RE Content Research Articles

Influences of complex modification of P and RE on microstructure and mechanical properties of hypereutectic Al-20Si alloy

P and RE complex modification of hypereutectic Al-Si alloys was conducted. The influences of P, RE content on the microstructure and mechanical properties of alloys were investigated. The complex modifications of P and RE make the coarse block primary silicon obviously refined and the large needle eutectic silicon modified to the fine fibrous or lamella ones. P mainly refines the primary silicon, but excess P is unfavorable to the refinement of primary silicon. RE can well refine the primary and eutectic silicon, but its modification effect on the eutectic silicon is more obvious. P can repress the modification of RE on the eutectic silicon. The alloys with the additions of 0.08% P and 0.60% RE have the optimal microstructure and the highest mechanical properties. Compared with the unmodified alloy, the primary silicon of alloys can be refined from 66.4 μm to 23.3 μm and the eutectic silicon can be refined from 8.3 μm to 5.2 μm. The tensile strength is improved from 256 MPa to 306 MPa and the elongation is improved from 0.35% to 0.48%.

Effect of RE Elements and Ni Contents on the Microstructure and Mechanical Properties of Rapidly Solidified Mg Ribbons

The effect of the concentration of Ni, Y and La-rich mischmetal on the thermal stability, microstructure and mechanical properties of ribbons tested in the temperature range 25-350°C have been evaluated. The low-alloyed materials were crystalline or partially crystalline while high-alloyed materials were amorphous. The amorphous alloys experienced numerous transformations during heating above 170°C. A transition in the amorphous state was observed in all alloys prior to the crystallization stage. The alloy composition determines the sequence of phase transformations during crystallization. In general, the structure of crystallised amorphous, even at high temperatures, is much finer than that of crystalline materials. A MgxREy intermetallic matrix with other intermetallic phases homogeneously distributed was observed in the crystallised ribbons with high RE contents. However, a magnesium matrix embedding other intermetallic phases was the microstructure observed for low-alloyed materials. The amorphous Mg-10Ni-2.5Y2.5-2.5La(MM) showed the higher tensile strength values up to 200 °C The crystalline Mg-2Ni-1Y-1La(MM) ribbon and the partially crystalline Mg-3Ni-1.5Y-1.5La(MM) alloy also exhibited high mechanical resistance levels which were maintained up to 250 °C. MgNi10Y2.5La(MM)2.5 amorphous and MgNi3Y1.5La(MM)1.5 crystalline broken above 500 and 400 MPa, respectively, at 100°C

Characterization and magnetic properties of Sm- and Gd-substituted CoFe 2O 4 nanoparticles prepared by forced hydrolysis in polyol

Pure nanoparticles of the CoFe 2− x RE x O 4 (RE = Gd, Sm; x = 0.0, 0.1) system have been prepared by forced hydrolysis in polyol. The insertion of Sm 3+ and Gd 3+ cations into the cobalt ferrite structure has been investigated. X-ray micro-analysis (EDX) shows that the RE contents are close to the nominal ones. X-ray diffraction (XRD) evidences a cell size increase with slight distortions in the spinel-like lattice indicating the entrance of RE 3+ ions. Micro-Raman spectroscopy confirms the cubic inverse-spinel structure and rules out the existence of impurities like hematite. Magnetic measurements (SQUID) show important differences in the magnetic properties of the unsubstituted and substituted particles. All the particles are superparamagnetic at room temperature and ferrimagnetic at low temperature. However, their main magnetic characteristics appear to be directly dependent on the RE content.

Creep and Corrosion Properties of the Extruded Magnesium Alloy Containing Rare Earth

Effects of microstructures on the creep and corrosion properties were investigated in the Mg-8A1 alloys with addition of the rare earth elements (La-rich Mischmetal, RE). The addition of RE to Mg-8A1 alloy may form a stable intermetallic phase, Al 11 RE 3 at elevated temperature, and suppress the βhase (Mg 17 Alj 2 ) with poor stability at high temperature. The corrosion rate of the alloy slightly decreases with increasing the added RE contents. The constant-load creep behavior was examined at 423, 448 and 473 K under stresses between 40 and 100MPa. The RE-containing alloy showed a prolonged period of stead-state creep compared to the Mg-8Al base alloy and slightly reduced minimum creep rates. A stress exponent of 2 estimated suggests that the creep behavior can be controlled by the grain boundary sliding. The apparent activation energy for creep of Mg-8Al and Mg-8Al-2RE alloys are 114 and 104 kJ mol -1 , respectively.

