Precipitation Of Zr Research Articles

Development of analytical method for zirconium determination in U–Pu–Zr alloy samples

The study focuses on developing a robust method for determining zirconium in U–Pu–Zr alloy samples, crucial for assessing fuel composition and ensuring uniformity. Using mandelic acid precipitation and spectrophotometric quantification with Arsenazo-III, the method achieves high sensitivity and reproducibility, crucial for handling microgram-levels of Pu. By optimizing conditions to maintain Pu in its + 3 oxidation state, interference during Zr precipitation is minimized. Comparative analyses with ICP-AES validate the accuracy and reliability of the results. This approach not only enhances analytical precision but also reduces radioactive waste, making it suitable for nuclear fuel characterization.

Effect of cryogenic milling on the mechanical and corrosion properties of ODS Hastelloy-N

This study entails the fabrication of two oxide-dispersion strengthened (ODS) Hastelloy-N (HN) alloys utilizing divergent methods. The first alloy was synthesized using cryogenic attritor milling coupled with spark plasma sintering (SPS), while the second was produced via room temperature attritor milling and SPS. The ODS HN alloy derived from cryogenic milling demonstrated superior strength relative to its commercial-grade counterpart. Conversely, the alloy produced through room temperature milling exhibited lower ultimate tensile strength (UTS), attributed to manufacturing defects and the precipitation of Zr at grain boundaries. Corrosion resistance in molten FLiNaK for both ODS samples was found to be inferior compared to commercial HN. Particularly, in the room temperature-milled ODS HN, Zr present at grain boundaries appeared to dissolve more readily than in cryogenic or commercial samples, facilitating enhanced penetration by molten salt. The cryogenically-milled ODS HN contained Zr, yet it was not segregated to grain boundaries. Although the homogeneously dispersed Mo-based compound in the cryogenically-milled ODS HN augmented mechanical properties, it also accelerated corrosion propagation beyond that of the commercial-grade alloy.

Optimizing mechanical and electrical properties of Cu–3Zr alloy by thermomechanical processing

Cu–3Zr alloy was prepared by powder metallurgy and two-stage thermomechanical process, and the microstructure evolution and properties were investigated. The results show that the microstructure of as-sintered Cu–3Zr alloy is consisted of the coarse Cu–Zr intermetallic compounds and equiaxed Cu grains. After extrusion, the second phase is smaller in cross section, while deformation texture of the Cu matrix can be seen from longitudinal section. After further drawing, the Cu grains are elongated and the Cu–Zr intermetallic phase is broken into fine particles. The yield strength (YS), ultimate tensile strength (UTS) and electrical conductivity are 593 MPa, 684 MPa, and 74%IACS, which are respectively increased by 38%, 34% and 21% as compared to the as-sintered Cu–3Zr alloy. Phase analysis and microstructural characterization demonstrate that the Cu5Zr, Cu8Zr3, and Cu10Zr7 precipitates are uniformly distributed in the Cu matrix. Cu5Zr/Cu and Cu8Zr3/Cu are combined in the form of coherent relation. Cu10Zr7/Cu are combined in the form of semi-coherent relation. The enhanced mechanical properties can be attributed to the multiple synergistical strengthening effect. The elongated Cu grains and fine Cu–Zr precipitation phases block the movement of dislocation, resulting in the remarkable enhancement of strength. Moreover, the elongated Cu grains can provide fast channel for the electron transport, giving rise to simultaneous increase of the electrical conductivity.

An experimentally validated mesoscale model for the effective thermal conductivity of U-Zr fuels

An experimentally validated mesoscale model was developed to simulate the effective thermal conductivity (ETC) of metallic U and U–Zr nuclear fuels. The effects of microstructure, temperature, composition, and interfacial thermal resistance (ITR) were investigated. Companion experiments were conducted to validate the model. The numerical simulations clearly demonstrate that accounting for the interface (Kapitza) thermal resistance and Zr precipitation is necessary to improve the model predictions. The dependence of the effective Kapitza resistance of depleted-U and U-10Zr on temperature was determined. For both materials, the largest difference between the model calculations and the experimental data was about 4.5%, which is within the precision of the experimental measurements.

