Sm Alloys Research Articles

Hydrogen Storage Performances of REMg11Ni (RE = Sm, Y) Alloys Prepared by Mechanical Milling

This study adopted mechanical milling to prepare Mg-based REMg11Ni (RE = Sm, Y) hydrogen storage alloys. The alloy structures were examined by X-ray diffraction and transmission electron microscopy. The isothermal hydrogenation thermodynamics and kinetics were determined by an automatic Sievert apparatus. The non-isothermal dehydrogenation performance of the alloys was tested by differential scanning calorimetry and thermogravimetry at different heating rates. The results showed a nanocrystalline and amorphous tendency for the alloys. The YMg11Ni alloy exhibited a larger hydrogen absorption capacity, faster hydriding rate, and lower temperature of onset hydrogen desorption than the SmMg11Ni alloy. The hydrogen desorption temperatures of the REMg11Ni (RE = Sm, Y) alloys were 557.6 K and 549.8 K (284.6 °C and 276.8 °C), respectively. The hydrogen desorption property of the RE = Y alloy was found superior to the RE = Sm alloy based on the time required to absorb 3 wt pct H2, i.e., the time needed by the RE = Y alloy was reduced to 1106, 456, 363, and 180 s, respectively, corresponding to the hydrogen desorption temperatures of 593 K, 613 K, 633 K, and 653 K (320 °C, 340 °C, 360 °C, and 380 °C), compared to 1488, 574, 390, and 192 s for the RE = Sm alloy under identical conditions. The dehydrogenation activation energies were 100.31 and 98.01 kJ/mol for the REMg11Ni (RE = Sm, Y) alloys, respectively, which agreed with those of the RE = Y alloy showing a superior hydrogen desorption property.

Electrical conductivity optimization of the Na3AlF6–Al2O3–Sm2O3 molten salts system for Al–Sm intermediate binary alloy production

Metal Sm has been widely used in making Al–Sm magnet alloy materials. Conventional distillation technology to produce Sm has the disadvantages of low productivity, high costs, and pollution generation. The objective of this study was to develop a molten salt electrolyte system to produce Al–Sm alloy directly, with focus on the electrical conductivity and optimal operating conditions to minimize the energy consumption. The continuously varying cell constant (CVCC) technique was used to measure the conductivity for the Na3AlF6–AlF3–LiF–MgF2–Al2O3–Sm2O3 electrolysis medium in the temperature range from 905 to 1055°C. The temperature (t) and the addition of Al2O3 (W(Al2O3)), Sm2O3 (W(Sm2O3)), and a combination of Al2O3 and Sm2O3 into the basic fluoride system were examined with respect to their effects on the conductivity (κ) and activation energy. The experimental results showed that the molten electrolyte conductivity increases with increasing temperature (t) and decreases with the addition of Al2O3 or Sm2O3 or both. We concluded that the optimal operation conditions for Al–Sm intermediate alloy production in the Na3AlF6–AlF3–LiF–MgF2–Al2O3–Sm2O3 system are W(Al2O3) + W(Sm2O3) = 3wt%, W(Al2O3):W(Sm2O3) = 7:3, and a temperature of 965 to 995°C, which results in satisfactory conductivity, low fluoride evaporation losses, and low energy consumption.

