Segregation Of Ce Research Articles

Role of Cerium on the Intricacies of Deformed State and Softening Mechanisms of Low‐Carbon Steels

The present study investigates the softening kinetics of two cerium (Ce)‐modified steels after 60% cold rolling and annealing at 600 °C for 2–16 h. Cold rolling accumulates substantial strain in the ferritic matrix of low Ce (LCe) steel (0.03 wt% Ce) compared to high Ce (HCe) steel (0.6 wt% Ce). The acicular ferrite and Fe3C partition the imposed strain preferentially inside the ferrite matrix of LCe sample. Contrarily, a homogenous strain distribution in HCe sample is promoted by soft Ce2O3 particles embedded in ferrite. Both the steels achieve partial recovery and recrystallization even after 16 h of annealing. LCe steel experiences a softening fraction of ≈28 vol% after 16 h, inferior to HCe steel (≈34 vol%). During initial stage of annealing, nucleation of strain‐free grains are observed in LCe sample due to availability of grain and interphase boundaries. Subsequently, recrystallization kinetics get delayed because of the pinning effect exerted by fine CeO2 and Fe3C particles. In HCe samples, the early stage of ferrite nucleation is hindered by the segregation of Ce at grain boundaries. However, at a later stage, the recrystallization kinetics are accelerated owing to the ineffective pinning of dislocations and boundaries by coarse Ce2Fe17 and Ce2C3 particles.

Substituting Ce with La and Nd in Al11Ce3: Effect on microstructure and mechanical properties

Microstructure and mechanical properties are studied for five cast, coarse-grained intermetallic alloys: binary Al11Ce3 and Al11La3, ternary Al11(Ce0.75La0.25)3 and Al11(Ce0.5La0.5)3, and quaternary Al11(Ce0.54La0.27Nd0.19)3 with mischmetal composition. All compounds exhibit a single phase indicating a solid solution among the three rare-earth elements (RE=Ce, La, and Nd) on the Ce sublattice of Al11RE3, in disagreement with Thermo-Calc prediction of segregation of Ce and (La, Nd) into two insoluble compounds. The lattice parameters of this orthorhombic Immm-structured α-Al11RE3 phase increase as La concentration increases, while the α-β phase transformation temperature decreases. The five Al11RE3 compounds show very similar (i) propensity for twinning, (ii) high hardness (4.1–4.3 GPa), and (iii) low indentation fracture toughness (0.48–0.65 MPa m1/2). The Al-Al11RE3 interface lattice mismatches, as calculated for two stable interface orientations, have comparable values across all examined compounds. These similarities imply that these Al11RE3 compounds will exhibit comparable strengthening and coarsening resistance in Al-RE-based eutectic alloys, thus positioning them as economically- and environmentally-favorable alternatives to the well-developed binary Al11Ce3 compound formed in current eutectic Al-Ce alloys.

Trace Ce addition for inhibiting Bi segregation induced embrittlement in ultrahigh-purity copper

Bismuth (Bi), as an impurity element in copper and copper-based alloys, usually leads to the catastrophic intergranular fracture even with a ppm concentration. However, the intrinsic mechanisms of the embrittlement remain largely unclear and the control of such a brittleness has been rarely reported. Here, we investigate the influence of trace amounts of Bi on the ductility of ultrahigh-purity copper (99.99999%) at temperatures between room temperature (RT) and 900 °C. On this basis, the ductility improvement of CuBi alloy by adding different concentration of Ce is also systematically studied. Compared to the ultrahigh-purity copper, the Bi-containing alloy exhibits a remarkable decrease in ductility, with the severe reduction occurs at 450–900 °C. This is caused by the grain boundary (GB) segregation of Bi layers, which reduces the GB cohesion because of the weak BiBi bonds. However, after trace Ce are added, the ductility of CuBi alloy in the temperature range of 450–900 °C is significantly increased. The obvious enhancement is due to the reaction behavior of Ce and Bi to form the precipitated phases, as well as the preferential segregation of Ce to GBs and phase boundaries, which change the existing form of Bi in copper. Our findings provide a comprehensive understanding on the microstructural origin of Bi-induced GB embrittlement and an effective way for inhibiting such an embrittlement.

