Zr Alloy System Research Articles

In situ synchrotron investigation of tensile deformation and failure mechanisms in cold spray Cr-coated Zr-alloy system

High energy synchrotron X-ray diffraction in the transmission mode was performed in situ during uniaxial tensile testing to understand the deformation and cracking behavior of cold spray Cr-coated Zr-alloy specimens in both the as-deposited and annealed conditions. The fracture surface of the specimens, examined using scanning electron microscopy, revealed that the Cr coatings in both samples remained strongly adherent to the substrates through the completion of the tensile test. Both elastic and plastic deformation mechanisms during tensile deformation were quantified using detailed X-ray line profile analysis. High dislocation density with a unique distribution of edge and screw fractions and non-zero lattice strain was determined to be present in the cold spray Cr coating due to high strain-rate deformation during cold spray deposition. The annealing treatment reduced both residual lattice strain and dislocation density (with preferentially higher reduction in edge fractions) in the Cr coating. This led to a heterogeneous distribution of dislocation density and character among different grains, that enhanced resistance to crack propagation in the annealed Cr coating. The mechanical properties of the Zr-alloy in both specimens were not significantly altered by the presence of the cold sprayed Cr coating on the surface.

High temperature oxidation of cold spray Cr-coated accident tolerant zirconium-alloy cladding with Nb diffusion barrier layer

Cr-Nb bilayer coatings on Optimized ZIRLO™ light water reactor (LWR) fuel cladding tubes were developed using cold spray deposition technology to increase the limiting operational temperature (i.e., binary Cr-Zr eutectic temperature, 1332 °C) of Cr-coated Zr-alloy system. The properties of the dual-layered coatings were improved by varying the type of Cr powder and post-annealing of the cold sprayed Nb layer. High temperature oxidation behavior of Cr-Nb-coated cladding at 1200 °C and 1425 °C in flowing steam were compared with those of Cr-coated cladding and uncoated cladding. At 1200 °C, both Cr-coated cladding and Cr-Nb coated cladding exhibited outstanding oxidation resistance and a continuous intermetallic compound layer (1 – 3 μm thickness) of predominantly Zr-Cr and Cr2Nb formed at the Cr/Zr and Cr/Nb interface, respectively. At 1425 °C, the Cr-coated Zr-alloy cladding showed enhanced oxidation due to rapid consumption of Cr coating by interdiffusion and liquid phase formation, and consequent destabilization of the outer protective Cr-oxide layer. However, the Nb diffusion barrier layer between the Cr coating and Zr-alloy substrate prevented the melting and the outer Cr coating provided excellent oxidation resistance. For this bi-layered system, a diffusion layer devoid of intermetallic phases was observed at the Nb/Zr interface due to the miscibility of the two metals. Reaction pathways that include both surface oxidation and interdiffusion effects within the coating-substrate system have been proposed based on experimental results.

High temperature zirconium alloys for fusion energy

This review considers current Zr alloys and opportunities for advanced zirconium alloys to meet the demands of a structural material in fusion reactors. Zr based materials in the breeder blanket offer the potential to increase the tritium breeding ratio above that of Fe, Si and V based materials. Current commercial Zr alloys might be considered as a material in water-cooled breeder blanket designs, due to the similar operating temperature to fission power plants. For breeder blankets designed to operate at higher temperatures, current commercial Zr alloys will not meet the high temperature strength and thermal creep requirements. Hence, Zr alloys with an operational temperature capability beyond that of current commercial fission alloys have been reviewed, specifically: binary Zr alloy systems Zr-Al, Zr-Be, Zr-Cr, Zr-Nb Zr-Ti, Zr-Si, Zr-Sn, Zr-V and Zr-W; as well as higher order Zr alloys Zr-Mo-Ti, Zr-Nb-Ti, Zr-Ti-Al-V and Zr-Mo-Sn. It is concluded that, with further work, higher order Zr alloys could achieve the required high temperature strength, alongside ductility, while maintaining a low thermal neutron cross-section. However, there is limited data and uncertainty regarding the structural performance and microstructural stability of the majority of advanced Zr alloys for temperatures 500–700 °C, at which they would be expected to operate for helium- and liquid metal-cooled breeder blanket designs.

On spinodal-like phase decomposition in U–50Zr alloy

Finely dispersed two phase microstructures resulting from a spinodal decomposition are of interest as they are associated with enhanced mechanical properties and excessive interfaces to mitigate defect related behavior. This study reports a spinodal-like phase decomposition in a U–50Zr alloy by thermal annealing at 620 °C and ion irradiation at 550 °C, with the latter temperature too low to initiate pure thermal phase transformation. The results hold broad impact for U–Zr alloy systems and its application as advanced nuclear fuel.

