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.     

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.     

An investigation of hydrogen storage kinetics of melt-spun nanocrystalline and amorphous MgeNi-type alloys

The nanocrystalline and amorphous Mg2Ni-type Mg2–xLaxNi (x=0,0.2) hydrogen storage alloys were synthesized by melt-spinning technique.The as-spun alloy ribbons were obtained.The microstructures of the as-spun ribbons were characterized by X-ray diffraction (XRD),high resolution transmission electronic microscopy (HRTEM) and electron diffraction (ED).The hydrogen absorption and desorption kinetics of the alloys were measured using an automatically controlled Sieverts apparatus,and their electrochemical kinetics were tested by an automatic galvanostatic system.The electrochemical impedance spectrums (EIS) were plotted by an electrochemical workstation (PARSTAT 2273).The hydrogen diffusion coefficients in the alloys were calculated by virtue of potential-step method.The obtained results showed that no amorphous phase was detected in the as-spun La-free alloy,but the as-spun alloys substituted by La held a major amorphous phase,con-firming that the substitution of La for Mg markedly intensified the glass forming ability of the Mg2Ni-type alloy.The substitution of La for Mg notably improved the electrochemical hydrogen storage kinetics of the Mg2Ni-type alloy.Furthermore,the hydrogen storage kinetics of the experimental alloys was evidently ameliorated with the spinning rate growing.     

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.     

Thermodynamic study of bulk metallic glass: Zr41.2Ti13.8Cu12.5Ni10.0Be22.5

Recently, multicomponent glass forming alloys have been found which exhibit extraordinary glass forming ability and cooling rates of less than 100 K/s are sufficient to suppress nucleation of crystalline compounds and consequently form a bulk metallic glass (BMG). The thermophysical properties of liquid metals and alloys in the undercooled state is become great interest of research in recent years. Due to the high thermal stability of undercooled melts of BMG glass formers the experimental data of the thermophysical properties of bulk metallic melts are available in the undercooled region. It is interesting to study the thermodynamics of such materials. The aim of the present work to discuss the thermodynamic behavior of BMG by estimating the Gibb’s free energy difference ΔG, enthalpy difference ΔH and entropy difference ΔS between the undercooled liquid and corresponding equilibrium solid phases. The study is made by estimating ΔG, ΔH and ΔS for BMG: Zr_41.2Ti_13.8Cu_12.5Ni_10.0Be_22.5 in the entire temperature range T _m (melting temperature) to T _g (glass transition temperature).     

Phase Equilibria and Phase Transition of the Ni–Fe–Ga Ferromagnetic Shape Memory Alloy System

Phase equilibria and martensitic and magnetic transitions of the β (B2 and L2₁) phase in the Ni–Fe–Ga system were investigated. The b phase was found to be in equilibrium with the γ (A1 structure) or γ′ (L1₂ structure) phase. The Curie temperature, T _c , equilibrium temperature, T _o 5 (Ms + Af)/2, martensitic transition starting temperature, M _s , and reverse transition finishing temperature, Af , of the β single–phase alloys were sensitive to the Fe and Ga compositions. The Fe substitution for Ni decreased and increased the T _o and T _c , respectively. The Ga substitution for Ni or Fe decreased both the T _o and T _c . The entropy change accompanying the reverse martensitic transition showed compositional dependence due to the magnetic contribution. The saturation magnetization I _s of the Ni–Fe–Ga system showed a strong dependence on the magnetic valence Z _M . The Is values of the Ni–Fe–Ga alloys annealed at 1023 K showed the same Z _m dependence as other ferromagnetic shape memory alloy (FSMA) systems. This article is based on a presentation made in the symposium entitled "Phase Transformations in Magnetic Materials," which occurred during the TMS Annual Meeting, March 12-16, 2006, in San Antonio, Texas, under the auspices of the Joint TMS–MPMD and ASMI–MSCTS Phase Transformations Committee.     

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.     

