Zr Solid Solution Research Articles

Effect of the energy density of pulsed electron beam on the microstructure and properties of Mo-Zr surface alloys

Lasers and electron beams have been widely used to synthesize various surface alloys (SAs) but no data have been reported so far on the molybdenum-zirconium (Mo-Zr) ones. To partially fill this knowledge gap, Mo-Zr SAs were formed by processing molybdenum films on zirconium substrates with low-energy high-current electron beams (LEHCEBs). The effect of the energy density of LEHCEBs on the microstructure, phase composition, nanohardness and corrosion resistance of the Mo-Zr SAs were investigated. Basically, the Mo-Zr SAs consisted of a solid solution of Mo in the β-Zr phase, Mo2Zr second phase particles (SPPs) and a solid solution Zr in Mo. Increasing in the energy density decreased the concentration of the SPPs and enhanced the content of the β-Zr phase. Also, it affected the depth of the highest concentration of the SPPs. In the zones of the highest molybdenum contents, the nanohardness values reached 9.4–12.7 GPa, which was higher by 3.2–4.4 times than that of the zirconium substrates. In a 3.5 % NaCl solution at room temperature, the corrosion current densities and the corrosion potentials were greater than those of the zirconium substrates by six and almost two times, respectively.

Model development for oxidation and degradation behavior of accident tolerant Cr coating on Zr alloy cladding under high temperature steam atmosphere

The oxidation and degradation mechanisms of Cr coating on Zr alloy cladding under high temperature steam atmosphere are summarized. Six basic phenomena are considered for model development, including: oxidation of Cr, growth of ZrCr2, formation of Zr(Cr) solid solution, outward diffusion of Zr, reduction of Cr2O3, and volatilization of Cr2O3. The mathematical analysis model is established and validated, demonstrating its good capacity to predict the increase and subsequent decrease in the thickness of Cr2O3 scale, as well as the thickness changes in other individual layers. The developed model is applied in the analysis of the structure evolution of Cr coating under steady state, transient heating conditions and postulated accident scenarios.

Preparation of a Durable CuO/ZnO/CeO2/ZrO2 Catalyst on an SiC Support by an Inverse Microemulsion/Precipitation Method for Methanol Steam Reforming

AbstractDurable CuO/ZnO/CeO2/ZrO2 catalyst on SiC support for methanol steam reforming (MSR) was prepared by the combination of inverse microemulsion method and precipitation method which is termed as inverse microemulsion/precipitation method. The presence of Ce−O−Zr solid solution facilitated the production of oxygen vacancies and Ce3+ species in the prepared CuO/ZnO/CeO2/ZrO2 catalyst. Owing to the unique tiny reaction pool and the addition of precipitant for inverse microemulsion/precipitation method, the particle size of the prepared catalyst was principally between 2 and 6 nm, with an average size of 3.66 nm. Besides, the small particle size and the highly dispersed of Cu species boosted the reduction performance of the catalyst, enabling the reduction temperature to be only 201 °C. The methanol conversion of the reduced catalyst was still reached 98.8 % after 150 h, considerably higher than that of solution combustion method (70 %), without carbon deposition and pronounced sintering after MSR reaction.

High strength Al−Mg−Sc−Zr alloy with heterogeneous grain structure and intragranular precipitation produced by laser powder bed fusion

In this study, the intrinsic heterogeneous grain structure derived from the special temperature gradient in additive manufacturing and the intragranular precipitation were utilized for constructing a high-strength Al−Mg−Sc−Zr alloy. The alternative distribution of the coarse-grained (CG) layer in the middle of the molten pool and ultrafine-grained (UFG) layer at the boundary between the adjacent two molten pools were produced by using laser powder bed fusion (L-PBF) technology. High contents of Sc and Zr elements were introduced into the Al−Mg alloy, which contributed to the stabilization of UFG boundaries in the form of sub-micro primary Al3(Sc, Zr) particles and resulted in the formation of supersaturated Sc and Zr solid solutions in CG. The afterward aging treatment or well-controlled hot isostatic pressing (HIP) induced uniform precipitation of the high-density nano-scale coherent Al3(Sc, Zr) phase in CG. The HIP also promoted a significant decrease in porosity of the alloy and resulted in a combination of high ultimate tensile strength of 560 MPa and elongation of 12 % of the L-PBF Al−Mg−Sc−Zr alloy. The high strength of the alloy was attributed to the hierarchical formation of the Sc-rich phase, exerting a “dragging effect” on intergranular boundary migration as well as a “pinning effect” on intragranular dislocation sliding.

