Fe-based Bulk Metallic Glasses Research Articles

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.

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.

Development of Fe-based glass former alloys for thermal spray coatings with optimized corrosion and wear properties

Corrosion and wear of alloys is a costly and hidden safety risk for components in petrochemical, agroindustry, and mining activities, which are key segments in Brazil and in many countries. Accelerating the development of highperformance and durable ferrous alloys and their insertion into engineering structural applications has never been more important. Glass former steels have drawn considerable attention in recent years, due to the remarkable combinations of strength and degradation control that can be achieved by tailoring corrosion and wear resistances, which places these alloys amongst the durable ferrous alloy ever developed. Recent results from our group indicate that coatings using these alloys can be produced from commercial grade precursors and industrially available thermal spraying routes. The development of Fe-based bulk metallic glass (BMG) alloys for degradation control will open the door to next-generation coatings with unprecedented combinations of corrosion and wear resistances. This work summarizes the development of Fe-based glassy coatings for corrosion and wear control performed in our research group in the last 17 years covering: i) glass forming ability of alloys, ii) development of Fe-based glass former alloys, iii) thermal spraying of Fe-based glass former alloys, and iv) scientific and technological impacts of this research.

Development of novel Fe-based bulk metallic glasses with excellent wear and corrosion resistance by adjusting the Cr and Mo contents

In this work, a series of novel Fe80–x–yCrxMoyP10C7B3 (x = 0, y = 0; x = 0, y = 4; x = 5, y = 4; x = 15, y = 4; x = 20, y = 4; x = 15, y = 8 in at.%; denoted as CrxMoy) bulk metallic glasses (BMGs) with critical diameters in the range 1.0–2.5 mm were fabricated. The effect of Cr and Mo contents on the glass forming ability (GFA), thermal stability, mechanical properties, corrosion behavior, and wear performance of the these Fe-based BMGs were systematically investigated. A partial substitution of Fe by Cr and Mo was found to enhance the GFA of the Fe-based BMGs. The sample Cr15Mo4 exhibited the maximum critical diameter (2.5 mm), maximum temperature range of the supercooled liquid phase (55 K), and highest activation energy for the primary crystallization process (184 kJ·mol−1). Uniaxial compression and microhardness tests revealed that the compressive strength and Vickers microhardness of the Fe-based BMGs were in the range 3.0–3.7 GPa and 794–958 HV0.1, respectively, and increased with increasing Cr/Mo content. Electrochemical tests in a 3.5 wt.% NaCl solution showed that the Fe-based BMGs exhibited a significantly higher corrosion resistance than 316L stainless steel (316L SS) and 304L stainless steel (304L SS). The corrosion resistance of the Fe-based BMGs generally improved with increasing Cr/Mo content. The sample Cr15Mo4 exhibited the highest corrosion resistance with a self-corrosion and passivation current density ∼10−8 A·cm−2 and ∼10−6 A·cm−2, respectively. X-ray photoelectron spectroscopy of the samples revealed that compared to Cr15Mo4, there was a higher proportion of defective high-valence metal cation (Fe3+, Cr6+, and Mo6+) oxides and a lower proportion of stable low-valence metal cation (Fe2+, Cr3+, and Mo4+) oxides in the passive films of Cr20Mo4 and Cr15Mo8. This explains the reason why adding more than 15 at.% Cr and 4 at.% Mo degrades the corrosion resistance of the Fe-based BMGs. The dry sliding wear test demonstrated that the Fe-based BMGs exhibited significantly better wear performance than 316L SS and 304L SS. The wear rate and coefficient of friction of the Fe-based BMGs decreased with increasing Cr/Mo content. The sample Cr15Mo8 exhibited the lowest wear rate and coefficient of friction of 0.98 × 10−5 mm3·N−1·m−1 and 0.38, respectively. The Fe-based BMGs synthesized in this work, especially Fe61Cr15Mo4P10C7B3, exhibited a high GFA and excellent corrosion and wear resistance. Therefore, they have immense potential for various engineering applications.

Tailoring the structural heterogeneity and electrochemical behavior of Fe-based bulk metallic glasses by Ar+ irradiation

The microstructure, electrochemical responses, and passive film characteristics of FeCrMoWCBY bulk metallic glasses (BMGs) under Ar+ irradiation were investigated. Under exposure to high irradiation fluence, BMGs retained a large portion of an amorphous structure and exhibited excellent corrosion resistance in 1 mol/l HCl solution. With the enhancive irradiation fluence, the increasing crystal-like clusters and even nanocrystals were gradually precipitated from the exterior amorphous matrix of BMGs. By reducing the proportions of Cr3+/Mo6+/W6+ cations and work functions at the outer passive film, the nano-crystallization destroyed the uniformity and stability of passive films, thus weakening the anti-corrosion capacity of irradiated BMGs. This finding facilitates the potential application of Fe-based BMGs under extreme nuclear-irradiated conditions.

