Fe-based Bulk Metallic Glasses Research Articles

Effect of particle materials on deposition behavior and microstructural features of films prepared via vacuum kinetic spraying

Vacuum kinetic spraying (VKS) is a particle deposition process by which various materials can be deposited as films, even at room temperature. In this study, Al2O3 (ceramic, completely brittle), Fe-based bulk metallic glass (BMG, brittle with some plastic deformability), and Ag (metal, completely ductile) were used as powder materials, and the effects of the particle materials on the deposition behavior and microstructural features of the film were investigated. Deposition tests were performed under identical experimental conditions, and the microstructural features were comprehensively analyzed. The deposition behavior and film microstructure of the three materials were completely different. The Al2O3 film formed at the lowest deposition rate was extremely dense and comprised nanocrystals with a relatively low surface roughness, indicating fragmentation-dominant deposition. The deposition rate of Ag was between those of the other two materials, and the film consisted of relatively dense large grains with nanopores and a smooth surface, resulting from plasticity-dominant deposition. The deposition rate of BMG was considerably high, and the resulting film consisted of a porous structure with relatively large fragments and an extremely rough film surface. These features of BMG were attributed to the insufficient fragmentation or plastic deformation of the particles. Consequently, even under identical deposition conditions, the deposition rate and behavior and the resulting film microstructure vary depending on the particle materials. Therefore, the microstructural features of the film must be examined before selecting powder materials and fabricating films through process optimization for each material.

Machine learning-enabled design of Fe-based bulk metallic glasses for superior thermal neutron absorption properties

Machine learning-enabled design of Fe-based bulk metallic glasses for superior thermal neutron absorption properties

Microstructure, hardness, and wear resistance of annealed Fe-based bulk metallic glasses by spark plasma sintering

Microstructure, hardness, and wear resistance of annealed Fe-based bulk metallic glasses by spark plasma sintering

FeSiBCCr bulk metallic glasses with excellent soft magnetic properties prepared using spark plasma sintering technology

Fe-based amorphous alloys have received much attention in the fields of electronics and electrical due to their excellent soft magnetic properties at high frequency. However, the controllable preparation of large-sized Fe-based bulk metallic glasses (BMGs) still faces numerous challenges. In this study, FeSiBCCr amorphous powders prepared by gas-water combined atomization were used as raw materials, and FeSiBCCr BMGs were prepared through spark plasma sintering (SPS) at different pressures. The microstructure, phase and magnetic properties of the compacts were systematically characterized using SEM, XRD, TEM, DSC, and VSM. The results showed that when the sintering pressure was 50 MPa, the slow densification process dominated by particle rearrangement at the initial densification process made the internal contact resistance of the compacts larger. This led to macroscopic inhomogeneous physical fields and severe local overheating during the later stages of sintering, causing the precipitation of α-(Fe, Si) and Fe3B phases. Although the material exhibited a relatively high saturation magnetization (Bs) of 1.08 ± 0.01 T, the low density and amorphous fraction resulted in a high coercivity (Hc) of 1060.8 ± 37.8 A·m-1. When the sintering pressure was increased to 250 MPa, the degree of particle densification significantly improved, and the temperature inhomogeneity was markedly suppressed due to reduced internal resistance. Thus, the prepared FeSiBCCr BMGs exhibited an extremely high density of 6.66 ± 0.06 g·cm-3 and excellent soft magnetic properties with Bs of 1.23 ± 0.01 T and Hc of 18.8 ± 1.8 A·m-1. This indicated that the FeSiBCCr BMGs prepared in this study exhibited broad application prospects in efficient electromagnetic conversion and advanced electronic devices.