Influence of Cerium and Yttrium on Cu-Cr-Zr Alloys

Testing results shows that alloying with Ce and Y improves the hardness and softens temperature of cold worked Cu-Cr-Zr alloys obviously, while the conductivity was fluctuant with the variation of RE content. Observation and analysis indicate that micro-dosage RE elements helps to refine microstructure and morphology of Cu-Cr-Zr-RE alloys, suppress microstructure coarsening and improves homogeneous level of Cu-Cr-Zr alloys. Alloying with 0.01% Ce causes about 1% IACS increment of conductivity, and reduces about 2 % ∼ 3.5% IACS conductivity after alloying with 0.03 % ∼ 0.04 % RE (Ce or Ce + Y) for Cu-Cr-Zr alloys. The microstructure of as-cast Cu-Cr-Zr alloy is refined after alloying with 0.01% Ce while the plasticity is improved slightly. Alloying with 0.01% ∼ 0.04% RE improves the softening temperature of deformed Cu-Cr-Zr alloys about 20 ∼ 40 K; hardness is also improved about 20 ∼ 35 HV. Test data indicate that alloying with Ce + Y raises softening temperature and hardness of Cu-Cr-Zr alloys more notably than alloying with pure Ce.

Comparison of superconducting properties of Ce added (Bi, Pb)-2212 with other rare earth additions

We have studied the effect of Ce addition on the superconducting properties of (Bi, Pb)-2212 and compared these properties with some of the important other rare earth (RE: La, Pr, Gd, Sm and Yb) additions in the system. The RE content was varied on a general stoichiometry of Bi 1.7Pb 0.4Sr 2.0Ca 1.1Cu 2.1RE x O y . The samples were characterized by powder X-ray diffraction, SEM, R– T measurements and transport J C measurements at 64 K. It is known that addition of RE in general enhances the superconducting properties of (Bi, Pb)-2212 such as T C and J C. But in the case of Ce the maximum T C and J C are obtained at x = 0.1, a lower level comparing with those of the other REs for which the optimum concentration is x ≥ 0.2. The metal insulator (MI) transition also occurs at a lower concentration ( x = 0.3) than the other rare earths, where it occurs at x > 0.5. The maximum values of T C and J C obtained in Ce addition are also lesser comparing with the other RE additions. These changes in the case of Ce addition comparing with the other REs are due to the tetravalent state of Ce in (Bi, Pb)-2212, whereas other REs are at trivalent state, and hence each Ce 4+ substitution in place of Ca 2+ and/or Sr 2+ supplies more electrons in comparison with the other rare earths. Thus, in the case of Ce addition, the optimum carrier concentration of the system for maximum T C and J C attains at a lower level of addition than the other REs.

Creep Behavior of Extruded Sheets of Magnesium Alloys Containing La-Rich Mischmetal

In this study, the effect of RE content on the microstructure and creep properties of Mg-SAl-xRE (x = 0, 1, 2 or 3 mass%) alloys were investigated. The microstructural analysis and phase characterizations of Mg-8Al alloy with 1-3 mass% RE (La-rich Mischmetal) additions were conducted. (i) The as-extruded Mg-8Al-xRE alloys consisted of an α-Mg matrix, β(Mg 17 Al 12 ) and Al 11 RE 3 compounds. (ii) Raising the extent of RE in the alloy also increases the amount and coarsening of the Al 11 RE 3 compounds, but the amount of β phase diminishes and turns into the fine particles. The creep rupture life increment measured at 423 K is around 40-100 MPa, and the creep rupture life over 423 K is also prolonged. The marked improvement in high-temperature tensile creep properties is attributed to the fine rod-like A 11 RE 3 compound having high thermal stability in the alloys.

