Effects of rare earth additions on structures and properties of rapidly solidified copper alloys

Abstract

Copper based Cu–RE alloys (where RE represents lanthanum, neodymium, or samarium) with alloying content up to 16 wt-% were prepared by chill block melt spinning into ribbons of thickness between 40 and 100 μm. The melt spun ribbons were heat treated isochronally for 2 h at 300, 400, 500, 600, 700, and 800°C, respectively. The melt spun and heat treated ribbons were tested for microhardness and resistivity and were characterised by optical and transmission electron microscopy (TEM) and X-ray diffractometry (XRD). Microstructures were of the typical zone B type for Cu–1RE and Cu–3RE ribbons and of the zone B/zone A type for Cu–5RE, Cu–8RE, and Cu–12RE ribbons. Only microstructures of the zone A type were found in Cu–15La ribbons. The metastable extended solid solubilities of the rare earth elements were evaluated by measurements of the lattice parameters of the supersaturated solid solutions and significant extension from the equilibrium solid solubility was found for all three alloys. The secondary phase was identified by TEM and XRD as Cu₆RE for all ribbons except Cu–15La ribbons in which metastable Cu₅La and Cu₁₃La phases were also found. Observations using TEM and XRD also showed a reduction in the α-Cu grain size of the as spun ribbons with increasing alloying content, producing nanosized α-Cu grains on the chill side of the ribbons. Heat treatment of the ribbons at 400°C for 2 h produced no significant coarsening of α-Cu grains as the size of these grains was still in the nanometer region. Both α-Cu and Cu₆RE grains coarsened as a result of heat treatment for 2 h at temperatures of 600°C and above for all the alloys.     

Phase transition of nanostructure zirconias doped with rare earth elements

Nanostructure zirconias doped with rare earth elements were obtained by coprecipitation. The morphology, structure, and phase transition of the as-prepared samples were studied. According to transmission electron microscopy, the particles appear in near spherical shape and have a mean particle sizes of about 150 nm without change with the rare earth elements. From laser Raman and X-ray diffraction results, it is known that the tetragonal phase of zirconia is stabilized by a certain concentration of the rare earth dopants, and the cubic phase is obtained if enough dopants are added. The crystal lattice increases with the increase of dopant concentration. Moreover, the heavy rare earths are better than the light ones in stabilizing effect. According to our study, laser Raman is more sensitive than X-ray diffraction in monitoring the phase transition.     

Structure and properties of rapidly solidified Mg-Al alloys

Three binary Mg-Al alloys containing nominally 5, 15, and 30 at % Al were prepared in the ingot and rapidly solidified flake conditions using the twin roll technique. The microstructure, mechanical properties, and electrochemical behavior of the extruded alloys in both the conditions were investigated. The hardness, tensile strength, and corrosion resistance increased with increasing Al content. Further, the hardness, tensile strength, and corrosion resistance of the rapidly solidified alloys were superior to the ingot-metallurgy alloys and this is attributed to the microstructural refinement and increased homogeneity in the rapidly solidified alloys.     

Structure and properties of rapidly solidified Al-Zr-Ti alloys

The Al-Zr-Ti system has recently been suggested as a candidate for Al-based materials capable of retaining a high strength during a long term exposure to high temperatures up to 700 K. The Al-1.25 at.% (Zr+Ti) alloys with a variable Zr : Ti ratio were rapidly solidified using the melt spinning method. The solidification structure was found inhomogeneous along the direction perpendicular to the ribbon plane and dependent on the Zr : Ti ratio. The microhardness values were correlated with the structure and chemical composition. The presence of second phase particles in the as melt-spun ribbons was proved by SAXS experiments. X-ray and electron diffraction experiments enabled to identify most of particles as the metastable Al₃(Zr_xTi_1–x) phase with the cubic L1₂ structure. Especially in the Zr-rich alloys, these particles precipitated preferentially in a fan-shaped morphology. The grains of the Ti-rich alloys were nearly free of these particles.     

Mechanical and magnetic properties of the rapidly quenched Cu2MnAl

Rapidly solidified Cu₂MnAl ribbons were fabricated by the chill-block melt-spinning technique as a function of rotation speed of an iron roller. The rapidly quenched ribbons were relatively ductile, and the total strain at failure for the bend test increased with increasing rotation speed of the roller. The effect of rapid quenching on long-range ordering in Cu₂MnAl alloy was studied by X-ray diffraction. The decomposition characteristics during isothermal ageing at temperatures between 350 and 600° C were also examined by X-ray diffraction, magnetization and Vickers hardness measurements. The decomposition reaction at temperatures below 400° C was Cu₂MnAl-Cu₉Al₄+T-Cu₃Mn₂Al+-Mn. However, at temperatures between 500 and 600° C, Cu₂MnAl decomposed into a new L2₁ type Cu₂MnAl and-Mn, and further annealing caused the appearance of-Cu₉Al₄. The decomposition rate of the rapidly quenched ribbons was faster than that of the water-quenched alloy.     