Relaxation Behavior of Ca-Based Bulk Metallic Glasses

The relaxation behavior of Ca₆₀Mg₂₀Zn₂₀, Ca₆₀Mg₂₀Cu₂₀, Ca₆₅Mg₁₅Zn₂₀, Ca₅₀Mg₂₀Cu₃₀, and Ca₅₅Mg₁₈Zn₁₁Cu₁₆ bulk metallic glasses was determined in the glass transition region using differential scanning calorimetry (DSC) with heating rates from 1 to 160 K/min. The activation enthalpy of structural relaxation and the fragility index m were found to be smaller in the glassy state (onset of the glass transition) than in the supercooled liquid state (end of glass transition). The Ca-based glass-forming liquids showed strong behavior of the relaxation time, with the fragility indexes m in the range of 33 to 40. The strong liquid behavior implies sluggish kinetics of crystallization in the supercooled liquid region and explains the very good glass-forming ability (GFA) of these alloys. The critical cooling rate for amorphization R _c of the Ca-based bulk metallic glasses was estimated to be in the range of 0.3 to 10 K/s, which is similar to R _c values for the best Pd- and Zr-based metallic glass-forming alloys discovered so far.     

Unique metallic glass formability and ultra-high tensile strength in AlNiFeGd alloys

The metallic glass formability of aluminum-rich AlNiFeGd alloys has been systematically investigated. The critical cooling rate required to form an amorphous state in this system is generally low, and comparable to that of some of the best metallic glass formers, such as PdCuSi. Amorphous ribbons up to 0.25 mm thick can easily be produced by the single-roller melt-spinning technique. Tensile strengths as high as 1280 MPa and Young's modulus of 75 GPa have been obtained. Bulk amorphous alloys with good mechanical properties are optimized in Al₈₅Ni₆Fe₃Gd₆. DSC and DTA studies reveal that the glass formability is unique for Al-based alloys because the reduced glass temperature T_rg for AlNiFeGd can be as low as 0.44. This is much lower than conventional theory would suggest for easy glass forming systems. A mechanism for the unusual glass formability is suggested.     

Oxidation behavior of multiphase Nb-Mo-Si-B intermetallics

The mixed substitution of Nb and Mo in the ternary systems Mo-Si-B and Nb-Si-B was studied with the goal of balancing oxidation resistance with mechanical behavior. The microstructure and oxidation behavior of six compositions in the Nb-Mo-Si-B system were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy, electron probe microanalysis (EPMA), and thermogravimetric analysis. Proper selection of the total metal content and the Nb/Mo ratio results in the co-existence of a T1 phase, as (Nb, Mo)₅Si₃B_x, and a solid solution (Nb,Mo) metal phase. At 800 °C, all compositions exhibited catastrophic oxidation, while changing to a quasi-steady-state mass gain at 1200 °C. The high rate constants at 1200 °C indicate that the scales formed were not passivating. A complex scale consisting of four layers formed that was about 350-to 450-μm thick after oxidation for 50 hours at 1200 °C. Borosilicate glass did form within the scale, but the significant prevalence of Nb₂O₅ within the glass, and the resulting inability of the glass to seal pores formed by the evaporation of MoO₃, contributed to the overall poor oxidation resistance compared to the ternary Mo-Si-B system. The Nb and Mo content of the alloy must be further studied and optimized before these alloys may be considered for further development for hightemperature applications. This article is based on a presentation made in the symposium entitled “Beyond Nickel-Base Superalloys,” which took place March 14–18, 2004, at the TMS Spring meeting in Charlotte, NC, under the auspices of the SMD-Corrosion and Environmental Effects Committee, the SMD-High Temperature Alloys Committee, the SMD-Mechanical Behavior of Materials Committee, and the SMD-Refractory Metals Committee.     

