Fe-based Metallic Glass Research Articles

Effect of Fe-based metallic glass on microstructure and properties of Hastelloy X manufactured by laser powder bed fusion

Hastelloy X is widely used in aerospace because of its excellent high-temperature performance. Laser powder bed fusion (LPBF) can be used to manufacture Hastelloy X and its reinforced materials with more complex structures and better performance. In this study, Hastelloy X reinforced materials added Fe-based metallic glass powder was manufactured using LPBF, and four sequences of 0, 3, 5, and 7 wt%. The introduction of Fe-based metallic glass powder has exhibited notable improvements in the mechanical properties at room and high temperatures. At room temperature (RT), the 5 wt% reinforced material exhibited a larger increase in hardness, with a yield strength and ultimate tensile strength of 856Mpa and 1081 MPa, and the reduction in elongation was only 9.6%. At high temperatures, introducing Fe-based metallic glass enhanced the yield strength and ultimate tensile strength, and the elongation was greatly improved at 800 ℃. The enhancements are mainly due to the grain size refinement caused by the introduction of Fe-based metallic glass powder, which increases dislocation density and grain boundary strengthening. In addition, as the content of Fe-based metallic glass increased, the corrosion resistance of the samples was also improved due to increased Cr and W content and the refinement of grains. This study provides a new research direction for improving the properties of Hastelloy X.

Microstructure and long-term corrosion resistance of plasma-sprayed FeCrMoCB metallic glass/Al2O3-13 wt%TiO2 composite coatings with sandwich-like and dispersed structures

Fe-based metallic glass/Al2O3-13 wt%TiO2 (AT13) composite coatings with sandwich-like (Fe–S20) and dispersed (Fe-D20) structures were prepared via atmosphere plasma spraying (APS). The differences in microstructure, mechanical properties, and corrosion mechanisms of composite coatings were investigated. The interfacial bonding between Fe-based metallic glasses and AT13 was analyzed by transmission electron microscope (TEM). The addition of AT13 in Fe-D20 could cause greater stress concentration in the coating. In turn, the layered stress distribution was observed in Fe–S20 coating due to the unique sandwich structure. Moreover, the introduction of AT13 improved the short-term corrosion resistance of matrix metallic glass. However, after long-term immersion, pitting corrosion occurred preferentially at the junction of AT13 and metallic glass substrate, leading to a significant decrease in the corrosion resistance of Fe-D20. Besides, the presence of AT13 hindered the growth of the passive film of Fe-based metallic glass. In summary, the long-term corrosion resistance of Fe–S20 with a sandwich structure was better than that of Fe-D20 with a dispersed structure. Thus, structure tuning has great prospects for plasma spraying ceramic composite coatings in the future.

Effects of different elements on the passivation behaviour of Fe-based metallic glasses in the NaCl solution

The passivation and microstructure of Fe-based metallic glasses (MGs) with different contents of essential elements in 3.5 wt% NaCl solution were investigated by electrochemical techniques such as potentiodynamic polarization (PDP), potentiostatic polarization (PSP) and Mott-Schottky (MS) as well as surficial stability analysis including X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). At the low passive potential region, the strongly Cr-enriched passive film on Fe48Cr15Mo14C15B6Y2 (Cr15Mo14) generates a higher resistance than that of Fe63Cr8Mo3.5C4B4Ni5P10Si2.5 (Cr8Mo3.5) with a Fe-rich film. As the potential increases, the enhanced hydration, e.g., Cr2O3 converted to Cr(OH)3, causes a film degradation of Cr15Mo14, while the stable Si-oxide is increasingly enriched and maintains the high film protection of Cr8Mo3.5. Consequently, the corrosion resistance of Cr8Mo3.5 becomes better than that of Cr15Mo14 at the high passive potential region.

Development of (Fe-Co-Ni)-Si-B metallic glass catalyst for promoting degradation of acid orange II azo-dye

Fe-based metallic glass (MG) catalyst, also called amorphous zero-valent iron (AZVI), is a functional material that has recently been in the spotlight due to its high reactivity compared to conventional catalysts for wastewater purification. In this study, novel Fe-based MG with excellent degradation rate and reusability was developed through systematic investigation by tailoring the contents of Co and Ni and structural design to form (Fe, Co, Ni)-rich clusters. We found that the process of dye degradation by a Fenton-like oxidative reaction with H2O2 can have low activation energy, assisted by a reductive reaction with nickel hydride formation. Consequently, the reductive and oxidative complex dye degradation mechanism can be effectively implemented to improve degradation rate and reusability, significantly superior to that of the commercial zero-valent iron(Fe0, ZVI) powder. Our findings revealed the compositional and structural key principles of Fe-based MG design, and are expected to provide new opportunities for industrial applications of advanced Fe-based MG.

