Nb Bulk Metallic Glasses Research Articles

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.

Impact of sulfur addition on the structure and dynamics of Ni–Nb alloy melts

We investigated the change in the structure and dynamics of a Ni–Nb bulk metallic glass upon sulfur addition on both microscopic and macroscopic scales. With the sulfur concentration of 3 at. %, where the composition Ni58Nb39S3 exhibits the best glass forming ability in the investigated sulfur concentration range, both the equilibrium and undercooled melt dynamics remain almost unchanged. Only in the glassy state does sulfur seem to result in mass transport less decoupled to the viscosity of the undercooled liquid, where the measured Ag tracer diffusion coefficient is slower in the ternary alloy. With the structural disorder introduced by the alloying sulfur, the improved glass forming ability is attributed to geometrical frustration, where crystal nucleation requires a depletion of sulfur and hence long range diffusion, as long as no primary sulfur-containing crystalline phase is involved.

Effect of Nb on the mechanical properties and toughening mechanism of Zr-Co-Al(-Nb) bulk metallic glasses

(Zr56Co28Al16)100-xNbx (x = 0, 0.25, 0.5, 0.75, 1) bulk metallic glasses (BMGs) were prepared by water-cooled copper die suction casting. It is found that the addition of Nb has a significant effect on the microstructures and the mechanical properties of Zr-Co-Al BMGs. Among the investigated alloys, (Zr56Co28Al16)99.25Nb0.75 BMG shows excellent mechanical properties, e.g. an ultimate compressive strength of 2318 ± 29 MPa and a plastic strain of 5.1 ± 0.1 %. Nb addition promotes the structural heterogeneity, and leads to the formation of nanoscale solid-like regions and liquid-like regions. The increase in free volume of the Zr-Co-Al-Nb bulk metallic glass plays a weak role in the increase in plasticity, while the most important factors should be the deformation-induced nanocrystallisation and the interaction between nanocrystals and shear bands.

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.

Laser powder bed fusion of FeCoBSiNb-Cu bulk metallic glass composites: Processing, microstructure and mechanical properties

Fe–Co–B–Si–Nb bulk metallic glasses are prone to the formation of micro-cracks during laser powder bed fusion (LPBF) additive manufacturing. Introducing ductile Cu into Fe–Co–B–Si–Nb bulk metallic glass alloy system rich with Fe and Co could be a promising solution to reduce or even eliminate micro-cracks since there is almost no miscibility of Cu in Fe and Co. In this work, processing, microstructure and mechanical properties of Cu-containing {(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 (at.%) bulk metallic glass composites (BMGCs) under different laser power and scanning speed by LPBF are investigated in detail. A moderate area energy density facilitates the fabrication of highly dense (relative density: up to ∼99.5%) and almost crack-free (crack density: ∼0.1 mm−1) FeCoBSiNb–Cu bulk samples. These bulk samples possess an interpenetrating composite microstructure mainly composed of an amorphous Fe(Co)-rich phase and a crystalline Cu-rich phase. A crystalline Cu-rich phase is distributed relatively homogeneously in an amorphous phase and helps to reduce and even eliminate micro-crack formation during LPBF processing. Also, the Cu-rich phase has the effect of a heat sink and thus speeds up heat dissipation, facilitating the formation of an amorphous phase. The microhardness of the ductile Cu-rich phase and the hard amorphous Fe(Co)-rich phase in the interpenetrating composite microstructure was evaluated. Compressive tests at room temperature indicate that the dense bulk samples exhibit a relatively high fracture strength and a large fracture strain. Additionally, bulk samples with lack-of-fusion pores show a larger fracture strain although their fracture strength is lower than that of dense bulk samples. It is concluded that the LPBF-processed FeCoBSiNb–Cu BMGCs constitute a promising wear-resistant material to be used for example as bearing materials.

