Melt-spun Alloys Research Articles

Effect of cooling rate on the crystallization and mechanical behaviour of Zr–Ga–Cu–Ni metallic glass composition

The effect of cooling rate on the mechanical behavior of Zr–Ga–Cu–Ni melt-spun glassy alloys has been studied using micro-indentation technique. The ribbons of alloy have been synthesized at three cooling rates corresponding to wheel speeds of 30, 40 and 50 m/s. The glass forming indicators and indentation characteristic have been investigated. The measurements by differential scanning calorimeters show that the ribbons synthesized at faster cooling rate contains larger amount of heats of relaxation, crystallization enthalpy and free volume. The indentation experiments demonstrate that with the same chemical composition, the ribbons synthesized at slow cooling rate exhibits higher hardness and yield strength than those synthesized at faster cooling rate. The ribbons synthesized at 50 m/s contains the large free volume and thus favors the formation of shear bands. The study is focused on investigations of these materials to understand the correlation between the cooling rate and the mechanical behavior of these alloys.

Microstructure, fracture, and thermal stability of Ni–Fe–Cu–P–B two-phase amorphous composite produced from the double-chamber crucible

The purpose of the work was investigation of the final microstructure and properties of the melt-spun Ni–Fe–Cu–P–B, Ni–Fe–B, and Ni–Cu–P alloys ejected as uniform liquid from the standard single-chamber crucible and from the double-chamber crucible as flux composed of the two Ni–Fe–B and Ni–Cu–P liquids cooled on a copper roller before formation of a uniform mixture. The methods applied in this study for microstructural investigations include scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Mössbauer spectroscopy. Thermal stability of the melt-spun alloys was tested using differential scanning calorimetry (DSC) and tensile test were performed. The results of the investigations are described and discussed in terms of the unique features of the two component melt spinning (TCMS) amorphous microstructure.

Microstructure and magnetic properties in as-cast and melt spun Co–Zr alloys

The microstructure formation during solidification of as-cast and melt-spun Co-rich (Co–13at.%, 16at.% and 18at.% Zr) Co–Zr alloys was studied. The microstructure evolution significantly differs during melt spinning owing to high cooling rate, although the volume fraction of α-Co was found to decrease with increasing Zr content in both as-cast and melt-spun alloys. The magnetization values decreased and the coercivity increased with increase in Zr content in both as-cast and melt-spun alloys. However, the melt-spun alloys showed a significantly higher coercivity which can be attributed to the finer scale of microstructure achieved due to the higher cooling rate.

Microstructural and magnetic properties of Nd-Fe-B alloys processed by equal-channel angular pressing

Equal-channel angular pressing (ECAP) is a well-established thermo-mechanical processing technique. This technique allows virtually unlimited strain and manipulation of texture by processing route, while the cross-section of the sample remains unchanged during processing. In order to clarify the effectiveness of ECAP on preparing anisotropic permanent magnets, the microstructure and magnetic properties of a melt-spun Nd13.5Fe73.8Co6.7B5.6Ga0.4 alloy processed at 773 K for 300 s by ECAP were investigated. Macrotexture analysis carried out for the exit channel of ECAP shows that the basal plane of the tetragonal Nd2Fe14B crystal aligns parallel to the shear band, i.e., the c-axis texture formation normal to the shear band induced by the ECAP process. Due to this texture formation, the technical magnetization behaviour becomes anisotropic, and the remanent magnetization is clearly enhanced along the direction perpendicular to the shear band. This anisotropic microstructure is realized at a relatively low processing temperature of 773 K, well below the melting point of the Nd-rich intergranular phase. As a consequence of this lower processing temperature, the nanostructure of the melt-spun alloy remains approximately 20 to 30 nm, considerably smaller than the typical grain size obtained after conventional die-upsetting. Our study demonstrates that equal-channel angular pressing has a potential for realising anisotropic nanostructured magnets.

The Effect of Melt Overheating on the Melt Structure Transition and Solidified Structures of Al-La Alloy

Although the effect of overheating treatment on solidification is due to the liquid structure state, its nature and rule are still unclear. In this article, the effect of melt overheating on the melt structure transition and solidified structures of Al100−x La x alloys (x = 2, 3, 5) was mainly studied with resistivity and rapid solidification methods. The resistivity of liquid Al-La alloy increases with the temperature and La content, and it shows the linear and nonlinear changes successively. The corrosion resistance and hardness of melt-spun alloy improves with the increase in melt temperature and La content. These results indicate that the melt structure becomes homogeneous, dense, and disordered with the increase in melt temperature, and a temperature-induced liquid–liquid structure change occurs at 880–960°C. The homogeneous and dense melt structure features are remained partly in this melt-spun alloy and have a beneficial influence on its corrosion resistance and hardness. It is useful to study on the melt structure and solidified structures with the rapid solidification and resistivity method.