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.

Multi-objective optimization for high-performance Fe-based metallic glasses via machine learning approach

Fe-based metallic glasses (MGs) are a class of promising soft magnetic materials that have received great attention in transformer industries. However, it is challenging to achieve a balance between saturation magnetization (Bs), glass-forming ability and plasticity due to their contradictory correlations in Fe-based MGs, which severely hinders the development of new Fe-based MGs with advanced performances. Inspired by the significant development in machine learning technology, we herein propose a multi-objective optimization strategy to search for Fe-based MGs with optimal combinations of critical casting size (Dmax), Bs, and plasticity. The objective functions are built in combination with neural network models for predicting Dmax and Bs, as well as empirical formula for plasticity. The effect of number of hidden layers is investigated and the dropout regularization method employed to improve the prediction performance. Our results show that the predictions of Bs and Dmax by using alloy composition as the sole input perform well, as evidenced by their r2 values of 0.963 and 0.874, respectively. Multi-objective optimization based on the genetic algorithm is executed to obtain the Pareto front and Pareto-optimal solutions. The Pareto-optimal alloys predicted for the Fe83C1BxSiyP16-x-y and FexCoyNi72-x-yB19.2Si4.8Nb4 systems are in good agreement with those reported in experiments. This work thus showcases potential applications for the design of high-performance Fe-MGs against conflicting objectives.

Improved ductility of annealed Fe-based metallic glass with good soft magnetic property by cryogenic thermal cycling

The brittleness after annealing treatment severely restricts the subsequent processing and application of Fe-based magnetic metallic glass. Through proper annealing treatment combined with cryogenic thermal cycling, we obtained excellent comprehensive properties of Fe-based metallic glass ribbons with not only good soft magnetic properties but also high bending deformation ability. After thermal cycling, the sample rejuvenated with higher energy state and larger size of soft regions, which facilitated the initiation and branching of shear bands, leading to the improvement of bending plasticity. Although the large soft regions may act as pining sites for domain walls, the domain structure and coercivity of the sample remained nearly identical because of the reduced number of crystal-like structures. Our study indicates that the cryogenic thermal cycling is an effective method to regulate mechanical and magnetic properties, which makes it powerful means to obtain excellent performance of Fe-based magnetic metallic glasses.

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.

Structural evolution of MgO layer in Mg-based composites reinforced by Metallic Glasses during the SPS sintering process

The SPS sintering process is used in this study to create 50 wt % micro-sized spherical Fe-based metallic glass powders reinforced magnesium matrix composites (FMGP). The release of trace amounts of Cr in Fe-based metallic glass particles due to a positive mixing enthalpy with Mg not only improves the mechanical suitability of the interface between the metallic glass and the matrix but also contributes to the solution to the increasing problem of fracture toughness of the composite. Following the inclusion of metallic glass particles (50 wt %), the tensile strength (23%), yield strength (50%), and plasticity (more than 8%) were significantly increased. The Cr diffused to the interface and dissolved into the MgO in the form of replacement, forming the oxidation transition layer with the MgO and α-Mg at the interface and distributed among a discontinuous form, according to the analysis of the high-resolution transmission diagram of the composites and the calibration of the diffraction spots of the magnesium matrix at the interface. This enhances mechanical interface matching and transforms the composite's fracture process from inter-crystalline to quasi-destructive, increasing the material's fracture toughness. Once established, the model's first-principles computation and analysis are consistent with the test results.

Laser-generated nanoparticles from Fe-based metallic glass in water and its amorphization control by pulsed laser processing

The laser synthesis and processing of colloids represents a group of scalable and “green” synthesis methods of crystalline metal oxides, that have recently made encouraging progresses in preparing amorphous as well as defect-rich nanoparticles. The relevant conditions and mechanisms that allow the design of amorphous metal oxides (AMOs) remain unknown. Consequently, in this work the synthesis of Fe-based partially amorphous oxide nanoparticles (NPs) by pulsed laser ablation in water was studied. Furthermore, both laser pulse duration and the number of laser pulse in pulsed laser fragmentation in liquid (LFL) allow a precise control of amorphization of AMOs in water. Hereby, a high-fluence nanosecond-LFL provides a significantly higher amorphization rate, whereas picosecond-LFL always presents minor fractions of crystalline α-Fe even with a higher specific energy input and laser intensity. Consequently, the laser fluence required for the repeated melting and quenching of NP appears to be the decisive parameter to control amorphization. During laser synthesis and processing of colloids, the amorphization of AMOs appears to be linked to the apparent size reduction effect, while a complete full amorphization of AMOs may be attributed to the stronger oxidation effects. This work will stimulate future studies using laser-generated AMO NPs for further functional purposes.