Unusual surface microstructural evolution of Nd–Ce–Fe–B sintered magnets by (Nd, Pr)Hx grain boundary diffusion

Usually the grain boundary diffusion process (GBDP) provides a facile approach toward high-coercivity Nd–Fe–B magnets by modulating the surface microstructure, i.e. constructing nonferromagnetic grain boundary layers and forming magnetically hardening shells of 2:14:1 main phase. However, by applying (Nd, Pr)H x GBDP to the 25 wt% Ce-substituted Nd–Ce–Fe–B sintered magnet, it is surprisingly discovered the ultimate coercivity below 12.4 kOe over a wide range of diffusion times. The low coercivity increment level of 1.5 kOe after an optimal 10 h diffusion is restrained by the unusual surface layer, i.e. an apparent Ce segregation at the surface region to form REFe 2 (RE = rare earth) intergranular phase at both triple junctions and grain boundaries, rather than the expected Nd/Pr-rich enrichment at the RE 2 Fe 14 B/RE-rich interface or at the GBs. Prolonging diffusion time from 6 to 20 h exacerbates the formation of REFe 2 phase and witnesses a more pronounced surface layer with a limited diffusion depth of ~80 μm, which is much lower than the reported GBDP Nd–Fe–B (millimeters) or Nd–La–Ce–Fe–B (hundreds of micrometers). The limited diffusion depth may be correlated to the blocked diffusion channel by the massive REFe 2 intergranular phase that replaces the conventional RE-rich phase. Above findings demonstrate that the characteristic REFe 2 phase highly affects the surface microstructural evolution of GBDP Nd–Ce–Fe–B magnet, and highlight future work toward sophisticated engineering of REFe 2 phase. • (Nd, Pr)H x GBDP yields unusual surface microstructure evolution of Nd–Ce–Fe–B sintered magnets. • REFe 2 TJ and GB phase forms preferentially at the diffusion surface. • Massive Ce segregates at surface region, rather than the expected Nd/Pr-rich intergranular phase. • Long-time diffusion of 20 h still restrains the diffusion depth to be below 100 μm. • The coercivity increment level of 1.5 kOe is much lower than other reported GBDP magnets.

Investigation on the effect of vacuum annealing time on structural and optical properties of YAG:Ce nanoparticles prepared by mixed-fuel microwave solution combustion synthesis

Cerium doped yttrium aluminum garnet (YAG:Ce) nanoparticles were synthesized via mixed-fuel microwave solution combustion synthesis and further optimized by post annealing treatment. The effects of vacuum annealing time and ambient on the phosphor structural, morphological, compositional, and optical properties were investigated in detail. The structural study performed with X-ray diffraction analysis and Rietveld refinement revealed a direct crystallization from amorphous into single phase YAG:Ce was achieved at 1050 °C for 1 h. The increase in annealing time enhances the powder crystallinity and promotes crystal growth to form larger particles (50–85 nm). However, prolonged annealing would cause the partial oxidation of Ce3+ into optically inert Ce4+ ions, which was likely due to the increased Ce segregation. X-ray photoelectron spectroscopy evidenced that vacuum annealing has a higher tendency to suppress Ce3+ oxidation in comparison to air annealing, resulting in a significant enhancement of photoluminescence emission intensity by 20%. The optimum emission intensity was obtained for YAG:Ce nanoparticles after 5 h of vacuum annealing treatment with color coordinates of (0.391, 0.569). The white light emitting diode (WLED) fabricated with the optimized YAG:Ce nanoparticles showed a cool-white light with a maximum luminous efficacy of radiation of 285 lm/W and a corresponding color rendering index of 83.