Effect of rare earth elements' surface treatment on tensile properties and microstructure of glass fiber-reinforced polytetrafluoroethylene composites

Three types of surface modifiers, N-β-aminoethyl-γ-aminopropyltrimethoxysilane coupling agent (SGS), a mixture of silane and rare earth elements (SGS/RES), and rare earth elements surface modifier (RES), were used to treat the glass fiber surface. Tensile tests of glass fiber–reinforced polytetrafluoroethylene (GF/PTFE) composites with different surface treatment conditions, surface modifiers, and glass fiber content were carried out. Finally, the fracture surface morphologies of GF/PTFE composites were investigated using scanning electron microscopy. Experimental results show that the tensile properties of the treated GF/PTFE composite increased compared with those of the untreated one. RES is superior to SGS/RES and SGS modifiers in promoting interfacial adhesion between the glass fiber and PTFE because of the effects of rare earth elements on the compatibility. Meanwhile, the optimum contents of rare earth elements for the improvement of the tensile properties of GF/PTFE composite were obtained for RES and SGS/RES modifiers. The interfacial adhesion of the GF/PTFE composites treated with RES or SGS/RES modifiers was mainly controlled by the contents of rare earth elements. The tensile properties of the GF/PTFE composites improved considerably when the content of rare earth elements in surface modifiers was 0.2–0.4 wt %, and the optimum tensile performance of GF/PTFE composites was obtained at 0.3 wt % RE content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1667–1672, 2002

Investigation of icosahedral phases in the Zn-Mg-(Y, Er) system by high resolution transmission electron microscopy

Icosahedral phases in Zn-Mg-RE(RE=Er, Y) alloys have been studied by high resolution transmission electron microscopy (HRTEM) and electron diffraction for different RE contents. From the electron diffraction patterns along the twofold axis, for Zn60Mg30+xY10−x a face centered icosahedral structure was found with x=0 whereas crystals with x in the range of 4 display a simple icosahedral structure. In the system with RE=Er a cubic approximant of the icosahedral quasicrystalline phase, the so-called ‘R-phase’, was found. The R-phase crystallizes in the space group F4̄3m with a0=2.02nm. The close relation between the R-phase and the icosahedral quasicrystal is shown by HRTEM imaging.

Structural studies on single crystals of Chevrel phase selenides REMo6Se8 (RE = La, Ce, Pr, Nd, or Sm) at 298 K.

We report on structural studies at room temperature of rare-earth based Chevrel phase selenides of the formula RExMo6Se8, where RE stands for a light rare-earth La (1), Ce (2), Pr (3), Nd (4), or Sm (5). The single crystals were grown at 1650 degrees C < T < 1690 degrees C from off-stoichiometric starting compositions, with the exception of 3, which was grown at 1710 degrees C from a stoichiometric charge (congruently melting material). The crystal structures were solved in space group R3 (No. 148; Z = 1) and found to be isostructural with the well-known Chevrel phases having large cations (e.g., PbMo6S8, REMo6S8). The structures are based on Mo6Se8 metallic clusters that are slightly rotated inside a pseudocubic rare-earth sublattice. Structural refinements revealed that the origin site, occupied by the RE atoms, exhibits slight deficiencies, leading to a RExMo6Se8 composition, with x ranging between approximately 0.82 and approximately 0.92: 1 La0.88Mo6Se8, arh = 6.7577(9) A, alpha rh = 88.62(2) degrees; 2a Ce0.82Mo6Se8, arh = 6.7407(6) A, alpha rh = 88.83(2) degrees; 2b Ce0.92Mo6Se8, arh = 6.7473(9) A, alpha rh = 88.69(2) degrees; 3 Pr0.86Mo6Se8, arh = 6.7385(6) A, alpha rh = 88.81(2) degrees; 4 Nd0.85Mo6Se8, arh = 6.7286(5) A, alpha rh = 88.85(1) degrees; and 5 Sm0.87Mo6Se8, arh = 6.7182(2) A, alpha rh = 88.956(3) degrees. All of the structural data presented in this work (lattice constants, positional parameters and interatomic distances) concern an average RE content of x approximately 0.87. In this way, any influence due to electronic effects (VEC number) can be discarded, and exact correlations between these parameters and the ionic radius of the rare-earth atoms can then be established.

Mechanical relaxation processes of hydrogen in dilute palladium-rare earth alloys

After charging with hydrogen, dilute Pd 100 − x RE x alloys (RE=Y, Ce, Gd) ( x = 1 … 9) show three thermally activated relaxation maxima of the internal friction between 10 and 300 K. Two of these maxima are identified as a Zener maximum of hydrogen pairs in the β-phase and as a Snoek-Köster maximum, which are both also observed in H-charged pure Pd. The third maximum appears only in the binary alloys. The activation parameters of this relaxation are τ 0 = 3·10 −12±0.5 s for me pre-exponential factor and the activation enthalpy lies between H a = 0.18 eV and H a = 0.26 eV. H a increases with increasing RE content whereas it decreases with increasing hydrogen content. The relaxation strength is independent of the RE content and depends linearly on the hydrogen concentration. These features are characteristic for the formation and reorientation of HRE (RE=Y, Ce, Gd) complexes. Furthermore, the shape factor of the strain ellipsoid of the HRE dipoles, which characterizes the anistropy and strength of the local atomic displacements, was determined as | λ 1– λ 2|=0.036.