Convolutional neural network guided prediction of saturation magnetic flux density of Fe-based metallic glasses

Fe-based metallic glasses (FeMGs) have recently garnered considerable research attention due to their unique characteristics, such as low core loss and high saturation magnetic flux density (Bs). They also have promising applications in modern electrical machines, such as inductors, motors, and transformers. For FeMGs with high Bs, a trial-and-error approach using various metalloid elements as constituents has been intensively carried out to consider satisfactory thermal stability. However, this approach is time-consuming and expensive because it requires a huge compositional space and results in a lack of understanding of metalloid effects on magnetic properties and thermal stability. In this study, we established a deep learning model using a convolutional neural network (CNN) based only on compositional descriptors of FeMG constituent elements to predict Bs as the representative magnetic property. In addition, an artificial neural network was applied with the same compositional descriptors for comparison, resulting in a lower prediction performance than that of the CNN model. The CNN model demonstrated high-performance metrics that included a determination coefficient (R2) of 0.960 and a low root-mean-square error of 0.067 T, indicating that the material composition-to-property map is well-defined. We further applied the CNN model to unseen datasets for Bs prediction and compared it with results reported in the existing literature. The predicted Bs values are in excellent agreement with the reported experimental results.

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.

Unveiling the local structure of the amorphous metal text {Fe}_{(1-x)}text {Zr}_x combining first-principles-based simulations and modelling of EXAFS spectra

Amorphous alloys exhibit useful properties such as the excellent soft magnetic behaviour of Fe-based metallic glasses. The detailed structure of amorphous text {Fe}_{(1-x)}text {Zr}_x with x = 0.07, 0.10, and 0.20 is in this work explored through a synergetic combination of atomistic simulations and experimental characterisation. Thin-film samples were investigated using X-ray diffraction and extended X-ray absorption fine structure (EXAFS), while the corresponding atomic structures were simulated using an efficient first-principles-based method called stochastic quenching (SQ). The simulated local atomic arrangements are investigated by constructing the radial- and angular-distribution functions, as well as by Voronoi tesselation. The radial distribution functions are then used to construct a model to fit simultaneously the experimental EXAFS data of multiple samples with different compositions, creating a simple yet accurate description of the atomic structures valid for any composition in the range x = 0.07 to 0.20, using a minimal number of free parameters. This approach significantly improves the accuracy of the fitted parameters and allows us to relate the compositional dependence of the amorphous structures with the magnetic properties. The proposed EXAFS fitting process can be generalised to other amorphous systems, contributing to the understanding of structure-property relationships and the development of amorphous alloys with tailored functional properties.

Network Tele-Microscopy in Metallic Glasses

Additive manufacturing (AM) can realize the rapid solidification for the formation of ultra-fine solidification microstructures and/or crystal growth reaching the marginal stability condition. The TEM observation of the nucleation and growth behavior of BCC dendrite embedded in Fe-based metallic glasses offers an unique opportunity for clarifying the morphology of the ultra-fine dendrite for the development of AM. The present study reported the network tele-microscopy observation of BCC-Fe dendrites embedded in an Fe-Si-B amorphous matrix obtained by the in-situ heating of TEM specimens using the ultra-high voltage electron microscope Hitachi H-3000.

Synergistic effect between pyrite and Fe-based metallic glass for the removal of azo dyes in wastewater

Fe-based metallic glasses (FeMGs) are popular reductants for the restoration of wastewater containing various pollutants, but it still suffers from surface passivation and a narrow applicable pH range. In this work, pyrite, an abundant iron sulfide, was used to enhance the reactivity of FeMGs for the removal of azo dye. Synergetic effects between pyrite and FeMGs improved the removal of Orange II when using an FeMGs/pyrite mixture, where the reaction rate constant kobs was 0.218 min−1, which was higher than when using FeMGs alone (0.114 min−1). Orange II was removed at pH0 ranging from 5.0 to 10.0 in the presence of pyrite, while it was inefficiently removed by FeMGs alone (10 g/L) at pH0 10.0. Mechanistic investigations showed that the synergistic effect between FeMGs and pyrite enhanced the surface corrosion of FeMGs and accelerated the Fe3+/Fe2+ redox cycle to generate more sorbed Fe2+, which was the dominant reactive species during Orange II removal. This study proposes an approach for enhancing the removal of dye wastewater by using FeMGs to treat mine waste.