Microstructure and mechanical properties of Al-Mg-Mn-Er-Zr alloys fabricated by laser powder bed fusion

This paper centers on high-strength Al-Mg-Mn-Er-Zr alloy, which was developed through the addition of Er, a cheap rare earth element, and suitable for additive manufacturing (3D printing). The microstructure and mechanical properties of Al-Mg-Mn-Er-Zr alloy of as-built and heat treated samples have been characterized, which shows: the precipitation of Al3Zr primary phase at the boundary of molten pool promotes heterogeneous nucleation and refines the grains, which suppresses the formation of solidification cracking in Al-Mg alloy. To bring the Er-Zr synergistic effect into play during the aging heat treatment, the nano-scale precipitation phase of Al3Er that diffuses nucleation at an earlier stage promotes the precipitation of Zr, leading to the formation of Al3(Er,Zr) core-shell structure and enhancing precipitation strengthening effect. Under the combined effects of multiple strengthening mechanisms, the yield strength could reach 440 ± 3 MPa; tensile strength, 520 ± 2 MPa and elongation 15.5 ± 1.0 %.

Processability, microstructure and precipitation of a Zr-modified 2618 aluminium alloy fabricated by laser powder bed fusion

Additive manufacturing offers the opportunity to produce complex geometries from novel alloys with improved properties. Adapting conventional alloys to the process-specific properties can facilitate rapid implementation of these materials in industrial practice. Nevertheless, the processing of conventional alloys by laser powder bed fusion is challenging, particularly in cases of pronounced susceptibility to hot cracking. Previous studies have demonstrated the positive influence of zirconium on the susceptibility to hot cracking of high-strength aluminum alloys, although its influence on precipitation formation, which is immensely important for 2xxx alloys, remains largely unexplored. This work investigates the optimum process parameters and precipitation formation of 2618 modified by zirconium in laser powder bed fusion. The addition of zirconium results in the production of a crack-free, high-density (~99.9%) material. The microstructure is characterized by a trimodal grain size distribution. Very fine (~0.5 µm) equiaxed grains, nucleated by L1 2 -Al 3 Zr precipitation at the melt pool boundary, followed by columnar-dendritic grains (5–15 µm long, 1–3 µm wide) and coarser equiaxed grains (1–3 µm) form during solidification. The grain boundaries are populated predominantly by (Al,Cu) 9 FeNi, but also by Mg 2 Si, Al 2 CuMg, and AlCu, which presumably impede grain growth and promote a very fine-grained, low-textured microstructure, even in regions where L1 2 -Al 3 Zr are absent. The as-built microhardness of 1360 ± 74 MPa exceeds that of the known high-strength Al alloys tailored to additive manufacturing, Addalloy™ and Scalmalloy®. The results provide a better understanding of precipitate formation in Zr-modified 2xxx series alloys and pave the way for the commercialization of further 2xxx alloys adapted to additive manufacturing. • 2618 is known to show pronounced solidification cracking issues when processed with LPBF. • Zr-modified 2618 exhibits high-density, crack-free microstructure with trimodal solidification morphology. • Far-from-equilibrium solidification leads to GB segregation of (Al,Cu) 9 FeNi, Mg 2 Si, Al 2 CuMg and AlCu. • Hardness exceeds that of conventionally produced 2xxx alloys (e.g. 2024, 2618) as well as Addalloy™ and Scalmalloy®.

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.

