Melt-spun Alloys Research Articles

Critical behavior and magnetocaloric effect of Gd65Mn35−xGex (x = 0, 5, and 10) melt-spun ribbons

Gd65Mn35−xGex (x = 0, 5, 10) alloy ribbons were prepared by melt-spinning. A fully amorphous structure was obtained for the alloys with x = 5 and 10, whereas, in melt-spun Gd65Mn35 ribbons, crystalline phases (α-Gd and GdMn2) precipitate in the amorphous matrix. The magnetic phase transition from ferromagnetic to paramagnetic is second order. The critical exponents are deduced from the Kouvel-Fisher method and scaling behavior. The obtained critical exponents are in agreement with the theoretical values of 3D Ising model. The Ising-like behavior suggests the presence of large anisotropy and short-range magnetic-coupling behavior. The maximum magnetic-entropy changes of the melt-spun alloys with x = 0, 5, and 10 for a magnetic field change from 0 to 5 T are 4.2, 4.1, and 4.5 Jkg−1 K−1, respectively. All three alloys have a broad temperature range of the magnetic-entropy peak, resulting in large refrigerant capacities.

Effect of Co on Si and Fe-containing intermetallic compounds (IMCs) in Al–20Si–5Fe alloys

The effects of cobalt addition on microstructure and mechanical properties of Al–20Si–5Fe–XCo (X=0, 1, 3, and 5) alloys were reported in this study. The alloys were produced by both conventional sand casting and melt-spinning at 20m/s disk velocity. Microstructures of the samples were investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Vickers micro-hardness tester was used for hardness measurements. Results showed that Co addition can alter morphology of Fe-bearing intermetallic compounds (IMCs) from long rod/needle-like structures to short rod-like ones, and lead to a more homogenous distribution in the microstructure. Addition of 5wt% Co leads to a decrease in average size of the primary silicon phases in as-cast Al–Si alloys. In melt-spun alloys, with the addition of Co, the microstructure became finer and more homogenously distributed, while thickness of the featureless zone has seen great increase. The optimum Fe to Co ratio was found to be 1 for suppressing the undesirable effect of Fe-bearing acicular/needle-like intermetallic compounds.

Ni-Hf非晶合金及其团簇式成分解析

Ni-Hf binary alloys are merely known as a category of marginal glass formers. In this system, the assessment of glass-forming abilities has not been made and the optimal glass-forming composition remains unclear. In the present work, Ni-Hf glass-forming compositions are explored using the atomic cluster plus glue atom model. Ni-Hf phase diagram shows a deep eutectic point at Ni65Hf35 which is associated two intermetallic phases, namely, Ni7Hf3 and Ni10Hf7. A predominant atomic cluster was first derived from the crystalline structures of the deep eutectic related phases, and several glass-forming compositions were determined considering the one or three glue atoms constraint condition. Rapid quenching results show that Ni71.43Hf28.57 and Ni68.75Hf31.25 metallic glasses can be made fully glassy. The latter can be well described with the model composition formula as [Ni-Ni7Hf5]Ni3. Among the melt-spun alloys, the Ni68.75Hf31.25 glass which locates in between the deep eutectic point and the Ni7Hf3 phase in the phase diagram, exhibited a highest crystallization temperature of 877 K and a lowest liquidus of 1482 K, and hence is suggested to be the optimal Ni-Hf glass former by the high reduced glass temperature criterion.

Effect of silicon addition on mechanical and electrical properties of Sn–Zn based alloys rapidly quenched from melt

Abstract In the present study, the effect of Si additions (0.1–0.5 wt.%) on mechanical and electrical properties of Sn–12Zn–3Bi based alloys was studied and analyzed. The investigation indicates that the mechanical properties of quaternary alloy Sn–12Zn–3Bi–0.5Si are higher than that of binary Sn–12Zn and ternary Sn–12Zn–3Bi melt spun-alloys. The addition of silicon to the Sn–12Zn–3Bi ternary system improves the electrical resistivity of the alloy and lowers the melting temperature. The Sn–12Zn–3Bi–0.3Si alloy has a melting point around 195 °C. Electrical resistivity of Sn–Zn–Bi–Si solder alloys, 9–14 μΩ cm, is much lower than that of Sn–37Pb solder. Test results indicate that adding small amount of Si can evidently improve the solderibility, mechanical, creep resistance, melting point and electrical properties of the binary Sn–12Zn and ternary Sn–12Zn–3Bi alloys. The change in mechanical and electrical properties is discussed based on the microstructural observations.

