Zr Phase Diagram Research Articles

Zirconium phase diagram from ab initio molecular dynamics

The paper presents analysis of precision of a phonon-based free energy calculation technique (Temperature Dependent Effective Potential method) in comparison with the thermodynamic integration method within classical molecular dynamics. It is shown that the use of the second order force constants is insufficient for accurate calculations of free energies at elevated temperatures due to noticeable anharmonic contributions to lattice vibrations. On the other hand, reliable calculations of the crystal phase equilibrium lines requires free energy accuracy better than 1–3 meV per atom. Based upon the obtained results the Temperature Dependent Effective Potential technique is applied to the detailed study of the solid-state Zr phase diagram from ab initio molecular dynamics that may be achieved if force constants up to the fourth order are used. The calculated zirconium phase diagram is in good agreement with experiment. The α−β−ω triple point was determined at P≈6.74 GPa, T≈837 K.

Experimental study of Fe-rich region in the Fe–Nb–Zr system at 1000 °C

The Fe-rich corner of the Fe–Nb–Zr phase diagram was studied at 1000 °C by using synchrotron x-ray powder diffraction (SXPD) technique and quantitative electron probe microanalysis (EPMA). The MgCu2 (C15) and MgZn2 (C14) structures corresponding to Fe2Zr and Fe2Nb Laves phases were observed in the Fe2Zr–Fe2Nb pseudo-binary system. The MgNi2 (C36) structure corresponding to Fe2(Zr1-xNbx) Laves phase was not found in any of the compositions explored at this temperature. The existence of two three-phase fields (C15 + Fe23Zr6 + C14) and (C14 + Fe(α) + Fe23Zr6) and five two-phase fields (Fe(α) + C14), (Fe(α) + Fe23Zr6), (C15 + Fe23Zr6), (C15 + C14) and (Fe23Zr6 + C14) is proposed in the present work.

Structure and stability of δ-UZr2 phase in U-50 wt% Zr alloy

ABSTRACT Thermodynamic stability of the hexagonal delta phase has been discussed for the U-50 wt% Zr alloy composition based on the XRD, FESEM, and EDS results, further corroborated by the ab-initio calculations. It has been shown that U-50 wt% Zr composition falls into a two-phase region in the U–Zr phase diagram at about 573 K, in contradiction to the published phase diagram. Crystallographic structure of the delta phase in terms of the atomic occupation has been elucidated using the near-neighbour analysis obtained from the EXAFS results. It is shown here that the (111) plane collapse mechanism of the parent bcc phase is not complete in the delta phase even after the sample was aged for 864 ks (240 h) at 573 K.

Metastable structures in magnetron sputtered W–Zr thin-film alloys

Binary W–Zr thin-film alloys with different metastable structures were prepared by dc magnetron co-sputtering of W and Zr targets in argon atmosphere on unheated and unbiased substrates. The effect of the elemental composition on the formation of different structures and phases was studied in a very wide range of 3–99 at.% Zr. The microstructure and properties of the films were related to the individual metastable structures prepared. We found that W-rich films with an α-W(Zr) solid solution structure can be prepared in much wider range of the elemental composition (up to 24 at.% Zr) than indicated in the equilibrium W–Zr phase diagram. These films exhibited an enhanced hardness (up to 16.1 GPa) and a reduced residual stress (down to −0.05 GPa). Amorphous W–Zr films with a very low surface roughness (down to 0.4 nm) and metallic glass features were prepared with the Zr content between 33 and 83 at.%. The hardness of these films gradually decreased with increasing Zr content due to reducing average bond energy. All films were in the compressive state in contrast to the crystalline ones. The structure of crystalline Zr-rich films with higher than 88 at.% Zr was predominantly dual-phased exhibiting a gradual transition from a metastable β-Zr(W) solid solution (86–96 at.% Zr) through a metastable ω-Zr(W) solid solution (94–100 at.% Zr) to the thermodynamically stable α-Zr phase (99–100 at.% Zr) with increasing Zr (decreasing W) content. We also observed the formation of dual-phase glassy-crystalline structures in the transition zones between fully crystalline and glassy films.