Fe-based bulk metallic glass with high thermal stability and corrosion resistance

Fe-based metallic glass is prone to crystallization at high temperature due to its thermodynamic instability, resulting in the loss of many excellent properties. In this work, we developed a new Fe-based bulk metallic glass with high Cr and W refractory elements. The results show that the glass transition temperature Tg reaches 880 K. The very high thermal stability can result in the formation of Cr-Cr bonds, W-W bonds, and (Cr,W)-(C,B) bonds with stronger bond energy in Fe-based bulk metallic glass. Moreover, FeCrWCBY bulk metallic glass exhibits good corrosion resistance in 3.5 % NaCl and aqua regia solutions. The self-corrosion current density of FeCrWCBY bulk metallic glass in NaCl solution is only 8.4 × 10–7 A/cm2, much lower than the result of Fe48Cr15Mo14C15B6Y2, known as amorphous steel. The high thermal stability and excellent corrosion resistance are decoded in details from atomic bonding properties and passivation film characteristics.

Exploring Microstructure and Magnetic Domain Evolution in the As-cast Soft Magnetic Fe74B20Nb2Hf2Si2 Alloy: A Comprehensive Study Using STEM, Lorentz TEM, and LM-STEM DPC Microscopy

This study delves into subtle changes in the microstructure and domain arrangement of a Fe74B20Nb2Hf2Si2 soft magnetic amorphous alloy. Utilizing transmission electron microscopy in Lorentz mode, low-magnification STEM, and differential phase contrast analysis (DPC), the research explores both the as-cast state and annealed samples. The results confirmed the formation of α-Fe, Fe23B6, Fe2(Hf, Nb), and Fe2B crystalline phases with increasing annealing temperature. Consequently, these crystallization stages induce significant alterations in magnetic domain size and spatial distribution due to microstructural changes. As the crystallization temperature rises, the volume fraction of crystalline phases increases, leading to modifications in the arrangement and size of magnetic domains. The decrease in magnetic domain size, associated with the formation of pinning sites during heat treatment, leads to alterations in soft magnetic properties. This includes an increase in coercivity (Hc) up to 40 A/m in the sample annealed at the temperature range of the third crystallization stage compared to the as-cast sample (1.5 A/m). Furthermore, as the annealing temperature rises, there is a corresponding increase in saturation magnetization (Ms), which reached to 1.71 T in the sample annealed within the temperature range of the third crystallization stage. These findings hold substantial implications for the practical applications of the Fe-based soft bulk metallic glasses (BMGs) alloy across various industries.

Effect of Si addition on Curie temperature and thermal expansion coefficient of (Fe71.2B24Y4.8)96Nb4 Invar bulk metallic glasses

The ultra-low thermal expansion coefficient α makes the Fe-Ni Invar alloys useful in various applications. Their low strength and low Curie temperature Tc are, however, limiting factors. Interestingly, some Fe-based bulk metallic glasses (BMGs), with inherent high strength, exhibit the clear Invar effect. In particular, the (Fe71.2B24Y4.8)96Nb4 BMG has the lowest α among Fe-based BMGs, but it unfortunately also has the lowest Tc. In this work, silicon was added into this alloy with the aim to elevate Tc while maintaining a low α. It was found that when silicon partially substituted boron, Tc did not increase significantly but α did, which is not ideal. On the other hand, when silicon partially substituted yttrium and niobium and especially niobium, Tc increased significantly while α did not, which is close to the ideal scenario. When 3% of niobium was substituted by silicon, Tc reached the maximum value of 296 °C while α remained a low value of 7.4 × 10−6/°C. Comparing to the Fe-Ni Invar alloy, although this BMG has an inferior α, it has much higher Tc (+115 °C) and strength (∼9 times), presenting a potential for application as a new Invar material with moderate (low) thermal expansion, high operating temperature, and high strength.