Structure and magnetic properties of Ni2(Mn,Co)Ga Heusler alloys rapidly solidified by melt-spinning

In this study microstructure and magnetic properties of cobalt substituted Ni2MnGa based ferromagnetic shape memory alloys (FMSA) are presented. Ni50Mn(25−x)CoxGa25 (x = 2, 5, 8, 11 at%) alloys were synthesized using the melt-spinning technique. Martensite, austenite and pre-martensitic tweed structures were found at room temperature for alloys containing 2, 5, 8 and 11% Co and melt-spun at two extreme wheels speeds viz., 20 m/s and 30 m/s. However, the alloy containing 5% Co melt-spun at a wheel speed of 20 m/s consists of 7 M or 14 layered Martensite phase. Magnetic properties such as saturation magnetization (Ms), martensitic transformation temperature (Tm) and Curie temperature (Tc) were measured and were found to be attractive for most of the melt-spun alloys containing higher “Co” concentrations. Upon annealing at 1273 K for 1 h, γ (gamma) phase was found to stabilize. The magnetic properties were found to correlate with the phase content of the Co substituted alloys.

Effect of Processing Method on the Microstructure of Nd4.5Fe77B18.5 Magnetic Alloy

The effects of processing method including arc-melted process, rapid solidification and laser crystallization on the microstructure of Nd4.5Fe77B18.5 alloy were investigated. The results showed that the microstructure of the arc-melted alloy was composed of Nd2Fe14B, Fe3B and α-Fe. The microstructure for the melt-spun alloy at the surface velocity of the wheel of 3m/s was similar to that of arc-melted one. However, the constituent phases were composed of Nd2Fe14B and Fe3B, and the α-Fe was suppressed for the melt-spun alloy at the surface velocity of the wheel of 5m/s. At the surface velocity of the wheel of 7m/s and 10m/s, the microstructures were composed of Fe3B and amorphous. Increasing cooling rate, the grain size decreased from micron to nanometer. The completely amorphous microstructure was obtained at the surface velocity of the wheel of 20m/s. The uniform Nd2Fe14B/Fe3B nanocomposites were obtained during the amorphous melt-spun crystallization by laser crystallization process. After laser crystallization at 400mm/min, the mean grain sizes of Nd2Fe14B and Fe3B reached 30nm and 20nm, respectively.

Crystallization mechanism and its correlation with structural and soft magnetic properties of FeSiBPCu nanocrystalline alloys

Correlation of crystallization mechanism with the structural and soft magnetic properties of FeSiBPCu nanocrystalline alloys has been investigated on the basis of Johnson–Mehl–Avrami kinetic model, transmission electron microscopy, and extended random anisotropy model. Pre-existent α-Fe clusters in melt-spun alloys with a size much smaller than critical nucleus size crystallize at a steadily increasing nucleation rate owing to the chain effect of rising constituent fluctuation. This unique crystallization mechanism leads to the formation of fine and uniform nanocrystallites and therefore superior soft magnetic properties. In contrast, pre-existent α-Fe clusters with a size approximate to the critical nucleus size nucleate gradually at the initial stage of crystallization process driven by thermal activation over the energy barrier of nucleation, and pre-existent α-Fe nanocrystallites with a size larger than critical nucleus size grow directly at the initial stage of crystallization process. Grains formed at the initial stage enlarge further in the subsequent crystallization process, which gives rise to a continuous decrease of the nucleation rate and the deterioration of soft magnetic properties.

Improved activation and hydrogen storage properties of a Mg 85Ni 15 melt-spun alloy via surface treatment with NH 4+ solution

An amorphous Mg 85Ni 15 melt-spun hydrogen storage alloy, processed by submersion in an aqueous solution of NH 4 +, is able to absorb nearly 5 mass% hydrogen at 473 K during the first hydrogenation cycle. The nanocrystalline microstructure formed during devitrification of the metallic glass is preserved by the lower required activation temperature of the NH 4 +-treated material compared to the as-spun material; and the kinetics of subsequent absorption/desorption cycles at 573 K are dramatically improved. The material activated at 473 K exhibits a decrease in hydride decomposition temperature by 30 K, observed via DSC and TPD experiments, compared to a sample activated at 573 K. The NH 4 +-treatment of a glassy alloy presented here provides a practical alternative to ball milling for forming a nanocrystalline material and facilitating activation, requiring much less time and a more commercially scalable option.

