Melt-spun Amorphous Ribbons Research Articles

Laser powder bed fusion of a nanocrystalline Finemet Fe-based alloy for soft magnetic applications

The aim of this work is to explore the laser powder bed fusion (LPBF) processability window of the nanocrystalline soft magnetic Finemet alloy. With that purpose, several laser power and scan speed values and a meander scanning strategy were probed to process simple geometry specimens. Good dimensional accuracy was obtained within the entire processing window investigated. Relative densities as high as 89% were achieved for processing conditions including high laser power and low scan speeds. The fraction of amorphous phase, which peaked at 49%, was found to be mostly dependent on the scan speed and only slightly influenced by the laser power. The microstructure of the crystalline domains is formed by ultrafine, equiaxed grains with random orientations. Irrespective of the processing conditions, the LPBF-processed samples exhibit a similar saturation magnetization, lower permeability, and higher coercivity than fully amorphous melt-spun ribbons of the same composition. The coercive field of the additively manufactured specimens is fairly independent of the relative density and exhibits a moderate inverse variation with the amorphous fraction. Consistent with earlier works, this study suggests that the average grain size is an important contributor to coercivity.

EFFECT OF CU AS МINORITY АLLOYING ЕLEMENT ON GLASS FORMING ABILITY AND CRYSTALLIZATION BEHAVIOR OF RAPIDLY SOLIDIFIED AL-SI-NI RIBBONS

The influence of copper as a minority alloying element in the process of rapid solidification of Al-Si-Ni ribbons produced by Chill Block Melt Spinning (CBMS) was investigated. XRD and TEM analyses proved a completely amorphous structure of the alloys Al74Ni16Si10 and (Al74Ni16Si10)98Cu2. The crystallization behaviour of these alloys was studied by DSC analysis. It was found that the crystallization of the amorphous alloys (Al74Ni16Si10)100-xCux, x=0, 2 runs in two steps. The temperatures Tx1 and Tx2 of each of the crystallization steps were determined. It was proven that the addition of 2 at. % copper does not significantly change Tx temperatures. The temperature difference ΔTx was calculated and it showed that more thermally stable is the copper containing alloy. Crystalline analogues of the amorphous alloys were obtained by annealing of the melt-spun amorphous ribbons at a temperature which exceeded by 170°C the onset crystallization temperature. The type and size of separated crystalline phases were determined by XRD. It was found that the addition of 2 at. % Cu to Al74Ni16Si10 alloy causes a separation of new phases - Cu3.8Ni and (Al, Cu)Ni3 and 54%, 24% and 7% size increase of the phases Al, Al3Ni, NiSi2 respectively.

Enhanced specific heat of the Sc79Fe21 nanoglass compared to the Sc79Fe21 amorphous melt-spun ribbon in a temperature range of 150–300 K

The specific heat of the Sc79Fe21 amorphous materials was measured in a temperature range of 150 to 300 K. The specific heat of the Sc79Fe21 nanoglass prepared by consolidation of glassy nanoparticles was approximately 2.5% higher than that of the Sc79Fe21 amorphous melt-spun ribbon. The enhanced specific heat was primarily ascribed to the interfaces within the nanoglass of heterogeneous structure, since both the reduced packing density and interfacial enrichment of the Sc increased the specific heat of the interfaces, while adding Fe to the cores reduced the specific heat.

Influence of heating on structure and mechanical characteristics of amorphous Al86Ni9Gd5 ribbons

Changes of structure and mechanical characteristics of amorphous Al86Ni9Gd5 melt-spun ribbons subjected to linear heating at a rate of 10 K/min were investigated by differential scanning calorimetry, X-ray diffraction, transmission electron microscopy, three-point bending testing and microhardness measurements. Non-monotonic changes of all mechanical characteristics were related to the structural variations occurring at three-stage transformation process. It was established that nanocrystallization of amorphous phase led to drop of all properties measured by three-point bend testing (the modulus of elasticity, bending limit at fracture and plasticity) while formation of the intermetallic compounds and coarsening of structure during subsequent transformation stages resulted in their partial recovery. On the contrary, microhardness had a maximum (about 4.5 GPa) in the samples with the ultra-fine grained partially crystallized structure. The potential for practical applications of the established effect of recovery of plasticity from zero in nanocomposite structure to about 1% in the fully crystallized sample with microhardness about 3 GPa was discussed.