Defects in lattices of (Fe1–xCox)17RE2compounds (RE = Gd and Tb)

Constitutional studies on certain Fe-RE, Co-RE, and Fe-Co-RE (RE = Gd and Tb) alloys showed that the intermetallic compounds having the stoichiometry (Fe1–xCox)17RE2 exhibited deviation from their ideal stoichiometric compositions. The deviation varied as the value of x changed from 0 to 1. To establish the cause of this deviation, theoretical densities for different defect structures were compared with the experimental densities of these compounds. The experimental data were in good agreement with the theoretical densities calculated on the basis of the assumption that there are vacant TM (TM =Fe, Co, or Fe + Co) sites in the lattices of these compounds. These vacant TM sites shift the composition of the respective compounds towards a higher RE content. The number of vacant TM sites was a function of x, e.g. the number of vacant TM sites varied from 1.8% in Fe17Gd2 to 6.9% in (Fe0.15Co0.85)17Gd2 in the TM-Gd compounds, whereas in the TM-Tb compounds the variation was from 1.8% for Fe17Tb2 to 5.8% for (Fe0.23Co0.77)17Tb2 and Co17Tb2.

Mixing Y(RE)BCO (RE=Nd, Sm) superconductors by crystal pulling method

Y1−xRExBa2Cu3O7−δ [Y(RE)BCO or REsBCO] superconductors were prepared by the crystal pulling method. The RE mixing content x in the crystal can be effectively controlled by the processing temperature. With an increase in processing temperature, the RE concentration in the liquid increased, which resulted in the higher RE substitution content in single crystals. The higher critical temperatures Tc above 92 K could be obtained by an optimized oxygenation treatment. The Tc value of Y(RE)BCO tends to be insensitive to the growth atmosphere of the oxygen partial pressure under a certain limit of the RE content. The Y.727Nd.273Ba2Cu3O7−δ and the Y.941Sm.059Ba2Cu3O7−δ samples show values of the critical current density Jc are about 2×104 Acm−2 at 1.2 T and 2.8×104 Acm−2 at 1.1 T for H//c, respectively, indicating that mixing REs 123 have obvious effects on Jc–H curves since RE ions are likely to substitute at both Y2+ and Ba2+ sites.

Diatomic Hydrogen-Metal Complexes in Dilute Palladium-Rare Earth Alloys

The internal friction of hydrogen-doped dilute Pd 100 - x RE x alloys (RE = Gd, Ce) (x = 1...9) shows three maxima in the temperature range between 10 K and 300 K. These maxima are interpreted as Zener peak of hydrogen in the β-phase (H a = 0.11 eV), Snoek-Koster peak (H a = 0.18 eV) and reorientation peak of diatomic H-RE complexes. The relaxation strength of the latter peak is independent of the RE concentration and depends linearly on the hydrogen content. A value of |λ 1 -λ 2 | = 0.036 for the elastic anisotropy of the H-RE complexes is obtained. In alloys with RE = Gd this peak saturates when the hydrogen content is comparable with the RE concentration, whereas in the case of RE = Ce saturation at much lower hydrogen contents is observed. The activation enthalpy H a of the H-RE reorientation varies with the RE as well as with the H concentration and lies between 0.18 eV and 0.26 eV. The activation enthalpy and the width of the peak increase with increasing RE content. Increasing the H content leads to a decrease of H a . These features of the reorientation of diatomic H-RE complexes are discussed in terms of a distribution of site enthalpies caused by elastic long-range interaction between a H-RE complex and further RE atoms in its vicinity.