Microstructure, Mechanical and Thermal Properties of Mg-0.5Ca-xZr Alloys

To evaluate the potential values in heat dissipation applications, this study investigated the microstructure, mechanical and thermal properties of the Mg-0.5Ca-xZr alloys (x = 0.5 and 1 wt.%) under the as-cast, as-extruded and aged states. The phase constituents of the Mg alloys were examined by X-ray diffraction analysis, and the microstructure was inspected by optical microscopy and scanning electron microscopy. The thermal conductivity and mechanical properties of the Mg alloys were measured by the laser flash method and tensile tests, respectively. The results showed that the Mg alloys exhibited the equiaxed microstructure which is composed of α-Mg, Zr and compound Mg2Ca. Both the extrusion process and increase of Zr content remarkably enhanced the mechanical strength of the Mg alloys and deteriorated the thermal performance simultaneously. It was also found that the thermal conductivity and mechanical strength of the Mg alloys increased gradually with the increase of aging time due to the higher precipitation of Zr and compound Mg2Ca during the aging treatment. TheMg-0.5Ca-0.5Zr alloy aged at 473 K for 48 h demonstratedhigher thermal conductivity than the required values of the Mg alloys used as heat dissipation materials. Moreover, theMg-0.5Ca-0.5Zr alloy exhibited similar mechanical strength to the commonly-used Mg alloys, highlighting its potential become a potential heat dissipation material in the future due to its good combination of high thermal performance and mechanical strength.

Effect of Scandium in Al–Sc and Al–Sc–Zr Alloys Under Precipitation Strengthening Mechanism at 350 °C Aging

In the present scenario, it is much needed of developing Al–Sc and Al–Sc–Zr alloys owing to its higher strength to weight for aerospace applications. The present study is dealt about effect of Scandium on micro hardness and micro structure of synthesized Al–Sc alloy and Al–Sc–Zr alloy under different weight percentage. The precipitation strengthening of as-cast structure, Al–Sc alloy and Al–Sc–Zr alloy have been analyzed during aging at 350 °C. From the experimental investigation, only little difference in micro hardness of developed alloys was observed during initial stage of aging. The peak hardness of Al–Sc–Zr alloy was maintained for a relatively longer period for producing better thermal stability. Three-dimensional atomic probing indicated that the precipitation of Zr in the precipitate at the initial stage of aging which can inhibit the growth of the precipitate’s size. TEM results showed that the Al–Sc–Zr alloy formed two precipitates of different sizes at the over-aging phase after the peak state of hardness.

Effect of solidification cooling rate on kinetics of continuous/discontinuous Al3(Sc,Zr) precipitation and the subsequent age-hardening response in cold-rolled AlMgSc(Zr) sheets

We explain the critical effect of casting processing route (i.e., the solidification cooling rate) on the kinetics of Sc–Zr precipitation upon solidification and, subsequently, on the age-hardening response of cold-rolled/aged Al–3Mg-0.36Sc-0.14Zr sheets. The evolution mechanisms of various types of Al3(Sc,Zr) precipitates are investigated in the as-cast specimens (fabricated via strip casting vs. mold casting techniques), as well as in the subsequently cold-rolled/aged sheet specimens. The Al3(Sc,Zr) precipitates appeared to have formed upon either discontinuous or continuous precipitation during cooling from solidification temperatures; the former leads to the formation of lamellar Al3(Sc,Zr) cells while the latter results in the formation of spherical precipitates, all of which possessing an L12 crystal structure and a coherent interface with the α-Al matrix. It is shown that slower cooling rates via mold casting lead to the occurrence of both continuous and discontinuous precipitation upon cooling from the solidification temperature. In contrast, higher cooling rates via strip casting results in the apparent prevention of all discontinuous precipitation reactions as well as in the suppression of continuous precipitation. The overall effect is the greater preservation of Sc supersaturation within the α-Al matrix of the as-cast specimens fabricated via strip casting which, subsequently, leads to higher precipitation kinetics and thus higher tensile properties upon age-hardening of the cold-rolled sheets.

