Magnetic behavior,transport properties and nanocrystallization of melt-spun YxCe50 − xCu42Al8 (0 ≤ x ≤ 50) amorphous system

Amorphous Y_xCe_50 ? xCu₄₂Al₈ (0 ≤ x ≤ 50) ribbons prepared by melt-spinning on the Cu wheel were subjected to X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and to the measurements of magnetization and resistivity in the temperature range from 1.7 to 300 K. Effective activation energies, characteristic crystallization temperatures and enthalpies of as-quenched alloys have been determined. Two stages of crystallization have been observed in most samples (except shallow effects in Ce₅₀Cu₄₂Al₈). The activation energies have been calculated from the Kissinger relation to be 247 ± 18 and 570 ± 56 kJ/mol for Y₂₅Ce₂₅Cu₄₂Al₈ and Y₅₀Cu₄₂Al₈, respectively. The absence of the endothermic effect for x = 50, usually associated with a glass transition, below the primary crystallization event, indicates the presence of dispersed polyamorphous packing with a wide range of local glass transitions. The magnetization versus temperature plot for Y₂₅Ce₂₅Cu₄₂Al₈ points to a magnetic ordering at temperatures considerably below 50 K. This observation has been confirmed by the temperature dependence of resistivity, which exhibits a singularity at the same temperature. Moreover, a negative temperature coefficient of resistivity, characteristic of disordered systems, was observed. The electrical resistivity in the Y₂₅Ce₂₅Cu₄₂Al₈ amorphous alloy is governed by the weak localization of electrons.     

Effect of crystallization behavior on the oxidation resistance of a Zr–Al–Cu metallic glass below the crystallization temperature

The crystallization behavior of Zr_65.0Al_7.5Cu_27.5 (at.%) metallic glass with 753 and 1053 K annealing treatment and its effect on oxidation resistance around the supercooled liquid region at 623 and 663 K was studied. The crystalline phase of bct-Zr₂Cu precipitates for the specimen annealed at 753 K was observed, while duplex structures of bct-Zr₂Cu and Zr₂Al formed in the specimen annealed at 1053 K. The oxidation resistance of the specimen depended on the amount of crystalline precipitates. Regardless of the exposure temperature, the annealed specimens showed higher oxidation resistance than the melt-spun one, especially for the specimen annealed at 1053 K. The formation of numerous crystalline phases of bct-Zr₂Cu and Zr₂Al from the matrix was responsible for improving the oxidation resistance due to their higher oxidation resistance and promotion of the development of Al₂O₃ and oxides of copper. The oxide constituents of the amorphous alloy after long exposure depended on the temperature. The oxide was composed of a large amount of CuO, some tetragonal and monoclinic-ZrO₂ and a minor amount of Cu₂O as well as a slight amount of Al₂O₃ for the melt-spun specimen during exposure at 623 K. Under the 663 K exposure, however, the oxide state of Cu³⁺ in the scale was also detected.     

Investigation of viscosity and crystallization in supercooled-liquid region of Zr-based glassy alloys

Using viscosity measurement method and in-situ heating synchrotron radiation, the viscosity of the (Zr_0.55Al_0.1Ni_0.05Cu_0.3)_100 ? xY_x (x = 0, 0.5, 1, 2) bulk metallic glasses (BMGs) in their supercooled liquid regions (SLRs) and the in-situ heating nucleation were investigated, respectively. In the SLR, the (Zr_0.55Al_0.1Ni_0.05Cu_0.3)₉₉Y₁ metallic glass which shows distinct plastic strain in compression exhibits higher viscosity than the other three BMGs, however their Poisson's ratios are almost the same. The synchrotron diffraction results show that crystallization happened in the SLR of the (Zr_0.55Al_0.1Ni_0.05Cu_0.3)₉₉Y₁ glassy alloy, which could be the reason for the higher viscosity and larger plastic strain in compression compared to the other three alloys. The fracture surfaces of the glassy alloys were observed and analyzed.     

Enhanced glass-forming ability of a Zr-based bulk metallic glass with yttrium doping

A significant enhancement in glass formation in a newly developed Zr₅₁Cu_20.7Ni₁₂Al_16.3 alloy has been achieved by yttrium doping. With just 0.5 at.% yttrium doping, the critical diameter of the as-cast alloys for glass formation has been increased from 3 mm to at least 10 mm. In the undoped, large-sized alloys, massive oxygen stabilized crystalline phases are observed but disappear in yttrium doped alloys. Very small amounts of stable α-Y₂O₃ phases found in the yttrium doped alloys, and their negligible effect on the metallic glasses’ properties, provide a superior solution to achieve metallic glasses with a high glass formability.     

