Glass-forming ability and magnetic properties of mechanically solid-state reacted Co100−xTix alloy powders

A high-energy ball milling technique using the mechanical alloying method has been employed for fabrication of glassy Co_100−xTi_x (25≤x≤67) alloy powders at room temperature. The fabricated glassy alloys in the Co-rich (33≥x) side exhibit good soft magnetic properties. The binary glassy alloys for which the glass transition temperatures (T_g) have rather high temperatures (above 800 K), show large supercooled liquid regions before crystallization (ΔT_x larger than 50 K). The reduced glass transition temperature (ratio between T_g and liquidus temperatures, T_l (T_g/T_l)) was found to be larger than 0.56. We have also performed post-annealing experiments on the mechanically deformed Co/Ti multilayered composite powders. The results show that annealing of the powders at 710 K leads to the formation of a glassy phase (thermally enhanced glass formation reaction), of which the heat of formation was measured directly. The similarity in the crystallization and magnetization behaviors between the two classes of as-annealed and as-mechanically alloyed glassy powders implies the formation of the same glass state.     

Thermal stability and magnetic properties of Gd–Fe–Al bulk amorphous alloys

Gd₆₅Fe₂₀Al₁₅, Gd₆₅Fe₁₅Al₂₀ and Gd₇₀Fe₁₅Al₁₅ bulk amorphous alloys were produced by copper mold casting method with the maximum diameters of 2, 1 and 1 mm, respectively. The crystallization temperature (T_x) and melting temperature (T_m) of the Gd₆₅Fe₂₀Al₁₅ bulk amorphous alloy are 808 and 943 K, respectively. Accordingly, the temperature interval of T_m and T_x, ΔT_m (=T_m − T_x), is as small as 135 K and the reduced crystallization temperature (T_x/T_m) is as high as 0.86. The small ΔT_m and high T_x/T_m values are presumed to be the origin for the achievement of the high amorphous-forming ability of the Gd–Fe–Al bulk amorphous alloy. The Gd₆₅Fe₂₀Al₁₅, Gd₆₅Fe₁₅Al₂₀ and Gd₇₀Fe₁₅Al₁₅ bulk amorphous cylinders with a diameter of 1 mm exhibit superparamagnetism at room temperature, while the amorphous ribbon shows the paramagnetism at room temperature. Finally, the mechanical properties of Gd₆₅Fe₂₀Al₁₅ bulk amorphous alloys are investigated.     

Thermal stability and mechanical properties of Gd-Co-A1 bulk glass alloys

The glass forming ability of Gd-Co-A1 ternary alloy systems with a composition ranging from 50% to 70% （molar fraction） for Gd and from 5% to 40% （molar fraction） for AI were investigated by copper mold casting and Gd60Co25Al15 bulk glass alloy cylinders with the maximum diameter of 5 mm were obtained. The reduced glass transformation temperature （TG/Tm） and the distance of supercooling region ATx are 0.616 and 45 K, respectively for this Gd-Co-A1 alloy. The compressive fracture strength （σf） and elastic modulus （E） of Gd-Co-A1 glassy alloys are 1 170-1 380 MPa and 59-70 GPa, respectively. The Gd-AI-Co bulk glassy alloys with high glass forming ability and good mechanical properties are promising for the future development as a new type function materials.     

Preparation, thermal stability, and magnetic properties of Fe---Co---Zr---Mo---W---B bulk metallic glass

A bulk metallic glass (BMG) cylinder of Fe₆₀Co₈Zr₁₀Mo₅W₂B₁₅ with a diameter of 1.5 mm was prepared by copper mould casting of industrial raw materials. The amorphous state and the crystallization behavior were investigated by X-ray diffraction (XRD). The thermal stability parameters, such as glass transition temperature (T_g), crystallization temperature (T_x), supercooled liquid region (ΔT_x) between T_g and T_x, and reduced glass transition temperature T_rg (T_g/T_m) were measured by differential scanning calorimetry (DSC) to be 891, 950, 59 K, and 0.62, respectively. The crystallization process took place through a single stage, and involved crystallization of the phases -Fe, ZrFe₂, Fe₃B, MoB₂, Mo₂FeB₂, and an unknown phase, as determined by X-ray analysis of the sample annealed for 1.5 ks at 1023 K, 50 K above the DSC peak temperature of crystallization. Mössbauer spectroscopy was studied for this alloy. The spectra exhibit a broadened and asymmetric doublet-like structure that indicated paramagnetic behavior and a fully amorphous structure. -Fe was found in the amorphous matrix for a cylinder with a diameter of 2.5 mm. The success of synthesis of the Fe-based bulk metallic glass from industrial materials is important for the future progress in research and practical application of new bulk metallic glasses.     

