Zr-Al System Research Articles

Experimental investigation of the U–Zr–Al ternary phase diagram: Isothermal sections at 673 K and 1073 K

Isothermal sections at 673K and 1073K of the ternary U–Zr–Al system were established in the whole concentration range, by means of powder X-ray diffraction, scanning electron microscopy–energy dispersive X-ray spectroscopy and differential thermal analysis. All measured compositions and unit-cell refinements were performed at room temperature from quenched samples annealed at 1073K and 673K for four and eight weeks respectively. For both temperatures, the Al-rich corner of the phase diagram is characterized by extended homogeneity ranges due to mutual exchange between U and Zr in UAl3 (cubic, AuCu3-type) and in the Laves phase UAl2 (cubic, MgCu2-type). Minute U solubility in ZrAl2 (hexagonal, MgZn2-type) and in Zr2Al (hexagonal, Ni2In-type) was evaluated to be of the order of 1at.%U. For the other binary compounds, the solubility of the third component was found negligible. At 1073K, the solid solution based on γU (cubic, W-type) which covers the U–Zr binary axis up to 95.5at.% Zr, allows also some limited solubility of Al [maximum of 5at.%]. For Al-content below 66at.%, most of the phase relations comprise equilibria between the Zr–Al binaries and the γ(U,Zr,Al) solid solution. At 673K, the U–Zr axis is found in agreement with the literature data and no Al solubility could be detected in αU, αZr and UZr2 (δ phase). The phase relations are mainly established between Zr–Al binaries and αU. For monolithic UMo fuel with a Zr diffusion barrier foil cladded with Al, the main interaction product is expected to involve the U-based alloy with the Zr–Al binary compounds and the pseudo-binary U1−xZrxAl2 and U1−xZrxAl3 phases.

Stability, elastic properties and electronic structures of the stable Zr–Al intermetallic compounds: A first-principles investigation

To better clarify and understand the phase stability and elastic properties of stable Zr–Al binary intermetallic compounds, the structural properties, phase stability, elastic properties, and electronic structures of these compounds in Zr–Al system have been systematically investigated by using first-principles calculations. The calculated equilibrium structures and enthalpies of formation in present work are in good agreement with the available experimental and other theoretical data, and the results of enthalpies of formation show that ZrAl2 is the most stable. The elastic properties, including elastic constants, Poisson’s ratio and anisotropy index, and Debye temperatures were also investigated. It is found that ZrAl is the most anisotropic in Zr–Al binary compounds. Furthermore, the electronic structures were discussed to reveal the bonding characteristics of the compounds.

Comparative study between two die cast methods for processing Cu–Zr–Al bulk metallic glasses

The composition of a glass former alloy and the cooling rate are both extremely important to determine the maximum glassy or critical thickness of a sample under a specific processing technique. This work compares the suction casting and the centrifugal casting techniques for processing two Cu–Zr–Al bulk metallic glasses where the main characteristics evaluated were the mold-filling ability, the average time per cycle, the oxygen contamination and the maximum thickness on which the glassy phase was obtained. The Cu–Zr–Al system was chosen due to its high glass forming ability, which is extensively reported in the literature. The wedge shape sample was chosen because it allows the evaluation of different thicknesses (hence cooling rates) at the same sample. Results revealed that the copper mold centrifugal casting had a higher oxygen contamination, whilst the mold-filling ability was similar in both processes. Also, for the centrifugal casting technique, the average time per cycle was higher and the maximum thickness in which glassy phase could be obtained was lower. A brief analysis considering the oxygen contamination on these alloys is also presented here, revealing the extreme importance of controlling this parameter.