Ferromagnetic bulk amorphous alloys

This article reviews our recent results on the development of ferromagnetic bulk amorphous alloys prepared by casting processes. The multicomponent Fe-(Al,Ga)-(P,C,B,Si) alloys are amorphized in the bulk form with diameters up to 2 mm, and the temperature interval of the supercooled liquid region before crystallization is in the range of 50 to 67 K. These bulk amorphous alloys exhibit good soft magnetic properties, i.e., high B _s of 1.1 to 1.2 T, low H _o of 2 to 6 A/m, and high μ _e of about 7000 at 1 kHz. The Nd-Fe-Al and Pr-Fe-Al bulk amorphous alloys are also produced in the diameter range of up to 12 mm by the copper mold casting process and exhibit rather good hard magnetic properties, i.e., B _r of about 0.1 T, high H _o of 300 to 400 kA/m, and rather high (JH)_max of 13 to 20 kJ/m³. The crystallization causes the disappearance of the hard magnetic properties. Furthermore, the melt-spun Nd-Fe-Al and Pr-Fe-Al alloy ribbons exhibit soft-type magnetic properties. Consequently, the hard magnetic properties are concluded to be obtained only for the bulk amorphous alloys. The bulk Nd- and Pr-Fe-Al amorphous alloys have an extremely high T _x/T_m of about 0.90 and a small ΔT _m(=T _m−T _x) of less than 100 K and, hence, their large glass-forming ability is due to the steep increase in viscosity in the supercooled liquid state. The high T _x/T_m enables the development of a fully relaxed, clustered amorphous structure including Nd-Nd and Nd-Fe atomic pairs. It is, therefore, presumed that the hard magnetic properties are due to the development of Nd-Nd and Nd-Fe atomic pairs with large random magnetic anisotropy. The Nd- and Pr-based bulk amorphous alloys can be regarded as a new type of clustered amorphous material, and the control of the clustered amorphous structure is expected to enable the appearance of novel functional properties which cannot be obtained for an ordinary amorphous structure. This article is based on a presentation made in the “Structure and Properties of Bulk Amorphous Alloys” Symposium as part of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10–11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees, and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory.     

Bulk amorphous metallic alloys: Synthesis by fluxing techniques and properties

Bulk amorphous alloys having dimensions of at least 1 cm in diameter have been prepared in the Pd-Ni-P, Pd-Cu-P, Pd-Cu-Ni-P, and Pd-Ni-Fe-P systems using a fluxing and water-quenching technique. The compositions for bulk glass formation have been determined in these systems. For these bulk metallic glasses, the difference between the crystallization temperature (T _x) and the glass transition temperature (T _g, ΔT=T _x−T _g) ranges from 60 to 110 K. These large values of ΔT open the possibility for the fabrication of amorphous near-net-shaped components using techniques such as injection molding. The thermal, elastic, and magnetic properties of these alloys have been studied, and we have found that bulk amorphous Pd₄₀Ni_22.5Fe_17.5P₂₀ has spin glass behavior for temperatures below 30 K. This article is based on a presentation made in the “Structure and Properties of Bulk Amorphous Alloys” Symposium as part of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10–11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees, and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory.     

Effect of Al Addition on Glass Forming Ability and Glass Stability of Ca-Mg-Zn-Cu Based Bulk Metallic Glasses

The effect of Al addition on glass forming ability (GFA) and stability of the glassy phase against crystallization was studied for Ca-Mg-Zn, Ca-Mg-Cu, and Ca-Mg-Zn-Cu alloys. The glassy alloys were produced by copper mold casting as wedge-shaped samples with thicknesses varying from 0.5 to 10 mm. Thermal properties, such as glass transition, crystallization and melting temperatures, as well as heats of crystallization and melting, were determined for the produced glasses. Partial substitution of Zn or Cu with Al was found to improve the glass stability (GS) against the general tendency to reduce the GFA. The 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, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.

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[(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.     

