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.     

Effects of Microalloying on Glass Forming Ability and Thermodynamic Fragility of Cu-Pr-Based Amorphous Alloys

The effects of microalloying of Ti and B on the glass formation of Cu60Pr30Ni10Al10-2xTixBx（x = 0, 0.05% （atom fraction）） amorphous alloys was investigated using differential scanning calorimetry （DSC） and X-ray diffraction （XRD）. XRD analysis showed that mieroalloying with 0.05% Ti and 0.05% B improved the glass forming ability （GFA）. The smaller difference in the Gibbs free energy between the liquid and crystalline states at the glass transition temperature （△G1-X（Tg）） and the smaller thermodynamic fragility index （△Sf/Tm, where ASf is the entropy of fusion, and Tm is the melting temperature） after mieroalloying correlated with the higher GFA.     

Magnetic properties and microstructure of Fe_(69.5-x)Nd_7B_(21)Nb_(2.5)Ga_x(x=0-1)alloys

The Fe_(69.5-x)Nd_7 B_(21)Nb_(2.5)Ga_x(x = 0-1)permanent magnets in the form of rods were prepared by annealing the bulk amorphous alloys.The magnetic properties,phase evolution and microstructure of the alloys were investigated systematically.It is found that the glass forming ability(GFA), microstructure and magnetic properties are sensitive to Ga content for Fe_(69.5-x)Nd_7 B_(21)Nb_(2.5)Ga_x(x = 0-1)bulk alloys.The annealed alloys are mainly composed of soft α-Fe,hard Nd_2 Fe_(14)B and nonmagnetic Nd_(1.1)Fe_4 B_4 phases.When x = 0.3,the optimally annealed magnets exhibit magnetic properties of the remanence Br = 0.63 T,intrinsic coercivity H_(cj) = 368.68 kA/m and maximum energy product(BH)_(max) = 33.73 kJ/m~3.Furthermore,magnetic field heat treatment at the temperature close to Curie temperature of Nd_2 Fe_(14)B phase was applied to the annealed Fe_(69.2)Nd_7 B_(21)Nb_(2.5)Ga_(0.3) magnet.The results of X-ray diffraction(XRD)and transmission electron microscopy(TEM)indicate that the magnetic field heat treatment can be beneficial for the precipitation of α-Fe.Thus,the B_r,H_(cj) and(BH)_(max) are enhanced by 8.7%,6.3% and 16.3%,respectively.     

Corrosion behavior of amorphous fe-cr-al-p-c ribbon alloys

Corrosion resistance of amorphous Fe₇₂Cr_8-xAl_xP₁₃C₇ ribbons produced by a rapid quenching method has been investigated in several solutions. The corrosion test for amorphous ribbons was carried out, and anodic polarization curves have been measured in the solutions. Resultantly, even in the amorphous Fe₇₂Cr_8-xAl_xP₁₃C₇ ribbons containing a low Cr content, this composition of amorphous alloys showed the high corrosion resistance.     

Effects of Phosphorus and Carbon Contents on Amorphous Forming Ability in Fe-based Amorphous Alloys Used for Thermal Spray Coatings

Cost-effective Fe-based amorphous alloys used for thermal spray coatings were developed by varying contents of P and C, and their microstructure, hardness, and corrosion resistance were analyzed. In order to achieve chemical compositions having high amorphous forming ability, thermodynamically calculated phase diagrams of Fe-Al-P-C-B five-component system were used, from which compositions of super-cooled liquid having the lowest driving force of formation of crystalline phases were obtained. The thermodynamic calculation results showed that only phases of Fe₃P and Fe₃C were formed in the Fe₇₈Al₂P_(18.3?x)C _x B_1.7 alloy system. Considering driving force curves of Fe₃P and Fe₃C, the carbon contents were selected to be 6.90 and 7.47 at. pct, when the thermodynamic calculation temperatures were 697 K (414 °C) and 715 K (442 °C), respectively. According to the microstructural analysis of suction-cast alloys, the Fe₇₈Al₂P_10.83C_7.47B_1.7 alloy showed a fully amorphous microstructure, whereas the Fe₇₈Al₂P_11.40C_6.9B_1.7 and Fe₇₈Al₂P_10.3C_8.0B_1.7 alloys contained Fe₃P and Fe₃C phases. This Fe₇₈Al₂P_10.83C_7.47B_1.7 alloy showed the better hardness and corrosion resistance than those of conventional thermal spray coating alloys, and its production cost could be lowered using cheaper alloying elements, thereby leading to the practical application to amorphous thermal spray coatings.     

