High Entropy Bulk Metallic Glass Research Articles

Minor Cr alloyed Fe–Co–Ni–P–B high entropy bulk metallic glass with excellent mechanical properties

In this study, we propose a new strategy for designing ductile Fe-based bulk metallic glasses by minor substitution, which strengthens the local solute-centered atomic clusters and increases the concentration of free volume. The locally modified structure results in a stronger barrier to the formation and propagation of shear bands, which appears to be decisive for enhancing both yielding strength and plasticity. Accordingly, (Fe1/3Co1/3Ni1/3)77.5Cr2.5(P1/2B1/2)20 high entropy bulk metallic glass has been developed by minor substitution of (Fe–Co–Ni) in (Fe1/3Co1/3Ni1/3)80 (P1/2B1/2)20 by Cr. The compressive yielding strength increased by approximately 200 MPa and plasticity was enhanced from 4.4% to 11.2%. We believe that the proposed design strategy will provide a new method for improving the plasticity of Fe-based bulk metallic glass, and therefore, expand its applications in engineering.

Influence of deep cryogenic cycling on the rejuvenation and plasticization of TiZrHfBeCu high-entropy bulk metallic glass

The effects of deep cryogenic cycling treatment (DCT) on the rejuvenation and room-temperature compressive properties of a TiZrHfBeCu high-entropy bulk metallic glass (HE-BMG) were studied. After DCT, the fully amorphous structure of TiZrHfBeCu HE-BMG remained, but the relaxation enthalpy showed obvious rejuvenation behavior. Upon increasing the number of cycles, the room-temperature plasticity of TiZrHfBeCu HE-BMG gradually increased from 0.62% to 5.38%, with no obvious change in the yield strength. The hardness and density of the high-entropy amorphous alloy decreased with the number of DCT cycles. The DCT-induced rejuvenation and plasticization mechanisms were explained based on the shear transformation zone (STZ) model. The effects of high mixing entropy and fragility on the rejuvenation behavior were also considered. This work confirmed that DCT is an effective method for the rejuvenation and plasticization of TiZrHfBeCu HE-BMG.

A new perspective to thermodynamical designing of high entropy bulk metallic glasses (HE-BMGs)

The present investigation involves an attempt to incorporate key thermodynamical and topological aspects of glass formation specifically the enthalpy of chemical mixing (ΔHmix), configurational entropy (ΔSconfig) and entropy due atomic size mismatch (ΔSσ) into a single parameter using the PHSS model to understand their role in designing new HE-BMG compositions. The model has been employed with 69 elements for quinary equiatomic alloys to investigate the possibilities of the alloys to form HE-BMGs. The application of the hard-sphere atomic radius in the evaluation of topological parameters through the PHSS model appears to be insufficient in designing new HE-BMG alloy systems due to the limitations of some of the associated assumptions. Most importantly, the effect of the alteration of the local electronic environment of atoms on their atomic radii in multi-component alloys has been incorporated into the model to further establish the defining role of topology in glass formation. The results revealed that the number of quinary equiatomic alloys forming HE-BMG systems is 368,275 (3.75% of 9,818,072 (69C5) total combinations). The modification in atomic radii has been found to pinpoint more precisely the HE-BMG alloy systems when compared to the hard-sphere model for atomic radii of pure elements. In a nutshell, this kind of statistical modelling approach can lead to the development of unprecedented determination of new HE-BMG compositions.

Influence of substitution of Cu by Ni on the crystallization kinetics of TiZrHfBeCu high entropy bulk metallic glass

The crystallization kinetics of TiZrHfBe(Cu, Ni) high entropy bulk metallic glasses have been studied using differential scanning calorimetry. Each alloy possesses a complex multi-step crystallization process due to the high entropy effect. It was found that substitution of Cu by Ni significantly improves the glass-forming ability but deteriorates the thermal stability of the TiZrHfBeCu alloy. The activation energies of glass transition and crystallization together with the fragility parameter for the Ni-free and Ni-containing alloys have been calculated. According to the calculated values of local Avrami exponent, the first crystallization event for the studied TiZrHfBe(Cu, Ni) alloys is dominated by a direct growth of crystal nuclei. Substitution of Cu by Ni favors the precipitation of Ni-containing intermetallic compounds and inhibits the formation of CuHf2 phase, resulting in the improvement of glass-forming ability.

Calculation of the Temperature Dependence of the Unrelaxed Shear Modulus of High-Entropy Bulk Metallic Glasses from Calorimetric Data

A method is proposed to calculate the temperature dependence of the unrelaxed shear modulus of high-entropy bulk metallic glasses from differential scanning calorimetry data. The results obtained by this method are shown to be in good agreement with the results of specially performed precision measurements of the unrelaxed shear modulus.