Phase stability of Fe23Zr6 and thermodynamic reassessment of Fe–Zr system

The stability of the Fe23Zr6 phase in Fe–Zr system was studied, and the partial Fe–Zr phase diagram was revised by means of X-ray diffraction, electron probe microanalysis and differential thermal analysis methods. On the basis of the experimental results in the present work and literature, the Fe–Zr system was reassessed using CALculation of PHAse Diagram (CALPHAD) method. Solution phases, liquid, fcc, bcc and hcp, are modeled as the substitutional solution. The intermetallic compounds, hex.-Fe2Zr, Fe2Zr, FeZr2 and FeZr3 phases, are treated as Fe2(Fe, Zr)1, (Fe, Zr)2(Fe, Zr)1, (Fe, Zr)1Zr2 and (Fe, Zr)1(Fe, Zr)3 by a two-sublattice model, respectively. The Fe23Zr6 phase is treated as stoichiometric compound. A set of self-consistent thermodynamic parameters of the Fe–Zr system was obtained. The results confirm the stability of Fe23Zr6 phase, improve the phase diagram of the Fe–Zr system and provide a theoretical reference for the development of Zr alloys.

The Co–Ni–Zr Phase Diagram in the Zr–ZrCo–ZrNi Region II. Liquidus Surface of the Phase Diagram. Interaction of Alloys with Hydrogen

The Co–Ni–Zr Phase Diagram in the Zr–ZrCo–ZrNi Region II. Liquidus Surface of the Phase Diagram. Interaction of Alloys with Hydrogen

The Co–Ni–Zr Phase Diagram in the Zr–ZrCo–ZrNi Region I. Phase Equilibria in the Zr–ZrCo–ZrNi System at Subsolidus Temperature, 900°C, and 800°C

The phase equilibria in the Zr–ZrCo–ZrNi system at subsolidus temperature and at 900 and 800°C were first studied using physicochemical analysis methods, and solidus surfaces and isothermal sections at 900 and 800°C were constructed. Isomorphic Zr2Co and Zr2Ni compounds with a tetragonal crystal structure of AlCu2 (θ) type form a continuous series of solid solutions dividing the Zr–ZrCo–ZrNi system into two subsystems: Zr–Zr2Co–Zr2Ni and ZrCo–ZrNi–Zr2Ni–Zr2Co. The equilibria on the solidus surface of the Zr–Zr2Co–ZrCo–Zr2Ni system and at 900°C differ significantly. This is associated with the Zr3Co-based η phase formed by peritectoid reaction 〈β − Zr〉 + 〈Zr2Co〉 → η at 980°C, being close to theL ↔ θ + β eutectic crystallization temperature (986°C), in the binary Zr–Co system. At 900 and 800°C, the 𝜂 phase dissolves up to 14.5% Ni. The solidus surface of the ternary Zr2Co–Zr2Ni–ZrCo–ZrNi system shows a three-phase equilibrium of the θ phase with the ZrCo (δ) and ZrNi (δ2) phases of the ZrCo–ZrNi quasibinary section: δ + δ2 + θ. The plane of this tie-line triangle extends significantly at 900 and 800°C as the solubility of nickel in the cubic ZrCo-based phase of CsCl type changes. At room temperature, all alloys of the ZrCo–ZrNi–Zr2Ni–Zr2Co subsystem should contain three phases: δ + δ2 + θ. The solidus surface of the Zr–ZrCo ZrNi system is thus completed by surfaces corresponding to the homogeneity regions of the δ, δ2, δ, and β phases, θ + δ + δ2 tie-line triangle plane, and ruled surfaces representing the upper boundary of the two-phase θ + δ2, θ + δ, and θ + δ volumes. At 900 and 800°C, two three-phase equilibria, η + θ + β and δ + δ2 + θ, are observed in the system.

Microstructure and Porosity Evolution of the Ti–35Zr Biomedical Alloy Produced by Elemental Powder Metallurgy

In the present study, the structure and porosity of binary Ti–35Zr (wt.%) alloy were investigated, allowing to consider powder metallurgy as a production method for new metallic materials for potential medical applications. The porous Ti–Zr alloys were obtained by milling, cold isostatic pressing and sintering. The pressure during cold isostatic pressing was a changing parameter and was respectively 250, 500, 750 and 1000 MPa. The X-ray diffraction study revealed only the α phase, which corresponds to the Ti–Zr phase diagram. The microstructure of the Ti–35Zr was observed by optical microscopy and scanning electron microscopy. These observations revealed that the volume fraction of the pores decreased from over 20% to about 7% with increasing pressure during the cold isostatic pressing. The microhardness measurements showed changes from 137 HV0.5 to 225 HV0.5.