Chemical and topological short-range orders in the ternary Ni–Zr–Al metallic glasses studied by Monte Carlo simulations

Based on the recently constructed Ni–Zr–Al n-body potential, Monte Carlo simulations are performed to study the glass formation and associated structural evolutions in the system. The micro-chemical inhomogeneity (MCI) parameter and Honeycutt and Anderson (HA) pair analysis are employed to investigate both the chemical short-range orders and topological short-range orders for the ternary Ni–Zr–Al metallic glasses. Results reveal that remarkable chemical short-range orders (CSROs) exist in the ternary Ni–Zr–Al metallic glasses and are strongly influenced by the chemical interactions among the constituent elements. Moreover, topological short-range orders are clearly formed in the ternary Ni–Zr–Al metallic glasses, with the most remarkable characteristic being the icosahedral local packing. Similarly to CSRO, the extent of icosahedral short-range orders formed in the Ni–Zr–Al system varies distinctly with the chemical composition. In addition, simulation results reveal that chemical short-range orders and topological short-range orders turn out to be influenced by different factors. Unlike CSRO, both chemical interactions and geometrical constraints play important roles in forming the topological short-range orders.

Only Formation of ZrAl<sub>3</sub> Phase Obtained by Self-Propagating Reaction from Zr-Al Elemental Powders

In this paper, the problem of ZrAl3 compound obtained by self-propagating reaction as the only and favorable formation phase was considered. It shows that the ZrAl3 phase could be synthesized by self-propagating reaction in Zr-Al system and was especially identified as the only phase by XRD, which was further confirmed by DTA. Using the theories of structural lattice of ZrAl3, Modified Effective Heat of Formation (MEHF) model, coupled with the First Nucleation Rule (FNR), the only formation of ZrAl3 phase in Zr-Al system could be reasonably interpreted.

Unique metallurgical microstructures and characteristics of nano-amorphous state bulk alloys formed under high gravity by very high speed centrifugal casting

ABSTRACTAn innovative “Rapid-Solidification Centrifugal Casting (RSCC) Process” was applied to manufacturing more high functional Fe-based magnetic alloys and some amorphous bulk metallic glassy alloys (BMGs) components. The molten alloys were poured into copper mold with rotation speed up to 6000rpm which can cause the maximum 4000 times as much centrifugal pressurization force as gravity. The bulk components of ring or very small three dimensional component samples of Fe and Zr alloy systems were successfully fabricated within only a few seconds at one process from melts with more cheap production cost. The molten raw BMG alloys (ZrAl system) and Fe-based soft-magnetic alloys(FeGaAl and FeSiB systems) by high frequency induction heating method were poured into copper mold. The fabricated BMG components of artificial tooth and ring of ZrAlNiCu alloy system are almost amorphous state by XRD profiles. Especially, the soft magnetic properties of two Fe-based alloys showed drastic change and were enhanced generally depending on the unique very fine, nano-scale columnar grains with strong texture toward radius direction for FeGaAl(Galfenol) alloy. The magnetization saturation Bs was enhanced up to1.97T in FeSiBPCu alloy. In consequence, according to synergistic effect of rapid solidification and high pressurization casting in this manufacturing process, RSCCP has the technical advantages of expansion of element composition, uniformity of the quality, reduction of internal defects and prevention of degradation at the time of secondary fabrication process of nano-crystalline-structured alloys and BMGs.

Local structure of the Zr–Al metallic glasses studied by proposed n-body potential through molecular dynamics simulation

An n-body potential is first constructed for the Zr–Al system and proven to be realistic by reproducing a number of important properties of the system. Applying the constructed potential, molecular dynamics simulations, chemical short-range order (CSRO) calculation, and Honeycutt and Anderson (HA) pair analysis are carried out to study the Zr–Al metallic glasses. It is found that for the binary Zr–Al system, metallic glasses are energetically favored to be formed within composition range of 35–75 at.% Al. The calculation shows that the CSRO parameter is negative and could be up to −0.17, remarkably indicating that there exists a chemical short-range order in the Zr–Al metallic glasses. The HA pair analysis also reveals that there are diverse short-range packing units in the Zr–Al metallic glasses, in which icosahedra and icosahedra/face-centered cubic (fcc)-defect structures are predominant.

ChemInform Abstract: Non-Selective Oxidation of ZrAl3.

The oxidation of ZrAl3 in dry oxygen in the temperature range 865–1073 K obeys a logarithmic rate law in the first period of reaction. An activation energy of 214 kJ mol−1 has been estimated. Some time after this first period, depending on the temperature, the protective oxide film transforms to a porous one and the reaction rate increases. The oxide layer consists of α-Al2O3, tetragonal ZrO2 and small amounts of monoclinic ZrO2, in contrast to the ZrO2 oxide layer formed during oxidation of other phases in the Zr-Al system, where the selective oxidation of zirconium takes place.