Prediction of Bulk Metallic Glass Formation in Cu–Zr–Ag–Hf System by Thermodynamic and Topological Modeling

Cu based bulk metallic glasses (BMGs) are widely studied because of their high glass forming ability (GFA) and interesting combination of properties such as high strength coupled with good ductility and low cost. With these attributes, Cu based BMGs are being projected as promising materials for practical applications. The process of glass formation in metallic systems is a challenging task and alloys should be cooled from the liquid state at rates faster than a critical cooling rate (R_c) to resist crystallization. Interestingly, composition plays an important role in achieving easy glass formation, which is usually measured in terms of R_c. In the present work, attempt has been made to identify the composition for easy glass formation in Cu based quaternary system by theoretical approach. A GFA parameter P_HS, which is a product of enthalpy of chemical mixing (?H_chem) and mismatch entropy normalized with Boltzmann??s constant (?S_??/k_B) is used to identify the best glass forming composition in Cu?CZr?CAg?CHf system. Further, a new parameter P_HSS, which is a product of P_HS and configurational entropy (??S_config/R) is found to illustrate strong correlation with GFA. An attempt has also been made to correlate P_HSS parameter with critical diameters and R_c using reported data in Cu?CZr?CAg?CHf system.     

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.     

Preparation and thermal stability of Zr-Ti-Al-Ni-Cu amorphous powders by mechanical alloying technique

This study examined the amorphization feasibility of Zr_70−x−y Ti _x Al _y Ni₁₀Cu₂₀ alloy powders by the mechanical alloying (MA) technique. According to the results, after 5 to 7 hours of milling, the mechanically alloyed powders were amorphous basically in the ranges of 0 to 12.5 at. pct Ti and 2.5 to 17.5 at. pct Al. These ranges are larger than those of bulk amorphous alloys prepared by a squeeze mold casting technique. Most of the amorphous mechanically alloyed powders exhibited a wide supercooled liquid region of more than 60 K before crystallization. The glass-transition and crystallization temperatures of mechanically alloyed samples were different from those prepared by squeeze casting. It is suspected that different thermal properties arise from the introduction of impurities during the MA process. The amorphization behavior of Zr₅₀Ti_7.5Al_12.5Ni₁₀Cu₂₀ was examined in detail. The X-ray diffraction and extended X-ray absorption fine structure (EXAFS) results show the fully amorphous powders formed after 5 hours of milling. A kinetically modified thermodynamic phase transformation process was observed for the glass-transition behavior in the Zr₅₀Ti_7.5Al_12.5Ni₁₀Cu₂₀ amorphous powder.     

Thermodynamic modeling of Zr-Ti-Cu-Ni-Be bulk metallic glass

In the present thermodynamic model, the optimization of bulk metallic glass forming compositions in Zr-Ti-Cu-Ni-Be system using enthalpy of chemical mixing (ΔH_chem) as thermodynamic, mismatch entropy (ΔS _σ /k_B) as topological and configurational entropy (ΔS_config/R) as statistical parameters were studied. The product of ΔH_chem and ΔS _σ /k_B which is termed as ΔP_HS in the ΔS_config/R range of 0.9 to 1.0 can be strongly correlated to glass forming ability. Using the contributions of ΔP_HS values of all ternary compositions possible in Zr-Ti-Cu-Ni-Be system, the final quinary composition is designed. Composition obtained from present model was found to closely match with compositions reported in literature.     