Ab initio investigation and thermodynamic modeling of the Mo–Ti–Zr system

Knowledge of the Mo–Ti–Zr phase diagram and its underlying thermodynamics is critically needed to guide the design of advanced U-Mo–Ti–Zr metallic fuel alloys for next-generation nuclear reactors as well as Ti–Mo–Zr–based biomaterials for medical applications. Here, we report on the development of a thermodynamic model for the Mo–Ti–Zr ternary system using the ab initio informed CALPHAD approach. Our ab initio evolutionary search discovers many experimentally unobserved stable compounds in the Mo–Ti system, but finds Ti–Zr to be a non-compound-forming system. In the Mo–Zr system, no stable compound other than the experimentally known C15 Mo2Zr Laves phase has been found. Phonon calculations within the harmonic approximation have been performed to obtain the vibrational formation entropies of all ordered binary compounds in Mo–Ti and Mo–Zr systems. The mixing energies of the liquid phase and the mechanically unstable but dynamically stabilized bcc phase are further obtained using high-temperature ab initio molecular dynamics (AIMD) simulations. The predicted binary and ternary phase diagrams show overall good agreement with experimental measurements. Future experimental validation of the predicted stable compounds in Mo–Ti system and our model-predicted low-temperature hcp miscibility gap in Ti–Zr system will be of great interest.

Experimental determination of the Ni–Ni5Zr eutectic point for binary Ni–Zr alloy phase diagram

The Ni–Ni5Zr eutectic alloy becomes a promising structural material owing to its high strength and desirable plasticity. However, those nominal eutectic alloys with previously assumed compositions of Ni-8.8 at.% Zr and Ni-9.0 at.% Zr were found to involve a considerable amount of primary (Ni) phase. Hereby, an experimental study was conducted by differential scanning calorimetry and careful electron microscopy to clarify the situation. A total of 13 alloys in the composition range of 8.8 ~ 11.0 at.% Zr were explored with respect to their phase transition temperatures and microstructure evolution characteristics. The Ni-9.9 at.% Zr alloy exhibited primary (Ni) phase, whereas the Ni-10.1 at.% Zr alloy displayed primary Ni5Zr phase. Finally, the eutectic point was determined as Ni-10.0 at.% Zr alloy with a transition temperature of 1467 K, and the relevant part of Ni–Zr phase diagram was revised accordingly.

The Ni–Zr Phase Diagram in the Range 25–60 at.% Ni

The constitution of the Ni–Zr phase diagram in the range 25–60 at.% Ni was refined using physicochemical analysis methods (metallography, X-ray diffraction, and differential thermal and electron microprobe analyses). The Zr2Ni and ZrNi phases were shown to melt at temperatures about 100 and 30°C lower than accepted previously. Upon analysis of the published data and our own experimental results, we concluded that the eutectic interaction between the Zr2Ni and ZrNi phases was not adequately confirmed. A modification of the equiatomic cubic phase was found for the first time.

In search of θ-(Pu,Zr) in binary Pu–Zr: Thermal and microstructural analyses of Pu − 30Zr alloy