Structural stability and oxidation resistance of amorphous Zr–Al alloys

We investigated the structural stability and oxidation resistance of Zr–Al films upon annealing in air. The concentration of Zr was varied from 0 to 100 at.%, with a step of 10 at.%. The films were fabricated using ultra-high vacuum based magnetron sputtering. The as-deposited films with Zr content from 17.3 at.% to 70.7 at.% were found to be X-ray amorphous at room temperature. When exposed to air a thin oxide layer, typically less than 6 nm, is formed. The thickness of the oxide layers increases when the samples are annealed in air and most of these are found to be fully oxidized at 700 °C with the formation of crystalline and amorphous oxides on the top of crystalline and amorphous metal films, respectively. The amorphous oxide layers are found to be dense, with well defined thicknesses. An experimental non-equilibrium phase diagram is provided, covering the whole concentration range of the Zr–Al system.

Reaction Synthesis of ZrAl3 Intermetallic Compound and Its Nucleation Behavior

Abstract Using self-propagating high-temperature synthesis (SHS) reaction, ZrAl 3 intermetallic compound was fabricated from Zr and Al elemental powders and its reaction behavior was investigated by XRD, DTA and SEM analysis. The result reveals that the synthesis process of ZrAl 3 begins with solid-solid reaction between Al and Zr, and then further extends to solid-liquid reaction, and finally was completed at afterburning stage. The ZrAl 3 grain takes on irregular block-like morphology and many sunken dendrites appear on its surface. In Zr-Al system, when the ratio of Zr/Al is ≤ 1, the formation of ZrAl 3 , the only phase, is independent on the expected composition of starting mixtures. Finally, the nucleation behavior of ZrAl 3 was discussed.

Cu–Zr–Al (Ti) bulk metallic glasses: Cluster selection rules and glass formation

The present paper investigates the bulk metallic glass formation in Cu–Zr–Al and Cu–Zr–Ti ternary systems by using the cluster line criterion. The binary basic clusters are first selected for constructing cluster lines. Three cluster selection rules are proposed: topologically dense packing, chemical short-range order and composition distance to deep eutectics. Three Cu–Zr clusters Cu 8Zr 5, Cu 6Zr 5 and Cu 5Zr 6 are selected according to the three rules. The bulk metallic glass-forming ranges in these two systems are determined. The thermal characteristic parameters of the Cu–Zr–Al BMGs on every composition line increase with increasing Al content and decrease with increasing Ti content in the Cu–Zr–Ti glass-forming range. The optimum bulk amorphous compositions in the Cu–Zr–Al system are Cu 58.1Zr 35.9Al 6 and Cu 39.7Zr 47.1Al 13.2, respectively, located in Cu 8Zr 5–Al and Cu 5Zr 6–Al cluster lines. In the Cu–Zr–Ti system, the Cu 64Zr 28.5Ti 7.5 composition with the largest T g/ T l is located in Cu 9Zr 4–Ti cluster line and the Cu 57.6Zr 32.4Ti 10 composition with the largest glass-forming ability is located in Cu 64Zr 36–Ti line.