High copper content bulk glass formation in bimetallic Cu-Hf system

We report in this article that strip-shaped amorphous samples with thicknesses from 0.5 to 2 mm were successfully synthesized for binary Cu-Hf alloys containing 60 to 68 at. pct Cu by the traditional copper mold casting method. The best glass former Cu₆₆Hf₃₄ with casting thickness up to 2 mm has an undercooled liquid region (ΔT=T _x −T _g , where T _g is the glass transition temperature and T _x is the onset temperature of the first crystallization event) of 51 K, which is somewhat narrow compared with other neighboring alloys in the same system. The bulk glassy Cu₆₆Hf₃₄ alloy exhibits Vicker’s Hardness (H _v ) ∼779 kg/mm², Young’s modulus ∼108 GPa, fracture strength ∼2.1 GPa, and an almost constant elastic elongation ∼1.8 pct upon compression. The discovery of Cu₆₆Hf₃₄ as a bulk glass confirms the existence of rather simple bulk-glass-forming metallic systems. Moreover, the present Cu-Hf alloys may be the highest copper content bulk metallic glasses reported to date, to the best of our knowledge.     

The development of protective borosilicate layers on a Mo-3Si-1B (weight percent) alloy

Molybdenum-based alloys with the addition of small amounts of silicon (2 to 4.5 wt pct) and boron (∼1 wt pct) can form a passivating layer that protects the alloy from further rapid oxidation. When such molybdenum-based alloys are exposed to oxidizing environments at high temperatures, a borosilicate glass layer can form that will reduce the transport of oxygen to the alloy to limit further oxidation. Oxidation is then controlled by diffusion through the borosilicate glass layer. The focus of this research was to study the development of the borosilicate layer on a Mo-3Si-1B (wt pct) alloy. The oxidation of this alloy was studied in a variety of gas environments over a range of temperatures in order to elucidate the critical factors that allow it to develop a protective borosilicate glass layer. The borosilicate glass layer is protective when no continuous channels exist in the layer extending from the gas interface to the alloy interface. The borosilicate layer is believed to contain channels in the early stages of development, and the elimination of the channels is obtained by appropriate control of the temperature and gas-flow conditions, whereby MoO₃ is removed via vaporization while the borosilicate viscosity is not increased due to loss of B₂O₃. Once the borosilicate layer is continuous and free of channels, subsequent oxidation occurs by inward diffusion of oxygen and outward diffusion of molybdenum through this layer, with vaporization of MoO₃ occurring at the gas/borosilicate-layer interface and MoO₂ and additional borosilicate forming at the alloy/MoO₂ interface.     

Magnetic states in Fe<Subscript>65</Subscript>(Ni<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>35</Subscript> alloys

The ferromagnetic-antiferromagnetic concentration transition in Fe₆₅(Ni_{1 − x} Mn _x )₃₅ alloys is studied by neutron diffraction and small-angle magnetic neutron scattering (SMNS). The Curie and Néel temperatures are measured, and the antiferromagnetic moments and the cross sections of SMNS by magnetic heterogeneities are determined. The parameters of spin density fluctuations in the heterogeneities are obtained. A cluster mechanism of the nucleation of magnetic phases is revealed, and the spin-glass freezing temperatures are estimated. A low-temperature diagram is constructed for the magnetic states of the alloys.     

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.     

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.     

The Effect of Purification on the Glass-Forming Ability of a Pd-Cu-Si Alloy

The copper mold casting method is now commonly used for preparing bulk metallic glasses (BMGs). In the present work, it was found that, by employing the copper mold casting method, Pd_77.5Cu₆Si_16.5 (at. pct) glassy rods with 1-mm diameter could be prepared, while the ?2-mm Pd_77.5Cu₆Si_16.5 casting rod possesses some crystalline phases embedded within the glass matrix, confirming that the critical size of the glassy alloy is about 1?mm. By melt purification with fluxing treatment, the critical size of the glassy rod prepared by copper mold casting is increased to 4?mm. Based on thermal property analysis, it was found that melt purification by the fluxing method can greatly enhance the thermal stability and increase the glass forming ability (GFA) of the Pd-Cu-Si alloys. The as-prepared ?4-mm Pd-Cu-Si glassy rod exhibits a reduced glass transition temperature (T _rg ) of 0.599, a supercooled liquid region (??T) of 74?K (74?°C), and a ?? parameter of 0.419.