Effect of Aluminium Addition on Glass Forming Ability of Nd55-x Al10＋x Fe15 Co20 （x = 0, 5, 10） Alloys

Nd55-x Al10＋x Fe15 （x =0, 5, 10） bulk glass-forming alloys with distinct glass transition in differential scanning calorimetry （DSC） traces were obtained by suction casting, The glass forming ability （GFA） of the alloys was investigated. It was found that the reduced glass transition temperature （Trg） and the parameter γ of the alloys increased with the increasing concentration of Al. The glass formation enthalpy of the alloys was calculated based on Miedema＇s model, and it was suggested that the GFA of the alloys could be enhanced by the decrease of the glass formation enthalpy with Al additions.     

Phase transition and magnetocaloric effect of Ni55.2Mn18.6Ga26.2-xGdx (x=0, 0.05, 0.15) alloys

Phase transition process and magnetic entropy change -ΔS of Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys were studied.Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys still underwent simultaneous structural and magnetic transitions and transform from ferro-magnetic martensitic phase to paramagnetic austenitic phase during heating. Under a field of 2 T, the maximum magnetic entropy change -ΔSM of Ni55.2Mn18.6Ga26.15Gd0.05 alloy was 7.7 J/kg.K at 317 K during heating and 8.6 J/kg.K at 314 K during cooling while it was 11.8 J/kg.K at 317 K in Ni55.2Mn18.6Ga26.05Gd0.15alloy during heating.     

Effect of Au Content on Thermal Stability and Mechanical Properties of Au-Cu-Ag-Si Bulk Metallic Glasses

The thermal stability, glass-forming ability (GFA), and mechanical and electrical properties of Au-based Au _x Si₁₇Cu_75.5–x Ag_7.5 (x = 40 to 75.5 at. pct) metallic glasses were investigated. The glass transition temperature (T _g ) and crystallization temperature (T _x ) decreased with increasing Au content. The ultralow T _g values below 373 K (100 °C) were obtained for alloys with x = 55 to 75.5. The alloys with x = 45 to 70 exhibited a high stabilization of supercooled liquid and a high GFA, and the supercooled liquid region and critical sample diameter for glass formation were in the range of 31 K to 50 K and 2 to 5 mm, respectively. The compressive fracture strength (σ _c,f ), Young’s modulus (E), and Vicker’s hardness (H _v ) of the bulk metallic glasses (BMGs) decreased with increasing Au content. A linear correlation between Au concentration and the characteristic temperature, i.e., T _g and T _x , and mechanical properties, i.e., σ _c,f , E, and H _v , as well as electrical resistivity can be found in the BMGs, which will be helpful for the composition design of the desirable Au-based BMGs with tunable physical properties.     

Glass-Forming Ability and Competitive Crystalline Phases for Lightweight Ti-Be–Based Alloys

The glass-forming ability (GFA) for the Ti-Be–based alloys in the Ti-Be-Zr ternary system is systematically studied. It was found that the best GFA obtained at a composition of Ti₄₁Be₃₄Zr₂₅ (at. pct) in the Ti-Be-Zr ternary system, and the bulk-metallic-glass (BMG) rod samples with a diameter of 5 mm were fabricated by Cu-mold casting. The competitive crystalline phases around the composition of the best GFA materials were determined by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The GFA of the ternary alloys was further improved by an addition of 4 at. pct vanadium (V). The largest supercooled liquid region, ΔT _x (ΔT _x  = T _x − T _g , T _g is the glass-transition temperature, and T _x the crystallization temperature), in the ternary alloy system reaches about 110 K (110 °C) for the Ti₃₅Be₃₂Zr₃₃ alloy.     