Fabrication of Cr4+,Nd3+:YAG transparent ceramics for self-Q-switched laser

Transparent 0.1 at.%Cr,1.0 at.%Nd:YAG (Y₃Al₅O₁₂) ceramics were fabricated by a solid-state reaction and vacuum sintering with CaO as a charge compensator and tetraethyl orthosilicate (TEOS) as a sintering aid using high-purity powders of Al₂O₃, Y₂O₃, Nd₂O₃ and Cr₂O₃. The mixed powder compacts were sintered at 1800 °C for 5 h and 30 h under vacuum. The optical transmittance of the Cr,Nd:YAG ceramics sintered at 1800 °C for 5 h and 30 h is ∼63% and ∼78% in the infrared wavelengths, respectively. The two samples exhibit pore-free structures and the average grain size is about 10 and 20 μm. For the sample sintered at 1800 °C for 5 h, the dominant fracture mechanism is the transgranular fracture. With increase of holding time up to 30 h, the ratio of intergranular fracture surfaces increase and more Cr³⁺ ions in the Cr,Nd:YAG ceramic transform to Cr⁴⁺. High-quality Cr⁴⁺,Nd³⁺:YAG transparent ceramics may be a potential self-Q-switched laser material.     

Internal stresses induced by plastic shear deformation of Zr–(Cu,Ag)–Al bulk metallic glasses

Effective internal shear stress σ_i induced by torsional deformation of Zr₄₆(Cu_4/5Ag_1/5)₄₆Al₈ and Zr₄₆Cu₄₆Al₈ bulk metallic glasses different by the glass-forming ability of the maternal melts has been determined by measurements of stress relaxation upon stepwise unloading. It has been found that the ratio σ_i/σ₀ (σ₀ is the initially applied shear stress) decreases upon increasing the temperature from ≈ 0.8 at T = 450K (T ≈ 0.64 × T_g) to ≈ 0.08 at T = 638K (T ≈ 0.91 × T_g) independently of σ₀ and glass composition. The obtained result is in good agreement with earlier data obtained on ribbon metallic glasses. The origin of deformation-induced internal stresses and their connection with deformation mechanisms of metallic glasses has been briefly discussed.     

Lightweight Ti–Zr–Be–Al bulk metallic glasses with improved glass-forming ability and compressive plasticity

A series of lightweight Ti–Zr–Be–Al bulk metallic glasses (BMGs) have been developed through the addition of Al to Ti–Zr–Be ternary glassy alloy. By replacing Be with Al, the critical size of the glassy rod has been increased from 5 mm for Ti₄₁Zr₂₅Be₃₄ alloy to 7 mm for Ti₄₁Zr₂₅Be₂₉Al₅ alloy, while the yield strength of Ti₄₁Zr₂₅Be_34 ? xAl_x (x = 2–10) has been greatly enhanced, resulting in a significant increase of the specific strength which is defined as yield strength/density. Among these newly developed Ti–Zr–Be–Al BMGs, Ti₄₁Zr₂₅Be₂₆Al₈ glassy alloy exhibits a high specific strength of 4.33 × 10⁵ Nm/kg and a very large compressive plastic strain of 47.0%, which are much larger than those (3.69 × 10⁵ Nm/kg and 2.9%, respectively) for Ti₄₁Zr₂₅Be₃₄ glassy alloy. The present results show that Al is an effective alloying element for improving the glass-forming ability (GFA) and mechanical properties of Ti-Zr-Be glassy alloy.     

Preparation and mechanical properties of a bulk icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy

A bulk Ti₄₅Zr₃₅Ni₁₇Cu₃ alloy, which consisted of the icosahedral quasicrystalline phase, was prepared by mechanical alloying(MA) and subsequent pulse discharge sintering. Ti₄₅Zr₃₅Ni₁₇Cu₃ amorphous powders (with particle size <50 μm) were obtained after mechanical alloying for more than 150 h from the mixture of the elemental powder. The transformation temperature range from amorphous phase to the quasicrystalline phase was from 400 K to 900 K. The mechanical properties of the bulk quasicrystalline alloy have been examined at room temperature. The Vickers hardness and compressive fracture strength were 620 ± 40 and 1030 ± 60 MPa, respectively. The bulk quasicrystalline alloy exhibited the elastic deformation by the compressive test. The fracture mode was brittle cleavage fracture.     