Designing new biocompatible glass-forming Ti75-x Zr10 Nbx Si15 (x = 0, 15) alloys: corrosion, passivity, and apatite formation.

Glass-forming Ti-based alloys are considered as potential new materials for implant applications. Ti75 Zr10 Si15 and Ti60 Zr10 Nb15 Si15 alloys (free of cytotoxic elements) can be produced as melt-spun ribbons with glassy matrix and embedded single β-type nanocrystals. The corrosion and passivation behavior of these alloys in their homogenized melt-spun states have been investigated in Ringer solution at 37°C in comparison to their cast multiphase crystalline counterparts and to cp-Ti and β-type Ti-40Nb. All tested materials showed very low corrosion rates as expressed in corrosion current densities icorr < 50 nA/cm(2). Electrochemical and surface analytical studies revealed a high stability of the new alloys passive states in a wide potential range. This corresponds to low passive current densities ipass = 2 ± 1 µA/cm(2) based on the growth of oxide films with thickness d <10 nm. A homogeneous constituent distribution in the melt-spun alloys is beneficial for stable surface passivity. The addition of Nb does not only improve the glass-forming ability and the mechanical properties but also supports a high pitting resistance even at extreme anodic polarization up to 4V versus SCE were oxide thickness values of d ∼35 nm are reached. With regard to the corrosion properties, the Nb-containing nearly single-phase glassy alloy can compete with the β-type Ti-40Nb alloy. SBF tests confirmed the ability for formation of hydroxyapatite on the melt-spun alloy surfaces. All these properties recommend the new glass-forming alloys for application as wear- and corrosion-resistant coating materials for implants.

Structural Heterogeneity of the Melt-spun (Fe, Co)-Si-B-P-Cu Alloy with Excellent Soft Magnetic Properties

A structural heterogeneity of a newly developed soft magnetic Fe81.2Co4Si0.5B9.5P4Cu0.8 melt-spun alloy has been studied by transmission electron microscopy (TEM) and electron diffraction. Hollow-cone dark-field TEM imaging revealed that the density of coherent scattering regions in the as-quenched Fe81.2Co4Si0.5B9.5P4Cu0.8 alloy is as high as that in the Fe85.2Si2B8P4Cu0.8 hetero-amorphous alloy (NANOMET®). According to the aberration-corrected high-resolution TEM, crystalline atomic clusters, typically of ∼1nm in diameter, are densely distributed in an amorphous matrix of Fe81.2Co4Si0.5B9.5P4Cu0.8 alloy, while nanobeam electron diffraction detected weak Bragg reflections from Fe clusters with the body centered cubic structure. These results unambiguously reveal structural heterogeneity of the as-quenched Fe81.2Co4Si0.5B9.5P4Cu0.8 alloy, which is similar to that observed in the NANOMET®.

Thermal stability, thermal expansion and grain-growth in exchange-coupled Fe–Pt–Ag–B bulk nanocomposite magnets

Rare-earth free (RE-free) exchange coupling nanocomposite magnets are intensively studied nowadays due to their potential use in applications demanding stable high-temperature operation and corrosion resistance. In this respect, the FePt alloy system is one of the most actively addressed potential permanent magnet solutions. In FePt alloys, promising magnetic features arise from the co-existence of hard magnetic L10 FePt and soft magnetic L12 Fe3Pt phases emerged from the same metastable precursor. The present work deals with an in-situ temperature-resolved synchrotron radiation study of the thermal stability, thermal expansion and microstructure evolution in exchange-coupled FePtAgB alloys. The as-cast microstructural state as well as the optimized magnetic behavior are given as reference and correlated to the observed microstructural evolution with temperature. The melt-spun Fe48Pt28Ag6B18 alloy ribbons were examined in situ by synchrotron X-ray powder diffraction from ambient temperature up to 600°C. The FePt–Fe3Pt exchange-coupled microstructure achieved by rapid solidification is not significantly altered during the high temperature exposure. The thermal expansion of the FePt L10 unit cell has been found to be strongly anisotropic, being essentially an in-plane expansion which may be seen as an anisotropic invar effect. For the FePt L10 phase, a significant deviation from linear thermal expansion is observed at the Curie temperature TC=477°C. This non-linear behavior above TC is tentatively linked to a diffusion/segregation mechanism of Ag. The promising hard magnetic properties as well as the direct formation of the L10 phase from the as-cast state are directly related to the presence of Ag in the intergranular regions.