Study of radiation-stimulated structural phase transformations in iradiated Zr by Mössbauer spectroscopy

The article considers the study of the influence of high-energy singly charged 57Fe ions with energy of 1 MeV, a beam current on the target of ~100 nA, a dose of 5x1016 ion/cm2, on the structural-phase state of zirconium. Using the methods of Mössbauer spectroscopy in transmission geometry (MS), conversion electron Mössbauer spectroscopy (CEMS), and scanning electron microscopy (SEM), we studied the effect of high-energy singly charged 57Fe ions on the structural-phase state of zirconium. The projective ranges of 57Fe ions in zirconium were determined, the number of target atoms subjected to irradiation was calculated, and the number of displacements caused by these ions was estimated. Radiation damage to zirconium materials was simulated by irradiating samples at a charged particle accelerator with probe Mössbauer atoms to obtain nuclear physical data from the zone of influence of these atoms on the structural and phase state of irradiated samples under conditions close to reactor conditions. The electronic state of the implant in these materials was evaluated. The concentration of implanted atoms in the near-surface layer and the volume of samples was calculated. In particular, it was shown that the projective range of 57Fe ions in zirconium was 497 nm, the total number of displaced atoms was 3.4х1020, and the number of displacements per atom (dpa) was 159. The solubility of Fe in Zr is 0.03%. However, when zirconium is irradiated with 57Fe ions, as a result of thermal recombination of vacancies and interstitial atoms within the cascade of displacements caused by thermal peaks, intermetallic compounds Zr3Fe, ZrFe2 and a Zr (Fe) solid solution are formed.

Nucleation and growth of nanoscale precipitates and the effect on properties during secondary isothermal aging in thin-band of Cu–0.8Cr–0.1Zr alloy

The precipitation behavior during secondary isothermal aging of Cu–0.8Cr–0.1Zr alloy, especially the nucleation and growth of nanoscale body-centered cubic (bcc) Cr and orthogonal Cu4Zr precipitates, were clarified through high-resolution crystal structure and atomic-scale composition analysis. Results demonstrated that the crystal-nucleus of face-centered cubic (fcc) Cr and fcc Zr would be preferentially precipitated in a coherent orientation relationship (OR) with fcc Cu-based matrix. As they grew up, fcc Cr gradually developed into stable bcc structure, and the OR with matrix changed from N-W to incoherent. While fcc Zr would change lattice constant by atomic diffusion and segregation to evolve into stable Cu4Zr with orthogonal structure, during which they were precipitated on the Cu–Cr–Zr solid solution through a process of discharging surrounding Cr atoms. Abundant dispersed nanoscale precipitates that induced by the secondary aging contributed to produce well-matched comprehensive properties (σb=669 MPa, I = 84.3 %IACS).

Microstructure and mechanical properties of Nb[sbnd]16Si alloys with Zr additions

To optimize the microstructure and fracture toughness of NbSi based alloys, the effect of Zr addition on the microstructure and mechanical properties was investigated in Nb16Si alloy. The results show that Zr element promotes the sluggish eutectoid reaction of (Nb, Zr)3Si → Nbss + α-(Nb, Zr)5Si3, and Nb-16Si-8Zr alloy only contains Nbss and α-(Nb, Zr)5Si3 phases. From the energy point of view, as the Zr content reaches 4 at.%, (Nb,X)5Si3 phase is more stable than (Nb, X)3Si phase. With the increase of Zr content, the fracture toughness increases since high Zr content refines eutectic structure and increases the content of primary Nbss. The thickness of primary Nbss has a strong influence on crack propagation. Most of the cracks can destroy primary Nbss phase with the thickness of (20 ± 2) μm and continue to propagate in the original direction. However, it will deflect when it intersects primary Nbss phase with a thickness of about (30 ± 2) μm. The improvement of compressive properties was caused by solid solution of Zr.