Thermal Stability and Crystallization Kinetics in Y-Based Metallic Glasses

The glass-forming ability (GFA) and thermal stability of Y_56–x Sc _x Al₂₄Co₂₀ (0 ≤ x ≤ 18) alloys produced by melt spinning and suction casting have been investigated. The results show that the addition of a Sc element improves the GFA of Y-based metallic glasses, and the Y₄₁Sc₁₅Al₂₄Co₂₀ alloy has a reduced glass transition temperature T _rg (=T _g /T _l ) as large as 0.641. A new bulk metallic glass (BMG), Y₄₁Sc₁₅Al₂₄Co₂₀, with a diameter of 5 mm was successfully fabricated. The superior GFA after the Sc addition can be attributed to the ability of Sc to effectively alleviate the detrimental effect of oxygen as well as appropriate atomic-size mismatch and large negative heat of mixing among constituent elements. Crystallization kinetic studies show that the activation energies for the Y₄₁Sc₁₅Al₂₄Co₂₀ BMG are E _g  = 4.92 eV and E _x  = 3.18 eV, for the glass transition and crystallization, respectively, which are the highest in all known rare-earth (RE)–based BMGs. The values of the fragility parameter m for the Y₅₆Al₂₄Co₂₀ and Y₄₁Sc₁₅Al₂₄Co₂₀ BMGs are 72 and 42, respectively. The significant decrease in m implies that the GFA and the thermal stability increase with the addition of Sc in the Y₅₆Al₂₄Co₂₀ alloy. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, FL, under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Measurements of Enthalpy Change of Reaction of Formation, Molar Heat Capacity and Constant-Volume Combustion Energy of Solid Complex Yb（Et2dtc）3（phen）

A ternary solid complex Yb(Et2dtc)3(phen) was obtained from the reaction of hydrous ytterbium chloride with sodium diethyldithiocarbamate (NaEt2dtc), and 1, 10-phenanthroline (o-phen·H2O) in absolute ethanol.The bonding characteristics of the complex were characterized by IR.The result shows Yb3 bands with two sulfur atoms in the Na(Et2dtc)3 and two nitrogen atoms in the o-phen.The enthalpy change of liquid-phase reaction of formation of the complex ΔrHθm (l), was determined as being (-24.838±0.114) kJ·mol-1 at 298.15 K, by an RD-496 Ⅲ type heat conduction microcalormeter.The enthalpy change of the solid-phase reaction of formation of the complex ΔrHθm (s), was calculated as being (108.015±0.479) kJ·mol-1 on the basis of an appropriate thermochemistry cycle.The thermodynamics of liquid-phase reaction of formation of the complex was investigated by changing the temperature during the liquid-phase reaction.Fundamental parameters, the activation enthalpy, ΔHθ≠, the activation entropy, ΔSθ≠, the activation free energy, ΔGθ≠, the apparent reaction rate constant k, the apparent activation energy E, the pre-exponential constant A, and the reaction order n, were obtained by a combination of the reaction thermodynamic and kinetic equations with the data from the thermokinetic experiments.At the same time, the molar heat capacity of the complex cm, p, was determined to be (86.34±1.74) J·mol-1·K-1 by the same microcalormeter.The constant-volume combustion energy of the complex, ΔcU, was determined to be (-17954.08±8.11) kJ·mol-1 by an RBC-Ⅱ type rotating-bomb calorimeter at 298.15 K.Its standard enthalpy of combustion, ΔcHθm, and standard enthalpy of formation, ΔfHθm, were calculated to be (-17973.29±8.11) kJ·mol-1 and (-770.36±9.02) kJ·mol-1, respectively.     

Dehydrogenation of nanocrystalline TiH2 and consequent consolidation to form dense Ti

Dehydrogenation of nanocrystalline TiH₂, produced by pulverization of commercially available powder, has been examined in detail by a combination of thermal analysis, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The dehydrogenation to form Ti occurs as a two-step process involving the formation of an intermediate phase, TiH. In-situ experiments on dehydrogenation inside a transmission electron microscope reveal the possibility of a powder-metallurgy process for consolidation of Ti components by vacuum annealing of nanocrystalline TiH₂ at ∼0.5T _m , where T _m is the melting point of Ti. Near-full densification of Ti has been achieved by sintering nanocrystalline TiH₂ under vacuum at ∼0.5T _m .     