Structure of AlNiGd nanocomposites with enhanced ductility produced by high pressure torsion processing

The fully consolidated bilayer (consisting of two amorphous Al86Ni9Gd5 melt-spun ribbons) disks with a diameter of 5 mm were produced using unconstrained high pressure torsion (HPT) processing subjecting for 2–5 turns at applied pressures of 2 and 4 GPa. The structure and mechanical properties of the disks as well as those of the as-prepared and heated up to 479 K ribbon samples were studied by X-ray diffraction analysis, transmission and scanning electron microscopy, three-point bending tests and measurements of microhardness. It was established that the heat treatment and consolidation resulted in formation of nanocomposite structures consisting of Al nanocrystals 21 and 6 nm in size, respectively, with enhanced microhardness. It was shown that the heat treatment of the ribbon led to a loss of the plastic strain (from 2 to 0.4%) while the consolidated disks retained the same level of plasticity as that in the as-cast amorphous ribbon. The possible reason of the enhanced plasticity of the nanophase composites obtained by deformation-induced crystallization was discussed.

Breaking Down SERS Detection Limit: Engineering of a Nanoporous Platform for High Sensing and Technology.

In this study, nanoporous gold (NPG) was synthesized by free corrosion dealloying of an amorphous precursor, Au20Cu48Ag7Pd5Si20 (at. %), in a mixture of nitric and hydrofluoric acid, starting from amorphous melt-spun ribbons. NPG revealed a 3D nanoporous structure composed of pores and multigrain ligaments of an average size of 60 nm. NPG was further anodized in oxalic acid at 8 V vs. Ag/AgCl reference electrode to obtain a bimodal morphology composed of ligaments disrupted in finer features. Both NPG and anodized samples (A-NPG) were found to be mechanically stable to bending and active for surface-enhanced Raman scattering (SERS). SERS activity of samples was investigated using 4,4′-bipyridine as a probe molecule. A detection limit of 10−16 M was found for both samples, but in A-NPG, the signal was strongly enhanced. The extremely high enhancement obtained for A-NPG is attributed both to the small size of ligaments and crystals of which they are made, as well as to the nanometric features resulting from anodization treatment. Such a microstructure showed homogenous SERS response in terms of average enhancement all across the surface, as demonstrated by mapping measurements. Furthermore, NPG and A-NPG were tested as electrodes for electrocatalytic applications, showing good properties. The engineering steps from the amorphous precursor to A-NPG led us to obtain a high-sensing platform, with extremely low detection limit and intrinsic properties, that might significantly contribute to the cutting-edge technology of the future.

Amorphous-crystalline Al-based laminates with enhanced plasticity produced by high pressure torsion

The consolidated disks consisted of two melt-spun Al86Ni9Gd5 amorphous ribbons inserted between two-layered stacks of Al foils were obtained by using unconstrained high-pressure torsion straining. Structure and mechanical properties of the Al-covered samples were studied by scanning electron microscopy, three-point bending testing and microhardness measurements and compared with those of consolidated disks consisted of two amorphous ribbons and of 12 layers of Al foils. It was established that the Al-covered disks had superior plasticity (3.6%) and intermediate average microhardness (1.95 GPa) compared with those of the uncovered and Al consolidated disks. The mixing of the Al and amorphous alloy was directly observed in the Al-covered disks which resulted in ductilisation and large variations of microhardness on surface and inside of the samples.

Effect of Y doping on surface crystallization and magnetic properties of a FeHfB nanocrystalline alloy

A Fe87Hf5B8 alloy forms a crystallization layer with textured coarse α-Fe grains in the free surface of the melt-spun amorphous ribbon, which deteriorates the uniformity of nanocrystalline structure after annealing and leads to a high coercivity (Hc) of over 16 A/m. Doping of 0.1–0.2 at.% Y into the Fe87Hf5B8 alloy inhibits the surface crystallization of the melt-spun precursor and contributes to a uniform and fine nanostructure in the whole annealed ribbons. The Y-doped nanocrystalline alloys possess lower Hc of around 9 A/m and maintain high saturation magnetic flux density of 1.70 T. The suppression of the surface crystallization by Y doping is attributed to the improvement of amorphous-forming ability, which is mainly caused by the reduction of oxygen impurity content in the alloys.