Unique energy-storage behavior related to structural heterogeneity in high-entropy metallic glass

Structural heterogeneity dominates energy-storage behavior of metallic glasses. Ti20Zr20Hf20Be20Cu7.5Ni12.5 high-entropy bulk metallic glass (HE-BMG) shows extraordinary energy-storage behavior under cryothermal cycling: the relaxation enthalpy monotonically increased with cryothermal cycling cycles, even after 240 cycles of treatment. By comparison, the relaxation enthalpy of Ti41Zr25Be22Ni12 BMGs reached a maximum only at 30 cycles and then dramatically decreased as prototypical BMGs reported. The as-cast HE-BMG demonstrates an extremely low fraction of loose-packing regions (~7.8%, fractions for Ti- and Zr-based BMGs are above 15.6%), indicating degraded structural heterogeneity that would induce smaller local internal stress during cryothermal cycling and eventually lead to the sluggish energy-storage behavior. In addition, the increase in the fraction of loose-packing regions accompanied by the energy storage also lead to significant improvement in ductility of the HE-BMG, the plastic strain increased from 0.6% (the as-cast sample) to 5.2% (the sample treated 240 cycles).

Strong beta relaxation in high entropy bulk metallic glasses

β relaxation of metallic glasses (MGs) has already been researched deeply in recent years. In contrast to MGs, which are usually composed of a principal element and another less solute element, we develop a series of new near equal-atomic high-entropy bulk MGs (HE-BMGs) that exhibit fully amorphous structures. The dynamic mechanical properties of HE-BMGs were investigated following a dynamic mechanical analysis. Pronounced β relaxation behaviors were observed in HE-BMGs over a wide range of temperatures and frequencies for each HE-BMG. The larger negative values of average chemical enthalpy and entropy can enhance β relaxation in HE-BMGs. These HE-BMGs may provide a new system to investigate and understand the origin of β relaxation in glassy solids.

Research progress on high-entropy bulk metallic glasses

As a new type of amorphous materials, high-entropy bulk metallic glasses (HE-BMGs) exhibit the characteristics of long-range disordered atomic arrangement similar to that of traditional BMGs and also contain an equimolar ratio of constituents similar to that of crystalline high-entropy alloys. Owing to their unique structural and compositional features, HE-BMGs exhibit peculiar physical, chemical, and mechanical properties. In this review paper, we briefly summarize recent progress on HE-BMGs and propose several important scientific problems that need to be investigated in the field of HE-BMGs. Specifically, the influence of high-mixing entropy on the formation of HE-BMGs. According to the confusion principle, the more components are present in an alloy, the more difficult becomes the crystallization of the alloy, and thus, the alloy easier forms an amorphous structure. However, it is determined that HE-BMGs have poor glass formation ability compared with that of their traditional BMG counterparts. High thermal stability and nano-crystallization of HE-BMGs. HE-BMGs exhibit slower crystallization kinetics and have a considerable potential in the fabrication of new types of high-entropy bulk nanostructured materials by partial crystallization. Unusual relationship between high thermal stability and poor glass forming ability of HE-BMGs.

Link between shear modulus and enthalpy changes of Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy bulk metallic glass

Mechanical and thermal properties of materials are intricately linked. Particularly, this fully applies to metallic glasses. In this work, we study shear modulus behavior and heat effects occurring upon heating up of Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy bulk metallic glass up to the full crystallization. In the framework of the Interstitialcy theory, we show that shear modulus relaxation data can be applied to quantitatively predict exo- and endothermal effects related to structural relaxation, glass transition and crystallization of this high entropy metallic glass. This fact suggests that the underlying physical mechanism responsible for this link can be conditioned by the relaxation of the system of structural defects, which by their properties are similar to dumbbell interstitials in metals.

Aspect ratio effects on the serrated flow dynamic of TiZrHfCuNiBe high entropy metallic glass

The effects of aspect ratio on serrated flow dynamic and plasticity of TiZrHfCuNiBe high entropy bulk metallic glass were investigated. With increasing of the aspect ratio, the stress drop time decreases and a ductile-to-brittle transition was observed, which indicates the motion of shear bands will berestricted in the specimens with smaller aspect ratio. Thus, the shear band velocity can be estimated based on the stick-slip dynamics, which enhances with increasing of the aspect ratio, while the critical shear band velocity is almost identical. Therefore, the specimens with larger aspect ratio will achieve the critical shear band velocity faster until fracture. When the aspect ratio is relatively small, the value of shear-band stability index is larger and promotes stable propagation of the shear bands. In addition, the plasticity and serration size are not monotonic correlated. Benefitting from the abundant secondary shear bands and the interactions at various scales, the plastic deformation can be regarded as the self-organized critical state for samples with better plasticity and lower aspect ratio. However, the self-organized critical state will switch to a chaotic state with increasing of the aspect ratio.