Structure of Y3TaNi6+xAl26: a filled-up substitution variant of the BaHg11 type

The crystal structure of Y₃TaNi_6+xAl₂₆ (refined composition Y₄TaNi_6+[7]Al_20+[6]) was determined by single-crystal X-ray diffraction (λ(Mo K) −0.71073 A. μ −17.827 mm¹, F(000) = 700, T = 293 K, wR = 0.015 for [8] unique reflections). This new quaternary aluminide crystallizes with a cubic structure. Pearson code cP49-12.85, (221) Pm-3m-ji'gdba, a = 8.3600(1) Å. V = 584.28(2) Å, Z = 1, M₁ = 1510.25, D_x = 4.292 mg mm¹. The structure of Y_xTaNi_6+xAl₂₆ is filled-up substitution variant of the BaHg₁₁ structure type with one additional atom site, partly occupied (around 15%) by Ni atoms, located at the centre of a cube formed by Al atoms. Distinct atom coordinates were refined for Ni and Al atoms on a site for which mixed occupation (approximately 50% Ni/50% Al) was found. The Ta atoms centre regular Al atom cuboctahedra, and the Y atoms 20-vertex polyhedra, formed by Al and Ni atoms, similar to those observed in CeMn₄Al₈ and YbFe₂Al₁₀.     

Thermochemistry of GaBO3 and phase equilibria in the Ga2O3–B2O3 system

Employing a Tian-Calvet-type calorimeter operating in the scanning mode at temperatures from 1120 to 1220 K, the enthalpy change, Δ_dH, associated with the decomposition of GaBO₃ (=1/2β-Ga₂O₃+1/2B₂O₃(liq.)) and the corresponding decomposition temperature, T_d, were determined: Δ_dH=30.34±0.6 kJ/mol, T_d=1190±5 K. Using the transposed-temperature-drop method the thermal enthalpy, H(T)−H(295 K), of GaBO₃ was measured as a function of temperature, T, in the region from 760 to 1610 K; the results obtained are

[H(T)−H(295 K)]/(J/mol)=104.8·(T/K)−31 300 (760 K<T<1190 K),

[H(T)−H(295 K)]/(J/mol)=138.8·(T/K)−41 480 (1190 K<T<1590 K).

On the basis of the experimental results, the enthalpy and entropy of formation, Δ_fH and Δ_fS, respectively, of GaBO₃ from the component oxides were derived:

Δ_fH=−30.34 kJ/mol,Δ_fS=−25.50 J/(K·mol) at 1190 K,

Δ_fH=−10.55 kJ/mol,Δ_fS=−5.48 J/(K·mol) at 298 K.

The enthalpy versus temperature curve shows, apart from a step associated with the decomposition of GaBO₃, a further step at 1593 K which is attributed to a monotectic equilibrium.     

Structure, hyperfine interactions and magnetization studies of mechanically alloyed Fe50Ge50 and Fe62Ge38

X-ray diffraction, Mössbauer spectroscopy and magnetization measurements were used to study the structure and some magnetic properties of Fe₅₀Ge₅₀ and Fe₆₂Ge₃₈ prepared by mechanical alloying from the elemental powders. In both cases in the early stages of milling the intermediate paramagnetic FeGe₂ phase was formed. The mechanical alloying process of Fe₅₀Ge₅₀ resulted in the formation of the paramagnetic FeGe (B20) phase with an average crystallite size of about 15 nm. In the case of the Fe₆₂Ge₃₈, the ferromagnetic Fe₅Ge₃ (β) phase with a Curie temperature of about 430 K was obtained. The average crystallite size was about 9 nm. The average hyperfine magnetic field of about 16 T allowed it to determine that more than four germanium atoms exist in the nearest environment of the ⁵⁷Fe isotopes in the Fe₅Ge₃ phase.     

纳米结构14Cr-ODS铁素体钢的制备与微观结构

采用机械合金化和热等静压技术制备纳米结构14Cr-ODS铁素体钢,利用SEM,XRD和EDS等手段分析了机械合金化过程中粉末形态和结构的变化以及合金元素的固溶情况,通过TEM研究了14Cr-ODS铁索体钢的微观结构及其在短时高温下的稳定性.结果表明,元素粉末经机械合金化过程中发生反复的冷焊和断裂导致粉末尺寸先增加（0-2 h）后下降（2-70 h）,晶粒尺寸随球磨时间的增加而减小,同时Cr,W和Y₂O₃等固溶入Fe基体中.纳米结构14Cr-ODS钢中存在3种析出相:极高密度的、尺寸在几个纳米的富Y-Ti-O团簇,少量Y₂Ti₂O₇析出相和块状富Cr-Ti相.经1250℃,8 h短时高温热处理后,纳米团簇显示出了良好的稳定性,Y₂Ti₂O₇相的密度增加.     