Microstructure and mechanical properties of rapidly solidified Al-Si-Fe-X base alloys

The effects of Ti and V additions on microstructure and mechanical properties of rapidly solidified Al-20w/oSi-5w/oFe alloy were investigated, respectively. The hypereutectic Al-Si-Fe base alloys were gas-atomized and hot-extruded to make the consolidated bars. The addition of 2w/oTi increased wear resistance and mechanical properties such as tensile strength, hardness and elongation. Based on TEM analyses, it can be concluded that the improved properties in the Al-Si-Fe alloys containing Ti were caused by the formation of DO₂₂-(Al,Si)₃ Ti phase finely dispersed in the matrix. On the contrary, V addition was less effective than Ti, in that V could not decompose as the expected Al₁₀V phase with a large v/o of precipitates; V was mostly solid-solutionized in the other unknown phase.     

Improving the hard magnetic properties by intragrain pinning for Ta doped nanocrystalline Ce-Fe-B alloys

To develop Ce based permanent magnets with high performance/cost ratio, Ta doping is was employed to enhance the magnetic performance of Ce-Fe-B alloys. For melt spun Ce₁₇Fe_78-xTa_xB₆ (x = 0–1) alloys, the coercivity H_c increases from 439 to 553 kA/m with increasing x value from 0 to 0.75. Microstructure characterizations indicate that Ta doping is helpful for grain refinement. A second phase of TaB₂ is observed in Ce₁₇Fe_77.25Ta_0.75B₆ alloy, which acts as the pinning center of the magnetic domains, resulting in the change of coercivity mechanism from nucleation type to nucleation + pinning type. The micromagnetic simulation confirms that non-magnetic particles within hard magnetic phase can increase the demagnetization field around them and it is crucial for preventing the further magnetization reverse by pinning effect. Take the advantage of Ta doping for enhancing the coercivity, Ce content of Ce-Fe-B alloy can be further cut down to increase the remanence J_r due to the reduced volume fraction of CeFe₂ phase and increased Fe/Ce ratio. As a result, a good combination of magnetic properties with H_c = 514 kA/m, J_r = 0.49 T, and the maximum energy product (BH)_max = 36 kJ/m³ have been obtained in Ce₁₅Fe_79.25Ta_0.75B₆ alloy. It is expected that the present work can serve as a useful reference for designing new permanent magnetic materials with low-cost.     

Structure, mechanical properties and electrical resistivity of rapidly solidified Pb-Sn-Cd and Pb-Bi-Sn-Cd alloys

A series of Pb-Sn-Cd alloys containing up to 60 wt % Bi were quenched from the melt to room temperature by melt spinning. The structure of rapidly solidified (melt spun), Pb-30 wt % Sn-10 wt % Cd, Pb-30 wt % Bi-20 wt % Sn-10 wt % Cd, and Pb-60 wt % Bi-10 wt % Sn-10 wt % Cd have been investigated by means of an X-ray diffraction technique. From X-ray analysis a crystalline metastable phase, designated (Pb-Bi) is detected. The formation of a metastable crystalline phase in the range of composition investigated causes a pronounced increase in the electrical resistivity. Desirable values of hardness and elastic constants are critically evaluated. It is also observed that the values of the Fermi energy are a few electron volts. Calculated values for the concentration of the conduction electrons, N, m_-3 of Pb -60 wt % Bi-10 wt % Sn-10 wt % Cd rapidly solidified is found to be 0.985×10₂₈ m_-3.     

Phase fields in rapidly solidified MnTi and MnAlTi alloys studied by X-ray diffraction

While rapid solidification causes little modification of phase fields in Mn_x Ti_1–x alloys forx < 30at%, alloys richer in manganese present metastable phases. A structure intermediate between crystalline and quasi-crystalline phases is observed in the range 0.3 <x < 0.45. Aluminium addition is found to stabilize the C14 phase down to manganese contents as low as 35 at % and Mn₃₅ (AlTi)₆₅ is found to be single-phased C14. The ternary alloy's C14 phase field emerges due to aluminium substitution for manganese at low manganese contents.     