Phase Composition and Magnetic Properties of Nd<Subscript>2</Subscript>Fe<Subscript>14</Subscript>B/α-Fe Nanocomposites Prepared by Mechanical Alloying

Combined studies of hard magnetic Nd₂Fe₁₄B/α-Fe nanocomposites are performed. They were prepared by mechanical alloying of melt-quenched Nd_7.4Pr_2.0Fe_76.6Co_4.2Zr_3.4B_6.4 and Nd_5.8Fe₈₀Co_4.9Ti_1.5Si_2.5B_5.3 alloys taken in mass proportions of 90/10 and 70/30. It is found that, after mechanical alloying, an amorphous–crystalline structure is formed; it consists of the hard magnetic Nd₂Fe₁₄B and soft magnetic (amorphous and α-Fe) phases. Subsequent annealing at ~500°C initiates the decomposition of the amorphous phase and the formation of the nanocrystalline Nd₂Fe₁₄B and α-Fe phases. This leads to an increase in the coercivity and the residual magnetization-to-saturation magnetization ratio (σ_r/σ_s ≥ 0.5). It is assumed that the magnetic hardening of powders is due to the formation of an exchange-coupled state, which results from the exchange interaction between α-Fe nanocrystals and the Nd₂Fe₁₄B phase.     

Selective microwave absorption in Nd3+ substituted barium ferrite composites

Microwave(MW) frequency based wireless communications and electronic devices became prospective due to several ramifications.To meet this need,a series of neodymium ions(Nd3+) substituted barium ferrite composites with composition(20)BaO:(80-x)Fe_2 O_3:(x)Nd_2 O_3(0≤x≤3 mol%) was prepared at1100℃using solid-state reaction method.We evaluated the effect of various Nd3+ions contents on the surface morphology,structure,and magnetic properties of the as-synthesized barium ferrite composites.Meanwhile,microwave reflection loss,complex permittivity and permeability were determined using the transmission/reflection line method in the X-band(8—12 GHz).SEM image of the composites shows that the surface morphology consists of rough and porous microstructures.XRD patterns of the un-doped composites reveal the existence of BaFe_(12)O_(19)(hexagonal) and Fe_(21.333)O_(32)(tetragonal) crystalline phases.Furthermore,a new hexagonal crystalline phase of Ba_6 Nd_2 Fe_4 O_(15) with the crystallite sizes between 15 and 67 nm is observed due to Nd3+ions substitution in the composite.The saturation magnetization of the composite containing 2 mol% of Nd3+does not exhibit any significant alteration compared to the one devoid of Nd3+.The complex relative permitivity and permeability of the achieved composites enriched in Ba_6 Nd_2 Fe_4 O_(15) and BaFe_2 O_4 phases disclose significant MW frequency dependence.The composites also display selective MW absorption in the X-band which could be useful for diverse applications.     

Structure, Properties, and Glass Forming Ability of Melt-Spun Fe-Zr-B-Cu Alloys with Different Zr/B Ratios

Melt-spun ribbons of Fe_99–x–y Zr _x B _y Cu₁ alloys with x + y = 11 and x + y = 13 were prepared under similar experimental conditions and characterized for structure and soft magnetic properties. Substitution of Zr by B changes the structure of as-spun ribbons from completely amorphous to cellular bcc solid solution coexisting with the amorphous phase at intercellular regions and then to completely dendritic solid solution. The glass forming ability (GFA) of the Fe-Zr-B-Cu system, evaluated from thermodynamic properties such as enthalpy of mixing and mismatch entropy, is found to be in good agreement with the experimental observations. Annealing of all ribbons leads to the precipitation of nanocrystalline bcc α-Fe phase from both amorphous phase and already existing bcc solid solution. A window of alloy compositions that exhibit the best combination of soft magnetic properties (high saturation magnetization and low coercivity) was identified.     