The effect of particle size on densification and mechanical properties of Fe-based bulk metallic glasses by spark plasma sintering

The effect of particle size on densification and mechanical properties of Fe-based bulk metallic glasses by spark plasma sintering

Unraveling the complexity of Fe-based bulk metallic glasses: Insights into dynamic mechanical relaxation in atomic-scale

This research conducts a thorough investigation into the structural and mechanical evolution of Fe74B20Nb2Hf2Si2 bulk metallic glass (BMG) subjected to thermal aging. Utilizing X-ray diffraction (XRD) and selected area electron diffraction (SAED), the study verifies the amorphous structure of the as-cast BMG, highlighting evidence of short-range ordering (SRO). Thermal aging conducted between 342 and 570 K induces substantial changes, notably the formation of Fe23B6 and α-Fe phases and reduced defect concentrations. During dynamic mechanical analysis, a significant shift was observed, which is characterized by a decrease in the intensity of β-relaxation and an increase in β-activation energy from 333.3±2.1 kJ/mol (for the sample aged at 342 K) to 384.6±5.6 kJ/mol (for the sample aged at 570 K). Nanoindentation evaluations reveal an increase in hardness from 11.85±0.22 GPa (for the as-cast BMG) to 14.65±0.41 GPa (for the sample aged at 570 K), accompanied by an increase in Young’s modulus from 211.61±3.00–244.24±2.00 GPa. These changes imply tighter atomic packing and diminished free volume due to aging, suggesting an advanced stage of structural relaxation. Additionally, the material demonstrates a decrease in plastic strain from 0.0052 in its as-cast state to 0.0026 at 342 K, progressing to brittle behavior with further aging. This study shows the pivotal role of precise aging temperature control in optimizing BMGs for diverse applications, illustrating the intricate interplay between thermodynamics and kinetics in material science.

Magneto-optical Properties of Iron-bulk Metallic Glasses Sustainably Produced from Iron-rich Sand Sludge

A large amount of sand sludge (SS) from rivers polluted with heavy metals is continuously dredged and often dumped into landfills, resulting in environmental pollution of soil and water. This work examines the feasibility of the utilization of iron-enriched SS from dredged polluted rivers to produce Fe-based bulk metallic glasses (Fe-BMG). Fe-BMG was prepared from SS by melt-quenching technique, and their magnetic and photochromic properties were studied. The chemical composition of the Fe-BMG was determined by X-ray fluorescence (XRF). The structural properties have been analyzed using the Raman spectroscopy (RS), vibrating sample magnetometer (VSM) and ultraviolet-visible (UV-VIS) spectroscopy. XRF results shows that Fe-BMG contains an iron proportion of 38.8% (wt.) as the hematite (\(\alpha\)-Fe2O3), and magnetite (Fe3O4) phases. The Raman “fingerprints” of \(\alpha\)-Fe2O3 and Fe3O4 were identified at 1330 cm−1, and 300-600 cm-1, respectively. The measured saturation magnetization of Fe-BMG samples is 3.0 emu/g at 60 kOe. A UV-VIS analysis of the Fe-BMG exposed to sunlight simulator reveals an enhanced transmission of light in the 400-700 cm-1 region. These findings confirmed the successful conversion of the hazardous SS into Fe-BMG with promising magneto-optical characteristics for a wide variety of technological applications.

Comparative Study of Microstructure and Phase Composition of Amorphous-Nanocrystalline Fe-Based Composite Material Produced by Laser Powder Bed Fusion in Argon and Helium Atmosphere.

Laser powder bed fusion (LPBF) is a prospective and promising technique of additive manufacturing of which there is a growing interest for the development and production of Fe-based bulk metallic glasses and amorphous-nanocrystalline composites. Many factors affect the quality and properties of the resulting material, and these factors are being actively investigated by many researchers, however, the factor of the inert gas atmosphere used in the process remains virtually unexplored for Fe-based metallic glasses and composites at this time. Here, we present the results of producing amorphous-nanocrystalline composites from amorphous Fe-based powder via LPBF using argon and helium atmospheres. The analysis of the microstructures and phase compositions demonstrated that using helium as an inert gas in the LPBF resulted in a nearly three-fold increase in the amorphization degree of the material. Additionally, it had a beneficial impact on phase composition and structure in a heat-affected zone. The received results may help to develop approaches to control and improve the structural-phase state of amorphous-nanocrystalline compositional materials obtained via LPBF.