Structural relaxation and glass transition behavior of novel (Ti33Zr33Hf33)50(Ni50Cu50)40Al10 alloy developed by equiatomic substitution

A series of glass forming alloys (Ti₃₃Zr₃₃Hf₃₃)_100−x−y(Ni₅₀Cu₅₀)_xAl_y (x = 20–70 at.% and y = 0–30 at.%) have been developed by equiatomic substitution of similar elements. Of these alloys (Ti₃₃Zr₃₃Hf₃₃)₅₀(Ni₅₀Cu₅₀)₄₀Al₁₀ was chosen in this study to investigate the structural relaxation and glass transition behavior. The as-quenched (Ti₃₃Zr₃₃Hf₃₃)₅₀(Ni₅₀Cu₅₀)₄₀Al₁₀ alloy was fully amorphous and had a wide supercooled liquid region ΔT = T_x(503 °C) − T_g(433 °C) = 70 °C, where T_g and T_x are the glass transition and crystallization temperatures, respectively. Low temperature pre-heat treatments of the (Ti₃₃Zr₃₃Hf₃₃)₅₀(Ni₅₀Cu₅₀)₄₀Al₁₀ alloy for 10 min at 310 °C, 370 °C and 390 °C caused structural relaxation accompanied by the formation of very fine scale lattice ordering. After these heat treatments, the glass transition became hard to observe in the (Ti₃₃Zr₃₃Hf₃₃)₅₀(Ni₅₀Cu₅₀)₄₀Al₁₀ alloy. Increasing the pre-heat treatment temperatures and holding times caused the glass transition to become more clearly detectable with increasing endothermic heat release.     

Bulk metallic glass formation in Cu–Zr–Ti ternary system

The formation of bulk metallic glasses (BMG) in the Cu-rich Cu–Zr–Ti ternary system is studied by using the ‘e/a-variant line criterion’. Three such lines, (Cu₉Zr₄)_1−xTi_x, (Cu_61.8Zr_38.2)_1−xTi_x and (Cu₅₆Zr₄₄)_1−xTi_x, are defined in the Cu–Zr–Ti system by linking three binary compositions Cu₉Zr₄, Cu_61.8Zr_38.2 and Cu₅₆Zr₄₄ to the third element Ti. The binary compositions Cu₉Zr₄, Cu_61.8Zr_38.2 and Cu₅₆Zr₄₄ correspond to specific Cu–Zr binary clusters. BMGs are obtained by copper mould suction casting method with Ti contents of 7.5–15 at.%, 7.5–12.5 at.% and 5–12 at.%, respectively along the (Cu₉Zr₄)_1−x Ti_x, (Cu_61.8Zr_38.2)_1−xTi_x and (Cu₅₆Zr₄₄)_1−xTi_x lines. The BMGs on each composition line manifest decreased thermal stabilities and glass forming abilities (GFAs) with increasing Ti contents. The maximum GFA appears at Cu₆₄Zr_28.5Ti_7.5, with characteristic thermal parameters of T_g = 736 K, T_x = 769 K, T_g/T_l = 0.627 and γ = 0.403, which are all superior to those reported for the known Cu₆₀Zr₃₀Ti₁₀ BMG.     

Growth and scintillation properties of Pr doped Gd3(Ga,Al)5O12 single crystals

Pr:Gd₃(Ga,Al)₅O₁₂ single crystals were grown by the micro-pulling down (μ-PD) method. All grown crystals were greenish and transparent with 3.0 mm in diameter, 15–30 mm in length. Neither visible inclusions nor cracks were observed. Luminescence and scintillation properties were measured. The substitution at the Al³⁺ sites by Ga³⁺ in garnet structure has been studied. In these crystals, Pr³⁺ 5d–4f emission is observed with 340 nm wavelength. Pr1%:Gd₃Ga₃Al₂O₁₂ shows highest emission intensity. The light yield of Pr:Gd₃Ga₃Al₂O₁₂ sample with 3 mmφ×1 mm size was around 4500 photon/MeV. Scintillation decay time was 7.9 ns (0.5%), 46 ns (0.7%) and 214 ns (98.8%).     