Study on the segregation behavior of Ce in CLYC crystals

Ce-doped Cs2LiYCl6 (CLYC) has widespread applications in homeland security owing to its excellent neutron/gamma discrimination ability. Ce3+ ions, as luminescent centers of CLYC, have a significant difference in effective ionic radius compared with Y3+, hinting at the severe inhomogeneous distribution of Ce3+ in CLYC. Still, only the relation between scintillation properties and nominal doping concentrations in CLYC crystals has been reported. The segregation behavior of Ce3+ ions along the ingot are still open for research. Herein, we measured the actual Ce3+ doping concentration along the CLYC ingot. Gamma-ray energy spectrum and powder XRD patterns of different samples were utilized to study the effects of Ce segregation on CLYC crystals. The effective segregation coefficient of Ce in CLYC crystals, keff = 0.22, was calculated. In most part of the ingots, the concentration of Ce3+ ions was lower than the nominal doping amount and rose rapidly at the tail. The scintillation properties of CLYC crystals along the ingot were affected by the distribution of Ce concentrations. This work may guide the optimization of properties for large-size CLYC crystals by modifying the distribution of Ce3+ ions.

Different segregation effects for Sc and Ce in an Al/δ´ interface

The behaviors of Sc and Ce segregation at Al (100)/δ´(100), Al (110)/δ´(110), and Al (111)/δ´(111) interfaces were theoretically predicted to explore the differences in the segregation effects in Al–Li alloys. The results show that Sc exhibits an evident trend to segregation to the Al/δ´ interface whereas this effect for Ce seems to be weak. The variation of the segregation energy is associated with the different orientation of the corresponding interface. The preferable segregated site is on the Al matrix side where the solutes tend to substitute the Al atom at the Li site for the first layer of the corresponding interface.

Crystal growth and scintillation properties of tube shape-controlled Ce-doped Y3Al5O12 single crystals grown by micro-pulling-down method

Tube shape-controlled Ce-doped Y3Al5O12 (tube-Ce:YAG) single-crystal scintillators were directly grown from a melt via the micro-pulling-down method using a specially-designed iridium crucible. Back-scattering Laue images and X-ray diffraction measurements revealed the tube-Ce:YAG was a single crystal with the YAG phase. Ce distribution in the tangential direction of the tube-Ce:YAG specimen showed that Ce concentrations around the capillary positions were lower than at the corners. This was caused by the small Ce segregation coefficient in the YAG single crystal and from the small convection in the meniscus. The scintillation properties of tube-Ce:YAG specimens were comparable with previously reported Ce:YAG single crystals.

A comparative study of hot ductility of unadded and Ce-added SA508-4N RPV steels

The hot ductility of the SA508-4N RPV steel samples, unadded and added with 0.015 wt.% Ce, has been investigated in the range 750–1000 °C. The study is carried out by using a Gleeble machine and various evaluation techniques. Between 750 and 1000 °C, the steel is located in the single-phase austenite region. In this region, the unadded steel presents a hot ductility trough between 750 and 900 °C and the reduction of area (RA) at the trough bottom is rather small, being just ~50% at 850 °C. However, the hot ductility of the steel can be substantially enhanced by a trace addition of Ce, so that the hot ductility trough is eliminated for the Ce-added steel. In the testing temperature range, the RA values of the Ce-added steel are all higher than ~75%. Microanalysis demonstrates that grain boundary segregation of Ce plays an important role in the improvement of hot ductility by enhancing the intergranular cohesion and thus suppressing the boundary sliding. Furthermore, the initial temperature of dynamic recrystallization occurrence can be lowered to ~850 °C from ~900 °C by the Ce addition. This implies that Ce can also facilitate the occurrence of dynamic recrystallization of SA508-4N RPV steel, thereby raising its hot ductility performance.

Structural, Textural, and Catalytic Properties of Ni-CexZr1−xO2 Catalysts for Methane Dry Reforming Prepared by Continuous Synthesis in Supercritical Isopropanol

A series of 5%Ni-CexZr1−xO2 (x = 0.3, 0.5, 0.7) catalysts has been prepared via one-pot solvothermal continuous synthesis in supercritical isopropanol and incipient wetness impregnation of CexZr1−xO2 obtained by the same route. The textural, structural, red-ox, and catalytic properties in methane dry reforming (MDR) of Ni-modified Ce-Zr oxides synthesized by two routes have been compared. It was shown by XRD, TEM, and Raman spectroscopy that the method of Ni introduction does not affect the phase composition of the catalysts, but determines the dispersion of NiO. Despite a high dispersion of NiO and near-uniform distribution of Ni within Ce-Zr particles observed for the one-pot catalysts, they have shown a lower activity and stability in MDR as compared with impregnated ones. This is a result of a low Ni concentration in the surface layer due to segregation of Ce and decoration of nickel nanoparticles with support species.