Induced and local anisotropies in amorphous CoZr–rare earth thin films containing Pr, Nd, and Tb

The induced in-plane and local magnetic anisotropies of rf sputtered (Co93Zr7)100−xREx thin films were investigated as a function of RE content for RE=Pr, Nd, and Tb by transverse biased initial susceptibility measurements at both film/air and glass/film interfaces. The deposition was performed in a magnetic field. The films exhibit a very well defined in-plane anisotropy with negligible long-range fluctuations and a small coercive field Hc, in accordance with the experimental data. The overall variations of the transverse susceptibility are related to the ripple. The variations of the local anisotropy with composition were measured. Both the induced anisotropy Ku and the local anisotropy Kloc increase with the increasing amount of RE in the layers. A clear relationship between Ku and Kloc could be established. The results are discussed in terms of the single-ion anisotropy of the rare earth. While the value of Ku is the same at both interfaces, the ripple constants were found to be slightly different. This last result is believed to be related to some local defects, the origin of which is also suggested. Also the coercive force is discussed and explained in terms of a theoretical model.

On the localized resonance mode in amorphous thin films: experimental observations

The overall properties of a new type of resonance mode specific to amorphous thin films are reported. This resonance mode was observed at 9.8 GHz — apart from the uniform mode — on a-Co 93− x Zr 7(RE) x thin films where RE = Nd, Pr, Tb or Dy and for low RE content i.e. 0 < x ≤ 4. The films exhibit a well defined in-plane uniaxial anisotropy field. For perpendicular orientation a single new resonance mode is observed with a resonance field H r ⪡ 4 πM s, while for parallel orientation a series of irregularly spaced modes are detected for fairly high applied fields. It is proposed that it could correspond to localized resonance related to the highly anisotropic local sites.

Crystal growth and characterization of RE-substituted Bi-Sr-Ca-Cu-O superconductors (RE = Y, Er, Yb)

Crystals of RE-substituted Bi-Sr-Ca-Cu-O (2212) superconductors (RE = Y, Er, Yb) were grown by a modified self-flux growth technique. A two-stage process with preliminary melt quenching was used to prepare well-defined platelet crystals with thicknesses of up to 5–20 μm. The mechanism of crystallization in sealed cavities is considered. The RE-substituted crystals show a decrease of T c with increase of RE content in crystals up to the loss of superconducting properties at a complete substitution Ca → RE(Y). The superconducting properties of Bi 2Sr 2Ga 1- x RE x Cu 2O y crystals are improved after air annealing at 750°C.

Correlations between the in-plane uniaxial anisotropy and magnetostriction in amorphous (Co/sub 93/Zr/sub 7/)/sub 100-x/(RE)/sub x/ thin films

The coherent anisotropy and the magnetostriction constants /spl lambda//sub s/ were studied in amorphous RF sputtered (Co/sub 93/Zr/sub 7/)/sub 100-x/(RE)/sub x/ (RE=rare earth) thin films for a large variety of magnetic rare earth, and the concentration range 0/spl les/x/spl les/3. During the deposition magnetic field of 700 Oe was applied in the film plane. For RE=Nd, Pr, Dy and Tb substitutions, a well defined in-plane uniaxial anisotropy is formed. K/sub u/ and /spl lambda//sub s/ both increase linearly with increasing RE content, the absolute values being related to the substitutional RE element. The magnitude of K/sub u/ correlates nicely with that of /spl lambda//sub s/, in agreement with a theoretical computation based on a single-ion anisotropy model for rare-earth atoms. When RE=Sm a more heterogeneous local magnetic structure forms as revealed by a biaxial anisotropy and the correlation between K/sub u/ and /spl lambda//sub s/ is no more observed. >

EXCHANGE-COUPLED QUADRILAYER FILMS FOR DIRECT OVERWRITE MO DISKS

The design of the direct overwrite magneto-optical disk with the exchange-coupled quadrilayer film using light intensity modulation is described. The relation between the overwrite characteristics and the magnetic properties of each layer was investigated. The writing sensitivity for the high power and the low power depended on the Curie temperature of the writing layer and the memory layer respectively. This system possesses a fairly wide composition tolerance, especially for RE content in each layer.

A Study of Sn-Pb-Re Solder

AbstractOne of the important way to improve the property of solder joints is to improve the property of solders, This paper is about a study of Sn-Pb-RE solder(RE-Rear Earth, mainly contains Ce and La). It has been shown that the final form of RE in SnPb60/40 solder is Sn-RE intermetallic compound, and a very little RE can change the solder microstructure greatly. The influence of RE on solder life of creep rupture is that Sn-Pn-RE solder has much long life than that of SnPb60/40, and the solder life increases with the increase of RE content.