Phase transition and hydrogen storage properties of melt-spun Mg 3LaNi 0.1 alloy

Nominal Mg 3LaNi 0.1 alloy was prepared by a single roller melt-spun method. The phase structure and hydrogen storage properties of the obtained ribbons were studied by X-Ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) analysis and pressure-composition isotherm (PCI) measurements. The melt-spun Mg 3LaNi 0.1 alloy was composed of Mg 3La phase, while fine LaMg 2Ni grains were precipitated after an aging treatment at room temperature. Both Mg 3La and LaMg 2Ni undertook disproportion reactions upon hydrogenation and decomposed into MgH 2, LaH 3 and Mg 2NiH 4. The melt-spun alloy shows excellent hydrogen absorption kinetics and lowered desorption temperature comparing with the induction-melted alloy, and a maximum hydrogen storage capacity of 3.1 wt.% and a minimum hydrogen desorption temperature of 224 °C were achieved. This improvement on the hydrogen storage properties was attributed to the catalytic role of in-situ formed nanocrystalline Mg 2Ni and LaH 2.

Topological instability and glass forming ability of Al–Ni–Sm alloys

The thermal crystallization of Al-based metallic glasses can be described in association with the topological instability λ criterion. In the present work, we report on the crystallization behavior and glass forming ability of Al-rich, Al–Ni–Sm alloys, designed with compositions corresponding to the same topological instability condition of λ ≈ 0.1. Amorphous melt-spun alloys were prepared with the following compositions, varying the ratio of Ni and Sm elements: Al 87.5Ni 4Sm 8.5, Al 83.5Ni 10Sm 6.5, Al 80.5Ni 14.5Sm 5 and Al 76.5Ni 20.5Sm 3. The glass forming ability of each alloy composition was evaluated based on the thermal parameters obtained from DSC runs and on X-ray diffraction patterns. Better glass forming ability was observed in compositions whose Sm content was increased and Ni content reduced. Thermal crystallization of the alloys with low Sm content showed only one crystallization peak and no glass transition event. In alloys with higher rare-earth content, a glass transition event was clearly detected before the crystallization event. The results are interpreted considering the different types and proportions of Sm–Al and Ni–Al clusters that can be formed in the alloys along the λ ≈ 0.1 line. They also emphasize the relevance of these different types of clusters in the amorphous phase in defining the stability of the glass and the types of thermal crystallization.

Magnetic and anomalous transport properties in Fe 2MnAl

This study investigated the magnetism and anomalous transport properties of the melt-spun ribbon Fe 2MnAl alloy. It is found that the alloy exhibits ferromagnetic order with the Curie temperature of ∼150 K, followed by another magnetic transition at T R ∼ 51 K. It is suggested there is antiferromagnetism pinning effect on the ferromagnetic matrix at the temperature below T R . A steep rise of the resistance below T R has been observed, which can be understood in terms of antiferromagnetic scattering. An appearance of the resistance maximum near the Curie temperature and the negative temperature dependence of the resistance above Curie temperature are associated with the magnetic phase transition from ferromagnetism to paramagnetism. A negative magnetoresistance at low temperature arising from inhomogeneous magnetic scattering is reported.

Improved hydrogenation-dehydrogenation characteristics of nanostructured melt-spun Mg-10Ni-2Mm alloy processed by rapid solidification

AbstractThe as-cast Mg-10Ni-2Mm (mole fraction, %) alloy was prepared by a simple and low-cost two-step method of pre-alloying and vacuum induction melting. The nanocrystalline alloy was obtained by the melt-spun process with the surface velocity of copper wheel of 10.5 m/s. The hydrogen storage properties were examined by PCT measurement. The enthalpy (ΔH) and entropy (ΔS) of the alloy determined by van't Hoff plots indicate that the thermodynamic performance of the nanocrystalline alloy is improved by fast diffusion ability of hydrogen in the nanocrystalline microstructure embedding nano-particles of intermetallics compounds Mg2Ni and MmMg12. The reaction kinetics of the melt-spun alloy is greatly improved due to short diffusion path of hydrogen in the nanocrystalline microstructure, resulting in better overall hydrogen storage properties. The hydrogen storage capacity is 5.09% (mass fraction, hereinafter the same), and the amount of hydrogen desorption is 4.86%. The hydrogen desorption rate of 95.5% in the alloy is available.