Efficient rejuvenation of heterogeneous {[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 bulk metallic glass upon cryogenic cycling treatment

The effects of cryogenic thermal cycling on deformation behaviour and structural variation of {[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 bulk metallic glass (BMG) were studied and compared with Cu-free [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 BMG. After thermal-cycled treatment between 393 K and cryogenic temperature, the {[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 BMG obtained a plastic strain of 7.4% combined with a high yield strength of 4350 MPa. The excellent soft magnetic properties were maintained after CTC treatment. The minor addition of Cu element results in an initial nano-sized heterogeneity in the matrix, which facilitates the rejuvenation process during thermal cycling, and brings to a low optimal thermal temperature of 393 K, making the {[(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4}99.9Cu0.1 BMG more attractive in industrial application. During thermal cycling, the formation of more soft regions leads to the increase of structural heterogeneities, which is beneficial to the initiation of shear transition zones and the formation of multiple shear bands, and thus results in the enhancement of plasticity. This study links the subtle variation of specific structure with macroscopic mechanical properties, and provides a new insight of composition selection for cryogenic thermal cycling treatment.

Microstructural evolution and mechanical properties in Zr–Cu–Al–Nb bulk metallic glass composites prepared by laser metal deposition

In this work, laser metal deposition (LMD), a direct energy deposition (DED) additive manufacturing technology, is used to prepare Zr59.3Cu28.8Al10.4Nb1.5 bulk metallic glass composites (BMGCs). Phase constitutions and thermal behavior of LMD-processed Zr–Cu–Al–Nb samples are examined using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The microstructure evolution parallel to the build direction is characterized in detail utilizing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron probe microscopy analysis (EPMA) and electron backscatter diffraction (EBSD). Young's modulus and hardness in typical microstructures are evaluated employing nanoindentation. Within each deposited layer, a periodic microstructure, exhibiting crystalline features of three distinctly different morphologies, is observed, depending on the location within that layer. Along the build direction, the dominating microstructure of the melt pool evolves from a nearly featureless amorphous state over fine nanocrystals to coarse nanocrystals while the morphology of most micro-scale dendritic crystals changes from flower-shaped to columnar, simultaneously a coarse microstructure appearing in upper layers. The fine Al-rich phases gradually coarsen directionally parallel to the build direction. Furthermore, the correlation between microstructure and mechanical properties is investigated. This work enhances our knowledge about microstructural characteristics and mechanical properties of BMGCs in-situ fabricated by DED additive manufacturing.

Tuning Glass Formation and Mechanical Properties of ZrCoAl(Nb) Bulk Metallic Glass with Nb Microalloying Process

In the present study, the effect of Nb addition on mechanical behavior and glass formation in (Zr56Co28Al16)100−xNb(x=0,2,4) bulk metallic glasses was studied. The differential scanning calorimetry (DSC) was used to investigate thermal properties of samples. Further, mechanical behavior of prepared samples was analyzed using quasi-static compressive tests. The results showed that 2 at.% minor addition of Nb enhances the glass forming ability (GFA), but larger amount of Nb (4%) deteriorates GFA. The X-ray diffraction patterns also confirmed that the structures of whole of studied compositions are amorphous. In addition, the compressive test results revealed that 2% addition of Nb significantly improves compressive ultimate strength (up to 2.5 GPa) and increases the plastic strain from 1.1% in the composition having no Nb content to ~ 6%. The observation of shear band branching and also the increase in the density of vein-like patterns in the fracture surface (studied by scanning electron microscopy) also confirm the improvement of plasticity in (Zr56Co28Al16)98Nb2 sample. Our finding highlights the effect of minor alloying on the formation and mechanical properties of bulk metallic glasses.

Role of initial stored energy on hydrogen microalloying of ZrCoAl(Nb) bulk metallic glasses

In this paper, the role of primary stored energy and structural heterogeneity on the subsequent effects of hydrogen microalloying in glassy alloys was studied. For this purpose, two bulk metallic glasses with different chemical compositions and initial stored energy, i.e. Zr60Co30Al10 and Zr55Co30Al10Nb5, were fabricated in a hydrogen-induced environment. Dynamic mechanical analysis and nanoindentation tests were carried out to evaluate relaxation behavior and mechanical properties of bulk metallic glasses, respectively. The nanoindentation results indicated declining serrations in load–displacement curves of hydrogen-affected samples. This event was related to the annihilation of localized deformation in hydrogen-affected samples under the external load. Moreover, the dynamic mechanical analysis showed that the hydrogen microalloying process improved the plasticity behavior of metallic glasses by activating fast β′ relaxation. Finally, the results unveiled that the higher initial structural heterogeneity and stored energy in the bulk metallic glass with the alloying composition of Zr55Co30Al10Nb5 led to the improvement of microalloying effects on the corresponding properties.