Mechanochemical reduction of MoO3/SiO2 powder mixtures by Al and carbon for the synthesis of nanocrystalline MoSi2

In this investigation, MoSi₂ intermetallic compound has been synthesized by reducing of MoO₃/SiO₂ powder mixtures by Al and carbon via mechanical alloying (MA). Powder mixtures were ball milled for 0–100 h and structural evolutions have been monitored by X-ray diffraction. In the Al system, both β-MoSi₂ (high temperature phase) and -MoSi₂ (low temperature phase) were obtained after 3 h of milling and after 70 h of milling the β-phase transformed to -phase. The crystallite size of -MoSi₂ and Al₂O₃ after milling for 100 h was 12 and 17 nm, respectively. In reducing with carbon, two different compositions with nominal carbon content of 13.7 and 24 wt.% were used that in both compositions, -MoSi₂ forms during 10 h of milling. Higher carbon content increases the amount of MoSi₂.     

Evolution of magnetic hardness in the HfFe6Ge6-type RMn6Sn6−xGax and RMn6Sn6−xInx compounds (R=Tb, Dy; 0.2≤x≤1.4)

The HfFe₆Ge₆-type RMn₆Sn_6−xX_x′ solid solutions (R=Tb, Dy, X′=Ga, In; x≤1.4) have been studied by powder magnetization measurements. All the series are characterized by ferrimagnetic ordering and by a decrease in Curie temperatures with the substitution (ΔT_c/Δx≈−39 K for X′=Ga and ΔT_c/Δx≈−75 K for X′=In). The RMn₆Sn_6−xGa_x systems are characterized by a strong decrease in the spin reorientation temperature with substitution (ΔT_t/Δx≈−191 K and −78 K for R=Tb and Dy, respectively) while this transition almost does not change in systems containing indium. The coercive fields drastically decrease with the substitution in the TbMn₆Sn_6−xGa_x system while the substitution of In for Sn has a weaker effect. The coercive fields of the Dy compounds do not vary greatly with the substitution in both series. The behaviour of the TbMn₆Sn_6−xGa_x is compared with the evolutions observed in the TmMn₆Sn_6−xGa_x series. This comparison strongly suggests that the replacement of Sn by Ga changes the sign of the A₀² crystal field parameter.     

Nanocrystalline LaNi4−xMn0.75Al0.25Cox electrode materials prepared by mechanical alloying (0≤x≤1.0)

Polycrystalline hydrogen storage alloys based on lanthanum (La) are commercially used as negative electrode materials for the nickel–metal hydride (Ni–MH_x) batteries. In this paper, mechanical alloying (MA) was used to synthesize nanocrystalline LaNi_4−xMn_0.75Al_0.25Co_x (x=0, 0.25, 0.5, 0.75 and 1.0) hydrogen storage materials. XRD analysis showed that, after 30 h milling, the starting mixture of the elements decomposed into an amorphous phase. Following the annealing in high purity argon at 700 °C for 0.5 h, XRD confirmed the formation of the CaCu₅-type structures with a crystallite sizes of about 25 nm. The nanocrystalline materials were used as negative electrodes for a Ni–MH_x battery. Cobalt substituting nickel in LaNi₄Mn_0.75Al_0.25 greatly improved the discharge capacity and cycle life of the LaNi₅ material. For example, in the nanocrystalline LaNi_3.75Mn_0.75Al_0.25Co_0.25 powder, discharge capacities up to 258 mA h g⁻¹ (at 40 mA g⁻¹ discharge current) were measured. Mechanical alloying is a suitable procedure to obtain LaNi₅-type alloy powders for electrochemical energy storage.     

Influence of High-Pressure Nitrogenation on the Structure,Magnetism and Microwave Absorption Properties of SmFe10Mo2

Nitrogenation of SmFe₁₀Mo₂ powders was performed in a self-made furnace under a high-purity N₂ atmosphere up to 40 MPa at 500 °C. Upon nitrogenation at atmospheric pressure, the lattice parameters a and c increase by 0.5% and 2.7%, respectively, whereas the Curie temperature T _C increases from 519 to 633 K. With further increasing the nitrogenation pressure to 20 and 40 MPa, the 1:12 main phase starts to decompose and a large amount of Mo and α-Fe precipitates. This leads to variation of Mo concentration in the 1:12 phase and causes a sharp decrease in T _C and in the coercivity. The relative complex permittivity and permeability of paraffin-SmFe₁₀Mo₂ composites show multi-resonant behavior. After nitrogenation, the magnetic loss of the powders decreases, which may originate from the influence of eddy currents due to the increase in the particle size.     