Density of Na3AlF6–AlF3–LiF–MgF2–Al2O3–Sm2O3 molten salt melt for Al–Sm alloy

Samarium (Sm) has been widely used in making aluminum (Al)–Sm magnet alloy materials. The research team for this study developed a molten salt electrolyte system which directly produces Al–Sm alloy to replace the energy intensive conventional distillation technology. In this study, molten melt density was measured and operation conditions were optimized to separate Al–Sm alloy product from the fluoride molten melt electrolysis media based on density differences. Archimedes' principle was applied to measure density for the basic molten fluoride system (BMFS: Na3AlF6–AlF3–LiF–MgF2) electrolysis media in the temperature range from 905 to 1055 °C. The impact of temperature (t) and the Al2O3 and Sm2O3 addition ratio (w(Al2O3), w(Sm2O3)) in the basic fluoride system on molten melt density was examined. The fluoride molten melt density relationship was determined to be: ρ = 3.11701 − 0.00802w(Al2O3) + 0.027825w(Sm2O3) − 0.00117t. The test results showed that molten density decreases with increase in temperature and Al2O3 addition ratio, and increases with the addition of Sm2O3, and/or Al2O3 + Sm2O3. The separation of Al–Sm (density 2.3 g/cm3) product melt from the BMFS melt is achieved by controlling the BMFS density to less than 2.0 g/cm3. It is concluded that the optimal operation conditions to control the BMFS molten salt density to less than 2.0 g/cm3 are: maintain addition of Al2O3 + Sm2O3 (w(Al2O3) + w(Sm2O3)) < 9% of Na3AlF6, Al2O3/Sm2O3 ratio (w(Al2O3):w(Sm2O3)) > 7:3, and temperature between 965 and 995 °C.

Effect of dysprosium on the kinetics and structural transformations during the decomposition of the supersaturated solid solution in magnesium–samarium alloys

The effect of dysprosium added in the amounts such that it does not form an individual phase in equilibrium with solid magnesium on the decomposition of the supersaturated magnesium solid solution in Mg–Sm alloys is studied. The presence of dysprosium in Mg–Sm alloys is found to retard the decomposition of the supersaturated magnesium solid solution and to increase the hardening effect upon aging. When these alloys are aged, dysprosium is partly retained in the magnesium solid solution and partly enters into the compositions of the phases that form during the decomposition of the solid solution and are characteristic of Mg–Sm alloys.

Molecular dynamics simulation of the effect of dislocations on the martensitic transformations in a two-dimensional model

MD simulation of direct and reverse MT in the framework of the 2D model of an ordered alloy shows that dislocations can be considered as the nucleation centers of martensite during direct MT. In the absence of dislocations, martensite nucleates homogeneously at lower temperatures. The reverse MT occurs in the presence of twinned martensite and domain walls in the system, which means that even in the absence of dislocations, the structure of the alloy is not ideal. During the reverse MT, the perfect dislocations split into partial dislocations. It should be noted that for selected model parameters MT is associated with large lattices deformations, therefore, temperature hysteresis is also large, which is not typical for SM alloys. However, the consideration of the Acta Mater. 95, 37 (2015). effects of SM and superelasticity is not prohibited in frame of 14. C. Ni, H. Ding, XJ.. Jin. J. Alloys Compd. 546, 1 (2013). this model, since the degree of coherence of the martensite 15. S. Kazanc, FA. . Celik, S. Ozgen. J. Phys. Chem. Solids. 74, and austenite lattices is quite high. One of the important 1836 (2013). problems for futher investigations is the studying of the MT 16. T. Suzuki, M. Shimno, K. Otsuka, X. Ren, A. Saxena. as the detonation process [36]. J. Alloys Compd. 577S, S113 (2013). 17. B. Wang, E. Sak-Saracino, N. Gunkelmann, Aknowledgements. S.V. D. acknowledges support from the H.M. Urbassek. Comp. Mater. Sci. 82, 399 (2014). Russian Foundation for Basic Research, grant No. 16-58-48001 18. C. Tatar, S. Kazanc. Current Applied Physics. 12, 98 IND_omi (design of the research, discussion of the results). (2012). J.A. B and V.G. P. are grateful for the financial support from 19. A.R. Kuznetsov, Yu.N. Gornostyrev, M.I. Katsnelson, the Russian Science Foundation, grant No. 15-12-10014 A. V. Trefilov. Mater. Sci Eng. A309–311068 (2001). (numerical simulations and writing the paper). R.I. B. thanks 20. I.N. Kar’kin, Yu.N. Gornostyrev, L.E. Kar’kina. Phys. financial support from the Russian Science Foundation, grant Solid State. 52, 431 (2010). No. 17-79-10410 (numerical simulations). The work of D. V. G. 21. Y. N. Gornostyrev, IN. . Kar’kin, LE. . Kar’kina. Phys. Solid was supported by the Saint-Petersburg State University, State. 53, 1388 (2011). research grant No. 6.65.43.2017 (discussion of the results). 22. J.A. Baimova, R.I. Babicheva, A.V. Lukyanov, V.G. Pushin,