Relating laser powder bed fusion process parameters to (micro)structure and to soft magnetic behaviour in a Fe-based bulk metallic glass

This work aims to establish fundamental processing-(micro)structure-property links in a commercial Fe-based Kuamet6B2 bulk metallic glass (BMG) processed by laser powder bed fusion (LPBF). With that purpose, amorphous powders were processed using a pulsed-wave system and a simple meander strategy. The laser power, the scan speed, and the hatch distance were varied over wide intervals within the conduction regime. The processability window leading to samples with good dimensional accuracy and mechanical stability was determined. Within this window, the manufactured samples were crystalline/amorphous composites and the crystalline regions were formed by equiaxed ultrafine and nanograins with random orientations. Processing parameters yielding the densest prints caused severe crystallization while, conversely, parameter sets allowing the material to retain a high amorphous fraction led to significant lack-of-fusion defects and residual cracking along directions perpendicular to crystalline/amorphous interfaces. Comparatively, for a fixed hatch distance, the scanning speed had a stronger effect than the laser power in the resulting amorphous fraction due to its stronger influence on the melt pool size and, in turn, on the corresponding HAZ volume. The saturation magnetization and the coercive field were inversely related to the amorphous fraction. This work allows to derive fundamental guidelines for the successful additive manufacturing of soft magnetic Fe-based bulk metallic glasses (BMGs) by laser powder bed fusion (LPBF).

Mass Production and Vast Application States of Bulk Metallic Glasses

Since the first synthesis of bulk metallic glasses (BMGs) by copper mold casting in 1990, much effort has been devoted to the searching of new BMG composition, the clarification of fundamental and engineering properties for BMGs and their industrialization. At present, BMGs have been formed in a large number of multicomponent alloy systems where the empirical three component rule is satisfied. Nowadays, commercialized BMGs are classified to Zr-based and Fe-based alloy groups. When we look at the industrialization of Zr-Al-Ni-Cu-based BMGs, the first commercialization was made for golf clubs in Japan in 1998, followed by watch parts etc. Since then, Zr-based BMGs have been used continuously up to 2013, though their application scale was in a limited state. Since 2014, the application scale was significantly extended in collaboration with the rapid developments of smartphones and electric vehicles. At present, the mass production facilities for Zr-based BMGs have been significantly developed and variety of BMG products have been produced. On the other hand, Fe-based soft magnetic BMGs were found in 1995. Their BMGs have also been used on a huge number of pieces in various kinds of electronic-magnetic instruments. These recent application states for Zr- and Fe-based BMGs are introduced together with new nanocrystalline Fe-based soft magnetic alloys developed through the derivation of alloy composition from Fe-based BMGs.

Consolidation and wear resistance of Fe based bulk metallic glass composites by spark plasma sintering

High densification and wear resistance are essential for the application of Fe-based bulk metallic glass composites. In this work, Fe-based composites were fabricated by spark plasma sintering. Firstly, under the pressure of 150 MPa, all samples achieved high densification, the microcontact pressure between powder particles decreased with increasing density. Then, as the sintering temperature was increased from 350 °C to 450 °C, the crystalline phases were identified as Fe3Si and Fe2B. The hard borides improved the hardness and wear resistance of composites. Finally, at sintering temperature of 400 °C, the sample exhibited the highest micro-Vickers hardness of 1168.8 Hv and the lowest friction coefficient of 0.59, the coefficient of friction was lower than that of bearing steel. FeSiB BMG composites showed dominant abrasive and oxidative wear mechanisms. FeSiB composites showed excellent hardness and wear resistance, which extends the potential application of bulk metallic glass in the field of engineering structural materials.