Atomic scale insights into the segregation/partitioning behaviour in as-sintered multi-main-phase Nd-Ce-Fe-B permanent magnets

As-sintered multi-main-phase Nd-Ce-Fe-B permanent magnets typically exhibit a higher coercivity than as-sintered single-main-phase Nd-Ce-Fe-B magnets with identical content of Ce. To clarify the microstructural features that are relevant to the coercivity, as-sintered multi-main-phase Nd-Ce-Fe-B permanent magnets are characterised by high-resolution magnetic force microscopy and atom probe tomography down to the atomic scale. Though inhomogeneous distribution of rare earth elements (Nd, Pr, and Ce) is observed inside 2:14:1 matrix grains, Ce atoms unexpectedly show similar partitioning behaviour (∼14–27% of rare earth element) at the edge of these grains in the vicinity of rare earth-rich grain boundary compared with as-sintered single-main-phase Nd-Ce-Fe-B magnets with a 20% Ce substitute of Nd and Pr. By contrast, the observation of stripe-liked magnetic domains pinned at the grain boundaries and a thin (Nd,Pr,Ce)-rich grain boundary with a composition of Nd9.9Pr2.6Ce19.0Fe65.3Co1.9Balance1.3 (at.%) jointly indicates the enrichment of Ce in grain boundaries benefit to the magnetic isolation of neighbouring matrix grains in the as-sintered state. Unusual Ce-rich clustering regions are also observed in the grain boundary, which also contribute to the coercivity enhancement. The segregation of Ce, Co, and Cu and rare-earth-Cu clusters are only observed at the interface between rare earth-Cu rich phase and matrix phase while no obvious elemental segregation and clusters are observed at the interface between the rare earth-Ga rich phase and matrix phase, suggesting the occurrence of rare earth-Cu rich phase may be one of the reasons for achieving high coercivity. These findings offer fresh insights into the as-sintered multi-main-phase Nd-Ce-Fe-B permanent magnets.

Heat treatment optimization of China low-activation ferritic/martensitic steel with cerium addition

Abstract Chinese Low-activation Ferritic/martensitic steel (CLF-1) with rare earth (RE) cerium (Ce) addition (RE-CLF-1) was prepared by a two-step method: vacuum induction melting (VIM) and vacuum arc re-melting (VAR) processes. The effect of heat treatment parameter on the microstructure and thermal mechanical property of the obtained RE-CLF-1 was studied. The heat treatment process of the RE-CLF-1 was finally optimized as two steps: (1) normalizing at 980 °C for 60 min, (2) tempering at 740 °C for 60 min, to get a complete martensitic structure and maintain its good mechanical property. For the Re-CLF-1 with optimized heat treatment, the elongation under uniaxial tensile test at room temperature was about ∼22 %, which is comparable to that of the CLF-1 steel. The yield strength and maximum tensile strength were up to ∼605 MPa and ∼738 MPa, respectively, which are larger than the CLF-1 steel, indicating its good mechanical property at room temperature. The ductile brittle transition temperature (DBTT) of the RE-CLF-1 steel was about −50 °C, which is higher than the CLF-1 steel. Additionally, Ce segregation around the M23C6 precipitate was observed, indicating that Ce could play an important role on the formation and clustering behavior of precipitates in RE-CLF-1 steel.

Enhancement in hard magnetic properties of nanocrystalline (Ce,Y)–Fe–Si–B alloys due to microstructure evolution caused by chemical heterogeneity

The nano-level chemical heterogeneity due to the Y segregation in RE2Fe14B phase and Ce segregation in REFe2 phase enhance the hard magnetic properties of (Y,Ce)-Fe-B alloys, which offers a potential approach to improve the cost performance of free-RE magnets.