Removing trace chromium from high concentration vanadium solution by photoreduction deposition with Ti–Zr solid solution

The preparation of ultrahigh-purity vanadium (>99.99 wt%) requires the removal of trace amounts of chromium, but economical vanadium purification is difficult to achieve using crude vanadium mother liquors (>98 wt%) because of the similar properties of V(V) and Cr(IV) ions. In this study, a Ti–Zr solid solution was used for the deep purification of high-concentration ammonium polyvanadate by removing trace chromium using photocatalytic reduction process. The results show that V(V) and Cr(VI) are competitively adsorbed and photoreduced, but V(V) adsorption is preferred and occurs more rapidly than that of Cr(VI). However, after the photoreduction product of V(V), V(IV) is desorbed, whereas after that of Cr(VI), Cr(III) is deposited on the photocatalyst, achieving the separation of vanadium and chromium. The 2 h removal efficiency of chromium exceeds 80%, and the chromium content in the obtained vanadium is less than 0.04 wt%. After precipitation, the chromium content in the obtained ammonium metavanadate is less than 0.001 wt%, and the purity of the final V2O5 product exceeds 99.99%, which meets the requirement for ultrahigh-purity vanadium products. The used photocatalyst can be regenerated and reused with stable performance. This work provides a reference method for ultrahigh-purity vanadium production and an example of the industrial application of the photoreduction process.

Microstructural characterisation and thermal stability of a metastable Mg-8.6 wt.% Zr alloy produced by physical vapour deposition

Abstract The thermal stability of a Mg-8.6 wt.% Zr alloy processed by physical vapour deposition has been studied using differential scanning calorimetry and transmission electron microscopy. The alloy, in the as-deposited condition, is a solid solution of Zr in the Mg matrix. The microstructure is characterised by elongated grains oriented with their [0001] direction parallel to the growth direction. After DSC experiments, three exothermic transformations have been observed. The first one takes place above the deposition temperature and is related to the recovery phenomena due to stress relaxation generated during the growth process. The second transformation corresponds to the breakdown of the solid solution by the precipitation of Zr in the Mg matrix. This reaction takes place in two stages: (i) Zr plates are formed in the basal plane and (ii) these initial precipitates grow along the [0001] direction. An epitaxial relationship between those Zr precipitates and the Mg matrix of [0001]Zr || [0001]Mg and [1120]Zr || [1120]Mg has been obtained. The third exothermic transformation appears above 720 K and is caused by the strong oxidation of the deposit.

Thermodynamic stabilization of nanocrystallinity

Abstract Nanocrystalline materials are polycrystals made up of nanometer-sized grains separated by a network of interfaces – grain or phase boundaries – that generally make a positive contribution to the total energy of the system. Consequently, there exists a thermodynamic driving force for reducing the overall interface area, which renders such systems intrinsically unstable against coarsening. The latter process entails interface migration and the concomitant deterioration of any property enhancements effected by the ultrafine grain size. We describe a strategy for significantly reducing or even eliminating the driving force for grain growth in nanocrystalline materials via the deliberate segregation of solute atoms into the core region of boundaries. Applied to Pd – Zr solid solutions containing up to 20 at.% Zr, the strategy yields nanocrystalline specimens manifesting an unusually high thermal stability with respect to grain growth, extending to the vicinity of the melting point. Parallels are drawn between the migration of grain boundaries in segregation-stabilized systems and antiphase domain boundaries in ordered alloys.