Two directional microstructure and effects of nanoscale dispersed Si particles on microhardness and tensile properties of AlSi7Mg melt-spun alloy

The two directional microstructure and multiple mechanical properties of the AlSi7Mg ribbon produced by melt-spun were investigated by optical microscopy (OM), field emission gun scanning electron microscope (FEGSEM), X-ray diffraction (XRD), microhardness and tensile tests. Both the surface and cross-sectional microstructure of the melt-spun ribbon were characterized in detail to give a clear and integrated description of the microstructure. Two kinds of nanoscale Si particles were observed, i.e., small Si particles ranging from 13 to 50nm and large Si particles ranging from 50nm to several hundreds of nanometers with clear size boundary were dispersed both in the interior and boundary of fine α-Al. XRD results revealed supersaturated solution of Si in Al matrix to be 0.62at.%. The ultimate tensile strength, yield strength, and hardness of the ribbon were 1.53, 1.75 and 1.56 times higher than that of the conventional cast ingot separately. The breaking elongation of the ribbon was 1.73% with intergranular fracture feature. The effects of nanoscale dispersed Si particles on the significant improvement of both hardness and tensile properties of the AlSi7Mg melt-spun ribbon were discussed in detail.

Effect of rapid solidification treatment on structure and electrochemical performance of low-Co AB5-type hydrogen storage alloy

The effect of rapid solidification on structure and electrochemical performance of the LaNi4.5Co0.25Al0.25 hydrogen storage alloy was investigated by X-ray powder diffraction and a simulated battery test, including maximum capacity, cycling stability, self-discharge, and high-rate discharge ability (HRD). All the melt-spun alloys were single-phase with the CaCu5-type structure (space group P6/mmm). In comparison to the as-cast alloy, the rapidly quenched alloys manifested an improved homogeneity of composition and expanded lattice parameters. The electrochemical measurements showed that the activation property, cycling stability and self-discharge of the alloy electrodes were also improved for the rapid solidified alloys. The HRD of the as-cast alloy was better than those of all the rapidly solidified alloys. As the quenching rate increased, the HRD and exchange current density first decreased and then increased.

Near room-temperature magnetocaloric properties of Gd–Ga alloys

The magnetocaloric properties of Gd–Ga alloys were examined with the aim to explore their potential application as magnetic refrigerants near room-temperature. A series of Gd100−xGax (x=0, 5, 10, 15, and 20at%) alloys were prepared by conventional melting and rapid solidification. Both as-cast and melt-spun alloys are comprised of α-Gd and Gd5Ga3 with differing microstructural characteristics. While the as-cast alloys have proeutectic α-Ga and eutectic α-Ga+Gd5Ga3 (grain size ~50–100µm), the melt-spun alloys have nanostructured (~50–100nm) α-Ga and Gd5Ga3. The Curie temperature (TC) derived from M–T curves indicates that alloying of Ga with Gd decreases TC. The decrease in TC for melt-spun alloys is gradual—~0.5K per at% of Ga, and the as-cast alloys (5≤x≤20) have similar TC (~286K). The saturation magnetization (MS) derived from M–H curves (260K), show that alloying of Ga with Gd decreases MS. MS for melt-spun alloys decreases from ~108emu/g for Gd to ~42emu/g for Gd80Ga20 and for as-cast alloys MS decreases from ~120emu/g for Gd to ~62emu/g for Gd80Ga20. Both maximum magnetic entropy change (−ΔSM)max and refrigerant capacity (RC) for as-cast and melt-spun alloys are lower than Gd. (−ΔSM)max decreases by ~1.55% and ~3.0% per atomic percent of Ga in as-cast and melt-spun alloys, respectively. A steeper decrease in RC is observed in melt-spun alloys than is observed for as-cast alloys—~433J/kg for Gd to ~235J/kg for Gd80Ga20 for melt spun alloys and ~462J/kg for Gd to ~306J/kg for Gd80Ga20 for as-cast. As-cast alloys appear to have better magnetocaloric properties than the melt-spun alloys. Alloying of diamagnetic Ga with Gd provides superior magnetocaloric properties compared to other diamagnetic elements in Group 13. The near room-temperature magnetocaloric properties of Gd–Ga alloys were comparable to a few first-order-transition based magnetic refrigerants.