The existing Pu–Zr binary phase diagrams report the stability of the compound θ-(Pu,Zr) in the low temperature region between 300 and 0 °C. Furthermore, the current understanding is that θ-(Pu–Zr) is thermodynamically favored over the metastable δ-(Pu,Zr) phase. In an effort to shed light on the phases formed in Pu–Zr binary alloys and reduce uncertainties in the poorly defined boundary between the θ-(Pu,Zr), (θ+δ), δ-(Pu,Zr), and (θ+α-Zr) regions, Pu − 30Zr (in wt.%, equivalent 53 at.%) alloys were subjected to microstructural characterization, annealing, and differential scanning calorimetry (DSC). The results indicate that the alloy is composed of δ-(Pu,Zr) matrix, with a number of smaller, randomly distributed α-Zr precipitates. The phase transition temperatures (determined based on the DSC data) and phases identified in Pu − 30Zr alloys (based on crystallographic data) compare well to those predicted by the phase diagrams with the exception of the θ-(Pu–Zr) phase. Our data indicates that θ-(Pu–Zr) is metastable and can be observed only within a small temperature window (100–300 °C). The consecutive heating cycles remove θ-(Pu–Zr) from the system, and no traces of θ-(Pu–Zr) remain at room temperature, as evidenced by microstructural characterization. This calls for reevaluation of the binary Pu–Zr phase diagram, with particular attention paid to the existence of θ-(Pu–Zr) and its stability.

Effect of Transition Metals Addition on the Microstructure and Incipient Melting of 354-Based Alloys

Thermal analysis of various 354 alloy melts was carried out to determine the sequence of reactions and phases formed during solidification under close-to-equilibrium cooling conditions. The main reactions observed comprised formation of the α-Al dendritic network at 598 °C followed by precipitation of the Al–Si eutectic and post-eutectic β-Al5FeSi phase at 560 °C; Mg2Si phase and transformation of the β-phase into π-Al8Mg3FeSi6 phase at 540 °C and 525 °C; and lastly, precipitation of Al2Cu and Q-Al5Mg8Cu2Si6 at 498 °C and 488 °C. As a result of the low solidification rate of the thermal analysis castings, all Zr-containing alloys are located in the L + Al3Zr region of the Al–Zr phase diagram during the melting stage. Three main reactions are detected with the addition of Ni, i.e., the formation of AlFeNi, AlCuNi and AlSiNiZr phases. Larger sizes of AlFeNi and AlCuNi phase particles were observed in higher Ni content alloys of 3.6 wt%. Mn addition helps in reducing the detrimental effects of the β-iron phase by replacing it with the less-detrimental Chinese script α-Al15(Fe,Mn)3Si2 phase and sludge particles. With the use of the multi-step solution treatment—involving higher solution temperatures and longer durations, an increased amount of incipient melting is likely to occur.

The Constitution of Co–Zr Phase Diagram

The constitution of Co–Zr alloys in the Zr2Co–Zr region is studied by physicochemical analyses (metallography, X-ray diffraction, differential thermal analysis). It is shown that the Zr3Co phase exists in the system, though the literature data on its existence and formation are contradictory. It forms in solid state at 981°C via peritectoid reaction + ↔ , and its homogeneity range at 900°C is no larger than 1 at.%. The eutectic point L ↔ + is found in the alloy with ~22 at.% Co. The microhardness of the Zr2Co and Zr3Co phases is determined.

Experimental and thermodynamic assessment of the La–Ti and La–Zr systems

The phase equilibria of the binary La–Ti and La–Zr system have been investigated between 900K and 2300K by combining conical nozzle levitation technique with in situ high energy synchrotron X-ray diffraction. The coexistence ranges of phases as well as experimental data of the liquidus and binodal line were obtained from the analysis of the diffraction data. The monotectic character of the La–Ti system is evident by the occurrence of two diffuse diffraction maxima according to the coexistence of two liquids above the monotectic temperature of 1845K±20K. The La–Zr phase diagram is a eutectic type, owning a metastable miscibility gap with a critical temperature close to the liquidus temperature. Based on the experimental data, thermodynamic descriptions of the La–Ti and La–Zr phase systems were derived.

Contribution to the description of the absorber rod behavior in severe accident conditions: An experimental investigation of the Ag–Zr phase diagram