Effect of Bonding Temperature on Microstructure and Mechanical Properties of 304L/Zircaloy‐4 Diffusion‐Bonded Joints with Ni/Ta Hybrid Interlayer

Diffusion bonding of stainless steel 304 L and zircaloy‐4 (Zr‐4) in solid state is conducted using Ni and Ta as the hybrid interlayer at the bonding temperature of 850−1000 °C for the bonding time of 30 min under the bonding pressure of 6 MPa in vacuum. The effect of the bonding temperature on the microstructure and the mechanical properties of the joints is investigated. The microstructure analysis is conducted by a scanning electron microscope, energy dispersive spectroscopy, and X‐ray diffraction. The mechanical properties of the joints are measured by a shear test and microhardness test. The results show that Ni3Ta intermetallic compounds are formed at the Ni/Ta interface, and the solid solution of Zr and Ta appears at the Ta/Zr‐4 interface. In the meantime, the maximum shear strength reaches 194 MPa and the highest hardness value across the interface of joints is 356 HV in the Ni3Ta layer.

Anisotropic atomic mobilities of hcp Zr(O) solid solution and their application in description of early-stage oxidation process of pure Zr

The anisotropic atomic mobilities in hcp Zr(O) were first assessed based on all the literature diffusivities along different orientations. The reliable set of atomic mobilities in hcp Zr(O) was then chosen through comprehensive comparison between the model-predicted diffusion properties with the experimental/theoretical data. It was interestingly found that the diffusion properties in hcp Zr(O) tend to be isotropic as the temperature increases, and an isotropic point exists for anisotropic interdiffusivities at each temperature. Furthermore, quantitative simulation of the early-stage oxidation process of pure Zr was performed, illustrating that the bulk diffusion along the a–b plane predominates the oxidation process.

Characterization of reactive spark plasma sintered (Zr,Ti)B2–ZrC–SiC composites

This investigation aims to evaluate the influence of SiC introduction on the microstructure development, mechanical characteristics, and densification behavior of (Zr,Ti)B2–ZrC materials. Two specimens, with/without SiC addition, were manufactured from the starting materials of ZrB2 and TiC by reactive spark plasma sintering (SPS) at 1800 °C under 30 MPa for 5 min. Both samples reached relative density values higher than 99%; however, the SiC addition improved this value by ~0.5%, standing at 99.9%. The SiC incorporation into the (Zr,Ti)B2–ZrC system led to an ultrahigh temperature ceramic (UHTC) with considerable hardness and elastic modulus. The TiC additive was completely consumed over the sintering process, participating in the in-situ formation of TiB2 and ZrC as a result of a chemical reaction with the ZrB2 matrix. Thanks to the diffusion of Ti and Zr atoms into the ZrB2 and TiB2 phases, respectively, a solid-solution of (Zr,Ti)B2 formed with various compositions in different areas. Thanks to the synergistic effects of grain refinement and solid-solution formation, the (Zr,Ti)B2–ZrC–SiC sample reached excellent mechanical properties such as an elastic modulus of 495 GPa and a hardness of 31.2 GPa.

Mechanical Property and Heat Treatment Behaviour of Ti-Zr-Fe Alloys

The element of zirconium (Zr) belongs to the same group 4 as Ti in the periodic table. Therefore it possesses similar chemical properties. The Ti-Zr binary system forms a continuous solid solution for both high temperature β phase with the body centered cubic (BCC) structure and low temperature α phase with the hexagonal close-packed (HCP) structure throughout the entire range of composition. As is well known, on the other hand, the element of iron (Fe) is not only inevitable but also effective element in Ti.By incorporating Fe at the stage of alloy design, off-grade sponge titanium can be employed. Both elements seem to be effective in strengthening the titanium alloys. The purpose of this work was to prepare Ti-Zr-Fe alloys and then mechanical property and heat treatment behaviours were investigated as a fundamental research. Ti-x mass% Zr-1mass% Fe alloys (x=0, 5, 10) were melted in a laboratory-scale arc furnace under a high purity argon atmosphere from the sponge Ti, the sponge Zr and the Fe wire. The resulting ingots were hot forged and rolled at approximately 1120 K to obtain plates of approximately 2 mm in thickness. Well-mixed and homogeneous samples could be obtained, oxygen contaminations were less than 0.09 %. Solid solution of Zr into Ti was confirmed by the XRD peak shift in α phase. Vickers hardness and proof stress increased with Zr content. No remarkable changes could be observed in the microstructures after the solution treatment at 1173 K. However, Young’s modulus increased at x=10 by the treatment.