Unique structural and magnetic traits of Nd3+-substituted Co–Zn nanoferrites

Because of the technological potential of magnetic spinel nanoferrites, we prepared neodymium ion (Nd³⁺)-substituted cobalt-zinc ferrites (CZFs) with the form Co_0.5Zn_0.5Nd_xFe_2–xO₄ (0.0 ≤ x ≤ 0.05) via a hydrothermal method. The as-prepared samples were thoroughly characterized using various analytical techniques. XRD, FTIR and FESEM analyses confirm the formation of a cubic spinel phase of the CZFNPs (CZF nanoparticles). A decrease in the lattice parameter due to the substitution of Fe³⁺ by Nd³⁺ in the lattice structures is manifested in the XRD refinement data. The magnetic properties of the proposed CZFNPs were evaluated in terms of the saturation magnetization, remanence, coercivity, squareness ratio and magnetic moment. These CZFNPs exhibit superparamagnetic behaviors at room temperature. Moreover, the Nd³⁺ inclusion does not significantly affect the measured magnetizations and coercivities of the CZFNPs. Samples containing 0.01 and 0.03 Nd³⁺ exhibit lower saturation magnetizations than that of the pristine product. The squareness ratios much less than 0.53 are ascribed to surface spin disordering. The unique magnetic traits of the synthesized CZFNPs are primarily attributed to the substitution of Fe³⁺ ions, with smaller ionic radii, by Nd³⁺ ions, with larger ionic radii. The proposed CZFNPs may be useful for diverse magneto-optic applications.     

Solid-state reaction synthesis and chemical stability studies in Nd-doped zirconolite-rich ceramics

In this study, Nd-bearing zirconolite-rich ceramics were prepared by solid-state reaction process using CaF_2,ZrO_2, Ti,TiO_2, Fe_2 O_3 and Nd_2O_3 as the raw materials. Neodymium was used as trivalent actinide surrogate and designed to substitute the Ca and Zr sites of zirconolite with general stoichiometry of Ca_(1-x)Zr_(1-x)Nd_(2 x)Ti_2O_7(0≤x≤0.3). Density of Fe-Nd-O sample reaches a maximum value of 4.13 g/cm~2 after being sintered at 1325 ℃ for 42 h. Three major phases, namely zirconolite, perovskite and pseudobrookite, are observed in all these samples. The EDX result shows that Nd_2O_3 can be successfully incorporated into the lattice structure of the prepared zirconolite-rich minerals and replace the Ca sites of zirconolite and perovskite with Fe~(3+) as the charge-compensating ion. Furthermore, the thermal conductivities are all in the range of 1.51-1.67 W/(m·K). The normalized elemental leaching rates of Ca and Nd in the Fe-Nd-0.2 sample keep in low values of 6.20 × 10~(-2) and 4.86 x 10~(-4) g/(m~2·d) after 42 d.     

Understanding the Effect of Oxygen on the Glass-Forming Ability of Zr55Cu55Al9Be9 Bulk Metallic Glass by ab initio Molecular Dynamics Simulations

Oxygen (O) is an inevitable impurity in bulk metallic glasses (BMGs) and its influence over the glass-forming ability (GFA) of BMGs is a longstanding controversy. The present ab initio molecular dynamics (AIMD) simulations indicate that the GFA decreases upon introducing 0.78 at. pct O in the amorphous Zr₅₅Cu₅₅Al₉Be₉ (at. pct), while examining the evolution of atomic configurations and kinetic properties in BMGs. This study includes a comprehensive analysis using pair correlation function (PCF), bond pair analysis (BPA), and Voronoi polyhedra construction. It is concluded that the incorporation of O leads to a decline in the closely packed icosahedral polyhedrons, where the atom O is coordinated with Be and Zr in the first nearest shell to form the O-centered clusters with enhanced ordering. Mean square displacement (MSD) analysis also shows that the trace O could induce remarkable acceleration of atomic mobility, therefore increasing crystallization tendency of the Zr₅₅Cu₅₅Al₉Be₉ alloy. The present results illuminate the role of O in the metallic glass-forming process and reveal the underlying role of O in the GFA of the Zr-Cu amorphous alloys.

     

Enhanced afterglow performance of CaAl_2O_4:Eu~(2+),Nd~(3+) phosphors by co-doping Gd~(3+)