The origin of high magnetic properties in (R,Zr)(Fe,Co)11.0–11.5Ti1.0–0.5Ny (y=1.0–1.4 for R=Nd, y=0 for R=Sm) compounds

Ten alloys and nitrogenated compounds of (R,Zr)(Fe,Co)11.0–11.5Ti1.0–0.5Ny (y=1.0–1.4 for R=Nd, y=0 for R=Sm) with a ThMn12-type structure were prepared. The average Fe–Fe interatomic distances, d(Fe–Fe), for Fe sites were calculated based on the reported atomic parameters. The hyperfine splittings (inner field (IF), in teslas) were measured by Mössbauer spectroscopy, and the IF increased with increasing d(Fe–Fe) for Fe sites, indicating a magneto-volume effect. The order of IF magnitude in Fe sites was Fe(8i)>Fe(8j)>Fe(8f) in all alloys. Co substitution for Fe sites, (Fe0.75Co0.25), increased the IF by 25% for the R=Nd alloy and 15% for the R=Sm alloy. Decreasing Ti content from −Ti1.0 to −Ti0.5, which increased the Fe and Co content, preserved the ThMn12 structure with Zr substitution for R(2a) sites, and caused a slight increase in the IF of 2% for the R=Nd alloy and 7% for the R=Sm alloy. Nitrogenation, where N was introduced into the 2b sites, also increased IF in R=Nd alloys, by 23% for the Co- and Zr-free alloys, NdFe11Ti1.0N1.5, and by 7% for the Co-containing, (Nd0.7Zr0.3) (Fe0.75Co0.25) 11.5Ti0.5N1.3 alloy. The IF values of the R=Nd alloys were slightly larger than those of the R=Sm alloys. In conclusion, the magneto-volume effect was clearly observed at the Fe sites, and Co substitution into Fe sites and nitrogenation (R=Nd alloys) compensated for the increased IF. Increasing the Fe and Co fractions also increased IF slightly.

The stability of newly developed (R,Zr)(Fe,Co)12−xTix alloys for permanent magnets

(R,Zr)(Fe,Co)12−xTix (R = Nd and Sm) alloys of ten different compositions were prepared by strip-casting. The elemental distribution of the sample particles after annealing was quite homogeneous. Existing phases in the prepared alloys were determined by X-ray diffraction and the occupation sites of the substituted elements (Ti, Co, and Zr) were determined using spherical aberration corrected scanning transmission electron microscopy. The ThMn12 structure is stable in Ti1.0 compounds for both R = Nd and Sm, but exhibited obvious precipitation of α-(Fe,Co) phases in low Ti content compounds with Ti0.5. Ti substitution into Fe(8i) sites is important for the stabilization of the ThMn12 structure. Furthermore, the stability of low Ti content compounds could be recovered by the substitution of Zr into R(2a) sites. Co was mainly in Fe(8j) and Fe(8f) sites, which contributed to the stability of the 1–12 structure by increasing the configuration entropy. Analysis based on three Fe hexagons and two local sub-structural units suggested that the stabilization of ThMn12 structure by Ti and Zr substitutions mainly originates by resolving local mismatches in interatomic distances in the structure.

ChemInform Abstract: Structure and Permanent Magnet Properties of Zr1‐xRxFe10Si2 Alloys with R: Y, La, Ce, Pr and Sm.

Abstract(Zr0.7Ln0.3) 1.1Fe10Si2 (Ln: Y, Ce, Pr, Sm) alloys are prepared by arc melting and subsequent melt spinning.

Effect of Ca addition on the microstructure and mechanical properties of as-cast Mg-Sm alloys.