Most pressurized water reactor (PWR) absorber rods are composed of an Ag–In–Cd (SIC) alloy inside a stainless steel (SS) cladding, themselves inserted into a Zircaloy tube. During a severe accident, the SIC alloy which melts at 800 °C does not practically interact with SS. However, the cladding failure results from its internal pressurization and its eutectic interaction with Zircaloy and occurs at temperatures greater than 1200 °C. The subsequent interaction between the SIC melt and the Zircaloy has a strong impact on the quantities of aerosols released into the primary circuit and finally on the iodine chemistry. Accurate knowledge of the Ag–Zr system is a prerequisite to address this issue. Within this concern, our experimental work is focused both on the investigation of the Ag–Zr phase diagram and on the determination of the thermodynamic properties of the intermetallic compounds in the system. Two intermetallic compounds (AgZr and AgZr2) were identified. Ag–Zr cast alloys with a Ag/Zr ratio of 1:1 elaborated using an arc-melting furnace, once annealed, contained only a single phase AgZr. From metallographic observations, it appears that AgZr2 likely forms by the peritectic reaction from liquid and the bcc (βZr) phase. The partial enthalpies of solution of silver and zirconium in aluminum were experimentally determined at 723 °C in order to determine the enthalpies of formation of the intermetallic compounds. For silver solution calorimetry in aluminum bath, our measurements were successful and in agreement with the previous data. Yet, this study shows that liquid aluminum should not be used as a solvent for zirconium below 1000 °C.

Thermodynamic modeling of the C–W–Zr system

On the basis of critical evaluation of the literature data, the ternary C–W–Zr phase diagram has been assessed by means of the CALPHAD technique. The individual solution phases, i.e., liquid, fcc, hcp, bcc, and W2Zr have been modeled. The modeling covers the whole composition and temperature ranges. A self-consistent thermodynamic description for the C–W–Zr system has been developed. Comprehensive comparisons between the present calculations and measured phase diagrams show that the reliable experimental information is satisfactorily accounted for by the present thermodynamic description. The liquidus projection, three-dimensional isometric view, and reaction scheme of the C–W–Zr system have been presented.

Dynamic stability of Zr under high pressure and high temperature

The phase transitions and structure stabilities of materials have always attracted much attention of the experimental and theoretical investigators. When calculating the phonon dispersion of the cubic structure of the transition metal Zr (β -Zr), the traditional methods always give the negative phonon frequencies. So the quasi-harmonic approximation cannot solve this kind of problem. We obtain the phonon dispersion of β -Zr at high pressure and high temperature by using the newly developed self-consistent ab initio lattice dynamics method, which can well consider the phonon-phonon interactions. And then the stable region of β -Zr in the high pressure and high temperature phase diagram is predicted. The full phase diagram of Zr is also predicted. We also obtain the high temperature equation of state (EOS) and thermal expansion of β -Zr, which can help to construct the EOS data base of Zr.

Effect of the Rate of Crystallization Cooling of a Mg – Zr Addition Alloy on the Structure of Magnesium Alloys Containing Rem

A rapidly cooled Mg – Zr addition alloy is obtained by remelting a commercial L-4 addition alloy and crystallizing the latter at elevated cooling rates. The possible phase transformations are analyzed on the basis of fragments of an equilibrium Mg – Zr phase diagram plotted with the use of the Thermo-Calc software. The process of segregation of zirconium particles in crystallization of the Mg – Zr addition alloy is studied under equilibrium conditions and under cooling at an elevated rate in the crystallization range. The effect of the crystallization cooling rate of the Mg – Zr addition alloy on the structure of magnesium alloy ML10 is determined. The behavior of zirconium introduced with the L-4 addition and with the rapidly cooled tested one in the melt in the production of alloy LM10 is analyzed. The causes of depletion of the melt of zirconium are determined. The more effective action of the tested Mg – Zr addition alloy on the structure of alloy ML10 as compared to commercial L-4 is explained.

Experimental investigation and thermodynamic description of the Mg–Y–Zr system

The Mg–Y–Zr system was studied via experimental investigation and thermodynamic modeling. Four diffusion couples and four key alloys of the Mg–Y–Zr system at 500 °C were prepared. The phase relations of the Mg–Y–Zr system were investigated by means of X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. No ternary compound was found at 500 °C. The solubility of (αZr) in the Mg–Y intermetallics, i.e., Mg24Y5, Mg2Y and MgY, was determined to be negligible. The differential scanning calorimetry measurement was performed on the Mg–Y–Zr alloys to obtain the phase transition temperature. The present thermodynamic calculations of the Mg–Y–Zr system matched well with the experimental data. The presently established Mg–Y–Zr phase diagram can offer a better understanding of the recent processing technique of creep-resistant magnesium alloys.