Cluster line criterion and Cu–Zr–Al bulk metallic glass formation

The cluster line approach is presented and applied for searching the optimum glass-forming composition in the Cu–Zr–Al system. Three cluster selection rules are proposed: topologically dense packing (atomic size-related), chemical short-range order as evaluated by dissimilar atomic pairs, and composition distance to deep eutectics. Three Cu–Zr clusters Cu 8Zr 5, Cu 6Zr 5 and Cu 5Zr 6 satisfy all the three rules and are selected to construct cluster lines. The bulk metallic glass-forming range in the Cu–Zr–Al ternary system is thus determined. It is found that the thermal stabilities and glass-forming abilities of the bulk metallic glasses manifest monotonously increased tendencies with the increased Al content. The optimum Cu-rich and Zr-rich bulk metallic glass compositions are Cu 58.1Zr 35.9Al 6 and Cu 39.7Zr 47.1Al 13.2 (number indicate at.%) and they are, respectively, located along the Cu 61.8Zr 38.2–Al and Cu 45.7Zr 54.3–Al cluster lines, where the deep eutectics exactly correspond to the dense packing clusters Cu 8Zr 5 and Cu 5Zr 6. The characteristic parameters (glass transition temperature T g and melting temperature T l) of Cu 58.1Zr 35.9Al 6 BMG are T g = 760 K and T g/ T l = 0.648, and those of Cu 39.7Zr 47.1Al 13.2 BMG are T g = 731 K and T g/ T l = 0.638.

Intermetallic compound formation in the Zr–Al–Si ternary system

The microstructure and composition of binary and ternary intermetallic compounds have been studied in a ternary diffusion couple of Zr and Al–Si eutectic alloy. The τ 1 and τ 3 phases always formed in the liquid part of the diffusion couple and τ 2 phase formed as a layer structure. Two intermetallics, ZrSi and ZrSi 2, of the Zr–Si binary system have been observed. A number of intermetallics, namely, ZrAl 3, ZrAl 2, Zr 2Al 3, ZrAl, Zr 3Al 2, Zr 5Al 4, Zr 5Al 3, Zr 2Al and Zr 3Al, of the Zr–Al system have been observed. The solubility of Si in the ZrAl 3 and ZrAl intermetallics is very small. In the other intermetallics, the solubility of Si is negligible. The results of this investigation also show two ternary invariant reactions. The microstructure of a number of phases has been presented.

A numerical model of peritectoid transformation

A rigorous numerical model of the diffusion-controlled peritectoid transformation based on the isoconcentration contour migration method is presented here. The model is capable of considering the concentration dependence of diffusivity in the participating phases. The predictions from the model show an encouraging agreement with the experimentally determined peritectoid kinetics in the Zr-Al system and dissolution kinetics in the Ni-Mo diffusion couple. An extensive parametric study through the present formulation indicates that the peritectoid kinetics may be considerably affected by the diffusivities and phase field widths (in the equilibrium diagram) of the concerned solids. In this regard, the field width and diffusivity in the peritectoid phase appear to exert the most significant influence on the reaction rate. The numerically calculated transformation kinetics have been effectively rationalized by means of two dimensionless parameters, φ 1 and φ 2, which are functions of the concerned phase field widths and diffusivity in the product phase. In addition, these parameters enable prediction of the minimum time required for the completion of peritectoid transformation without going through any rigorous computation.

Formation of metastable phase equilibrium andamorphisation in Al 26Zr 74 alloy by gasatomization and by further mechanical alloying

At the present day, the mechanical alloying of certain metallic componentsis actually a single method of obtaining a material with the required level of physical and chemicalcharacteristics. Zr–Al system alloys are the perspective getter materials. The level of getterproperties depends on the structural phase state of the produced specimens. The highly dispersiveand amorphous materials have the highest level of getter properties.

Investigation of the Ni-Zr-Al alloy in the undercooled liquid region

NiZrAl system exhibits a broad temperature interval between the glass transition and crystallization temperature, giving thus a possibility of studying microstructural changes taking place both in amorphous and in the undercooled-liquid states. The changes in positron annihilation lifetime spectra in thermally treated Ni 25 Zr 55 Al 20 alloy, as observed previously (3), indicating that positrons annihilate at places with different properties, have been supported by resistivity measurements. Sequential annealing above and below T g is found to activate different micromechanisms controlling microstructural atomic rearangements and affecting the properties of the alloy; the influence of such treatment on nucleation mechanism is discussed.