Effect of micro-additions of Ge, In or Sn on precipitation in dilute Al-Sc-Zr alloys

Trace amounts of inoculants - germanium (0.02 at%), indium (0.02 at%) or tin (0.01 at%) - were added to a ternary Al-0.06Sc-0.06Zr at% alloy to study their effects on Al3(Sc,Zr) precipitation. During isothermal aging at 300 °C, the In- and Sn-containing alloys exhibit an early microhardness increases, which is attributed to In or Sn clustering. Peak isothermal microhardness due to Al3(Sc,Zr) precipitation is achieved simultaneously (~4 h) for the three inoculated alloys and an inoculant-free alloy. Isochronal aging produces a low-temperature microhardening response for the In- and Sn-containing alloys, followed by two microhardness peaks at 350 and 450 °C for all four alloys, associated with precipitation of Sc and Zr, respectively. Atom-probe tomography demonstrates partitioning of Ge and Sn (up to 0.5 at%) from the matrix to the Al3(Sc,Zr) precipitates, with partitioning to Sc-rich precipitate cores (for isothermal aging) or to both Sc-rich cores and Zr-rich shells (for isochronal aging). Inoculant partitioning at precipitate cores and early low-temperature microhardness increases are consistent with inoculant clustering to form nucleation sites for Sc and Zr precipitation. Inoculant segregation at the precipitate shells can be explained by co-precipitation of the fast-diffusing inoculant element and the slow-diffusing Zr, between which an attractive binding energy exists. When compared to the inoculant-free control alloy with a somewhat higher Sc content, the three inoculated alloys exhibit a 2- to 10-fold decrease in creep rates at 300 °C for stresses above ~18 MPa, but a small reduction in creep threshold stresses from 12 to ~10 MPa.

Zr precipitation kinetics in irradiated fuel dissolution solution by TIMS and ICP-MS: a combined study

This study presents the combined analysis of leftover zirconium in irradiated fuel dissolution solution through time. Thermo-ionisation mass spectrometry was used to analyse the kinetics start and final aliquots with uncertainties lower than 3%, while inductively coupled plasma-mass spectrometry (ICP-MS) was used for intermediary aliquots. In order to obtain low uncertainties using ICP-MS, dissolution solutions were spiked with lutetium, used as a process tracer, in order to perform a relative analysis. The analytical parameters were optimised and uncertainties were lower than 3% for real nuclear samples. This method shows the input of ICP-MS for concentration evolutions determination.

Effect of rotating magnetic field on the microstructure and properties of Cu–Ag–Zr alloy

Abstract A long time of homogenization treatment is needed to eliminate the microsegregation of solutes during the preparation of many copper alloys, resulting in a waste of time and energy. In the present study, we demonstrated that the application of rotating magnetic field (RMF) on a newly developed Cu–Ag–Zr alloy during solidification can efficiently reduce the microsegregation of Zr solute, which can be proven by the variation of the electrical conductivity and hardness with a prolonged time of solution treatment. For a short solute treatment time of 1 h and aging time of 4 h, the amount of Zr precipitate increases and becomes more refined due to the Zr microsegregation reduction under RMF, resulting in an obvious improvement of the tensile strength and Brinell hardness of Cu–0.1Ag–0.3Zr alloy. Furthermore, the coarse columnar grain turns into homogeneous equiaxed grain and the macrosegregation decreases under the effect of RMF.

Existing forms and effects of carbon on the surface structure and hardness of ZrTiAlV alloys with various Zr contents

The existing forms and effects of carbon on the surface structure and hardness of ZrTiAlV alloys with various Zr contents were investigated in this study. Each sample of ZrTiAlV–C alloys with Zr content below 17.3at.% is composed of (TiZr)C compound, a few β phases, and matrix α phase. The Zr content in the compound increases with increased Zr content in alloys. At 17.3at.% Zr content, both ZrC and (TiZr)C compounds are simultaneously observed. Only ZrC compound in addition to solid solutions is observed when the Zr content exceeds 17.3at.%. Comparison of the XRD results of ZrTiAlV–C alloys with those of ZrTiAlV alloys shows that the addition of carbon to ZrTiAlV alloys can restrain the precipitation of Zr–Al compound. Microstructures show that the grain size of carbide in ZrTiAlV–C alloys decreases with increased Zr content. Hardness tests show that addition of carbon markedly affects the mechanical properties of ZrTiAlV alloys as the Zr content changes. The hardness of ZrTiAlV alloys with Zr content below 17.3at.% gradually increases. However, a rapid decrease is observed when the Zr content is 25.95at.%. Then, a plateau is observed when the Zr content ranges from 25.95at.% to 60.55at.%, and a rapid increase is observed when the Zr content is 69.2at.%. However, the curve of hardness vs. Zr content of ZrTiAlV–C alloys is characterized as a parabola. The maximum hardness of ZrTiAlV–C alloys is 53.9HRC when the Zr content is 43.25%. The maximum hardness increases by about 11% compared with the maximum hardness of ZrTiAlV alloys with various Zr contents. Otherwise, hardness tests also indicate that the strengthening effect of carbide on the β phase is better than that on the α phase.