Thermochemical Study on Ternary Solid Complex of La(Gly)2 (Ala)3 Cl3 ·2H2O (s)

The complex of lanthanum chloride with Glycine and Alanine, La(Gly)₂(Ala)₃Cl₃ · 2H₂O, was synthesized and characterized by IR, elementary analysis, thermogravimetric analysis, and chemical analysis. The dissolution enthalpies of LaCl₃ · 7H₂O(s), 2Gly(s) + 3Ala(s) and La(Gly)₂(Ala)₃Cl₃ · 2H₂O(s) were determined in 2 mol · L⁻¹ HCl by a solution-reaction isoperibol calorimeter. By designing a thermochemical cycle in terms of Hess' Law and through calculation, the reaction enthalpy of lanthanum chloride seven-hydrate with Glycine and Alanine was obtained: Δ_rH^θ_m(298.15 K) = (29.652 ± 0.504) kJ · mol⁻¹, and the standard enthalpy of formation of La(Gly)₂(Ala)₃Cl₃ · 2H₂O(s) Δ_fH^θ_m[La(Gly)₂ (Ala)₃Cl₃ · 2H₂O, s, 298.15 K] = −4467.6 ± 8.3 kJ · mol⁻¹.     

Thermochemical Properties of the Complexes RE(HSal)3·2H2O(RE = La, Ce, Pr, Nd, Sm)

Five solid rare earth salicylate complexes were synthesized by low hydrated lathanide chloride and salicylic acid. The complexes in this experiment were identified as the general formula RE(HSal)₃·2H₂O(RE = La, Ce, Pr, Nd, Sm) by elemental analysis and EDTA volumetric analysis. IR spectra of the complexes show that carboxyl of salicylic acid coordinates to RE³⁺ ions. Electrochemical behaviors of the complexes on the glass-carbon electrode were researched with cyclic voltammetry (CV). It is indicated that the electrochemical process of the complexes is a one-electron redox process and the electrochemical reversibility of complexes is less than that of the lanthanide chlorides. The constant-volume combustion energies of complexes, Δ_cU, were determined with a precise rotating-bomb calorimeter at 298.15 K. Their standard molar enthalpies of combustion, Δ_cH_m^θ, and standard molar enthalpies of formation, Δ_fH_m^θ, were calculated.     

Characterization of Ti carbosulfide precipitation in Ti microalloyed steels

The morphology and composition of the Ti carbosulfides observed in a family of steels containing 0.05 to 0.25 wt pct Ti were determined using optical and electron microscopy, electron microprobe analysis, and energy-dispersive X-ray (EDX) and secondary ion mass spectrometer (SIMS) techniques. It is demonstrated that the Ti carbosulfide phase has a Ti: S mole fraction ratio of 2∶1 and contains an appreciable level of carbon, its identity being Ti₄C₂S₂. The solubility product of Ti₄C₂S₂ in austenite is derived to be log [Ti] [C]^0.5[S]^0.5=−15,600/T+6.50 and that of TiS to be log [Ti] [S]=−17.640/T+8.20. The former lies between the values for TiN and TiC, whereas the latter is more soluble than TiC. Stringer inclusions consisting of globular Ti₄C₂S₂ surrounded by elongated MnS were observed in the steels with 0.05 to 0.18 wt pct Ti. The volume fraction of the stringers is shown to be related to the sulfur partition coefficient through an empirical power law function. W.J.Lju, formerly with the Department of Metallurgical Engineering, McGill University     

Thermochemical Study on Coordination Complex of Samarium with Salicylic Acid and 8-Hydroxyquinoline