Evolution of Structure-Scaling and Magnetic Properties during Thermal Loading of Melt-Spun Fe&lt;sub&gt;70&lt;/sub&gt;Cr&lt;sub&gt;15&lt;/sub&gt;B&lt;sub&gt;15&lt;/sub&gt;(Sn) Alloys

We have studied the scaling evolution of the structure and magnetic properties of the melt-spun Fe70Cr15B15(Sn) alloys. The magnetic percolation cluster about the percolation threshold forms at the vitrification stage that is determined by both the kinetics of magnetic and of transport properties and the variation of fractal dimensionality. Alloying by tin of contact surface of ribbon decreases the temperature of the cluster formation. It is shown that the evolution of a fractal ordering affects the kinetics of the physical properties of the alloys. The spectra of fractal dimensionality identify the symmetry character of melt-spun alloys. Fractal dimensionDfis reduced at the increasing complexity of hierarchical system.

Microstructure of multistage annealed nanocrystalline SmCo2Fe2B alloy with enhanced magnetic properties

The microstructure and chemistry of SmCo2Fe2B melt-spun alloy after multistage annealing was investigated using high resolution transmission electron microscopy (HRTEM) and 3D atom probe tomography. The multistage annealing resulted in an increase in both the coercivity and magnetization. The presence of Sm(Co,Fe)4B (1:4:1) and Sm2(Co,Fe)17Bx (2:17:x) magnetic phases were confirmed using both techniques. Fe2B at a scale of ∼5 nm was found by HRTEM precipitating within the 1:4:1 phase after the second-stage annealing. Ordering within the 2:17:x phase was directly identified both by the presence of antiphase boundaries observed by TEM and the interconnected isocomposition surface network found in 3D atom probe results in addition to radial distribution function analysis. The variations in the local chemistry after the secondary annealing were considered pivotal in improving the magnetic properties.

AMORHIZATION AND LIQUID STATE SEPARATION IN Ni80-2xCuxFexP20 ALLOYS

The aim of the work is to study the ability and potential of glass formation in Ni-Fe-Cu-P alloys. A series of alloys were produced in arc furnace (i.e. Ni 70 Fe 5 Cu 5 P 20 , Ni 60 Fe 10 Cu 10 P 20 , Ni 50 Fe 15 Cu 15 P 20 , Ni 40 Fe 20 Cu 20 P 20 , Ni 30 Fe 25 Cu 25 P 20 , Ni 20 Fe 30 Cu 30 P 20 ). The primary microstructure of the ingots was studied. The ribbons in as-melt-spun state were characterized by X-ray diffraction (XRD). The Ni 70 Fe 5 Cu 5 P 20 , Ni 60 Fe 10 Cu 10 P 20 melt-spun alloys were found to be amorphous. For higher copper and iron concentrations crystalline structure was obtained after melt spinning. This correlated with the tendency for the formation of the Fe-based phases enriched in P and Cu-based poorly alloyed phases which resulted in formation of crystalline microstructure in melt-spun ribbons. For higher concentration of Fe and Cu, microstructures of the alloys contained constituents resultant from tendency for separation in the liquid state. It is observed that formation of the crystalline melt-spun ribbons is caused by attraction of phosphorus by iron and formation of copper-based fcc phase.

Microstructure of the Ni–Fe–Cu–P melt-spun ribbons produced from the single-chamber and from the double-chamber crucibles

The aim of the work was to investigate the influence of the processing on the final microstructure and properties of the melt-spun Ni–Fe–Cu–P, Ni–Fe–P and Ni–Cu–P alloys ejected in two ways. In the first case, the alloy was molten in a simple single-chamber crucible, then ejected as uniform liquid. In the second case the double-chamber crucible was used, and the flux composed of the two Ni–Fe–P and Ni–Cu–P liquids was cooled on a copper roller before forming a uniform mixture. The two component melt spinning (TCMS) was performed starting from the Ni40Fe40P20 and Ni70Cu10P20 alloys. Three of the alloys i.e. Ni55Fe20Cu4P20, Ni40Fe40P20 and Ni70Cu10P20 were melt-spun from the traditional single-chamber crucible. The methods applied in this study for microstructural investigations include scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Mössbauer spectroscopy. Thermal stability of the melt-spun alloys was tested using differential scanning calorimetry (DSC). The results of the investigations are described and discussed in terms of the unique features of the TCMS amorphous microstructure. It is shown that this complex phase composition of the amorphous alloy favors formation of the ductile fracture and the multiple shear band formation.