Comparison and process study of hot-pressed and hot-deformed Nd-Fe-B magnets prepared by amorphous and nanocrystalline powders

Hot-pressed and hot-deformed Nd-Fe-B magnets are generally made from rapidly quenched powder after crystallization treatment. In this work, the amorphous melt-spun ribbons are also employed directly as the precursor. The amorphous and crystallized powders with the composition of Nd28.47Pr0.56FebalB0.97Co3.63Al0.13Nb0.56Zr0.44 were employed for fabricating hot-pressed and hot-deformed magnets. The influences of processing parameters on the microstructure and magnetic properties have been investigated. For the hot-pressed magnets produced from both crystallized and amorphous powders, the grain pre-orientation and magnetic properties including coercivity, remanence and maximum energy product increase with the increasing temperature, pressure and holding time in the ranges of 650–800 °C, 300–600 MPa and 30–150 min, respectively. The hard magnetic properties of the hot-pressed magnets obtained from amorphous powder are slightly higher than those from crystalline powder due to the smaller grain size of the former. The magnetic properties of hot-deformed magnets are mainly determined by the deformation temperature and not influenced by the state of the powder and hot-pressed precursors. The hot-pressed magnets and hot deformed magnets with different microstructures exhibit different magnetization mechanisms. The optimal hot-deformation temperature is found to be 750 °C for obtaining a high maximum energy product of 39 MGOe. The present results suggest that the rapidly quenched amorphous powder can be used to not only directly prepare hot-pressed magnets with higher magnetic properties, but also to reduce the process step for hot-deformed Nd-Fe-B magnets.

High-pressure torsion of Zr-based bulk metallic glasses and amorphous melt-spun ribbons

High-pressure torsion allows one to achieve high strains of bulk metal glasses without their destruction. The article presents the results of studies on the effect of high-pressure torsion on the amorphous alloys of the same composition but obtained in different ways: in a form of a bulk plate and a melt-spun ribbon. It is shown that the degree of nonequilibrium after high-pressure torsion, determined by the diffraction and calorimetry methods, increases for bulk metallic glass, approaching the values characteristic for melt-spun alloy.

Variation in the structure of the amorphous NiTi-based alloys during mechanical vibrations

The aim of the present work is to study the influence of the vibration temperature, frequency and amplitude on the structure of amorphous NiTi-based shape memory alloys. The Ti40.7Hf9.5Ni44.8Cu5, Ti40.7Hf9.5Ni41.8Cu8 and Ti50Ni25Cu25 melt-spun amorphous thin ribbons were subjected to low-frequency mechanical vibrations in a Dynamical Mechanical Analyser or ultrasonic vibrations in anvil. The results of the study have shown that the mechanical vibrations lead to a structural relaxation and initiate the beginning stage of the crystallisation in the amorphous NiTi-based shape memory alloys. During the vibrations with an amplitude of 4 μm, crystalline clusters, with a size of 4–6 nm, appear in the amorphous matrix. On an increase in the vibration temperature or frequency, the size of the crystalline clusters hardly changes. The clusters that form during the vibrations do not influence the crystallisation temperature but decrease the crystallisation enthalpy.

Influence of Cu Content on Structure and Magnetic Properties in Fe86-xCuxB14 Alloys.

Influence of Cu content on thermodynamic parameters (configurational entropy, Gibbs free energy of mixing, Gibbs free energy of amorphous phase formation), crystallization kinetics, structure and magnetic properties of Fe86-xCuxB14 (x = 0, 0.4, 0.55, 0.7, 1) alloys is investigated. The chemical composition has been optimized using a thermodynamic approach to obtain a minimum of Gibbs free energy of amorphous phase formation (minimum at 0.55 at.% of Cu). By using differential scanning calorimetry method the crystallization kinetics of amorphous melt-spun ribbons was analyzed. It was found that the average activation energy of α-Fe phase crystallization is in the range from 201.8 to 228.74 kJ/mol for studied samples. In order to obtain the lowest power core loss values, the isothermal annealing process was optimized in the temperature range from 260 °C to 400 °C. Materials annealed at optimal temperature had power core losses at 1 T/50 Hz—0.13–0.25 W/kg, magnetic saturation—1.47–1.6 T and coercivity—9.71–13.1 A/m. These samples were characterized by the amorphous structure with small amount of α-Fe nanocrystallites. The studies of complex permeability allowed to determine a minimum of both permeability values at 0.55 at.% of Cu. At the end of this work a correlation between thermodynamic parameters and kinetics, structure and magnetic properties were described.

Pragmatic Approach to Design Silicon Alloy Anode by the Equilibrium Method.