It is knownthat rare earthions ,8-hydroxyquino-line and salicylic acid are antibacterial[1 ～5].Synthesisand characterization of the rare earth complexes withsalicylic acid were reported by Sun[6].Synthesis andcharacterization of the rare earth complexes …     

Effect of Nb Concentration on Thermal Stability and Glass-Forming Ability of Soft Magnetic (Fe,Co)-Gd-Nb-B Glassy Alloys

Addition of a small amount of Nb to the (Fe,Co)-Gd-B glassy alloy in (Fe_0.9Co_0.1)_71.5−x Nb _x Gd_3.5B₂₅ increased the stabilization of supercooled liquid. The largest supercooled liquid region of 104 K was obtained for the x = 2 alloy. A distinct two-stage-like glass transition was observed with further incresing Nb content. The nanoscale (Fe,Co)₂₃B₆ phase precipitated in the glassy matrix after annealing, while the two-stage-like glass transition disappeared, indicating that the anomalous glass transition behavior originates from the exothermic reaction for the formation of the (Fe,Co)₂₃B₆ phase in the supercooled liquid region. The glass-forming ability (GFA) also increased by addition of Nb, leading to formation of the bulk glass form for the Nb-doped alloys. The best GFA with a diameter of over 3 mm was achieved for the x = 4 alloy. The (Fe,Co)-Gd-Nb-B glassy alloys exhibited good magnetic properties, i.e., rather high saturation magnetization of 0.81 to 1.22 T, low coercive force of 2.5 to 5.8 A/m, and low saturated magnetostriction of 9 to 19 × 10⁻⁶. In addition, the glassy alloys also possessed very high compressive fracture strength of 3842 to 3916 MPa and high Vickers hardness of 1025 to 1076.     

Preparation and thermoelectric properties of ternary rare earth sulfide γ-Ce3–xEuxS4

The effect of Eu-substitution on the density and thermoelectric properties of ternary sulfide Ce_3–xEu_xS₄ (0≤x≤0.8) compacts was investigated. Ce_3–xEu_xS₄ powders were prepared via the sulfurization of the oxide using CS₂ gas at 1473 K. The pressureless sintered Ce_3–xEu_xS₄ compacts in the atmosphere were crystallized in the γ-phase. The density of the Ce_3–xEu_xS₄ compacts increased with the increasing of Eu-substitution. Eu-substitution yielded a higher Seebeck coefficient and lower electrical resistivity. The highest value of the thermoelectric power factor of 1.41×10⁻⁴ W/K²m was obtained for the Ce_2.2Eu_0.8S₄ compact at 673 K. It indicated that Eu-substitution was effective for improving thermoelectric properties of Ce_3–xEu_xS₄.     

On the Gibbs energy of formation of wustite

Gibbs energy change for the reactionxFe_(s) + 1/2O_2(g) = Fe _x O_(s) has been redetermined using the galvanic cell (−) Fe_(s), Fe _x O_(s)∥ZrO₂ − CaO∥NiO_(s), Ni_(s)(+) in the temperature range 866 to 1340 K. The results are at variance with earlier works in that they reflect the transformations occurring in the iron phase. The Gibbs energy function is represented by two nonlinear equations,viz., ΔG° (866 to 1184 K) = −251480 − 18.100T + 10.187T lnT ± 210 J/mol and ΔG° (1184 to 1340 K) = −286248 + 181.419T - 13.858T lnT ± 210 J/mol. Formerly Research Assistant at the Department of Theoretical Metallurgy, The Royal Institute of Technology, Stockholm     

[(Fe<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>)<Subscript>0.75</Subscript>B<Subscript>0.20</Subscript>Si<Subscript>0.05</Subscript>]<Subscript>96</Subscript>Nb<Subscript>4</Subscript> Metallic Glasses with Small Cu Additions