Mechanism of amorphous state formation, crystalline structure, and hyperfine interactions in DyMn6−xGe6Fex (≤x≤6) alloys

Metallic glass formation is observed in rapidly quenched quaternary DyMn6−xGe6Fex (0≤x≤6) alloys. The easy formation of amorphous states competes with the nucleation of ternary 1:6:6 rare earth-transition metal-metal compounds DyMn6Ge6 and DyFe6Ge6. The ribbon shaped samples were quenched and investigated by x-ray diffraction, differential scanning calorimetry, and F57e Mössbauer spectrometry. Melt-spun alloys from the series of DyMn6−xGe6Fex with x=0, 2≤x≤3, and x=6 do not display an amorphous state but a crystalline chemically disordered structure similar to that of TbCu7- or TbFe6Sn6-type (space group P6/mmm). Amorphous samples exhibit two crystallization steps but there is no clear evidence for a glass transition effect in the calorimetric data. The Kissinger analysis was performed to calculate the effective activation energy Ea, which is equal to 345±20 kJ/mol for amorphous DyMn5.5Ge6Fe0.5 alloy. Mössbauer spectra at 77 and 300 K consist of either magnetic sextets or quadrupolar doublets for high and low Fe content, respectively. The features reflect the dilution of Fe on crystallographic sites and the subsequent increase in topological and chemical disorder when the Mn content increases. The Miedema's semiempirical model was used to calculate the formation enthalpies of amorphous alloys (ΔHform). The calculated values are consistent with experimental results. The present model allows thus to explain the better glass forming ability for the compositions with high Mn content, where ΔHform is the most negative.

Structure, mechanical properties and imprint-ability of Pd–Cu–Ni–P glassy alloy thin film prepared by a pulsed-laser deposition method

With the aim of preparing nano-hole array for bit patterned media of ultra high density data storage, fabrication and imprint-ability of Pd–Cu–Ni–P glassy alloy thin film was investigated. By using a pulsed-laser deposition method, the Pd-based glassy alloy thin film was successfully fabricated. The thermal characteristics of the obtained film were very close to those of the melt-spun glassy alloy ribbon. The obtained film has very smooth surface and high hardness, which are suitable for nano-imprint processing. Nano-imprint-ability of the obtained film is demonstrated by using dot array mold with a dot diameter of 30 nm. The periodic dot pattern of the mold was precisely transcribed. These results suggest that the Pd–Cu–Ni–P glassy alloy thin films are potential nano-imprinting materials for fabricating bit patterned media.

Effect of rapid solidification on mechanical properties of a lead free Sn–3.5Ag solder

The melt-spinning processes of Sn–3.5Ag, Sn–3.5Ag–2In, Sn–3.5Ag–2Bi and Sn–3.5Ag–2Zn lead free solders were investigated and analyzed. The results showed that formation of intermetallic compounds of ɛ-Ag 3Sn, In 0.2Sn 0.8 and AgZn embedded in Sn matrix phase, were produced during melt-spinning technique not found under equilibrium conditions. Addition of small amount (2 wt.%) In, Bi, or Zn refines the grain size, increases H v, delay the fracture strength and improves creep resistance. The ternary alloys exhibits mechanical properties superior to that of the binary alloy Sn–3.5Ag because it has a uniform fine dispersion of precipitates and small effective grain size. It is found that in the lead free solder has composition of Sn–3.5Ag–2In, Sn–3.5Ag–2Bi and Sn–3.5Ag–2Zn melt-spun alloys, have eutectic composition which could be attributed to the shift of eutectic point under rapid solidification. The addition of indium, bismuth and zinc to the Sn–Ag binary system lowers the melting temperature.