In order to effectively improve the afterglow properties of CaAl_2 O_4:Eu~(2+),Nd~(3+) phosphors,a series of Ca_(0.982-x)Al_2 O_4:0.012 Eu~(2+),0.006 Nd~(3+),xGd~(3+)(x=0,0.012,0.024,0.036,0.048,0.060 mol) phosphors were prepared by a high-temperature solid-phase approach.Crystalline composition and microstructure were characterized by XRD,TEM,HRTEM,and XPS,luminescence properties were systematically analyzed by fluorescence spectra,afterglow decay curves and TL glow curve.Results show that all of Ca_(0.982-x)Al_2 O_4:0.012 Eu~(2+),0.006 Nd~(3+),xGd~(3+)phosphors belong to monoclinic CaAl_2 O_4,without other cystalline phase.The blue emission at 442 nm is observed,which is assigned to the 4 f~65 d→4 f~7 transition of Eu~(2+) ions.Doping with appropriate amount of Gd~(3+) ions(x=0.036 mol) significantly improves the afterglow properties of phosphors,but the excessive doping of Gd~(3+) induces the fluorescent quenching.The doping of moderate Gd3+changes the traps states,the trap depth varies from 0.598 to 0.644 eV and the trap concentration is also greatly improved,thus significantly improving afterglow performance.     

Effect of La–Y co-substitution on magnetic properties and microstructure of NdFeB alloy ribbons

Committed to obtaining cost-effective NdFeB based permanent magnets, Nd_27–xLa₃Y_xFe_balAl_0.1Cu_0.1B₁ (x = 0–3) alloys were fabricated to detect the magnetic properties and microstructure. When x = 1.8, coercivity of 1004 kA/m and the magnetic remanence of 0.75 T are obtained, which are close to those of the original Nd₃₀Fe_balAl_0.1Cu_0.1B₁ alloy ribbons. The temperature coefficient of coercivity (β) and the temperature coefficient of remanence (α) of the LaY-substituted alloys are better than those of the original alloys. The research results manifest that La is mainly distributed in the grain boundary phases and plays the role of refining the main grains, optimizing the grain boundary phases and improving the wettability between the main phases and the grain boundary phases, while Y tends to enrich in the main phases and enhances the short-range exchange coupling.     

Formation,Structure, and Crystallization Behavior of Cu-Based Bulk Glass-Forming Alloys

We studied Cu-Zr–based alloys having exceptionally high glass-forming ability (GFA) and investigated the influence of Ag and Al addition on their structure and crystallization behavior. Most of the bulk glassy alloys (BGAs) do not contain any crystals, while some samples studied by high-resolution transmission electron microscopy (HRTEM) were found to contain well-developed medium-range order zones and nanoparticles in a bulk form. The crystallization kinetics of Cu₅₅Zr₄₅, Cu₅₀Zr₅₀, Cu_55–x Zr₄₅Ag _x (x = 0, 10, 20), Cu₄₅Zr₄₅Al₅Ag₅, Cu₄₄Ag₁₅Zr₃₆Ti₅, and Cu₃₆Zr₄₈Al₈Ag₈ glassy alloys was analyzed. An influence of the cooling rate on the formation of glassy phase and thermal stability of the Cu-based glassy alloys on heating was also studied. The crystallization kinetics and phase composition of the ribbon-shape and bulk glassy samples of Cu₃₆Zr₄₈Al₈Ag₈ alloys were also analyzed. The results also indicate that the best glass-forming compositions are possibly located at slightly off-eutectic area, owing to the shift of the eutectic point due to the nonequilibrium processing conditions.     

Helium ion irradiation effects on neodymium and cerium co-doped Gd2Zr2O7 pyrochlore ceramic

This paper studies the helium ions irradiation effects on Nd and Ce co-doped Gd_2 Zr_2 O_7 ceramics. where Nd replaces the Gd site and Ce replaces the Zr site respectively. A series of(Gd_(1-x)Nd_x)_2(Zr_(1-y)Ce_y)_2 O_7(0 ≤ x, y ≤ 1) ceramics were irradiated with a 500 keV He ions at room temperature at fluences ranging from 1 × 10~(15) to 1 × 10~(17) ions/cm~2. The irradiated samples were characterized using GIXRD, Raman and SEM measurements. From the GIXRD and Raman observations, the results indicate that all the samples display a deficient fluorite structure after irradiation. The irradiation toleration increases with the irradiation depth increasing under experimental conditions, and Nd_2 Ce_2 O_7 has the best irradiation stability in the(Gd_(1-x)Nd_x)_2(Zr_(1-y)Ce_y)_2 O_7(0≤ x. y≤1). Based on SEM results, the irradiated samples are still relatively dense and uniform, and no second phase exists.