Silicon fascinates with incredibly high theoretical energy density as an anode material and considered as a primary candidate to replace well-established graphite. However, further commercialization is hindered by the abnormal volume changes of Si in every single cycle. Silicon embedded in a buffer matrix using the melt-spinning process is a promising approach; however, its metastable nature significantly reduces the microstructure homogeneity, the quality of the composition, and, therefore, the electrochemical performances. Herein, we developed a new approach to design a high-performance Si-alloy with improved microstructure uniformity and electrochemical properties. Namely, annealing at a certain temperature of the melt-spun amorphous alloy ribbon allowed us to evenly distribute Si nanocrystallites in the microstructure with control of average grain size. As a result, the Si-alloy electrode delivers an initial discharge capacity of 900 mAh g-1 and exhibits a high coulombic efficiency of >99% from the second cycle with a capacity retention of ∼98% after 100 cycles. This study provides powerful insights and evidence for the successful application of the proposed approach for commercial purposes.

On the mechanisms limiting power loss in amorphous CoFeB-based melt-spun ribbons

The mechanisms that limit the power loss performance in melt-spun amorphous ribbons have been investigated through DC and AC magnetic characterization methods. The measured total power loss is resolved into hysteresis, eddy current, and anomalous losses. The anomalous loss is found to account for more than 90% of the total loss, which significantly reduced by annealing in a transverse magnetic field. This is attributed to the reorientation of preferred magnetisation axis perpendicular to the length of ribbons. Transverse magnetic annealing promotes the relative contribution of domain rotation over domain wall motion during magnetisation reversal process. Magnetic annealing also causes a measurable decrease in the domain width, which promotes pinning and inhibits domain wall motion, thus further favoring coherent domain rotation as the primary mechanism of magnetization. This combination accounts for a 75% decrease in the total power loss in the so-processed ribbons and renders them attractive for applications in mid-and high-frequency power supplies and inverters.

Comparative study on sintering behavior of Al86Ni6Y4.5Co2La1.5 mechanically alloyed amorphous powder and melt-spun ribbon

In this research work, the sintering characteristics of Al86Ni6Y4.5Co2La1.5 mechanically alloyed amorphous powders and milled melt spun ribbon have been compared. Mechanically alloyed amorphous powders were synthesized via 200 h high energy ball milling. Melt spun ribbons were synthesized by single roller melt spinning technique and grounded to powder form by ball milling. Mechanically induced partial crystallization occurred in the ribbons during milling. Significantly higher amount of contaminations such as carbon, oxygen and iron were observed in the mechanically alloyed amorphous powders compared to the milled ribbons. Both powders were consolidated via spark plasma sintering. Superior particle bonding was found in the sample consolidated from milled ribbons, ascribed to the lower amount of contamination that could not effectively restrict the viscous flow and diffusion of atoms. Various complex crystalline phases evolved in the sample consolidated from milled ribbon particles due to the presence of crystalline phases in the powders which acted as nucleation sites, whereas the amorphous phase was mostly retained in its counterpart. Vickers microhardness of the consolidated alloys from milled ribbon and mechanically alloyed amorphous powders were 3.60 ± 0.13 GPa and 2.53 ± 0.09 GPa, respectively. The higher hardness in the former case was attributed to the superior particle bonding and distribution of hard intermetallic phases in the amorphous matrix.

Effect of Sm on thermal and mechanical properties of Cu-Zr-Al bulk metallic glasses

The effect of rare-earth (Sm) microalloying on the thermal stability and phase selection along with the effect of nanocrystallization on the mechanical properties of amorphous melt-spun ribbons of Zr50Cu40Al10, Zr49Cu39.2Al9.8Sm2 and Zr48Cu38.4Al9.6Sm4 alloys were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), Vickers and nanoindentation hardness tests and micropillar compression analysis. XRD and TEM analyses showed that all samples were fully amorphous in as-spun state; however, crystallization sequences for the Sm-free and the Sm micro-alloyed samples were different during devitrification. Combined study of XRD, DSC and TEM on melt-spun ribbons show that Zr48Cu38.4Al9.6Sm4 have nanocrystallization of Cu2Sm phase with an average diameter of 10 nm, which was absent in Zr50Cu40Al10, prior to crystallization of Cu10Zr7 phase. The nanoindentation and micropillar compression tests revealed Cu2Sm nanocrystals embedded in Zr48Cu38.4Al9.6Sm4 alloy improves strength and hardness. On the other hand, presence of these nanocrystals deteriorate shear band stability and thus result in a catastrophic brittle fracture through a single shear band burst.