The nature of the atomic-scale Invar effect in Fe-based bulk metallic glasses

Fe-based bulk metallic glasses (BMGs) universally show an anomalously low coefficient of thermal expansion below their Curie temperature. This effect is known as the Invar effect, is rarely seen in crystalline materials and also vanishes after the crystallization of BMGs. While it is known that Co and Ni reduce the strength of the Invar effect, the influence of other elements is unknown. Moreover, it is unclear to what extent structural modifications and magnetic interactions of minor alloying elements contribute to the Invar effect. Using synchrotron-based in-situ X-ray diffraction, we show that (Fe71B24RE5)96Nb4 BMGs with the rare earth elements (RE) = Tm, Er, Ho also reveal the Invar effect. This can be seen in the diffraction peaks that shift in accordance with the macroscopically measured thermal expansion. In comparison to a similar FeBYNb BMG, the Invar effect is not influenced by the substitution of Y with RE. This suggests that the minor alloying elements do not contribute to the Invar effect. Neither their influence on the atomic arrangement, the (anti)ferromagnetic interactions of the 4f electrons of the RE elements nor paramagnetic interactions such as those from Y and Nb have an influence on the Invar effect. These elements only serve to increase the glass-forming ability and the formation of a disordered Fe network but do not contribute themselves to the Invar effect. Additionally, their (anti-)ferromagnetic interaction with Fe does not influence the magneto-structural correlations of the Fe network. Therefore, the Invar effect in these materials not only originates at the atomic scale but can be attributed solely to the magnetic interaction in the disordered Fe network.

Effects of B/P and Co/Fe substitutions on glass-forming ability and soft magnetic properties of a Fe80P13C7 metallic glass

New soft magnetic Fe-based Fe–Co–P–B–C bulk metallic glasses (BMGs) with the highest saturation magnetic flux density (Bs) up to 1.68 T among current Fe-based BMGs have been developed. Initial replacement of P by 2–6 at.% B enhances the thermal stability, glass-forming ability (GFA), and soft magnetic properties of a Fe80P13C7 alloy. A Fe80P9B4C7 BMG with a supercooled liquid region of 38 K, Bs of 1.63 T, and coercivity (Hc) of 0.9 A/m has been obtained by copper mold casting. Substitution of Fe by 5–10 at.% Co in the Fe80P9B4C7 alloy further enhances the GFA and Bs, but leads to a moderate increase in Hc. A critical sample diameter of 1.5 mm, Bs of 1.68 T, and Hc of 6.2 A/m can be achieved for a Fe70Co10P9B4C7 BMG. The improvement of the GFA is attributed to the enhanced stability of alloy melts achieved by similar B/P and Co/Fe substitution.

Evaluation of room temperature creep deformation of in situ Fe-based bulk metallic glass nanocomposites by instrumented indentation

In the present work, Fe57Cr9Mo5B16P7C6 (at. %) in situ bulk metallic glass nanocomposites of varying crystallinity, i.e. 0 to 80 vol. %, were synthesized by spark plasma sintering. Room temperature indentation creep behaviour of these composites was evaluated with nanoindentation technique. Effect of crystalline phase content on overall creep behaviour of the BMG composites was evaluated. Creep resistance of the BMG composites was improved with increase in the amount of crystalline phases up to 40 vol. %. Improved creep resistance is attributed to the presence of nanocrystalline phases in amorphous matrix and lower defect concentration in the BMG composite samples. However, excess crystallinity imparted brittleness and resulted in poor creep performance of the BMG composites. Derived stress exponent values are significantly lesser for the BMG composite sample in comparison to the amorphous compact indicating the transition in the mode of plastic deformation from inhomogeneous to nearly homogeneous. Loading rate has more pronounced influence on final creep displacement of fully amorphous sample in comparison to that of BMG composite.

Optimizing laser additive manufacturing process for Fe-based nano-crystalline magnetic materials