Prediction of the Phase Composition of High-Entropy Аlloys Based on Cr–Nb–Ti–V–Zr Using the Calphad Method

Based on the CALPHAD method, a description of the Cr–Nb–Ti–V–Zr alloy system was formulated and temperature dependences of changes in the phase composition of high-entropy CrxNbTiVZr alloys (for x = 0.5, 0.75, 1, and 1.25) were calculated.

A detailed HAADF-STEM study of precipitate evolution in Mg–Gd alloy

The magnesium-gadolinium (Mg–Gd) system provides an ideal model alloy for precipitation hardening. Evolution of precipitates in a Mg–16.2Gd–0.4Zr (wt.%) alloy during isothermal ageing from 150 °C to 300 °C was systemically studied using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The widely accepted four-stage precipitation sequence of the Mg–Gd(–Zr) alloy system has been accordingly updated to: super-saturated solid solution (S.S.S.S.) → ordered solute clusters → GP zones → β′ → βF' + tail-like hybrid structures → β1 → β. In addition to carefully revealing an updated precipitation sequence, new insights into the relationships amongst different precipitate phases were obtained and rationalised. (1) Solute clusters and GP zones form during the early stages of ageing and share the same structural unit; (2) Formation of β′ phase is accomplished via ordered stacking of zigzag GP zones along 101¯0α; (3) Coarsening of β′ phase promotes the formation of βF' phase and tail-like hybrid structures; (4) βF' phase facilitates the nucleation of β1 phase; and (5) β1 and β phases maintain a low-energy Σ9 interface and β1 phase finally transforms to equilibrium β phase in situ. The precipitate evolution at the grain boundaries during ageing were also investigated and grain boundary precipitate free zones were observed in Mg–16.2Gd–0.4Zr alloy aged at 250 °C or above.

Fabrication of ultra-high strength magnesium alloys over 540 MPa with low alloying concentration by double continuously extrusion

Abstract We prepare a new type of patented biodegradable biomedical Mg–Nd–Zn–Zr (JDBM) alloy system and impose double continuously extrusion (DCE) processing. The lowest processing temperature is 250 °C for JDBM-2.1Nd and 310 °C for JDBM-2.8Nd, which increases with the Nd concentration. The highest yield strength of 541 MPa is achieved in JDBM-2.1 Nd samples when extruded at 250 °C and the elongation is about 3.7%. Moreover, the alloy with a lower alloying element content can reach a higher yield strength while that with a higher alloying element content can reach a larger elongation after DCE processing. However, when extruded under the same conditions, the alloy with a higher alloying contents exhibits better tensile properties.

Thermodynamic calculation study on phase structures of Pt-Ir-M(Y, Zr, Mo)

The energy and electronic structure of the solid solutions of Pt-Ir-M (M=Mo,Y,Zr) alloy systems were investigated using the first-principle pseudo-potential plane-wave method. The results show that, adding the same percentage content, 1% Mo doped in Au-Pd solid solution is the most stable phase structure. When doped with Y and Zr, they are likely to react with Au-Pd to form the corresponding intermetallic compounds.

Thermodynamic analysis of the interactions between Nb–Si alloy and molding material

Thermodynamic behavior of the interactions between niobium silicon and ZrO2 or Y2O3 molding materials was investigated. The effects of temperature and alloy compositions on the activity coefficient of each component in Nb–Si–Y and Nb–Si–Zr alloy system were investigated in detail. We found that the activity coefficient of each component increases with the increasing of temperature in both alloy systems. In addition, the activity coefficient of Nb, Y and Zr decreased with the increase of Si content which promotes the interface reaction. The presence of Y increases the activity coefficient of the solvent Nb largely, while the presence of Zr increases the activity coefficient of Nb slightly.

First principles studies on structural, elastic and electronic properties of new Ti[sbnd]Mo[sbnd]Nb[sbnd]Zr alloys for biomedical applications

Stress shielding phenomenon has become a major drawback to the use of metallic biomaterials for orthopaedic implants applications. In this study, a TiMo(Nb, Zr and Nb+Zr) alloy system was investigated to design and develop novel low elastic Young's modulus Ti based alloy for implant application. The development and application of predictive modelling and simulation are transforming the materials engineering discovery process. To this end, ab initio calculation was used to evaluate the effects of composition on structural, elastic and electronic properties of the materials. The data obtained from both theory and experiment were analysed and compared with each other. Notable findings include low elastic Young's modulus values of 70.2GPa, 80.6GPa, 76.5GPa, 59.1GPa and 32.3GPa for the Ti6Mo6Zr, Ti6Mo6Nb, Ti6Mo6Nb2Zr, Ti6Mo5Nb3Zr and Ti6Mo4Nb4Zr alloys, respectively ascribed to the unique elastic softening of their C′ and C44 shear moduli. The consistency in both results is discussed in terms of the sensitivity of the physical and electronic properties to the alloying additions. Thus, the result indicates the approach can enhance the reduction of elastic Young's modulus of metallic biomaterials for replacing some commonly used high modulus materials and prevent stress shielding in orthopaedic implants.