Microstructure and soft magnetic properties of Finemet-type ribbons obtained by twin-roller melt-spinning

Abstract Soft magnetic ribbons of Finemet-type (Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 ) alloys are synthesized by the twin-roller melt-spinning technique directly from the melt, at tangential wheel speeds of 15, 18, 19 and 20 m/s. The microstructure and the magnetic properties are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA) and hysteresis loops measurements. Samples cooled at 20 m/s are amorphous, while those quenched at lower wheel speeds are partially crystalline. All samples studied present saturation magnetization values (150–160 A m 2 /kg) higher than the commercial Finemet alloys (∼135 A m 2 /kg), obtained by controlled crystallization of amorphous single-roller melt-spun alloys. Optimal soft magnetic properties – σ S =(154±8) A m 2 /kg and H C =(6.9±0.9) A/m – are found in samples quenched at 19 m/s, consisting of size-distributed bcc Fe–Si nanograins (∼18 nm in average) embedded in an amorphous residual matrix. A minority nanocrystalline magnetic phase (≤10 nm) is also detected.

Manganese-like metastable phases in the Fe–Mo system: experimental study and thermodynamic modeling. I. Crystalline state of Fe–Mo melt-spinning alloys

The β-Mn structure (π-phase) is revealed on contact and free surfaces of Fe63Mo37 melt-spinning ribbons. The full-profile analysis (Rietveld analysis) of diffraction patterns for a mixture of polycrystalline phases has identified, along with the metastable π phase, bcc solid solutions, μ and σ phases, and an intermediate bcc phase in the Fe–Mo phase diagram.

Properties and microstructure of the (Fe, Ni)–Cu–(P, Si, B) melt‐spun alloys

The work presents the microstructure characterization of the new (Fe, Ni)-Cu-(P, Si, B) melt-spun glass forming alloys investigated by means of transmission electron microscope. The results are compared with the data obtained by other complementary methods such as XRD and Mössbauer spectroscopy. The phases occurring during the crystallization of the glassy matrix are identified and characterized in terms of a long-range order and a short-range order. The thermal stability of the alloy is characterized by differential scanning calorimetry. The study describes the mechanical and magnetic properties of the new alloys at room temperature as well as characteristics resulting from heating the as-cast melt-spun alloy at elevated temperatures. The changes of the properties of the alloy at elevated temperatures are correlated with the microstructural changes.

TEM studies of melt‐spun alloys with liquid miscibility gap

The microstructures of the Fe-Cu-based alloys melt-spun from various temperatures are presented. Two compositions, with different Fe and Cu content, revealing liquid miscibility gap, were studied. Nonuniform, large-elongated areas were observed for lower melt-spinning temperatures, indicating liquid/liquid phase separation in the crucible before cooling. An increase of the melt ejection temperature, followed by rapid cooling, brought about precipitation process within homogeneous melt. Studies of the system with higher Fe content proved amorphous nature of the matrix and crystalline structure of the primary formed Cu-rich precipitates. Moreover, generations of the secondary spherical particles, precipitated within the previously formed Cu-rich melt, were observed. The microstructure of the melt-spun alloy with a higher Cu content, on the other hand, consisted of the Fe-rich amorphous spherical particles formed during cooling of the Cu-rich liquid. The precipitation of the secondary Cu-rich particles in the primary formed Fe-rich was also observed.

Microstructure and electrochemical properties of melt-spun Nd 0.8Mg 0.2(Ni 0.8Co 0.2) 3.8 hydrogen storage alloy

The effects of rapid solidification on the microstructure and electrochemical properties of Nd 0.8Mg 0.2(Ni 0.8Co 0.2) 3.8 alloy were systematically investigated. The microstructure of alloys was characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and transmission electron microscopy (TEM). It was found that the melt-spun Nd 0.8Mg 0.2(Ni 0.8Co 0.2) 3.8 ribbons became thinner and the average grain size of the ribbons became smaller with increasing wheel speed. A fraction of amorphous phase was observed for the ribbons melt-spun at high wheel speed (≥20 m/s). Microstructural characterization revealed that two phases: (Nd,Mg) 2(Ni,Co) 7 main phase (Ce 2Ni 7 type structure) and NdNi 5 second phase (CaCu 5 type structure), existed in the samples in cast state and melt-spun. The cycle stability of the melt-spun alloys was significantly enhanced as compared with cast alloy, and the sample prepared at wheel speed of 20 m/s exhibited good comprehensive electrochemical properties.