Enhancement of plasticity for FeCoBSiNb bulk metallic glass with superhigh strength through cryogenic thermal cycling

The mechanical properties and atomic-scale structure of the [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 bulk metallic glass (BMG) treated with cryogenic thermal cycling were studied. The obtained Fe-based BMG shows an improvement of plastic strain from 1.4 to 6.1% and maintains a high yield strength over 4000 MPa. The high structural disorder degree caused by rejuvenation, as well as the fine-tuned crystal-like ordering structures induced by internal stress, contribute to the formation of multiple shear bands, and thus results in the enhancement of plasticity. This work provides a new insight to develop plastic Fe-based BMGs through modulating atomic-scale structure.

Preparation of Fe-Co-B-Si-Nb bulk metallic glasses by laser powder bed fusion: Microstructure and properties

In this work, laser powder bed fusion (LPBF) was employed for the preparation of {(Fe0.6Co0.4)0.75B0.2Si0.05}96Nb4 bulk metallic glasses (BMGs). Microstructural evolution, thermal stability and mechanical properties of LPBF-processed samples using different laser power and scanning speed were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microscopy analysis (EPMA), electron backscatter diffraction (EBSD), differential scanning calorimetry (DSC) and nanoindentation. The results show that low area energy input facilitates the formation of Fe-Co-B-Si-Nb BMGs with a large amorphous fraction. LPBF-processed sample with an area energy density of 1.25 J/mm2 (at a laser power of 60 W and a scanning speed of 600 mm/s) exhibits a nearly fully glassy microstructure with an amorphous fraction of approximately 99%, meanwhile possessing almost identical characteristic temperatures and enthalpy of crystallization as the as-atomized powder. The microstructure and mechanical properties of LPBF-processed samples are correlated with the processing parameters during LPBF. This work demonstrates that LPBF is a promising method to prepare fully amorphous Fe-Co-B-Si-Nb BMGs. The results provide key insights for the fabrication of BMGs and BMGs composites with the desired microstructure and properties by additive manufacturing.

Toughness enhancement and heterogeneous softening of a cryogenically cycled Zr–Cu–Ni–Al–Nb bulk metallic glass

In this study, as-cast and cold-rolled Zr63.78Cu14.72Ni10Al10Nb1.5 bulk metallic glass (BMG) samples were subjected to 20, 70, 120, and 170 cryogenic thermal cycles prior to fracture toughness testing. Thermal cycling raised the fracture toughness by promoting plastic deformation and stable crack growth, with the most significant increase occurring after the first 20 thermal cycles. Thermally cycled samples showed more tortuous crack paths and stable crack propagation left periodic blunting marks spaced at ∼57.5 μm on the fracture surface corresponding to each increment of crack advance. Microhardness mapping revealed a microstructure of hard and soft domains (∼63 μm × 105 μm), and thermal cycling heterogeneously softened the hard domains while the soft domains remained apparently unchanged. In addition to the observed softening, large increases in the relaxation enthalpy, and thus the average free volume, were found over the first ∼70 thermal cycles. While cold rolling the samples prior to the thermal cycling did not raise the mean fracture toughness values, the scatter was reduced compared to as-cast thermal cycled samples. This was attributed to the introduction of shear bands giving a more repeatable initial microstructure than casting.

Processing of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 Bulk Metallic Glass Alloy by Cu Mould Casting and Spark Plasma Sintering

The present investigation deals with the processing of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 bulk metallic glass (BMG) using different techniques. The maximum plate thickness for the amorphous phase formation has been found to be 1.25 mm using a conventional BMG casting technique (forced infiltration casting). For enhancing the dimension, an alternate processing route was employed to produce the BMG in the form of compacts. In this case, the dimensions are not restricted by the glass forming ability of the alloy. The process involved the preparation of amorphous ribbons using a melt spinner followed by high energy ball milling to crush the ribbons into very fine particles. The powder was then compacted in the form of pellets using spark plasma sintering technique. Density achieved was almost near to theoretical density (99%). The density was found to increase with a decrease in the particle size of glassy powder, which could be achieved by increasing the duration of high energy ball milling. The maximum densification occurred when the holding temperature was within undercooled liquid regime (∆Tx). Further increase of temperature beyond crystallization temperature (Tx) resulted in decreasing the compact density.