Bulk glass formability for Cu–Hf–Zr–Ag and Cu–Zr–Ag–Si alloys

The effects of the gradual substitution of Zr by Hf on glass formability and thermal stability in the Cu₄₅Zr_45?xHf_xAg₁₀ alloys and the effects of small additions of Si on glass formability in the Cu₄₅Zr₄₅Ag₁₀ alloy are reported and discussed. The samples were prepared as ribbons of thickness in the range 25–200 μm by melt spinning and as conical bulk shapes, with a length of 50 mm and cone base diameters in the range 2–10 mm, by suction die casting. The alloy Cu₄₅Zr₄₅Ag₁₀ had a critical cylindrical rod diameter for glass formation, d_c, of 3.5 mm but substitution of 1.5 and 3.5 at.% Zr by Hf resulted in substantial increases to 5.5 and 4.5 mm, respectively. However, for x in the range 5–40 at.%, d_c was reduced to <1 mm_. The small addition of Si proved to be beneficial to the glass forming ability (GFA), increasing d_c up to 5.5 mm for 0.5 at.% Si. Thus the chemical and atomic size similarities of Hf and Zr do not guarantee that bulk glass formation will be maintained on substituting large proportions of Zr by Hf though small substitutions of Hf and of minor additions of Si were beneficial to the GFA. These effects are discussed in terms of the possible influence of the alloying additions on the liquid structure and on the number density of heterogeneous nucleants.     

The luminescence of Pr3+ ions doped in Y4Al2O9 by sol–gel synthesis

The Pr³⁺-doped Y₄Al₂O₉ powders were synthesized by sol–gel method. Powder X-ray diffraction and SEM techniques were used to check for Y₄Al₂O₉ powders. The Li⁺ co-doping with Pr³⁺ has an influence on the sintering temperature and morphology of the Y₄Al₂O₉ powders produced from the gel. The emission spectra under different excitations, e.g., the 488 nm line of an argon-ion laser, X-ray and UV light, were investigated. The luminescence intensity of Y₄Al₂O₉:Pr³⁺ could be increased with Li⁺ co-doping. Luminescence properties of Pr³⁺ ions in the two samples have some difference. In the Y₄Al₂O₉:Pr³⁺, the emission at 490 nm from ³P₀ is dominant, while, the Y₄Al₂O₉:(Pr³⁺ + Li⁺) system was characterized by a red emission at 607 and 610 nm corresponding to the ¹D₂ → ³H₄ inner transition of Pr³⁺ ions; and these two emissions show different excitation band from the 4f5d state.     

Effects of Zn on the glass forming ability and mechanical properties of MgLi-based bulk metallic glasses

Through the addition of Zn element, Mg-Li-Cu-Zn-(Y, Gd) bulk metallic glasses (BMGs) with diameter of 2 mm have been successfully fabricated by conventional copper mold injection casting method. The X-ray diffractometer (XRD) patterns and differential scanning calorimeter (DSC) traces demonstrated that the as-cast Mg₆₀Li₅Cu₂₀Zn₅(Y, Gd)₁₀ BMGs were fully amorphous phase. By the minor addition of 5 at.% Zn, the supercooled liquid regions (SLR) of Mg₆₀Li₅Cu₂₀Zn₅(Y, Gd)₁₀ BMGs increased 6 K and 3 K respectively compared with that of Zn-free samples, which implied that their glass forming ability (GFA) and thermal stability were improved. It was also proved that the addition of Zn effectively enhanced the alloys’ fracture strength (453 MPa and 456 MPa) and elastic strain (0.75% and 0.92%), which were much higher than that of Mg₆₀Li₅Cu₂₅Y₁₀ BMG (403 MPa, 0.62%) and Mg₆₀Li₅Cu₂₅Gd₁₀ BMG (412 MPa, 0.82%).     

Tensile properties of ZrCu-based bulk metallic glasses at ambient and cryogenic temperatures

The tensile behaviors of a series of (Zr_47.5Cu_47.5Al₅)_1 ? x(Zr₈₀Nb₂₀)_x (x = 0, 0.05, 0.10, 0.15) bulk metallic glasses were studied at ambient and cryogenic (77 K) temperatures. It is found that the tensile strength of the alloys increases as the temperature decreases from 298 K to 77 K. The maximum enhancement is 15.7%, and the toughness of these alloys does not deteriorate at low temperatures. We demonstrate that the higher energy required to raise the temperature in the shear bands from the cryogenic temperature to glass transition temperature is the origin of the tensile strength enhancement at low temperatures.     