Gibbs free energy of formation of the ternary oxide Nd3RuO7

The Gibbs free energy of formation of Nd₃RuO₇(s) has been determined using solid-state electrochemical cell employing oxide ion conducting electrolyte. The electromotive force (e.m.f.) of the following solid-state electrochemical cell has been measured, in the temperature range from 929.3 to 1228.6 K.

Cell: (−)Pt/{Nd₃RuO₇(s) + Nd₂O₃(s) + Ru(s)}//CSZ//O₂(p(O₂) = 21.21 kPa)/Pt(+)

The Gibbs free energy of formation of Nd₃RuO₇(s) from elements in their standard state, calculated by the least squares regression analysis of the data obtained in the present study, can be given by:

{Δ_fG°(Nd₃RuO₇, s)/(kJ mol⁻¹) ± 1.6} = −3074.3 + 0.6097(T/K); (929.3 ≤ T/K ≤ 1228.6).

The uncertainty estimate for Δ_fG°(T) includes the standard deviation in e.m.f. and the uncertainty in the data taken from the literature. The intercept and the slope of the above equation correspond to the enthalpy of formation and entropy, respectively, at the average experimental temperature of T_av. = 1079 K.     

Magnetocaloric effect in Pr6Co1.67Si3 compound

Magnetic properties and magnetocaloric effects of Pr₆Co_1.67Si₃ compound have been investigated by magnetization measurements. The saturation moment at 5 K is found to be 10.7μ_B. The compound undergoes two magnetic transitions below Curie temperature T_C = 48 K and shows a reversible second-order magnetic transition around T_C. A magnetic entropy change ΔS = 6.9 J/(kg K) is observed for a magnetic field change from 0 to 5 T. The full width at half maximum of the ΔS peak is found to be about 38 K.     

Neutron diffraction study in amorphous Ni30Ta70 alloy powders by mechanical alloying

A mixture of elemental Ni and Ta powders with an atomic ratio of 3∶7 was subjected to mechanical alloying (MA). An amorphous Ni₃₀Ta₇₀ alloy was formed after 80 hrs of milling, the amorphization by rapid quenching technique of which has not been reported. The atomic structural changes were observed by neutron diffraction in the amorphization process during MA. The radial distribution function RDF(r) shows that peaks of fcc-Ni and bcc-Ta crystal broaden first and gradually approach those characteristic of an amorphous phase with increasing MA time. A local atomic environment around Ni and Ta atoms was studied by analyzing the first peak in the total pair distribution function g(r) after the completion of amorphization. We reach our conclusion from this analysis that the amorphization in the Ni₃₀Ta₇₀ alloy takes place by the penetration of smaller Ni atoms into the bcc-Ta lattice.     

Electrical, magnetic and elastic properties of La1.2(Sr1−xCax)1.8Mn2O7 (0.0 ≤ x ≤ 0.4)

Polycrystalline bulk samples of double layered manganite system La_1.2(Sr_1−xCa_x)_1.8Mn₂O₇ (0.0 ≤ x ≤ 0.4) were prepared by sol–gel method. After characterizing the samples using XRD and SEM, their electrical, magnetic and elastic properties were investigated. The lattice parameters and cell volume show a monotonous decrease with increase of Ca content, whereas the grain size is found to increase with increasing Ca content. The value of T_IM is found to decrease with Ca content up to x = 0.3 and then a slight increase of T_IM is observed. The low temperature upturn of resistivity is attributed to the spin-glass-like behavior, which is also evidenced by the irreversibility observed between ZFC and FC magnetizations. The conduction mechanism above T_IM can be explained by Mott VRH model. The present magnetization and ultrasonic studies indicate that the system shows a secondary transition at T^*, which decreases with increasing Ca content. Further, the T^* seems to be intrinsic to the present double layered manganite system.     

A new Cu–Hf–Al ternary bulk metallic glass with high glass forming ability and ductility

We have discovered a new Cu-based bulk metallic glass (BMG). Although of a simple Cu₄₉Hf₄₂Al₉ ternary composition, the as-cast alloy is a monolithic, uniform BMG with a critical diameter as large as 10 mm. The width of the supercooled liquid region ΔT_x and the reduced glass transition temperature T_rg for this glass are 85 K and 0.62, respectively. In addition to its high glass-forming ability and high density of 11 g/cc, this BMG exhibits high ductility with a compressive plastic strain of 11–13%, making it a good candidate for applications as well as for studies of deformation behavior of Cu-based BMGs.     

