates by reactive magnetron sputtering with different negative substrate bias. The mass density of Zr–Si films increases with substrate bias voltage up to − 150 V. The deposition rate decreased with the negative substrate bias from 5.4 nm/min to 1.8 nm/min. XRD measurements show that the Zr–Si barriers have amorphous structure in the as-deposited state. The FE-SEM images show that the sizes of spherical granules on the Zr–Si film surface increase with increasing the substrate bias. The Cu/Zr–Si/Si structures were prepared and annealed in Ar ambient at temperatures varying from 500 to 650 °C for an hour. It is shown from the comparison study that the Zr–Si film deposited with − 150 V is better at maintaining good performance in Cu/Zr–Si/Si contact system than that of Zr–Si film deposited with − 50 V.

On the amorphous and nanocrystalline Zr–Cu and Zr–Ti co-sputtered thin films

In the current study, we examined and compared the mixing and vitrification behavior of the Zr–Cu and Zr–Ti binary systems in the form of co-sputtered thin films with or without post-annealing. The co-sputtered Zr–Cu films are all amorphous under various co-sputtering conditions, suggesting the high vitrification tendency. The amorphous Zr–Cu thin film will start to crystallize into nano-crystalline Zr 2Cu and Zr 7Cu 10 phases upon long exposure at temperatures above 350 °C. On the other hand, it is difficult to form amorphous film with the Zr–Ti system, except at a low sputtering power of 30–50 W. The low powers enable the co-sputtered Zr–Ti thin film to exhibit the diffuse hump in the X-ray diffraction. Examination by high resolution transmission electron microscopy reveals numerous fine nano-crystalline phases around 2 nm in the amorphous matrix. Upon exposure at 700 °C, the Zr–Ti films transform into crystalline hexagonal close-packed α and body-centered cubic β phases.

Structural relaxation and nanoindentation response in Zr–Cu–Ti amorphous thin films

Ternary Zr–Cu–Ti system, especial with a high Ti content, is normally difficult to be fully vitrified. In this paper, we demonstrate that cosputtering can produce amorphous Zr–Cu–Ti thin films with an excessive Ti content even as high as 19%. Sub-Tg annealing of the film induces the formation of medium-range-ordered clusters and to raise the nanohardness by 35% to 6.6GPa. The promising mechanical properties of the sub-Tg annealed Zr52Cu29Ti19 films offer great potential for microelectromechanical system applications.

Hydrogen separation from dry gas mixtures using a membrane module consisting of palladium-coated amorphous-alloy

Amorphous alloy membranes are anticipated as substitutes for expensive palladium membranes. Hydrogen separation modules consisting of four amorphous Zr 36Ni 64 membranes have been developed to demonstrate their practical usefulness. First, surface investigation showed that 50-mm-wide membranes are smoother on the surface and are therefore expected to be better in terms of sealing than 20-mm-wide membranes. A four-membrane module was assembled without leakage for 0.92 MPa inside to the atmospheric outside. Using this module, pure hydrogen was obtained as effluent from the permeation side. The 82.7% recovery and 31.7 mL (STP)/min were attained in separation from CO and CO 2 containing a gas mixture simulating methanol reformed gas. Therefore, the practical availability of amorphous alloy membranes was demonstrated.

Evaluation of the barrier capability of Zr–Si films with different substrate temperature for Cu metallization

Barrier capability of Zr–Si diffusion barriers in Cu metallization has been investigated. Amorphous Zr–Si diffusion barriers were deposited on the Si substrates by RF reactive magnetron sputtering under various substrate temperatures. An increase in substrate temperature results in a slightly decreased deposition rate together with an increase in mass density. An increase in substrate temperature also results in grain growth as deduced from field emission scanning electron microscopy (FE-SEM) micrographs. X-ray diffraction (XRD) spectra and Auger electron spectroscopy (AES) depth profiles for Cu/Zr–Si(RT)/Si and Cu/Zr–Si(300 °C)/Si samples subjected to anneal at various temperatures show that the thermal stability was strongly correlated with the deposition temperature (consequently different density and chemical composition etc.) of the Zr–Si barrier layers. ZrSi(300 °C) with higher mass density make the Cu/Zr–Si(300 °C)/Si sample more stable. The appearance of Cu 3Si in the Cu/Zr–Si/Si sample is attributed to the failure mechanism which may be associated with the diffusion of Cu and Si via the grain boundaries of the Zr–Si barriers.