Fe-based amorphous magnetic alloys offer new opportunities for magnetic sensors, actuators and magnetostrictive transducers due to their high saturation magnetostriction (λs = 20–40 ppm) compared with that of amorphous Co-based alloys (λs = −3 to −5 ppm). Due to the conventional production limitations of Fe-based glassy alloys, including dimensional limitations and poor mechanical properties, this has led to a search for novel fabrication techniques. Recently, the laser powder bed fusion (LPBF) technique has attracted attention for the production of Fe-based magnetic bulk metallic glasses (BMGs) as it provides high densification, which brings about excellent mechanical properties, and high cooling rate during the process. Optimization of process parameters in the LPBF technique have been studied using the volumetric energy input (E), which includes the major build parameters; laser power (P), scan speed (v), layer thickness (t) and hatch spacing (h). This study investigates how the major process parameters influence the physical and magnetic properties of LPBF-processed Fe-based amorphous/nanocrystalline composites ((Fe87.38Si6.85B2.54Cr2.46C0.77 (mass %)). Various process parameter combinations with P (90, 100, 120 and 150 W) and v (700, 1000 and 1300 mm/s) were applied with t of 30, 50 and 70 µm and h of 20, 30, 40, 50 and 60 µm. It was found that bulk density improves as P and t increases, v and h decreases, i.e., high E is necessary, however, 99.45% of bulk density was achieved with E of 61.22 J/mm3 (P = 150 W, v=700 mm/s, h=50 µm and t = 70 µm), which indicates the importance of understanding how parameters affect the specific materials. In addition, the magnetic properties differ significantly due to the nanocrystalline phases present in the microstructure, with their size depending on the process parameters considerably. Owing to the laser scanning nature, the microstructure evolves as molten pools (MP) and heat affected zones (HAZ) due to the high thermal gradient that occurred between laser tracks. MP form around the scans, containing α-Fe(Si) nanograins mainly, whereas HAZ generally contains Fe2B and Fe3Si nanocrystalline clusters. The size and quantities of those nanocrystallites determine the magnetic properties. With the same E (60 J/mm3), v (1000 mm/s) and t (50 µm), only changing P and h caused samples to have different saturation magnetization; 206 emu/gr (P: 90 W and h: 30 µm) and 150 emu/gr (P: 150 W and h: 50 µm). In general, the saturation magnetisation, Ms of LPBF-processed samples changes between 130 and 206 emu/gr, which is much higher than that of feedstock powder (102 emu/gr) due to their nanocrystalline structures. The coercivity (Hc) is in the range of 14.55 and 34.68 Oe, which is considered high for soft-magnetic behaviour (Hc ≤ 12.5 Oe), resulting from the larger crystallite size and the presence of defects (pores and cracks) in the microstructure.

Glass-to-glass transition enables superhigh thermal stability and glass formability for thermoplastic shaping of FeBNbYCr alloys

Fe-based bulk metallic glasses (BMGs) exhibit attractive properties, yet their thermal stability and glass formability (GFA) are always lower than the other thermoplastic shaping (TPS) alloys. Here, we developed a new Cr-doped Fe65B22.8Nb3.7Y4.5Cr4 alloy with a super-wide supercooled liquid region (SCLR) (ΔTx=112 K) and high GFA (≥ 3 mm) with industrial materials. Glassy rods can maintain the glassy structure after annealing and hot pressing at 923 K, and exhibit a high fracture strength of > 3000 MPa and hardness of > 900 Hv in annealed states. The BMG rods can be conveniently TPS in the SCLR with low compressive stress of < 250 MPa. It is found that the additional glass-to-glass transition (GGT) in the SCLR effectively improves the GFA and thermal stability, by complicating and postponing the transition and crystallization process. The introduction of GGT offers a new strategy to develop high-performance BMGs for precision TPS.

In situ processing of Fe-based bulk metallic glass nanocomposites in supercooled liquid region by spark plasma sintering

Current study reports fabrication of in-situ Fe-based bulk metallic glass (BMG) nanocomposites by carrying out spark plasma sintering of Fe57Cr9Mo5B16P7C6 amorphous alloy powder. In situ BMG composites were synthesized with varying amount of crystalline phases by controlled partial devitrification in supercooled liquid region. Application of high consolidation pressure (400 MPa) during sintering contributed to enhanced viscous flow in the amorphous powder resulted in high densification (> 97 %) in the sintered compacts. Microstructural and phase evolution in the consolidated BMGs and BMG nanocomposites were systematically investigated with respect to sintering conditions. Microscale heterogeneity with respect to phase evolution in the sintered samples was evaluated by nanoindentation studies. Hardness of the sintered BMG nanocomposites was found to be significantly higher than the sintered BMGs ascribed to the evolution of hard intermetallic phases during devitrification.