This study investigated the effect of Ca addition on the microstructure and mechanical properties of as-cast Mg-4Sm alloys. The addition of 1.0 wt% Ca led to a significant grain refinement of Mg-4.0Sm alloys owing to the formation of rod-like Mg2Ca phases that acted as active nucleates for the Mg matrix. The as-cast Mg-4.0Sm-1.0Ca alloy showed the smallest grain size at 45 μm. Furthermore, the Mg-4.0Sm-1.0Ca alloy exhibited greater hardness, higher tensile strength, and higher yield tensile strength and elongation than the other two alloys with different Ca contents. These results were attributed to the grain refinement and precipitation strengthening of the Mg2Ca and Mg41Sm5 phases. Microsc. Res. Tech. 79:707-711, 2016. © 2016 Wiley Periodicals, Inc.

Structure and thermoelectric performance of β-Cu2Se doped with Fe, Ni, Mn, In, Zn or Sm

Cu1.99A0.01Se (A = Fe, Ni, Mn, In, Zn or Sm) alloys with high thermoelectric performance were prepared through a conventional melting, ball milling and quenching route, followed by a spark plasma sintering technique. Elemental doping did not change the structure type of Cu2Se. All the samples showed p-type conduction. All the doping elements except Indium reduced the electric resistivity and modified the carrier concentration, leading to a significant increase in the power factor. The lattice distortion and point defects due to the substitution of Cu became new phonon scattering centers, leading to a significant decrease in thermal conductivity. All the samples except the In-doped sample obtained better thermoelectric properties compared with the undoped Cu2Se sample. The values of the figure of merit ZT of the samples doped with Zn, Mn, Ni, Fe and Sm were 1.25, 1.28, 1.51, 1.07 and 1.07 at 823 K, respectively. In Cu2−xNixSe system, High ZT value of 1.51 is obtained for the sample of x = 0.0075 and 0.010 at 823 K.

Effects of ultrasonic vibration on microstructure evolution and elevated-temperature mechanical properties of hot-extruded Mg-6Al-0.8Zn-2.0Sm wrought magnesium alloys

The effects of ultrasonic vibration on microstructure evolution and elevated-temperature mechanical properties of hot-extruded Mg-6Al-0.8Zn-2.0Sm wrought magnesium alloys have been investigated. The results show that morphology of relatively coarser Al2Sm phases in the alloy exhibit petal-shaped. However, after being treated by ultrasonic vibration, the Al2Sm phase morphology changes to fine particles. The ultimate tensile strength of the ultrasonic treated Mg-6Al-0.8Zn-2.0Sm alloy at 150 °C has a highest value of 298 MPa and elongation of 20.8%. The maximum pressure caused by transient cavitation is far greater than the shear strength of the Al2Sm phase, which makes the coarse petal-shaped Al2Sm phase break apart into fine polygon particles. Acoustic streaming than makes the broken polygonal Al2Sm particles smooth and uniformly disperse.

Precipitation in Mg-Sm binary alloy during isothermal ageing: atomic-scale insights from scanning transmission electron microscopy

The paper reports on an atomic-scale investigation into the precipitation hardening process in Mg-2.5Sm(wt%) alloy, using advanced Cs-corrected high angle annular dark field – scanning transmission electron microscopy (HAADF-STEM). Various novel precipitate structures existing in different ageing conditions are identified and discussed in depth. In the under-aged sample, three nucleation mechanisms are observed: βL, βH and β′, which are uniformly-scattered atomic-size rare earth clusters, displaying a significant strengthening effect in a very short ageing time of 30min. In the peak-aged sample, the main strengthening structures are needle-like precipitates composed of zigzag line repetitive units and hexagonal repetitive units. In the over-aged sample, the needle-like precipitates grow coarse and a subset of the precipitates transform into β1 precipitates, both of which are detrimental to the mechanical properties. From an engineering perspective, it is of great interest to design advanced Mg-RE materials with the uniformly-scattered atomic-size rare earth clusters, because they are effective strengthening structures requiring short ageing time. In the second place, the paper reveals three types of transformation processes occurring during the precipitation: the transformation between βL precipitates and needle-like precipitates, the transformation within needle-like precipitates along [0001]Mg and the transformation between needle-like precipitates and β1 precipitates. The RE atoms remain coherent with the α-Mg matrix before they transform into β1 precipitates.