Hydrolysis Constant and Coordination Geometry of Zirconium(IV)

The solubility of zirconium was studied by comparing recent experimental data with predictions using an electrostatic hard sphere model. In the model, an antiprismatic structure was assumed for a mononuclear hydrolysis species of zirconium, and the formation of an oligomeric species such as Zr4(OH)8 8+ was considered by combining antiprismatic structure units, which was supported by the theoretical approach. By taking the known values of the solubility products, the hydrolysis constants of these mononuclear and polynuclear species were evaluated and were found to be consistent with the experimental solubility data of amorphous Zr(OH)4 and crystalline ZrO2.

Formation of amorphous Zr 41.2Ti 13.8Ni 10Cu 12.5Be 22.5 coatings via the ElectroSpark Deposition process

The ElectroSpark Deposition (ESD) process was successfully used to transfer amorphous material from an electrode to an amorphous substrate without crystallizing either material. The resulting deposit was confirmed to be amorphous using X-ray diffraction. The deposit shows hardness values of 508 Hv ± 20 in comparison to the 514 Hv ± 14 measured for the substrate with no evidence of a heat affected zone. The growth rate appears to increase linearly as a function of the number of layers deposited. The relationship between the deposition processing parameters and the growth rate was determined and growth rates ranging between 10 μm/pass and 15 μm/pass were obtained for the optimal processing parameters. The amorphous structure and deposit quality (porosity, surface undulation) were preserved throughout the experiments. It is envisioned that this process can be used for the weld repair of worn bulk amorphous materials and coatings.

Laser Flash-Photolysis Study of Organic−Inorganic Materials Derived from Zirconium Phosphates/Phosphonates of Ru(bpy)3 and C60 as Electron Donor−Acceptor Pairs

The laser flash photolysis of material 1 (layered γ-ZrP containing covalently attached Ru(bpy)3- and C60-phosphonates), dyad 2, and material 3 (amorphous solid Zr(n-BuO) derivative of dyad 2) was accomplished. Zirconium salts, regardless of their amorphous or layered structures, appear to be excellent hosts for developing long-lived charge-separated states between C60 and Ru(bpy)3 derivatives. Moreover, the presented evidence points to the important fact that the inorganic scaffolding acted as a semiconductor, harvesting the electrons and/or holes produced at the active organic components. These findings suggest that the studied materials could be suitable for the building of practical solar cells.

Correlation between mechanical, thermal and electronic properties in Zr–Ni, Cu amorphous alloys

We show that mechanical properties (stiffness and hardness) of Zr–Ni, Cu amorphous alloys increase linearly with Ni, Cu content over a wide composition range (22 ≤ x Ni,Cu ≤ 65 at%). This correlates with the observed increase in the Debye temperatures and densities with x and shows that the strength of interatomic bonding increases with x in these alloys. Accordingly, the thermal stability (e.g. the crystallization and glass transition temperatures) of these alloys also increases with x. Since the electronic density of states at the Fermi level decreases linearly with x within the same x-range, a very simple relationship exists between the electronic structure and mechanical and thermal properties. We also deduce the mechanical properties of hypothetic amorphous Zr and briefly discuss the possibility of its preparation.

Fracture toughness of bulk metallic glass welds made using nanostructured reactive multilayer foils

We measured the fracture toughness of joints in amorphous Zr 57 Ti 5 Ni 8 Cu 20 Al 10 made using Al/Ni reactive multilayer foils. The highest fracture toughness measured was ∼12 MPa m 1/2 . Based on the fracture toughness and the crack propagation paths, we conclude that virtually all of the toughness can be ascribed to the presence of metallic glass ligaments in the joint. Increasing the stress applied during joining increases the area fraction of these ligaments and so increases the fracture toughness as well.

Magnetic susceptibility and atomic structure of paramagnetic Zr–(Co, Ni, Cu) amorphous alloys

The experimental results for the magnetic susceptibility and superconducting transition temperature of amorphous Zr–(Co,Ni,Cu) alloys extending over a wide composition range are analyzed in some detail. By combining the results of this analysis with the literature results for the electronic density of states at EF for the same alloy systems we obtained a set of parameters associated with the electronic structure of the amorphous Zr. The comparison of these parameters with the results of the band structure calculations for different crystalline phases of Zr and with the results of the atomic structure and crystallization studies of the same alloy systems indicates an fcc-like local atomic structure for amorphous Zr.

Evolution of microstructure and non-equilibrium phases in electron beam treated Zr 55Cu 30Al 10Ni 5 bulk amorphous alloy

Electron beam (EB) is becoming very popular for the modification of the surfaces as it involves localized melting and fast cooling which helps in achieving the non-equilibrium phases as well as fine microstructure. Surface modification of Zr-based amorphous alloy Zr 55Cu 30Al 10Ni 5 has been carried out by EB melting. Differential scanning calorimetry (DSC) was employed to determine the supercooled liquid region and activation energy of crystallization. The as-cast and modified surfaces of amorphous alloy at different beam conditions were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. Various phases like NiZr 2, CuZr 2 and Cu 10Zr 7 were identified which resulted in the enhancement of hardness of the modified alloy surface.