Chemical states of ppm cerium in steel by ToF‐SIMS analysis

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was employed for an analysis of the rare earth element Ce in pure iron and steel. Secondary ion images showed that the amount of the segregation of Ce and its oxides was much less as the concentration of Ce decreased to about 11 ppm in the pure iron. In terms of depth profiling from the surface to the matrix, variation of the CeO+/Ce+ ratio in a Ce oxides sample and a pure Ce sample exhibited difference between oxidized state and metallic state. It was demonstrated that metallic Ce was presented when the ratio of CeO+/Ce+ decreased to approximately 2 and even smaller. Oxygen content with concentration of tens of ppm may influence the ratio obviously. Such ToF‐SIMS analysis was also feasible to discern the states of cerium in a Q345E steel with concentration in ppm level.

Effect of minor rare earth cerium addition on the hot ductility of a reactor pressure vessel steel

The hot ductility of the specimens for a reactor pressure vessel steel (SA508-III), undoped and doped with minor rare earth Ce, is studied through hot tensile tests by means of a Gleeble machine in conjunction with scanning electron microscopy, optical microscopy, and field emission gun scanning transmission electron microscopy. Both the undoped and Ce-doped specimens are heated at 1300 °C and then cooled down to different test temperatures between 650 and 1050 °C, followed by tensile deformation up to fracture. As demonstrated by the results, for the undoped steel, there is a wide and deep hot ductility trough and the bottom of the trough is flat and wide (700–850 °C), being only about 60% in reduction of area (RA). However, for the Ce-doped steel, the hot ductility trough becomes considerably narrower and shallower. In addition, the flat and wide bottom of the trough disappears. Overall, the Ce-doped specimens exhibit a much higher hot ductility than the undoped ones, being over 70%RA at temperatures above 800 °C. Therefore, the minor addition of rare earth Ce can considerably enhance the hot ductility of the steel. It may be expected that this Ce-doped steel will have a high performance in hot working. As shown by microanalysis, the segregation of Ce to austenite grain boundaries occurs, which could play an important role in the enhancement of ductility in the high-temperature single austenite range (above 700 °C). Moreover, the Ce-induced grain refinement may also contribute to the hot ductility improvement.

Lattice Expansion in Optimally Doped Manganese Oxide: An Effective Structural Parameter for Enhanced Thermochemical Water Splitting

Earth abundant transition-metal oxides have attracted broad interest for thermochemical production of renewable fuels and other gaseous commodities. Despite progress, a major challenge remains in achieving fast and reversible redox kinetics as well as large oxygen exchange capacities. Here, we present insights on the optimal doping of manganese oxide nanocrystals for their efficient and stable utilization as redox material for thermochemical water splitting. The detailed investigation of the evolution of the material properties over a broad range of possible Ce-Mn compounds reveals a single key structural parameter affecting the thermochemical performance. We observe that the expansion of the MnO lattice is essential for activating its reduction from oxide to carbide and thus for H2O splitting during its subsequent reoxidation. This is optimally achieved for a very narrow window of dopant concentration peaking at 3% Ce content, which provides the largest distortion of the manganese oxide crystal lattice. In contrast, smaller or higher Ce amounts of 1 and 5%, respectively, result in significantly smaller lattice expansions either due to an insufficient dopant amount or to the segregation of Ce in large CeO2 domains. We use these findings to propose a mechanism for the enhancement of the redox kinetics of this metal oxide, which may provide guidance for the design of a family of future materials for thermochemistry.

Evolution of REFe2 (RE = rare earth) phase in Nd-Ce-Fe-B magnets and resultant Ce segregation

REFe2 (RE = rare earth) phase has been considered to form spontaneously in Nd-Ce-Fe-B cast strips and inherit into sintered magnets. However, here we report that REFe2 phase, which is absent in starting strip, occurs in as-sintered magnet with an identical composition of 25 wt% Ce. More interestingly, the formation of REFe2 induces apparent Ce-enriched shell surrounding RE2Fe14B grain, which is further exacerbated in annealed magnet containing a higher fraction of REFe2 phase. Influences of increasing REFe2 fraction on magnetic performance are revealed. Above findings on REFe2 phase evolution and resultant Ce segregation may shed lights on fabricating high-performance Nd-Ce-Fe-B.