Preparation and photoluminescence properties of Sm3+-doped ZrO2 nanotube arrays

Zr–Sm (3 at.% Sm) alloy was prepared through a powder metallurgical method. Sm3+-doped ZrO2 nanotube arrays have been achieved directly by anodizing the Zr–Sm alloy. The effects of electrolyte and annealing temperature on the morphologies and structures of the nanotube arrays were studied. The photoluminescence properties of Sm3+-doped ZrO2 nanotube arrays prepared in aqueous solution and formamide + glycerol solution were studied in detail as well. Results show that tetragonal ZrO2 promoted the photoluminescence efficiency of this system. Under excitation at 407 nm, the sample prepared in aqueous solution annealed at 600 °C displayed the strongest emission peak at 571 nm, corresponding to the 4G5/2 → 6H5/2 samarium transition.

On grain coarsening and refining of the Mg–3Al alloy by Sm

The effect of Sm on the microstructure of a Mg–3Al alloy has been investigated where it was found that the size of the primary α-Mg grains was significantly coarsened by the addition of 0.7 wt. % Sm, but dramatically refined by 2.1 wt. % Sm. It is proposed that the coarsening effect of Sm is due to a decrease in the nucleation potency of the native Al–Fe–C–O particles when they transform to the lower potency Al–Fe–Sm–C–O particles. The grain refinement observed when 2.1 wt. % Sm is added, is caused by the formation of potent Al2Sm nucleant particles prior to the solidification of α-Mg. The “Interdependence Theory” was then applied to describe the nucleant selection process in the Mg–3Al–2.1Sm alloy.

Electrochemical corrosion behavior of Pb–Ca–Sn–Sm grid alloy in H2SO4 solution

The electrochemical corrosion behavior of Pb-0.23 wt.% Ca-0.93 wt.% Sn and Pb-0.23 wt.% Ca-0.92 wt.% Sn-0.18 wt.% Sm alloys in 4.8 M H2SO4 at 25 °C was studied using open circuit potential (OCP), cyclic polarization, electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV) and Mott–Schottky plot. The findings of this study show that the samarium added to Pb–Ca–Sn alloy increases the general corrosion resistance of this alloy and inhibits the growth of the anodic corrosion layer, it can promote the pitting corrosion tendency of Pb–Ca–Sn alloy. Mott–Schottky plot also reveals that the anodic films on Pb–Ca–Sn and Pb–Ca–Sn–Sm alloys at +1.5 V vs. SCE exhibit an n-type semi-conductive character. Sm increases the slope of Mott–Schottky plot, implying the reduction of the defect density within the anodic film, which is beneficial to increase the resistance of anodic film.

Thermal crystallization of an Al88Ni6Sm6 metallic glass

This work essentially deals with the first stages of crystallization of melt spun Al1−(x+y)NixSmy metallic glasses. Specific emphasis is given to the microstructural and kinetics aspects of primary crystallization because of the high specific strength of this class of materials in the partially crystallized state. The nanometric size of the crystalline particles is measured either by direct transmission electron microscopy or by indirect X-ray diffractometry. The Kissinger model as well as the Friedman model free method is used to estimate the local activation energies and the results obtained with both kinds of approaches are compared. A sustained attention is also paid to the nature of the crystallization phenomenon at the origin of the second exothermic peak in differential scanning calorimetry. This result is indeed the subject of controversy in the literature data concerned by Al–Ni–Sm alloys.