Effect of Zr addition on phase transformation and precipitation in B-added hot stamping steel

The effect of Zr addition on phase transformation and precipitation in B-added hot stamping steels was investigated. First, a thermodynamic calculation was conducted to compare the thermodynamic stability of nitride precipitates for various nitride-forming elements. The equilibrium temperatures for phase transformation and nitride precipitation in B-added hot stamping steels containing Zr were also calculated. The phase transformation kinetics of B-added hot stamping steels with various Zr contents were evaluated by both dilatometry and metallography. It was verified that Zr addition can provide protection of the B-hardenability effect, which produce a fully martensitic microstructure after hot stamping. To confirm the existence of Zr precipitation in the hot stamping steels, transmission electron microscopy and energy dispersive spectroscopy were used. A large number of precipitates were observed in the form of (Ti, Zr)N. The effect of Zr addition in B-added hot stamping steel to provide effective B-protection resulting in an increase of hardenability was identified and discussed.

Role of silicon in accelerating the nucleation of Al3(Sc,Zr) precipitates in dilute Al–Sc–Zr alloys

The effects of adding 0.02 or 0.06at.% Si to Al–0.06Sc–0.06Zr (at.%) are studied to determine the impact of Si on accelerating Al3(Sc,Zr) precipitation kinetics in dilute Al–Sc-based alloys. Precipitation in the 0.06at.% Si alloy, measured by microhardness and atom-probe tomography (APT), is accelerated for aging times <4h at 275 and 300°C, compared with the 0.02at.% Si alloy. Experimental partial radial distribution functions of the α-Al matrix of the high-Si alloy reveal considerable Si–Sc clustering, which is attributed to attractive Si–Sc binding energies at the first and second nearest-neighbor distances, as confirmed by first-principles calculations. Calculations also indicate that Si–Sc binding decreases both the vacancy formation energy near Sc and the Sc migration energy in Al. APT further demonstrates that Si partitions preferentially to the Sc-enriched core rather than the Zr-enriched shell in the core/shell Al3(Sc,Zr) (L12) precipitates in the high-Si alloy subjected to double aging (8h/300°C for Sc precipitation and 32days/400°C for Zr precipitation). Calculations of the driving force for Si partitioning confirm that: (i) Si partitions preferentially to the Al3(Sc,Zr) (L12) precipitates, occupying the Al sublattice site; (ii) Si increases the driving force for the precipitation of Al3Sc; and (iii) Si partitions preferentially to Al3Sc (L12) rather than Al3Zr (L12).

Influence of phonon confinement, surface stress, and zirconium doping on the Raman vibrational properties of anatase TiO2 nanoparticles