Utilizing a novel modifier to realize multi-refinement and optimized heat treatment of A356 alloy

Al-5Sr-8Ce master alloy was fabricated as a novel modifier, and its effect on the microstructure and tensile properties of A356 alloy was systematically investigated. The solution treatment time was also optimized based on the modification efficiency of Al-5Sr-8Ce. Results showed that Al-5Sr-8Ce mainly comprised α-Al, Al4Sr, and Al11Ce3 phases. With increasing addition of Al-5Sr-8Ce to 0.4 wt%, both the grain size and secondary dendrite arm space (SDAS) were significantly refined, while the eutectic Si morphology was modified from plate-like to small granular and rod-like morphologies. Grain growth inhibition caused by Ce segregation and the formation of Ce containing intermetallic compounds along the grain boundary was mainly responsible for the grain refinement. The excellent modification effect was attributed to the enhanced Sr modification and the inhibited growth of eutectic Si under the action of Ce. The multi-refinement of microstructure by Al-5Sr-8Ce improved the tensile properties of alloy, in particular a significant increase in elongation. However, the excess addition of Al-5Sr-8Ce (>0.4 wt%) increased the formation of coarse Ce containing intermetallic compounds, deteriorating the ultimate strength and elongation of the modified alloy. Based on the excellent Si modification by adding 0.4 wt% Al-5Sr-8Ce, the solution treatment time was successfully shortened to 90 min.

Improvement of hot ductility of C-Mn Steel containing arsenic by rare earth Ce

The effect of different Ce content on the hot ductility of C-Mn steel containing arsenic was investigated at the temperature ranging from 700 to 1100 °C conducting Gleebel-1500 thermal-mechanical simulator. The reduction of area (RA%) was used to evaluate the hot ductility. The 0.16 mass% As widened the ductility trough range and especially, decreased the RA value at 850–950 °C. Conversely, adding Ce in the steel could remedy the arsenic-induced hot ductility deterioration. Moreover, with the increase of Ce content from 0 to 0.035 mass%, the RA value at 800–950 °C significantly increased, compared to that of the arsenic steel. When the content of Ce reached 0.027–0.035 mass%, the RA value at 800–850 °C was even higher than that of steel without As. Besides, the corresponding fracture morphology was changed from intergranular feature to ductile and/or interdendritic feature. Grain refinement by Ce addition, the formation of arsenious rare earth inclusions and grain boundary segregation of Ce were considered to improve the hot ductility of the steel containing As.

Chemical segregation in a 12Ce-ZrO2/3Y-ZrO2 ceramic composite

In restorative dentistry, 3Y-ZrO2 ceramics are widely accepted for fabricating dental crowns, bridges and implants due to their good biocompatibility, excellent mechanical properties and high aesthetics potential. However, they suffer from low temperature degradation (LTD) in the presence of water species, which generates a loss in their surface mechanical integrity. If ceria is used instead of yttria, as in 12Ce-ZrO2, both higher fracture toughness and resistance to LTD are achieved. The composition of solutes inside the grains and at the grain boundaries is essential for understanding their role in LTD. In the present work, a microstructural study by means of wavelength-dispersive spectroscopy, transmission electron microscopy and atom probe tomography has been conducted by investigating the distribution of elements such as Ce, Y, Al and Zr in the solid solution of zirconia that results from mixing 85wt% 12Ce-ZrO2 and 15wt% 3Y-ZrO2 and sintering at two different temperatures, 1450 and 1600°C. It is shown that the solid solution inside the grains after sintering at any of the two temperatures is not homogenous, being closer to the expected equilibrium concentration when sintering at 1600°C. Segregation of Ce, Y and Al to the grain boundaries is also analysed by atom probe tomography showing that the segregations are stronger in the specimens sintered at the higher temperature.