Electrochemical preparation of Al–Sm intermetallic compound whisker in LiCl–KCl Eutectic Melts

This work presents the electrochemical study of Sm(III) on an aluminum electrode in LiCl–KCl melts at 773K by different electrochemical methods. Three electrochemical signals in cyclic voltammetry, square wave voltammetry, open circuit chronopotentiometry, and cathode polarization curve are attributed to different kinds of Al–Sm intermetallic compounds, Al2Sm, Al3Sm, and Al4Sm, respectively. Al–Sm alloy with different phase structure (Al2Sm and Al3Sm) could be obtained by the potentiostatic electrolysis with the change of electrolytic potentials and time. Al–Sm alloy containing whiskers (Al4Sm) was obtained by potentiostatic electrolysis (−2.10V) on an aluminum electrode for 7hours with the change of electrolytic temperature and cooling rate in LiCl–KCl–SmCl3 (16.5wt. %) melts. The XRD and SEM&EDS were employed to investigate the phase composition and microstructure of Al–Sm alloy. SEM analysis shows that lots of needle−like precipitates formed in Al–Sm alloy, and their ratios of length to diameter are found to be greater than 10 to 1. The TEM and electron diffraction pattern were performed to investigate the crystal structure of the needle–like precipitates. The results show that the needle−like precipitates are intermetallic compound whiskers. The micro–hardness test and potentiodynamic polarization test illustrate that the micro–hardness and corrosion property of Al–Sm alloy containing whiskers are remarkably improved in comparison with the Al–Sm alloy without whiskers, respectively.

Enhancement of hydrogen evolution in alkaline water electrolysis by using nickel-rare earth alloys

Nickel–dysprosium (Ni–Dy) and nickel–samarium (Ni–Sm) alloys with 5 and 10 at% of rare earth metal were prepared by arc melting and by induction furnace melting, respectively. The alloys microstructure, morphology and chemical composition were inspected by scanning electron microscopy and energy dispersive X-ray analysis; phases crystal structure and lattice parameters were confirmed by X-ray diffraction analysis. The alloys were used for fabrication of electrodes for hydrogen evolution reaction (HER) in alkaline media and studied using polarisation measurements. Tafel analysis suggests that HER is limited by the Volmer step at all four electrodes. Determined kinetic parameters indicate better electrocatalytic performance for HER of Ni-RE alloys with 5 at% of RE compared to those with 10 at% of RE. Activation energies were evaluated to be in the 47–71 kJ mol−1 range.

Microstructures and mechanical properties of Mg–Al–Sm series heat-resistant magnesium alloys

The microstructures and phase compositions of the as-cast and die-cast Mg–6.02Al–1.03Sm, Mg–6.05Al–0.98Sm–0.56Bi and Mg–5.95Al–1.01Sm–0.57Zn alloys were investigated. Meanwhile, the tensile mechanical and flow properties were tested. The results show that the as-cast microstructure of Mg–6.02Al–1.03Sm alloy is composed of α-Mg matrix, discontinuous β-Mg17Al12 phase and small block Al2Sm phase with high thermal stability. Rod Mg3Bi2 phase precipitates when Bi is added, while the added metal Zn dissolves into α-Mg matrix and β-Mg17Al12 phase. The as-cast alloys exhibit the excellent tensile mechanical property. The tensile strength (σb) and elongation (Δ) can reach 205–235 MPa and 8.5%–16.0% at ambient temperature, respectively. Meanwhile, they can also exceed 160 MPa and 14.0% at 423 K, respectively. The die-cast microstructures are refined obviously, and meanwhile the broken second phases distribute dispersedly. The die-cast alloys exhibit better tensile mechanical properties with the values of σb and Δ of 240–285 MPa and 8.5%–16.5% at ambient temperature, respectively, and excellent flow property with the flow length of 1870–2420 mm. The die-cast tensile fractures at ambient temperature exhibit a typical character of ductile fracture.

Study on formation and properties of Al–Li–Sm alloy containing whiskers in molten salts

An Al–Li–Sm alloy containing whiskers was obtained by galvanostatic electrolysis in LiCl–KCl melts after the addition of 10 wt% SmCl3 on a liquid aluminum electrode at 973 K.