AbstractWe present a comprehensive analysis of the Raman spectra of pure and zirconium‐doped anatase TiO2 nanoparticles. To account for the wavenumber shifts of the Eg(ν6) mode as a function of particle size (L) and dopant concentration (x), a modification of the standard phonon confinement model (PCM) is introduced, which takes into account the contribution of surface stress by means of the Laplace–Young equation. Together with X‐ray diffraction (XRD) and transmission electron microscopy data, our analysis shows that the surface stress contribution to the observed blue shift of the Raman wavenumber is of the same magnitude as the spatial phonon confinement effect. Annealing experiments show that Zr‐doped nanoparticles exhibit retarded grain growth and delayed anatase‐to‐rutile phase transition by up to 200 K compared to pure anatase TiO2. XRD shows that Zr doping leads to a unit cell expansion of the anatase structure. Applying the modified PCM to the x‐dependent variations of the Eg(ν6) Raman mode, the mode‐Grüneisen parameter is found to increase abruptly at x &gt; 0.07 with a concomitant mode softening. This coincides with the x range over which the Zr cations are reported to be displaced from their position in the tetrahedral lattice, and where Zr precipitation occurs upon annealing. The results have implications for the interpretation of Raman spectra of ionic metal oxide nanoparticles and how these are modified upon cation doping. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Preparation of alumina-doped yttria-stabilized zirconia nanopowders by microwave-assisted peroxyl-complex coprecipitation

Alumina-doped yttria-stabilized zirconia (ADYSZ) nanopowders were prepared by microwave-assisted peroxyl-complex coprecipitation (MAPCC) using ZrOCl 2·8H 2O, Y 2O 3 and AlCl 3·6H 2O as starting materials, NH 3·H 2O as precipitant and H 2O 2 as complexant. The effects of adding H 2O 2 and microwave drying on the preparation and properties of ADYSZ were investigated. The precursors and nanopowders were studied by EDX, XRD, SEM and TEM techniques. The results show that the uniformity of component distribution within ADYSZ nanopowders is improved by adding appropriate dosage of H 2O 2. Complexing reaction between H 2O 2 and Zr 4+ ion restrains the hydrolyzation and precipitation of Zr 4+ ion. With the addition of H 2O 2, Al 3+, Y 3+ and Zr 4+ ions can be precipitated synchronously in a relatively narrow range of pH value. H 2O 2 also improves the filterability of the wet precipitate. The highly hydrophilic precipitates can be quickly and effectively separated from aqueous solution. During microwave drying process, the moisture of wet precursors is selectively heated. Quick expansion of steam vapor within the wet colloidal particles causes the aggregations burst into numerous tiny lumps. Compared with oven drying, microwave drying can not only shorten drying time but also reduce aggregation intensity of the resultant ADYSZ nanopowders.

Optical, electrical, and diffusion properties of hafnium and zirconium in single-crystal silicon

A study of optical, electrical, and diffusion properties of Hf and Zr in silicon is presented. Photoluminescence spectra were observed in Hf-implanted silicon. Isotope substitution confirms that the observed signal is Hf related. Several deep-level defects were found for Hf in both the upper and lower half of silicon band gap, and their parameters were tabulated. Dominant defect in deep-level spectra was determined to be a donor. Diffusion study of Zr-implanted samples indicated that Zr tends to diffuse out to the surface. Outdiffusion and precipitation of Zr which was found to form platelets, as confirmed by transmission electron microscopy, does not allow the traditional diffusion models to be used; however, an estimate of Zr diffusivity was performed, yielding a value of 2.8×10 −15 cm 2/s at 1100 °C.

Active and recyclable sulphated zirconia catalysts for the acylation of aromatic compounds

Mesoporous sulphated zirconia catalysts have been prepared by precipitation of Zr(OH) 4 at constant basic pH and tested for the acylation of anisole with benzoic anhydride. All samples have been characterized by N 2 physisorption, ion chromatography and thermal analysis coupled with MS analysis of evolved gases (EGA). The samples possessed high specific surface areas and mean pore size in the mesopore range. TG/DSC/EGA analysis allowed us to observe all phenomena related to the calcination process and to better understand the catalyst behavior. Observed phenomena are physisorbed water elimination, dehydroxylation, sulphating agent decomposition, phase transitions and sulphate species removal. Catalytic tests were carried out at different temperatures (30–50 °C) after a thermal treatment. The effects of the precipitation pH, calcination temperature and activation temperature on the catalytic performances were studied. Reuse of the catalyst was also appraised.