Mechanical and fatigue properties of plasma sprayed (Fe0.9Co0.1)76Mo4(P0.45C0.2B0.2Si0.15)20 and Fe56.04Co13.45Nb5.5B25 metallic glasses

Metallic glasses (MG) are unique materials with a continuous and homogeneous structure. Thermally sprayed deposits are characterized by a nonuniform microstructure, with numerous interparticle and intersplat interfaces. This paper addresses the difference between conventionally manufactured and thermally sprayed MG's by microstructural characterization of the MG coatings (MGC) and their mechanical testing using the unified bending methodology. Two thick coatings of (Fe0.9Co0.1)76Mo4(P0.45C0.2B0.2Si0.15)20, and Fe56.04Co13.45Nb5.5B25 were prepared on steel substrates with atmospheric plasma spraying (APS) using gas atomized powders. The relative glassy phase content of 92 % was obtained for (Fe0.9Co0.1)76Mo4(P0.45C0.2B0.2Si0.15)20 coating and 53 % for Fe56.04Co13.45Nb5.5B25 coating. The strain-stress curves for both coatings show brittle behavior without any plasticity. The tensile strength was 142 ± 27 MPa for Fe56.04Co13.45Nb5.5B25, and 152 ± 36 MPa for (Fe0.9Co0.1)76Mo4(P0.45C0.2B0.2Si0.15)20. In the comparison of both MGCs, the Fe56.04Co13.45Nb5.5B25 coating has a higher crack growth resistance (significantly in fatigue, less significantly in the fracture toughness test). The obtained fracture toughness is much higher than usually reported in the literature for Fe-based metallic glasses.

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.

Yield strength of “brittle” metallic glass

“Brittle” metallic glass (MG) usually fractures catastrophically in a shattering mode under macroscopic compression, because cleavage cracking of splitting that originates from extrinsic flaws dominates the failure of such alloys, which brings challenges for studying yield strength. Here we show that the plastic yielding behavior in a brittle Fe-based MG can be successfully activated by decreasing the sample size to micrometer scale to avoid the possible large tensile stress concentrators. The yield strength was found to be at least 33% higher than the fracture strength measured with bulk samples for the present brittle MG. The results further demonstrate that the critical stresses for shear band initiation and propagation are size-independent, while the required stress for cleavage cracking increases with decreasing sample size. The competition of thermodynamic driving forces between the two processes of shear banding and cleavage cracking hence leads to the size-induced brittle-to ductile-transition. These findings clarify the physical nature of the strength of “brittle” MG, implying the great opportunity for using high-strength brittle MGs in devices with small dimensions.

Can Severe Plastic Deformation Tune Nanocrystallization in Fe-Based Metallic Glasses?

The effects of severe plastic deformation (SPD) by means of high-pressure torsion (HPT) on the structural properties of the two iron-based metallic glasses Fe73.9Cu1Nb3Si15.5B6.6 and Fe81.2Co4Si0.5B9.5P4Cu0.8 have been investigated and compared. While for Fe73.9Cu1Nb3Si15.5B6.6, HPT processing allows us to extend the known consolidation and deformation ranges, HPT processing of Fe81.2Co4Si0.5B9.5P4Cu0.8 for the first time ever achieves consolidation and deformation with a minimum number of cracks. Using numerous analyses such as X-ray diffraction, dynamic mechanical analyses, and differential scanning calorimetry, as well as optical and transmission electron microscopy, clearly reveals that Fe81.2Co4Si0.5B9.5P4Cu0.8 exhibits HPT-induced crystallization phenomena, while Fe73.9Cu1Nb3Si15.5B6.6 does not crystallize even at the highest HPT-deformation degrees applied. The reasons for these findings are discussed in terms of differences in the deformation energies expended, and the number and composition of the individual crystalline phases formed. The results appear promising for obtaining improved magnetic properties of glassy alloys without additional thermal treatment.

Effect of stress relaxation on soft magnetic properties of Fe76Si9B10P5 metallic glass

Stress relief can improve the soft magnetic properties of Fe-based metallic glasses (MGs) and is vital for industrial applications. In this work, we investigated the evolution of soft magnetic properties, relaxation dynamics, and mechanical properties of Fe-based MGs under different applied tensile strains and stress relaxation times. We found that stress relaxation can significantly reduce coercivity Hc by 95% compared with as-quenched state. Furthermore, the coercivity Hc, apparent activation volume Vact and time constant tr all show analogous two-stage variation with annealing time, accompanied by approximate crossovers. This suggests that the microstructure change emerges, further verified by the domain wall motion and the transition from elastic to plastic. These results are helpful in preparing Fe-based MGs with excellent soft magnetic and mechanical properties by controlling the stress relaxation condition.