Recently, (Fe-Co)-B-Si-Nb bulk metallic glasses (BMGs) were produced. Such BMGs exhibit high glass-forming ability (GFA) as well as good mechanical and magnetic properties. These alloys combine the advantages of functional and structural materials. The soft magnetic properties can be enhanced by nanocrystallization. To force the nanocrystallization, small content of Cu was added to the starting composition. In this article, {[(Fe_0.5Co_0.5)_0.75Si_0.05B_0.20]_0.96Nb_0.04}_100–x Cu _x glassy alloys (x = 1, 2, and 3) were chosen for investigation. The GFA and the thermal stability of these alloys were evaluated. The effects of crystallization during heat-treatment processes on the phase evolution and the magnetic properties, including M _s , H _c , and T _c , in these alloys were investigated. The phase analyses were done with the help of the X-ray diffraction patterns recorded in situ by using the synchrotron radiation in transmission configuration.     

Effects of Alloying Elements on the Thermal Stability and Corrosion Resistance of an Fe-based Metallic Glass with Low Glass Transition Temperature

The effects of alloying elements on the thermal stability, glass-forming ability (GFA), corrosion resistance, and magnetic and mechanical properties of a soft magnetic Fe₇₅P₁₀C₁₀B₅ metallic glass with a low glass transition temperature (T _g) of 723 K (450°C) were investigated. The addition of Mo, Ni, and Co significantly increased the stabilization of supercooled liquid, GFA, and corrosion resistance in the H₂SO₄ solution. The maximum critical diameter (d _c) of 4 mm for glass formation was obtained for the Fe₅₅Co₁₀Ni₅Mo₅P₁₀C₁₀B₅ alloy, which shows the largest supercooled liquid region (ΔT _x ) of 89 K (89 °C). The substitution of Cr for Mo further enhanced the corrosion resistance of the Fe₅₅Co₁₀Ni₅Mo₅P₁₀C₁₀B₅, while the ΔT _x and d _c decreased. The (Fe, Ni, Co)₇₀(Mo, Cr)₅P₁₀C₁₀B₅ bulk metallic glasses showed low T _g of 711 K to 735 K (438 °C to 462 °C), wide ΔT _x of 67 K to 89 K, high saturation magnetization of 0.79 to 0.93 T, low coercive force of 2.36 to 6.61 A m^?1, high compressive yield strength of 3271 to 3370 MPa, and plastic strain of 0.8 to 2.3 pct. In addition, the mechanism for enhancing stability of supercooled liquid was discussed in terms of the precipitated phases during crystallization.     

Chemical potentials of oxygen for three-phase assemblages of CaSiO3(s) + Ca3Si2O7(s) + {CaO + SiO2 + FexO} melt and Ca3Si2O7(s) + Ca2SiO4(s) + {CaO + SiO2 + FexO} melt

By employing an electrochemical technique involving stabilized zirconia as solid electrolyte and Mo + MoO₂ mixture as reference electrode, the equilibrium oxygen partial pressures for three-phase assemblages of CaSiO₃(s) + Ca₃Si₂O₇(s) + {CaO + SiO₂ + Fe_xO} melt and Ca₃Si₂O₇(s) + Ca₂SiO₄(s) + {CaO + SiO₂ + Fe_xO} melt were determined as: - log {P_O2 (CS + C₃S₂ + L)/bar} = - 3.22 13000/(T/K) ± 0.05 - log {P_O2 (C₃S₂ + C₂S + L)/bar} = - 0.92 16400/ (T/K) ± 0.04. respectively, where CS, C₃S₂ and C₂S indicate CaSiO₃(s), Ca₃Si₂O₇(s). and Ca₂SiO₄(s), respectively.     