Microstructure and magnetic properties of rare earth Nd-Fe system alloys produced by containerless processing

Nd_xFe_100?1.5xB_0.5x alloys (x=10, 11.8, and 14) were solidified from the undercooled melts by drop tube processing. The samples contained a large amount of the metastable phase with the composition near to their bulk composition in each alloy. The volume fraction of the metastable phase increased as the sample diameter decreased. The metastable phase was partially decomposed into very fine lamellar grains of the Nd₂Fe₁₄B and α-Fe or Nd₂Fe₁₄B and some Nd-rich phase by solid-state reaction in the samples with a diameter of 1200μm. The solidification behavior of the metastable phase was explained in terms of a hypothetic scheme of the pseudobinary Nd-Fe-B phase diagram     

Synthesis and properties of rare earth doped lamp phosphors

Red, blue and green emitting lamp phosphors such as Eu³⁺ doped Y₂O₃ (red phosphor), Eu²⁺ doped Ba_0·64Al₁₂O_18·64, BaMgAl₁₀O₁₇ and BaMg₂Al₁₆O₂₇ (blue phosphors) and Ce_0·67Tb_0·33MgAl₁₁O₁₉ and Eu²⁺, Mn²⁺ doped BaMgAl₁₀O₁₇ (green phosphors) have been prepared by the combustion of the corresponding metal nitrates (oxidizer) and oxalyl dihydrazide/urea/carbohydrazide (fuel) mixtures at 400°–500°C within 5 min. The formation of these phosphors has been confirmed by their characteristic powder X-ray diffraction patterns and fluorescence spectra. The phosphors showed characteristic emission bands at 611 nm (red emission), 430–450 nm (blue emission) and 515–540 nm (green emission). The fine-particle nature of the combustion derived phosphors has been investigated using powder density, particle size and BET surface area measurements. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

不同稀土元素掺杂M型钡铁氧体超微粉末的磁性研究

利用溶胶－凝胶自蔓延高温合成法制备了4种稀土元素（La、Nd、Sm、Gd）掺杂钡铁氧体超微粉末。就烯土元素的种类、稀土掺杂量、合成工艺条件对钡铁氧体磁学性能的影响进行了较系统的研究。采用振动样品磁强计对粉末的磁学性能进行了检测。     

Optical properties of zirconia doped with yttria and some rare earth oxides

Nanometric powders of cubic zirconia stabilized with yttria and rare element oxides (Sm, Nd, Gd) were prepared by crystallization under hydrothermal conditions. The powders were uniaxially compacted, repressed isostatically, pressure-less sintered in oxygen atmosphere and hot isostatically pressed under 300 MPa Ar atmosphere. Fully dense samples were polished from both sides. The optical properties were analyzed based on the spectral dependence of the transmittance (T) and reflectance (R). Spectroscopic measurements have shown that all materials fabricated in the present work are highly transparent, with total transmission above 90% towards the long-wavelength end of the near-IR range of the spectrum. Discussion of these results will be given.     

Structure and magnetic properties of directionally solidified Bi-MnBi eutectic alloys

An alloy containing about 2 at% Mn and 98 at% Bi should solidify at 230°C to give a eutectic consisting of about 3 vol % ferromagnetic MnBi in a matrix of diamagnetic Bi. Directional solidification of this alloy produces a structure of elongated parallel MnBi rods with diameters from 0.1 to 1.5 μm, decreasing with increasing growth rate. Samples solidified slowly (growth rate less than 5 cm/h) show magnetic properties at room temperature and down to 4.2 K that are consistent with the known magnetic properties of bulk equilibrium MnBi. Samples solidified more rapidly (20-80 cm/h) show considerably more complicated magnetic behavior. At room temperature they have less than half the moment expected for the equilibrium MnBi composition, and a second magnetic phase appears when the temperature is lowered below about 240 K. The coercive field of this phase rises rapidly with decreasing temperature, reaching the limit of our experimental apparatus (about 120 kOe) near 100 K. Magnetic measurements with the field applied perpendicular to the growth axis show the effects of anisotropy, due to particle alignment, although samples prepared at very rapid freezing rates (300 cm/h) appear to be poorly aligned. Samples prepared by arc melting on a water-cooled hearth are similar to high-growth-rate samples. Annealing at 200°C was necessary in order to obtain reproducible magnetic data. The results are generally consistent with the presence in the samples of a mixture of the normal equilibrium MnBi phase and a variant of the known high-temperature phase (HTP) with a substantially depressed Curie temperature. Structural studies using electron diffraction from thinned sections indicate the presence of both normal (LTP) and high-temperature (HTP) MnBi.     

Structure and mechanical properties of rapidly solidified magnesium based Mg-Al-Zn-RE alloys consolidated by extrusion

Magnesium based Mg-9Al-lZn-5RE (RE = La or Nd) alloys were rapidly solidified by chill block melt spinning. The resulting ribbons were cold packed into an aluminium alloy can and extruded at temperatures of 230 and 340°C and ratios of 20:1 or 25:1. Tensile and hardness tests of the extruded and heat treated materials were carried out. The tensile strength and elongation to fracture of the as extruded material were 478 MN m^?2 and 6·5% respectively and those of the material heat treated for 2 h at 350° C were 420 MN m^?2 and 20% respectively. The microstructure of these specimens was studied by X-ray diffraction and transmission electron microscopy. Intermetallics of Al₁₁ La₃ or Al₂Nd were found at grain boundaries and in the matrix which had a grain size of between 0–26 and 0–8 μm, while Mg₁₇Al₁₂ precipitates were present in the specimens extruded at a lower temperature (230° C). Yield strengths were consistent with the Hall-Petch relationship with grain size established earlier for this class of material.