Microstructural studies on cast Zr3Al-3wt%Nb

In the binary Zr-Al system, Zr[sub 3]Al is the intermetallic phase richest in zirconium. In view of its low absorption cross section for thermal neutrons and its good strength and corrosion resistance, Zr[sub 3]Al may have possible applications as a structural material in thermal reactors. This phase has the ordered cubic L1[sub 2] structure and forms through the peritectoid reaction: [beta]-Zr + Zr[sub 2]Al[minus] > Zr[sub 3]Al, the reaction temperature being 1,292 K. Structurally Zr[sub 3]Al is quite similar to the [alpha][sub 2] or the Ti[sub 3]Al phase (ordered hexagonal DO[sub 19] structure) in the Ti-Al system, the two structures differing only in the stacking sequence of the close packed atomic layers. But for its inherent brittleness, Ti[sub 3]Al is a promising structural material for aerospace applications. It has, however, been demonstrated that niobium additions can reduce the brittleness of this phase. Studies on the Ti[sub 3]Al-Nb system have also shown that niobium stabilizes the high temperature [beta] phase (bcc structure) which, on cooling, can decompose through various phase reactions, generating some interesting microstructures. Similar studies on the Zr[sub 3]Al-Nb system have not been reported yet. The present paper describes some microstructural observations made on a cast Zr[sub 3]Al-3wt%Nb alloy.

High-temperature oxidation behaviour in the Zr-Al system

The oxidation behaviour of phases in the Zr-Al system has been studied in dry oxygen at elevated temperatures and isothermally. The oxidation of α-Zr-1 mass% Al, Zr 3Al, Zr 2Al, ZrAl and Zr 2Al 3 obeys a parabolic rate law, while the oxidation of ZrAl 2 and ZrAl 3 obeys a logarithmic rate equation. Zr 3Al, Zr 2Al, ZrAl, Zr 2Al 3 and ZrAl 2 are selectively oxidized to give tetragonal and monoclinic ZrO 2 as the oxidation product. During this process aluminium escapes oxidation by diffusion into the bulk of the alloy and forms there Zr 2Al, Zr 5Al 3, Zr 2Al 3, ZrAl 2 and ZrAl 3 respectively, as a secondary product of oxidation. The new phases formed near the oxide alloy interface of higher aluminium content than the matrix phase, are the adjoining phases in the phase diagram of the Zr-Al system.

Metastable phases of the Zr-Al system obtained by mechanical attrition and rapid soldification

The equilibrium phase diagram of the Zr-Al system, shows the existence at room temperature of the L1{sub 2} line compound Zr{sub 3}Al. The peritectoid reaction which leads to its formation, starting from the mixture {alpha}Zr + Zr{sub 2}Al, was thoroughly investigated. Apart from the interesting technological aspects several researchers have been concerned with the disordering, i.e., destruction of the long-range crystalline order, and amorphization of this intermetallic compound. Probably because of the links with nuclear reactors, the first experiments in this field involved electron and ion irradiation. More recent experiments using Kr{sup +} ions extended the early findings. In this paper, amorphization was observed and instability deduced from measurements of the shear modulus. For this reason, a parallel was drawn between this solid-state reaction and melting. Another factor considered necessary to a successful amorphization is the increase in the free energy of the system caused by the reduction of long-range order. A critical value of the long-range order parameter, S, measured from the intensity of the electron diffraction spots, of 0.2 has been reported as necessary to the appearance of the first amorphous regions.

Alloying Effects on Hydrogen Gettering Properties for Zr-Al System

This paper discusses alloying effects on absorption and desorption kinetics of deuterium for Zr-Al alloys, studied with mass analyzed thermal desorption spectroscopy using a conventional high vacuum system. It is found that the absorption rate of deuterium was proportional to the 1/2 power of deuterium gas pressure. On the other hand, the desorption process obeyed the second order kinetics with respect to the amount of absorbed deuterium. The temperature dependence of the rate constants revealed that the activation energies for both the absorption and desorption processes were lowered by the increase in the Al content in the alloys. Through potential diagrams for the absorption and desorption of deuterium, it was also found that the heat of deuterium (hydrogen) solution decreased with increasing Al composition. In addition, the x-ray diffraction spectroscopy showed the formation of a Zr{sub 4}Al{sub 3} phase in the Zr{sub 3}Al{sub 2} sample owing to repeated absorption and desorption cycles. The results suggest that the electronic factors, for example, work function, electron density, d-band character and so on, play an important role for the alloying effects rather than crystallographic structures.