Enthalpies of formation of liquid and solid (gallium + palladium) alloys

The enthalpies of formation of liquid (Ga + Pd) alloys were determined by direct reaction calorimetry in the temperature range 1322 <T/K < 1761 and the molar fraction range 0 <x _Pd < 0.87. The enthalpies are very negative with a minimum Δ_mix H _m = −70.4 ± 3.0 kJ mol_-1 atx _Pd = 0.6, independent of the temperature. Limiting partial molar enthalpies of palladium and gallium were calculated as Δh _m (Ga liquid in ∞liquid Pd) = −265 ± 10 kJ mol₋₁ and Δh _m (Pd liquid in ∞liquid Ga) = -144 ± 5 kJ mol₋₁. The integral molar enthalpy is given by Δ_mix H _m =x(1-x) (-143.73 -232.47x + 985.77x ²-4457.8.x ³ + 6161.1x ⁴ + 2577.4x ⁵), wherex = x _Pd. Moreover, values for the enthalpies of formation and fusion of PdGa, Pd₂Ga, and the solid solution (withx _Pd = 0.8571) have been proposed. These results have been discussed taking into account the equilibrium phase diagram. Formerly Ph.D. student, Université de Provence     

Electrical Transport and Giant Magnetoresistance in （ 1 - x ） La0.67 Ca0.33 MnO3/x CuO Composites

Samples with nominal composition of （1 - x）La0.67Ca0.33MnO3 （LCMO）/xCuO （x = 0%, 2%, 4% and 20% ） were made using a special experimental method. The temperature dependence of the resistivity （ρ） of the composites was investigated in the temperature range of 10 - 300 K and different magnetic fields of H = 0, 0.1, 0.3, 0.5, 1.0 and 3.0 T. The results showed that CuO percentage x had important effects on metal-insulator transition temperature （Tp）, zero field peak resistivity （ρmax）, and magnetoresistance （MR） properties of the composites. Tp shifted sharply towards low temperature with the increase of x in the range of x ≤4%, but was almost independent of x at high level of CuO content. Composites with x = 4 % and 20 % exhibited similar electrical transmission behavior. Compared with pure LCMO, enhanced magnetoresistance could be clearly observed even in a quite low magnetic field of 0.3 T. For x =4% and 20% samples, the MR value at 0.3 T could reach as high as - 88% and - 90%, respectively. XRD and SEM analysis showed that the substantial enhancement of MR, especially near Tp, was because of local spin disorder between contiguous LCMO ferromagnetic particles caused by the addition of CuO.     

Synthesis of new bulk metallic glassy Ti60Al15Cu10W10Ni5 alloy by hot-pressing the mechanically alloyed powders at the supercooled liquid region

The mechanical alloying method has been used to fabricate multicomponent Ti₆₀Al₁₅Cu₁₀W₁₀Ni₅ glassy alloy powders, using a low-energy ball-milling technique. The glassy powders that were obtained after 720 ks of milling have a sphere-like morphology with an average particle size of 0.38 μm in diameter. This new glassy alloy exhibits a glass transition temperature (T _g) at 733 K. It crystallizes at a crystallization temperature (T _x ) of 804 K through a single sharp exothermic peak, with an enthalpy change of crystallization (ΔH _x ) of −5.20 kJ/mol. The supercooled liquid region before crystallization ΔT _x of the obtained glassy powders shows a large value (71 K). The reduced glass transition temperature (ratio betweenT _g and liquidus temperatures,T ₁(T _G /T ₁) was found to be 0.46. The synthetic glassy powders were uniaxial hot-pressed into consolidated round objects with large dimensions (20 mm in diameter × 30 mm in height) in an argon gas atmosphere at several temperatures with a pressure of 936 MPa. The samples that were consolidated at the temperature range of 755 to 775 K (within the ΔT _x region) are fully dense (∼99.85 pct) and maintain the chemically homogeneous glassy structure. These hot-pressed glassy samples exhibit excellent mechanical properties for Ti-base metallic glasses. They have high Vickers microhardness values, in the range between 8.0 and 8.2 GPa. They also show high fracture strength (2.28 GPa) with an extraordinarily high Young’s modulus of 153 GPa. Neither yielding stress nor plastic strain could be detected for this glassy alloy, which shows an elastic strain of 1.39 pct.