Room-temperature mechanically induced solid-state devitrifications of glassy Zr65Al7.5Ni10Cu12.5Pd5 alloy powders

The high-energy ball milling technique was employed for synthesizing a single phase of glassy Zr₆₅Al_7.5Ni₁₀Cu_12.5Pd₅ alloy powder, using a room-temperature mechanical alloying method. Whereas the glass transition temperature of the obtained glassy alloy is 683 K, the crystallization temperature is 783 K. The mechanically alloyed Zr₆₅Al_7.5Ni₁₀Cu_12.5Pd₅ glassy powders maintain their unique disordered structure through a large supercooled liquid region (100 K). The possibility of devitrification of the synthetic glassy phase upon increasing the ball milling time was investigated. The results have shown that the glassy powder that is obtained after 173 ks of milling is subjected to numerous lattice imperfections and tends to transform into a metastable big-cube phase after further ball milling (259–432 ks). After 540 ks of milling, a complete glassy–metastable phase transformation is achieved and the end-product of this stage of milling is nanocrystalline big-cube powder that has a lattice constant of 1.2293 nm. As the milling time increases (720 ks), the obtained big-cube phase can no longer withstand the shear and impact stresses that are generated by the milling media and is transformed into a new metastable phase of nanocrystalline fcc-Zr₆₅Al_7.5Ni₁₀Cu_12.5Pd₅. The fcc-metastable phase transforms into a mixture of Zr₂Cu and Zr₆NiAl₂ crystalline phases at rather high temperature, as high as 993 K.     

Hydrogenation of oxygen-stabilized Zr3NiOx compounds

It is shown that oxygen-stabilized compounds Zr₃NiO_x (x=0.4, 0.6, 0.8, 1.0) interact with hydrogen at ambient temperature and pressure forming saturated hydrides with a filled Re₃B-type structure. The hydrogen storage capacity decreases with increasing oxygen content from 6.65 H/f.u. for Zr₃NiO_0.4 down to 5.58 H/f.u. for Zr₃NiO_1.0. A slight decrease of the crystal lattice parameters of the parent compounds and a substantial increase of these parameters for the saturated hydrides were observed with increasing oxygen content. The partial hydrogen-induced lattice expansion, ΔV/at. H, increases from 2.333 ų for Zr₃NiO_0.4H_6.65 to 3.047 ų for Zr₃NiO_1.0H_5.58. Joint Rietveld refinement using X-ray and neutron powder diffraction data showed a distribution of deuterium atoms on similar positions as in oxygen-free Zr₃FeD_x and Zr₃CoD_x. The oxygen atoms move during deuteration from the octahedral site to one trigonal bi-pyramidal and two tetragonal interstices that are fully occupied in the saturated deuterides jointly by deuterium and oxygen. After deuterium desorption the oxygen atoms fully return to the initial octahedral site.     

Thermoelectric properties of Fe0.98Co0.02Si2 with ZrO2 and rare-earth oxide dispersion by mechanical alloying

The n-type Co-doped β-FeSi₂ (Fe_0.98Co_0.02Si₂) with dispersion of several oxides, such as ZrO₂ or several rare-earth oxides (Y₂O₃, Nd₂O₃, Sm₂O₃ and Gd₂O₃), was synthesized by mechanical alloying and subsequent hot pressing. The effects of these oxide dispersions on the thermoelectric properties of Fe_0.98Co_0.02Si₂ were investigated. ZrO₂ was decomposed in the β phase, and the ZrSi and -FeSi phases, which are metallic phases, were formed in the samples with ZrO₂ addition. The Seebeck coefficient and the electrical resistivity were significantly decreased with increasing amount of ZrO₂, indicating that a part of the Zr atoms was substituted for Fe atoms in the β phase. In the case of the samples with rare-earth oxide addition, a decomposition of a large amount of these added oxides did not occur. However, the rare-earth oxide addition caused a slight increase in the amount of the phase. The Seebeck coefficient was significantly enhanced by the rare-earth oxide addition especially in the low temperature range. These facts indicated that a small amount of rare-earth oxides was decomposed in the β phase, and rare-earth elements were substituted for Fe atoms as a p-type dopant, resulting in the decrease in the carrier concentration. The rare-earth oxide addition was also effective in reducing the thermal conductivity.