Unified upper temperature for cryogenic thermal cycling treatment in Fe-based bulk metallic glasses

Fe-based bulk metallic glasses have high fracture strength and large elastic limit. However, the extremely poor plasticity at room temperature severely renders their wide use as structural materials. In this work, three Fe-based bulk metallic glasses were selected to explore the effect of the upper temperature for cryogenic thermal cycling treatment on the plasticity of the specimens after rejuvenation. It was found that all three Fe-based bulk metallic glasses exhibit the largest plasticity when the upper temperature is about 0.62Tg, where Tg is glass transition temperature. The underlying mechanism is understood by the evolution of the structural heterogeneity dominates by the competition between structural rejuvenation and physical aging during the CTC treatment. When the upper temperature is relatively low, the structural rejuvenation dominates, which causes an increase of the plasticity of bulk metallic glasses; Otherwise, a too high upper temperature leads to a physical aging, resulting in the decline of plasticity. This work will provide process reference for the cryogenic thermal cycling treatment of Fe-based bulk metallic glasses.

Laser additive manufacturing of ductile Fe-based bulk metallic glass composite

• Fe-based BMGCs with high strength and record-breaking ductility was fabricated via LAM technique. • An appropriate amount of stainless steel can effectively ductile the Fe-based BMG without seriously sacrificing strength. • Dual-phase structure was achieved by simply transporting the second phase into laser molten pool in the form of powder during LAM process. Laser additive manufacturing (LAM) is a promising technology for processing bulk metallic glass (BMG) with freeform geometries or unlimited size. However, the inherently brittle Fe-based BMGs produced by LAM have always been plagued by the micro-cracking induced by the large thermal stresses during the LAM process. To solve this dilemma, 316L stainless steel (SS) with excellent toughness and similar elemental composition was carefully selected as the second phase to form Fe-based BMG composites (BMGCs). The obtained Fe-based BMGCs are equipped with a heterogeneous structure, i.e., the 316L SS phase is wrapped by the metallic glass and forms a unique "fishbone" structure with a micron - scale. Excitedly, the special structure nicely improves a plastic strain of the Fe-based BMGC with a strength of 2355 MPa to ∼17%, achieving a record-breaking achievement among Fe-based amorphous with critical dimensions over 1mm.

Effects of Various Processing Parameters on Mechanical Properties and Biocompatibility of Fe-based Bulk Metallic Glass Processed via Selective Laser Melting at Constant Energy Density

The unique properties of bulk metallic glass (BMG) render it an excellent material for bone-implant applications. BMG samples are difficult to produce directly because of the critical cooling rate of molding. Advancements in additive manufacturing technologies, such as selective laser melting (SLM), have enabled the development of BMG. The successful production of materials via SLM relies significantly on the processing parameters; meanwhile, the overall energy density affects the crystallization and, thus, the final properties. Therefore, to further determine the effects of the processing parameters, SLM is performed in this study to print Fe-based BMG with different properties three dimensionally using selected processing parameters but a constant energy density. The printed amorphous Fe-based BMG outperforms the typical 316 L stainless steel (316 L SS) in terms of mechanical properties and corrosion resistance. Moreover, observations from nanoindentation tests indicate that the hardness and elastic modulus of the Fe-based BMG can be customized explicitly by adjusting the SLM processing parameters. Indirect cytotoxicity results show that the Fe-based BMG can enhance the viability of SAOS2 cells, as compared with 316 L SS. These intriguing results show that Fe-based BMG should be investigated further for orthopedic implant applications.

Atomic structure of an FeCrMoCBY metallic glass revealed by high energy x-ray diffraction

Amorphous bulk metallic glasses with the composition Fe48Cr15Mo14C15B6Y2 have been of interest due to their special mechanical and electronic properties, including corrosion resistance, high yield-strength, large elasticity, catalytic performance, and soft ferromagnetism. Here, we apply a reverse Monte Carlo technique to unravel the atomic structure of these glasses. The pair-distribution functions for various atomic pairs are computed based on the high-energy x-ray diffraction data we have taken from an amorphous sample. Monte Carlo cycles are used to move the atomic positions until the model reproduces the experimental pair-distribution function. The resulting fitted model is consistent with our ab initio simulations of the metallic glass. Our study contributes to the understanding of functional properties of Fe-based bulk metallic glasses driven by disorder effects.

Effect of Mo addition on the properties of Fe-Co-Zr-W-B bulk metallic glasses

In this work, Fe55-xCo10Zr10W5B20Mox (x = 0, 2 and 4 at.%) bulk metallic glasses (BMGs) were successfully prepared from industrial raw materials. The alloy with 0 at.% Mo exhibits very high thermal stability with the glass transition temperature of 884 K and supercooled liquid phase region width of 108 K. The electrochemical tests in 3.5 wt.% NaCl solution show that the corrosion resistance of the present Fe-based BMGs is much better than 316L SS and further the alloy of 2 at.% Mo have the highest corrosion resistance among the present Fe-based BMGs. The wear test shows that the friction coefficient and wear rate of the present Fe-based BMGs are obviously lower than those of 316L SS and have a decreasing trend with increasing the Mo content, which is well positively correlated with the microhardness of the alloys.