Acicular microstructure formation and strengthening behavior of Ti-4%Fe alloys by Zr addition

Commercial pure Ti alloys are favorable for biomedical applications; however, they need to be strengthened by the addition of alloying elements. Herein, Ti-Fe alloys modified with Zr were explored to produce alloys that exhibit high strength and ductility and are biocompatible. Ti-Fe extruded materials with Zr solutes were prepared by combining solid sintering and hot extrusion. X-ray diffraction results revealed that the lattice constant of α-Ti and β-Ti increased proportionally with the Zr content, indicating the Zr solid solution behavior. In situ and ex situ observations of the microstructure formation revealed the element Zr, a weak β-stabilizer, and a decreased phase transformation temperature. However, during the cooling process after hot extrusion, the grain growth stagnated at the same temperature, irrespective of the Zr content, resulting in both α-Ti grain refinement and increased β-phase area fraction. The tensile test results demonstrated that 1010 MPa 0.2% yield strength of the Ti-4Fe-13Zr extruded material increased to 156%, compared with that of the base Ti-4Fe material. Furthermore, Labusch model and the Hall-Petch equation were used to quantitatively evaluate the strengthening mechanism derived from the Zr solid solution and the changes in the grain size.

Quantitative strengthening evaluation of powder metallurgy Ti–Zr binary alloys with high strength and ductility

Titanium is well-known for its high strength, good corrosion resistance, and biocompatibility. For further improvement of its mechanical properties, it is alloyed with other elements, such as zirconium. In this study, pre-mixed pure Ti powder and ZrH2 particles were employed to prepare extruded Ti–Zr alloys with a low hydrogen content via dehydrogenation after sintering. The Zr solutes were uniformly dissolved in the α-Ti matrix by applying the optimal conditions for homogenization and water-quenching heat treatment. The synthesized Ti–Zr alloys consisted of the equiaxed fine α-Ti grains via dynamic recrystallization during extrusion. When the ZrH2 particle content was less than 10 wt%, the extruded Ti–Zr alloys showed a large tensile elongation of more than 25% at room temperature with a yield stress of approximately 850 MPa. In the case of Ti–10% ZrH2 powder, the mean α-Ti grain size was 2.7 μm, which was smaller than that of extruded pure Ti (3.5 μm). By applying the Hall–Petch equation for grain refinement and Labusch model for Zr solid solution to quantitatively estimate the increase in the yield stress, it was clarified that both factors had an equal effect for Ti–5 and –10 wt% ZrH2 powder even with the dominance of solid-solution strengthening by Zr solutes for alloys with small Zr content.

Effect of Mechanical Alloying and Sintering on Phase Transformation, Microstructural Evolution, Mechanical Properties and Density of Zr-Cr Alloy

The purpose of present research was production ofZr-based alloy as the nuclear fuel cladding by mechanical alloying (MA) and sintering process. Firstly, Zr and Cr powders were mechanically alloyed to produce the refractory and hard Zr-10 wt% Cr alloy, and then, the powder mixtures were consolidated by press and following sintering at temperature of 800˚C min. The phase evolution, microstructural changes, microhardness, and density of the Zr-10 wt% Cr alloy were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness measurement, and the Archimedes method. The results showed that the MA increased the solid solubility of the immiscible powders of Cr and Zr; therefore, the Cr atoms were completely dissolved in the Zr lattice after 24 h of the milling time and the nanostructured Zr(Cr) solid solution was obtained with the high microhardness value of about 491 Hv. Also, the results of the density measurement indicated that the resulted density was close to 98% of the theoretical density.