대량용해 Ti0.85Zr0.13(Fex-V)0.56Mn1.47Ni0.05수소저장합금의 용융방사공정을 통한 수소저장특성

Hydrogen storage as a metal hydride is the most promising alternative because of its relatively large hydrogen storage capacities near room temperature. TiMn2-based C14 Laves phases alloys are one of the promising hydrogen storage materials with easy activation, good hydriding-dehydriding kinetics, high hydrogen storage capacity and relatively low cost. In this work, multi-component, hyper-stoichiometric C14 Laves phase alloys were prepared by a vacuum induction melting for a hydrogen storage tank. Since pure vanadium (V) is quite expensive, the substitution of the V element in these alloys has been tried and some interesting results were achieved by replacing V by commercial ferrovanadium (FeV) raw material. In addition, the melt-spinning process, which was applied to the manufacturing of some of these alloys, could make the plateau slopes much flatter, which resulted in the increase of reversible hydrogen storage capacity. The improvement of sloping properties of melt-spun alloys was mainly attributed to the homogeneity of chemical composition.

Microstructure and tailoring hydrogenation performance of Y-doped Mg2Ni alloys

In this work, the microstructure and the hydrogenation properties of melt-spun Mg67Ni33−xYx alloys are studied with the purpose to investigate the influence of Y doping and rapid solidification on hydrogenation performance of Mg2Ni. Mg67Ni33−xYx (x = 0, 1, 3, 6) alloys are firstly prepared in an electric resistance furnace under the protection of a covering reagent. Then, the as-cast alloys are re-melted and spun on a rotating copper roller. The phase compositions and microstructures of as-cast and melt-spun alloys are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) with an energy dispersive spectrometer (EDS). The hydrogen activation properties and absorption/desorption kinetics of melt-spun Mg67Ni33−xYx (x = 0, 1, 3, 6) ribbons are evaluated using an automatic Sieverts apparatus. The melt-spun Mg67Ni32Y alloy preserves high hydrogen absorption capacity and kinetics and absorbs 96% of the maximum capacity (3.79 wt. %) within 8 min. The lattice distortion caused by Y doping and the shrinkage porosity by melt-spun not only raise the hydrogen absorption/desorption rate, but significantly improve the hydrogen storage capacity of Mg67Ni33−xYx (x = 0, 1, 3, 6) alloys. The activation and hydrogen absorption/desorption mechanisms are also discussed based on a nucleation and growth theory.

Structural modifications in a Mn54Al43C3 melt-spun alloy induced by mechanical milling and subsequent annealing investigated by atom probe tomography

The structural changes upon milling and subsequent annealing of a Mn54Al43C3 alloy containing the intermetallic tetragonal L10 MnAl phase (τ phase) as the major phase were investigated by X-ray diffraction and atom probe tomography. The analyses show that milling the starting powder for 10h leads to the nanostructuration of the sample. The milled sample is partly oxidised and contains both non oxidised Mn60±5Al40±5 regions and oxidised regions. Annealing the powder for 1h at 500°C leads to enrichment in Al of the oxidised regions, and to the phase transformation of the non-oxidised regions into a nanostructured β-Mn-like phase with a composition close to Mn3Al2.

Changes of Structure and Magnetic Properties of Fe&lt;sub&gt;66&lt;/sub&gt;Co&lt;sub&gt;24&lt;/sub&gt;Si&lt;sub&gt;3&lt;/sub&gt;B&lt;sub&gt;7&lt;/sub&gt; Amorphous Alloy under Heat Treatment

In this paper features of structure at the atomic level, magnetic properties, and mechanisms of structural relaxation during thermal annealing of melt-spun ribbon Fe66Co24Si3B7(ribbon thickness is 28 microns) will be discussed. By means of differential scanning calorimetry and X-ray diffraction analysis of melt-spun alloy it has been shown that structural relaxation processes have complex multi-step nature, primarily related with instability of alloy. Using this data it has been shown that magnetic structure-sensitive properties, such as coercivity and magnetic moment, can be considered as structural relaxation indicators in amorphous alloys. The original amorphous material when heated to crystallization temperature partially passes to the crystalline state, causing the increase in residual magnetic moment and coercivity.

A nanoporous composite by dealloying rapidly quenched Co75Pd20Si5

In this work we report the fabrication of a nanoporous composite by electrochemical dealloying a rapidly quenched Co75Pd20Si5 alloy in a 0.5M H2SO4 aqueous solution. The melt-spun alloy exhibited a two-phase microstructure with the precipitation of an unknown secondary phase on the FCC solid solution matrix. Upon dealloying, a nanoporous composite was formed, which consisted of nanoligaments of two different length scales, namely, ~ 5-10 nm and ~ 100-150 nm. The sample surface was free of cracks and the as-dealloyed ribbons exhibited good mechanical integrity. The secondary phase was found to be more corrosion-resistant than the FCC solid solution phase under the same electrochemical conditions, and after dealloying the framework structure of the phase preserved to reinforce the dealloyed microstructure.