On the role of Ag in enhanced age hardening kinetics of Mg–Gd–Ag–Zr alloys

The addition of Ag to the age hardenable Mg–Gd–Zr alloy system dramatically enhances early stage age hardening kinetics. Using atom probe tomography (APT), Ag-rich clusters were detected in a Ag-containing Mg–Gd–Zr alloy immediately after solution treatment and water quenching. During subsequent isothermal ageing at 200 °C, a high density of basal precipitates was observed during the early stages of ageing. These basal precipitates were enriched with Ag and Gd, as confirmed by APT. It is posited that Ag-rich clusters in the context of quenched-in vacancies can attract Gd atoms, increasing diffusion kinetics to facilitate the formation of the Ag + Gd-rich basal precipitates. The rapid formation of Ag + Gd-rich precipitates was responsible for accelerated ageing.

Microstructure of α-U and δ-UZr2 phase uranium–zirconium alloys irradiated with 140-keV He+ ion-beam

Ion-beam irradiation has been conducted to demonstrate and assess solid phase dependence of fission gas bubble nucleation and growth in metallic nuclear fuels. Differential formation and growth of irradiation-induced voids and bubbles were observed from as-cast uranium-zirconium (U–Zr) alloys including 0.1 and 40 wt% zirconium. The U–Zr alloys were irradiated with 140-keV He+ ions with fluences ranged from 1 × 1014 ions/cm2 to 5 × 1016 ions/cm2. Several larger spherical bubbles (<∼70 nm) were revealed from an irradiated single α-U phase alloy (U–0.1Zr) in which observed bubbles were mobile under 200-keV electron beam of transmission electron microscope (TEM). In-situ mergence and leakage of the bubbles in the uranium-rich alloy was also evident during the observation. In contrast, numerous number of small (∼6 nm) angular voids, or low pressure bubbles, were found in an irradiated δ-UZr2 phase alloy (U–40Zr), in which the radiation-induced nanostructure was stationary throughout the observation. This study may reaffirm higher radiation-susceptibility of the α-U phase than the δ-UZr2 phase, which could strengthen the needs of separate accounting of solid phase effects for metallic fuel performance modeling particularly regarding the fuel restructuring phenomena, such as fission gas swelling and constituent redistribution, since conventional models are commonly adopted homogeneous medium assumption, not in accordance with the results of post-irradiation examinations of used metallic nuclear fuel in which the formation of several concentric phase zone was distinct corresponding to a steep radial temperature gradient in the fuel pin and multiple isotherm lines in the binary phase diagram of U–Zr alloy system.

Response to letter “Electron correlation and relativity of the 5f electrons in the U[sbnd]Zr alloy system”

In the Letter [Söderlind et al., J. Nucl. Mater. 444, 356 (2014)], Söderlind et al. state their interpretation that 1) we view electron correlation to be strong and including spin-orbit coupling (SOC) to be necessary for U metal and UZr alloy in our article [Xiong et al., J. Nucl. Mater. 443, 331 (2013)]. Further, they argue that 2) density functional theory (DFT) without adding the Hubbard U potential, especially when solved using all electron methods, already models U and UZr accurately, and 3) adding the Hubbard U potential to DFT in DFT + U models U and UZr worse than DFT according to volume, bulk modulus, and magnetic moments predicted from their calculations of the γU phase of elemental U metal. With respect to Söderlind et al.’s interpretation 1), we clarify that our opinions are that U and UZr are not strongly, but weakly to moderately correlated and that including SOC is beneficial but not necessary for modeling most ground state properties of U and UZr. With respect to Söderlind et al.’s argument 2) we demonstrate that previously neglected and very recent experimental data suggest that DFT in Söderlind's full-potential linear muffin-tin orbital calculations [Söderlind, Phys. Rev. B 66, 085113 (2002)] in fact models the bulk modulus and elastic constants of αU with errors considerably larger than other related elements, e.g., most transition metals. With respect to Söderlind et al.’s argument 3) we argue that they have inappropriately focused on just one phase (the BCC γU phase of U metal), neglecting the other phases which represent the majority of our evidence, and made overgeneralizations based on results at only one Ueff value of 2 eV. We therefore maintain our original conclusion that the accuracy of DFT for modeling U and UZr has room for improvement and DFT + U can be of value for this purpose on at least some ground state properties.