Density, Thermal Stability and Mechanical Properties of Zr-Ti-Al-Cu-Ni Bulk Amorphous Alloys with High Al Plus Ti Concentrations

Bulk amorphous Zr 70-x-y Ti x Al y Cu 20 Ni 10 alloys with a thickness of 2.5 mm were formed in a wide composition range of 0 to 10 at%Ti and 7.5 to 15 at%Al by a squeeze casting process. The bulk amorphous alloys containing 0 to 5%Ti and 12.5 to 15%Al exhibit good combined properties of high tensile fracture strength above 1850 MPa, high specific strength of 28.4 × 10 5 N.m/kg and high T g / T m above 0.60 which have not been obtained for the Zr-based amorphous alloys reported hitherto. These bulk amorphous alloys have small difference in density of 0.3 to 0.6% between ascast amorphous and crystallized states. The high dense random packing fraction in the multicomponent amorphous structure seems to cause the high glass-forming ability and the high thermal stability of the supercooled liquid region by the decrease in atomic mobility. Furthermore, the crystallized phases change from NiZr 2 +CuZr+Zr 3 Al in the range of 5 to 15%Al and 0 to 2.5%Ti to NiZr+CuZr 2 +Zr 3 Al in the range of 5 to 15%Al and 2.5 to 7.5%Ti. The melting temperatures (T m ) of these crystallized compounds increase in the order of ZrNi > Zr 2 Ni > Zr 2 Cu > ZrCu and hence the crystallized structure of the 5%Ti-containing alloys is composed of ZrNi and Zr 2 Cu with higher T m . The change in the amorphous structure leading to the precipitation of the compounds with higher T m may be the reason for the higher mechanical strength in the higher Al and Ti contents.

Mechanical properties and ion irradiation of bulk amorphous Zr 55Cu 30Al 10Ni 5 alloy

The bulk amorphous Zr 55Cu 30Al 10Ni 5 alloy is one of the widely studied Zr-based alloys due to very attractive thermal and mechanical properties. Alloy ribbons and bulk samples were synthesized by Cu mould casting and characterized by SEM/EDS, DSC and XRD. Mechanical properties like Vicker’s hardness, nanohardness and elastic modulus etc. were measured. Ion irradiation of the samples was carried out to enhance the surface properties without altering the amorphous nature of the bulk material. Ion irradiation by singly charged Ar + enhanced the hardness as well as elastic modulus considerably.

Oxidation behavior of amorphous and nanoquasicrystalline Zr–Pd and Zr–Pt alloys

Oxidation behavior of amorphous and nanoquasicrystalline Zr 70Pd 30 and Zr 80Pt 20 alloys melt-spun at different wheel speeds has been studied in air by non-isothermal and isothermal techniques. Oxidation resistance of amorphous alloys has been found to be the lowest in comparison to the partially and fully crystallized Zr alloys. It has also been observed that oxidation does not induce crystallization of the amorphous phase. It has been shown that the oxygen diffusion rate increases gradually in the order of crystalline, nanoquasicrystalline, partially nanocrystalline and amorphous states of these alloys. Possible micromechanism of oxidation and the role of different grain/interface boundaries on the oxygen diffusion has been discussed.

Hydrogen solution properties in a series of amorphous Zr–Hf–Ni alloys at elevated temperatures

Amorphous alloys are anticipated as new membrane materials for high purity hydrogen production, as substitutes for expensive palladium alloys. For amorphous Zr–Ni-based alloys reported to date, hydrogen permeability increases with Zr content. Hydrogen solution properties in a series of amorphous Zr–Hf–Ni ternary alloys were measured carefully using the Sieverts method and residual hydrogen measurements to investigate the reason. Results indicate that hydrogen solubility in the ternary alloys increases with increasing Zr to improve hydrogen permeability, not because of the geometrical atomic structure but because of higher hydrogen affinity of Zr than that of Hf. Increased permeability with Zr in other amorphous Zr–Ni-based alloys is also expected to be attributable to the same reason. Additionally, hydrogen was found with low mobility, and was not removable even after 10 h evacuation at 573 K; the importance of decreasing low mobility hydrogen as a countermeasure against hydrogen embrittlement was pointed out. Equilibrium hydrogen concentration was found not to obey Sieverts’ law with respect to hydrogen pressure. Rather, it was linear roughly to the quarter power. Parameters to reproduce pressure–composition isotherms were determined using Kirchheim's theory.