Effect of Mo on properties of the industrial Fe–B-alloy-derived Fe-based bulk metallic glasses

The experimental results concerning the effects of Mo on the glass-forming ability (GFA), thermal stability, and mechanical, anticorrosion, and magnetic properties of an (Fe71.2B24Y4.8)96Nb4 bulk metallic glass (BMG) were presented. An industrial Fe–B alloy was used as the raw material, and a series of Fe-based BMGs were synthesized. In BMGs with the Mo contents of approximately 1at%–2at%, the cast alloy reached a critical diameter of 6 mm. The hardness and fracture strength also reached their maximum values in this alloy system. However, the anticorrosion and magnetic properties of the BMGs were not substantially improved by the addition of Mo. The low cost, good GFA, high hardness, and high fracture strength of the Fe-based BMGs developed in this work suggest that they are potential candidates for commercial applications.

Composition dependence of the microstructure and mechanical behavior of Ti–Zr–Cu–Pd–Sn–Nb bulk metallic glass composites

Ti-based bulk metallic glass composite alloys Ti56Zr6Cu19.8Pd8.4Sn1.8Nb8, Ti64Zr4Cu13.2Pd5.6Sn1.2Nb12 and Ti68Cu13.2Pd5.6Sn1.2Nb12 were designed to obtain the microstructure composing of β-Ti dendrites and glassy matrix. The compressive and three-point bending properties were investigated. It was found that the actual microstructure of the Nb-added alloys consisted of primarily precipitated β-Ti dendrites, network-like glassy matrix, and extra island-like Ti2Cu intermetallic phase with different volume fractions. Under compressive loading, all the Nb-added alloys presented higher yield strength combined with remarkably increased plasticity. Under bending condition, however, the alloys Ti56Zr6Cu19.8Pd8.4Sn1.8Nb8 and Ti64Zr4Cu13.2Pd5.6Sn1.2Nb12 with higher Ti2Cu volume fractions became completely brittle. The alloy Ti68Cu13.2Pd5.6Sn1.2Nb12 could keep its plastic deformability due to the decreased Ti2Cu volume fraction. Compressive deforming behavior of the Nb-added alloys was determined by the ductile β-Ti phase and glassy matrix, nevertheless, bending deforming behavior of the alloys was determined by the volume fraction and distribution of the brittle intermetallics.

Effect of Copper and Zirconium Addition on Properties of Fe-Co-Si-B-Nb Bulk Metallic Glasses

In this research work, iron-based bulk metallic glasses (BMGs) have been fabricated, characterized and compared with Fe-Si alloy. BMG alloys of composition ((Fe0.6Co0.4)0.75B0.20Si0.05)96Nb4) were synthesized by suction casting technique using chilled copper die. Effect of copper and zirconium addition on magnetic, mechanical, thermal and electrochemical behavior of ((Fe0.6Co0.4)0.75B0.20Si0.05)96Nb4 BMGs was investigated. Furthermore, effect of annealing on nano-crystallization and subsequently on magnetic and mechanical behavior was also analyzed. Amorphousness of structure was evidenced by XRD analysis and microscopic visualization, whereas nano-crystallization behavior was identified by peak broadening of XRD patterns. Magnetic properties, measured by vibrating sample magnetometer, were found to be improved for as-cast BMG alloys by copper addition and further enhanced by nano-crystallization after annealing. Mechanical properties were observed to be increased by zirconium addition while slightly declined by copper addition. Potentiodynamic polarization analysis manifested the positive role of zirconium in enhancing corrosion resistance of BMGs in acidic, basic and brine mediums. Moreover, mechanical properties and corrosion analysis results affirmed the superiority of BMG alloys over Fe-Si alloy.