Thermodynamic considerations in the use of nickel–beryllium alloy to braze Zircaloy-4

To better control beryllium exposure during the manufacture of CANDU® fuel bundles, a nickel–beryllium brazing alloy to affix appendages to Zircaloy-4 is being considered. A Ni-2wt%Be shows promise in substantially reducing beryllium volatility while minimally perturbing existing fabrication processes. Thermodynamic models of the condensed phases of the binary Zr–Be, Ni–Be and Ni–Zr alloy systems provide a basis for the construction of a provisional ternary phase diagram that in particular identifies the domain of the liquid phase. The modeling also permits the computation of the partial pressures of Be and related matters associated with the control of surface oxide on Zircaloy-4.

First principles theoretical investigations of low Young's modulus beta Ti-Nb and Ti-Nb-Zr alloys compositions for biomedical applications.

High alloyed β-phase stabilized titanium alloys are known to provide comparable Young's modulus as that to the human bones (~30 GPa) but is marred by its high density. In the present study the low titanium alloyed compositions of binary Ti-Nb and ternary Ti-Nb-Zr alloy systems, having stable β-phase with low Young's modulus are identified using first principles density functional framework. The theoretical results suggest that the addition of Nb in Ti and Zr in Ti-Nb increases the stability of the β-phase. The β-phase in binary Ti-Nb alloys is found to be fully stabilized from 22 at.% of Nb onwards. The calculated Young's moduli of binary β-Ti-Nb alloy system are found to be lower than that of pure titanium (116 GPa). For Ti-25(at.%)Nb composition the calculated Young's modulus comes out to be ~80 GPa. In ternary Ti-Nb-Zr alloy system, the Young's modulus of Ti-25(at.%)Nb-6.25(at.%)Zr composition is calculated to be ~50 GPa. Furthermore, the directional Young's moduli of these two selected binary (Ti-25(at.%)Nb) and ternary alloy (Ti-25(at.%)Nb-6.25(at.%)Zr) compositions are found to be nearly isotropic in all crystallographic directions.

First principles study of low Young's modulus Ti–Nb–Zr alloy system

The Young's moduli of Ti–Nb–Zr alloy system with the nominal compositions of Ti24Nb, Ti20Nb12Zr, Ti17Nb21Zr, Ti11Nb38Zr, Ti6Nb53Zr and Ti70Zr were investigated by using first principles calculations and experimental measurements. The results show that, as the valence electron concentration of these alloys decreases, the calculated Young's modulus steadily decrease, but the experimental Young's modulus first decreases and then increases. This increase is attributed to the β phase stability of these alloys, which can be estimated by the modified Born stability criteria. From these results guidelines are provided for the development of low Young's modulus β-phase Ti alloys: the tetragonal shear constant C′ should be around 2.44GPa and the valence electron concentration should be in the range of 4.06–4.17.

A study of low Young′s modulus Ti–Nb–Zr alloys using d electrons alloy theory

Six kinds of alloys in Ti–Nb–Zr alloy system were designed using d electrons alloy theory, and the relations between their Young′s modulus and electron parameters were investigated. The results show that the Young′s moduli of the designed alloys are low, with a minimum of 38.8 GPa. A formula was proposed to represent the interatomic bonding force of these alloys, which showed good agreement with the Young′s modulus. Low Young′s modulus β-Ti alloys can be designed by evaluating their interatomic bonding force.

Disordered bcc γ-phase to δ-phase transformation in Zr-rich U-Zr alloy

The transformation mechanism of hexagonal delta phase from the disordered bcc gamma phase has not been reported before in the Zr-rich U–Zr alloy system. With the help of X-ray diffraction, transmission electron microscopy (TEM) and high-resolution TEM analyses it was shown that the gamma to delta conversion takes place by the lattice collapse mechanism of omega transformation. It was also ascertained that a higher aging temperature or time promotes the growth of all four variants of the delta phase within a parent gamma grain. In addition, ab initio electronic structure calculations showed that the bcc to hexagonal transformation, involving partial ordering of the parent bcc phase followed by (111) plane collapse, is energetically favorable.

Critical strain for mechanical alloying of Cu–Ag, Cu–Ni and Cu–Zr by high-pressure torsion

Cu–Ag, Cu–Ni and Cu–Zr alloy systems were subjected to high-pressure torsion with various rotations from 0.5 to 50, which can reach very large equivalent strains of up to 3000. The processed samples finally transformed into Cu–Zr, Cu–Ag amorphous alloys and Cu–Ni solid solution from elemental metals after being deformed to critical equivalent strains of 427, 592 and 411, respectively. The feasibility of mechanical alloying can therefore be evaluated in terms of critical equivalent strain through the high-pressure torsion process.

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.