Effect of Zr-doping on Pd/Ce Zr1−O2 catalysts for oxidative carbonylation of phenol

Abstract Ce–Zr solid solution (CexZr1−xO2, CZO) was prepared by the citric acid sol–gel method. The CZO was then used as a support for Pd/CZO catalysts for the oxidative carbonylation of phenol to diphenyl carbonate. The Pd/CZO catalyst showed enhanced activity and diphenyl carbonate selectivity compared with the Pd/CeO2 catalyst. The catalytic performance of Pd/CZO was influenced by the calcination temperature of the CZO support. X-ray diffraction, scanning electron microscopy, N2 adsorption–desorption measurements, X-ray photoelectron spectroscopy and H2 temperature-programmed reduction measurements were used to investigate the effects of Zr doping and calcination temperature. The catalytic performance of Pd/CZO and Pd/CeO2 for the oxidative carbonylation of phenol was affected by several factors, including the specific surface area, Ce3+ and/or oxygen vacancy content, oxygen species type and Pd(II) content of the catalyst. All these properties were influenced by Zr doping and the calcination temperature of the CZO support.

Microstructural evolution and mechanical properties of carbon nanotubes–reinforced TZM composites synthesized by powder metallurgy

A strategy utilizing carbon nanotubes (CNTs) was put forward to prepare Titanium–zirconium–molybdenum (TZM) composites, which comprised Mo–0.5Ti–0.1Zr–0.03CNTs (wt.%), via high–energy ball milling (HEBM), followed by spark plasma sintering (SPS). The microstructural evolution of the TZM composite powders and the sintered samples were characterized by X–ray diffraction (XRD) and scanning electron microscopy (SEM). Their Vickers hardness and compression mechanical properties were also investigated. Results revealed that during the HEBM of TZM composite powders, the fracture mechanism dominated the early stages, followed by the agglomeration mechanism, finally reaching the balance between the fragments and the agglomerates. An increase in milling time resulted in decreased grain size and increased lattice parameter. The changes in microstructure of the composite powders induced by ball milling improved the relative density, Vickers hardness, and yield strength. Transmission electron microscopy (TEM) showed that during long ball–milling time, a Mo–Ti–Zr solid solution formed with the addition of Ti and Zr after sintering. Second–phase particles (TiZrC2) and many dislocation lines were found in the deformed samples.

First principle study of occupancy, bonding characteristics and alloying effect of Zr, Nb, V in bulk γ-Fe(C)

The total energy, binding characteristics, density of states, charge distribution and differential charge density of γ-Fe(C)-M crystal cells formed by solid solution of Zr, Nb and V in γ-Fe(C) were calculated by using the first-principles method. Thus, the mechanism of Zr, Nb, and V with γ-Fe(C) was investigated in this paper. The results show that Zr, Nb and V all preferentially replaced the Fe atoms which are at the top angle in γ-Fe(C). Crystal cell reaches its highest stability after V solid solution. Nb reaches after it, and Zr is relatively weak. In the γ-Fe(C)-Zr cell, Fe-Zr covalent bond and Zr-C ionic bond are the main chemical bonds. In the γ-Fe(C)-Nb and γ-Fe(C)-V cells, Fe-Nb and Fe-V covalent bonds are the main chemical bonds with a number of Nb-C and V-C ionic bonds. After solid solution, the electron cloud density around C atom changed little, while Fe atom changed obviously. The orbital electrons around Fe atoms in γFe(C)-V has maximal distribution, which means that the electrons delocalized most and most of the electrons are bonding. It is the main factor for the increase in the binding energy of crystal cell. The effects of Zr, Nb, V solution on austenitic stability are investigated by studying the influence of alloy element on γFe(C) electronic structure.