Erratum to: Thermal stability, mechanical properties and corrosion behavior of a Mg–Cu–Ag–Gd metallic glass with Nb addition

By the minor addition of Nb to a Mg–Cu–Ag–Gd alloy, a Mg–Cu–Ag–Gd–Nb bulk metallic glass (BMG) with improved thermal stability and corrosion resistance as well as good mechanical properties was developed. Mg54Cu26.5Ag8.5Gd11−x Nb x (x = 0, 1) BMGs with a diameter of 2 mm were fabricated by copper-mold casting. The Mg54Cu26.5Ag8.5Gd10Nb1 BMG exhibits enlarged supercooled liquid region of 58 K. Electrochemical measurements indicate that the addition of Nb improves the corrosion resistance of the Mg-based BMG in NaCl solution evidenced by the increased corrosion potential, though no significant effect of Nb on the corrosion behavior of the BMG in NaOH solution is observed. The Mg–Cu–Ag–Gd–Nb BMG also shows high compressive strength up to 890 MPa and elastic strain of about 1.9%.

Effect of Nb Content on Mechanical Behavior and Structural Properties of W/(Zr55Cu30Al10Ni5)100−x Nb x Composite

In the present study, (Zr55Cu30Al10Ni5)100−x Nb(x=0,1,2,3) bulk metallic glass matrix/tungsten wire composites were fabricated by infiltration process. Structural studies were investigated by scanning electron microscopy and X-ray diffraction method. Also, mechanical behaviors of the materials were analyzed using quasi-static compressive tests. Results indicated that the best mechanical properties i.e., 2105 MPa compressive ultimate strength and 28 pct plastic strain before failure, were achieved in the composite sample with X = 2. It was also found that adding Nb to the matrix modified interface structure in W fiber/(Zr55Cu30Al10Ni5)98Nb2 since the stable diffusion band formation acts as a functionally graded layer. Finally, the observation of multiple shear bands formation in the matrix could confirm the excellent plastic deformation behavior of the composite.

Effect of replacing Nb with (Mo and Zr) on glass forming ability, magnetic and mechanical properties of FeCoBSiNb bulk metallic glass

Abstract In this work, effects of replacing Nb with either Mo or Zr on glass forming ability (GFA), thermal stability, magnetic and mechanical properties of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 bulk metallic glass were studied. The rod and ribbon samples were prepared using copper mold casting and melt spinner respectively. The replacement of Mo instead of Nb does not affect the crystallization behavior but the GFA is decreased. However an increases in plasticity up to 4% and saturation magnetization (Ms) by 10% is observed for the equal atomic percentage of Mo, with further increase in the Mo content GFA still decreases (dc = 1 mm) and Ms remains the same. In case of [(Fe0.5Co0.5)0.75B0.2Si0.05]96 Zr4 three distinct crystallization events were observed, the glass transition (Tg) and on set of crystallization (Tx) were decreased by 18 K and 23 K respectively. The GFA decreased drastically however the Ms remains the same.

The Effects of a High Magnetic Field on the Annealing of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb₄ Bulk Metallic Glass.

In contrast with amorphous alloys, nanocrystalline soft magnetic materials show improved thermal stability and higher soft magnetic properties. The nanocrystalline soft magnetic composites are usually fabricated by partially crystallizing from parent amorphous alloys. This paper reports our experimental observation on the sequence of crystallization in metallic glass under a high magnetic field (HMF). An application of a HMF to bulk metallic glass (BMG) of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 prioritizes the precipitation of α-(Fe,Co) phase separated from the subsequent precipitation of borides, (Fe,Co)23B6, upon isothermal annealing at a glass transition temperature. Furthermore, it was observed that, through the annealing treatment under a HMF, a soft magnetic nanocomposite, in which only α-(Fe,Co) phase uniformly distributes in amorphous matrix, was achieved for boron-bearing BMG. The promotion of the α-Fe or (Fe,Co) phase and the prevention of the boride phases during the isothermal annealing process help to produce high-quality soft magnetic nanocomposite materials. The mechanism by which a HMF influences the crystallization sequence was interpreted via certain changes in Gibbs free energies for two ferromagnetic phases. This finding evidences that the annealing treatment under a HMF is suitable for enhancing the soft magnetic properties of high B content (Fe,Co)-based bulk amorphous and nanocrystalline materials.