Nano-crystallization behavior of Zr–Cu–Al bulk glass-forming alloy

The glass-forming ability and devitrification behavior of a Zr₅₅Cu₃₅Al₁₀ bulk glass-forming alloy were examined to elucidate the very high nanocrystallization product density (> 10²³ m^?3). The crystallization kinetics and structural changes in the glassy alloy were studied using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The observed sequential phase formation during isothermal reaction and the high nanocrystal density are consistent with the influence of residual oxygen even at low levels (< 500 ppm) to promote nucleation.     

The effects of microalloying on thermal stability,mechanical property and corrosion resistance of Mg-based bulk metallic glasses

(Mg₆₅Cu₂₀Y₁₀Zn₅)₉₈ M₂ (M = Ti, Cr) bulk metallic glasses with diameter of 3 mm were prepared by copper mold casting. The effects of Ti or Cr on thermal stability, mechanical property and corrosion resistance were systematically investigated. It's shown that the Glass forming ability of the Mg₆₅Cu₂₀Y₁₀Zn₅ bulk metallic glasses slightly decreases with the addition of the elements. Whereas, the strength and corrosion resistance significantly increase. The superior corrosion resistance of the amorphous sample containing Ti or Cr is presented for the forming of homogeneous passive layer with highly protective oxides.     

Synthesis and characterization of bulk amorphous Zr65Cu18Ni9Al8 and [Zr0.65Cu0.18Ni0.09Al0.08]98Er2 alloys

Bulk metallic glasses (BMGs), especially Zr-based BMGs, have attracted lot of attention of materials scientists because of their very attractive physical, thermal and mechanical properties and a few unique applications. In the present study, Zr₆₅Cu₁₈Ni₉Al₈ alloy was designed according to the criterion of conduction electron/atom (e/a ratio) ∼1.395 and average atomic size of alloy (R_a) ∼0.1498 nm. Addition of 2 at.% Er was carried out in the base alloy to investigate its effect on thermal and mechanical properties. Characterization of alloys was performed using the techniques of XRD, DSC, and SEM/EDS. Mechanical properties like Vicker’s microhardness, nanohardness, elastic modulus, density and fracture strength were measured. Average shear angle was found to be ∼35 ± 1° for base alloy and about 31 ± 1° for alloy containing 2 at.% Er. Wide supercooled liquid regions of 129 K and 119 K were found for the base alloy and the alloy containing 2 at.% Er.     

Atomic structure and hydrogen storage properties of amorphous–quasicrystalline Zr–Cu–Ni–Al melt-spun ribbons

A structural state of the Zr–Cu–Ni–Al melt-spun ribbons has been investigated by means of X-ray diffraction analysis. It was established that conditions of ribbon production have a very strong effect on their structural state. The Zr_69.3Cu_9.7Ni_15.1Al_5.9 ribbons produced at the surface wheel velocity of 44 m/s have an amorphous state at the contact side and mixed amorphous–quasicrystalline state at the free side. At the same time the Zr_67.5Cu_12.5Ni₁₂Al₈ ribbons are fully amorphous in case of producing velocity of 44 m/s and have only small features of quasicrystalline peaks on the amorphous halo on the free side in case of producing velocity of 30 m/s in contrast to an amorphous structure on the contact side. The uncoated by Pd amorphous and amorphous–quasicrystalline Zr–Cu–Ni–Al ribbons have a property of absorbing a large amount of hydrogen. Parameters of the amorphous state were calculated for the ribbons as-prepared and hydrogenated. The temperature coefficient of resistivity for all ribbons is negative in range of 20–380 °C, what as well as the high resistivity values is typical to the Zr–Cu–Ni–Al based systems in amorphous and quasicrystalline states.     

Effects of sintering temperature on microstructure and property evolution of Fe81Cu2Nb3Si14 soft magnetic materials fabricated from amorphous melt-spun ribbons by spark plasma sintering technique

Bulk Fe₈₁Cu₂Nb₃Si₁₄ soft magnetic materials were fabricated by spark plasma sintering (SPS) of amorphous powder, which was prepared by ball milling of melt-spun ribbons. Effects of sintering temperature on the evolution of microstructure and related properties were systematically investigated. Results show that the as-milled powders exhibit similar microstructure and thermal property in comparison with the original melt-spun ribbons. With an increase in the sintering temperature, the relative density, microhardness and saturation magnetization of the sintered samples improved obviously, but the coercive force decreased at the beginning and then increased with the increase of sintering temperature. The sintered samples exhibit typical soft magnetic characteristic. The desirable soft magnetic property of the sintered samples was achieved by SPS at 630 °C. Meanwhile, microstructure and densification behaviors of the sintered samples were also investigated.