Effect of preparation cooling rate on magnetocaloric effect of Fe80P13C7 amorphous alloy

Abstract In this work, the magnetocaloric effect (MCE) of Fe80P13C7 melt-spun amorphous ribbon and bulk glassy rod has been investigated and so the effect of the preparation cooling rate on the MCE of the present Fe-based amorphous alloy is studied. The value of peak of isothermal magnetic entropy change ( | Δ S M peak | ) and refrigerant capacity (RC) for the Fe80P13C7 amorphous ribbon is larger than those of the glassy rod under varies applied field. Hence, we consider that the demagnetization field effect may have a significant influence on the MCE measurement results of the Fe80P13C7 glassy rod. After the demagnetization field correction, the values of | Δ S M peak | and RCAREA for the Fe80P13C7 glassy rod are close or even superior to those of the amorphous ribbon. Further, it is indicated from the | Δ S M peak | ∝ H n relationship that the glassy rod has more homogeneous internal atomic structure compared with the amorphous ribbon. It has been proposed that more homogeneous structure could lead to greater magnetocaloric properties, and therefore we suggest that the intrinsic MCE performance of the Fe80P13C7 glassy rod prepared at a lower cooling rate should be better than that of the amorphous ribbon.

Thermal stability, magnetic and magnetocaloric properties of Gd55Co35M10 (M = Si, Zr and Nb) melt-spun ribbons

The thermal stability, magnetic and magnetocaloric properties of Gd55Co35M10 (M = Si, Zr and Nb) melts-pun ribbons were studied. The relatively high reduced glass transition temperature (Tx1/Tm > 0.60) and low melting point (Tm) resulted in excellent glass forming ability (GFA). The Curie temperatures (TC) of melt-spun amorphous ribbons Gd55Co35M10 for M = Si, Zr and Nb were 166, 148 and 173 K, respectively. For a magnetic field change of 2 T, the values of maximum magnetic entropy change (−ΔSM)max for Gd55Co35Si10, Gd55Co35Zr10 and Gd55Co35Nb10 were found to be 2.86, 4.28 and 4.05 J kg−1K−1, while the refrigeration capacity (RC) values were 154, 274 and 174 J kg–1, respectively. The RCFWHM values of amorphous alloys Gd55Co35M10 (M = Si, Zr and Nb) are comparable to or larger than that of LaFe11.6Si1.4 crystalline alloy. Large values of (−ΔSM)max and RC along with good thermal stability make Gd55Co35M10 (M = Si, Zr and Nb) amorphous alloys be potential materials for magnetic cooling operating in a wide temperature range from 150 to 175 K, e.g., as part of a gas liquefaction process.

Influence of crystallization treatment on structure, magnetic properties and magnetocaloric effect of Gd71Ni29 melt-spun ribbons

The influence of crystallization treatment on the structure, magnetic properties and magnetocaloric effect of Gd71Ni29 melt-spun ribbons has been investigated in detail. Annealing of the melt-spun samples at 610 K for 30 min, a majority phase with a Fe3C-type orthorhombic structure (space group, Pnma) and a minority phase with a CrB-type orthorhombic structure (space group, Cmcm) were obtained in the amorphous matrix. The amorphous melt-spun ribbons undergo a second-order ferromagnetic to paramagnetic phase transition at 122 K. For the annealed samples, two magnetic phase transitions caused by amorphous matrix and Gd3Ni phases occur at 82 and 100 K, respectively. The maximum magnetic entropy change (–ΔSM)max is 9.0 J/(kgˑK) (5T) at 122 K for the melt-spun ribbons. The values of (–ΔSM)max in annealed ribbons are 1.0 and 5.7 J/(kgˑK), corresponding to the two adjacent magnetic transitions.

The effect of Co addition on magnetic and structural properties of nanocrystalline (Fe,Co)-Si-B-P-Cu alloys

Magnetic properties of amorphous and nanocrystalline Fe85.2−xCoxSi0.5B9.5P4Cu0.8 (x = 0, 4, 10, 15, 20, 25, 35, 40, 50 and 57 at%) alloys have been investigated and their detailed structural parameters have been quantitatively investigated by X-ray diffraction, transmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and three dimensional atom probe (3DAP). The nanocrystalline structure that forms by annealing the melt-spun amorphous ribbon at above 400 °C comprises a bcc phase and a residual amorphous phase. Both coercivity and magnetostriction of the nanocrystalline state increase with increasing Co content, from Hc = 4 A m−1 to 29 A m−1 and from λs = 14 ppm–55 ppm, respectively. The saturation polarization Js reaches a maximum of about 1.88 T at a Co-content of about 25 at%. The dependence of magnetic properties on the Co content can be explained by the composite rule of the intrinsic magnetic properties of the constituent phases. We also found the grain size dependence of coercivity to change from the well-known D6 dependence to D3-dependence in the composition range where the magnetocrystalline anisotropy constant vanishes.