MST/3495     

Structure, mechanical metallurgy and electrical transport properties of rapidly solidified Pb50Sn50-xBix alloys

Electrical transport properties, structure and mechanical properties of Pb₅₀Sn_50-xBi_x(0≤x≤50) alloys have been studied and analyzed. The addition of bismuth in the amounts of 30 wt % and 50 wt % results in the appearance of the crystalline metastable χ(Pb-Bi) phase. Y phase is also identified and it is found at 50 wt % bismuth. Electrical transport is sensitive to the alloys composition, decreasing as the bismuth content increases. The Vickers hardness number is sensitive to the structure of the quenched ribbons. The lowest value of H_v is 55 MPa for the Pb₅₀Sn₂₀Bi₃₀ alloy, which is attributed to the formation of the metastable χ(Pb-Bi) after a rapid quench from the melt. Values of the equivalent Fermi temperature, T_F Fermi velocity, V_F and the Fermi wave vector, K_F , are also computed. © 2000 Kluwer Academic Publishers     

Structure and properties of rapidly solidified Al rich Al-Mn-Si alloys Part I Melt spun ribbons

The evolution of microstructure as-spun and during subsequent heat treatment at 200 to 500°C for up to 1000 h has been studied for Al-6.3 Mn-3.3 Si, Al-8.3 Mn-3.7 Si and Al-14.5 Mn-5.8 Si (wt %) alloys, containing 17, 26 and 48 vol % AlMnSi at equilibrium respectively. Microstructure as-spun ranged from primary icosahedral phase nucleating radial cellular Al arrays to less regular duplex arrays of Al and AlMnSi with decreasing alloy content and decreased section thickness or reduced distance from the chill surface. Heat treatment in the range 200 to 500°C transformed any icosahedral phase present to AlMnSi along with spheroidization and coarsening/coalescence of AlMnSi, to produce isolated spheroids when volume fraction f was lower and very stable interlinked chains at higher f. Measured coarsening rates of AlMnSi were a factor of 10 below predictions of LSW theory at lower f but were within a factor of 2 of prediction at highest f. Hardness was governed by a combination of Hall-Petch and matrix solid solution hardening as-spun supplanted by particle-radius dependent Orowan combined with matrix Hall-Petch hardening for the evolution of hardness during prior long term heat treatment at 425°C.     

Influence of doped rare earth elements on electronic properties of the R0.25Ca0.75MnO3 systems

The influence of doped rare earth elements on the some electronic properties of perovskite systems R_0.25Ca_0.75MnO₃ (R = La, Nd, Eu, Tb, Ho, Y) is investigated using the density functional theory with Dmol3 code. The density of states, band structure, tolerance factor and Jahn–Teller splitting energy were calculated. By doping the different rare earth elements, the systems show different changing in the crystal structure, hopping amplitude, and electrical resistivity. Among these doping compounds, the Eu_0.25Ca_0.75MnO₃ exhibits the strongest structural change corresponding to the largest Jahn–Teller splitting.     

Elastic properties of ZnF2-PbO-TeO2 glasses doped with certain rare earth ions

The elastic moduli (Y, η, σ andH) and some thermodynamical parameters, such as Debye temperatureθ _D, diffusion constantD _i and latent heat of melting ΔH _m, of ZnF₂-PbO-TeO₂ glasses doped with some rare earth (Pr³⁺, Nd³⁺, Eu³⁺ and Tb³⁺) ions are determined as functions of temperature using piezo electric composite oscillator technique. All the parameters are found to decrease with increase in the atomic number Z of the rare earth ions and with increase in the temperature of measurement. The results are explained on the basis of the density of localized bonding defect states within the band gap of the material.     

稀土激发的CaMgSi2O6的长余辉发光特性

使用固相反应法在还原气氛中制备了具有长余辉性能的CaMgSi2O6发光材料。研究了不同的共激发离子(Dy^3 和Nd^3 )对于材料发光性能的影响。光谱分析表明了这些磷光体在438nm处有一个宽的发射峰,这个发射峰是由Eu^2 的4f^6 5d^1能级到4f^7能级的跃迁所导致的,而Eu^2 在透辉石中形成六配位的发光中心。获得的3种磷光体都具有长余辉发光性能。其中共掺杂Eu^2 和Dy^3 材料比单掺Eu^2 和共掺Eu^2 扣Nd^3 的材料具有更好的余辉强度扣更长的余辉时间，其原因在于Dy^3 在CaMgSi2O6晶格中形成了更深的和更高密度的陷阱。