A nanoindentation study of Ti-based high entropy bulk metallic glasses at elevated temperatures

Nanoindentation was used to explore the mechanical properties of high entropy bulk metallic glasses (HE-BMGs) from room to elevated temperatures. Two Ti-based HE-BMGs and two conventional counterparts were investigated. Below the glass transition temperature, softening is observed for conventional BMGs with increasing temperature, whereas hardness keeps almost unchanged for HE-BMGs. The resistance to thermal softening might originate from the highly stable high entropy structure, which retards atomic diffusion and rearrangement for shear transformation. Above the glass transition temperature, HE-BMGs show quite low hardness and pronounced creep deformation, suggesting that high entropy may facilitate fast diffusion in the viscous flow.

Identifying the high entropy effect on plastic dynamics in bulk metallic glasses: A nanoindentation study at room and elevated temperatures

In this study, the spatiotemporal dynamic analyses of intermittent plastic flow in the nanoindentation of different Bulk metallic glasses (BMGs), at various temperatures, were carefully performed to provide insight into the amorphous structural-property relationship. Based on the displacement-time series and largest Lyapunov exponent during serrated flow, two distinct types of dynamic behaviors were identified at room temperature, i.e., the serrated flow dynamics transforms form a self-organized critical state in traditional BMGs to a more chaotic state in high entropy BMGs (HE-BMGs). This may originate from their local structural difference that the solvent-solute architecture in conventional BMGs is broken in HE-BMGs. Furthermore, sluggish diffusion in HE-BMG can effectively retard relaxation kinetics, which leads to the deviation of HE-BMGs from the conventional BMGs in terms of the relationship between the chaotic behavior and temperature. Indeed, the insignificant change in dynamic complexity of HE-BMG conforms to its increased structural stability at elevated temperatures, which was soundly elucidated from both topological and kinetic factors. This study is of significance in understanding the configuration complexity and structure stability in HE-BMGs and helpful for designing BMGs with promising properties against external mechanical and thermal agitations.

New FeNiCrMo(P, C, B) high-entropy bulk metallic glasses with unusual thermal stability and corrosion resistance

New Fe20–35Ni20Cr20–30Mo5–15(P0.6C0.2B0.2)20 bulk metallic glasses with excellent thermal stability, strength, and corrosion resistance have been developed through the high-entropy alloy design strategy. The high-entropy bulk metallic glasses (HE-BMGs) possess larger supercooled liquid regions of ∼69 K, higher crystallization onset temperatures of ∼852 K, larger undercoolings of ∼109 K, and more sluggish crystallization process upon heating than the conventional metallic glass benefited from the high mixing entropy effect. The HE-BMGs also exhibit ultrahigh strength of ∼3.4 GPa, Vickers hardness of ∼1107, and superior corrosion resistance in acids and NaCl solutions by formation of highly stable Cr- and Mo-enriched passive films. The new metal-metalloid HE-BMG system and exceptional properties give the alloys good promise for both scientific and engineering applications.

Non-Isothermal Crystallization Kinetics of a Rapidly Solidified as-Cast TiZrHfNiCu High Entropy Bulk Metallic Glass

This paper aims to investigate the thermal behavior and crystallization kinetics of TiZrHfNiCu high entropy bulk metallic glass (HE-BMG) alloy using the standard procedure of Differential Scanning Calorimetric (DSC) annealing technique. The alloy was produced using an arc melting machine with a critical diameter of 1.5 mm. The crystallization kinetics and phase transformation mechanism of TiZrHfNiCu HE-BMG was investigated under the isochronal condition at a single heating run based on the Johnson-Mehl- Avrami (JMA) theory. In isochronal heating, the apparent activation energy for glass transition and crystallization events was analyzed by Kissinger and Ozawa methods. The average activation energy value for crystallization of TiZrHfNiCu amorphous alloys in isochronal modes was 226.41 kJ/mol for the first crystallization and 297.72 kJ/mol for second crystallization stages. The crystallization mechanism of the first step was dominated by two- and three-dimensional growth with increasing nucleation rate, while the crystallization mechanism in the second stage was dominated by two-dimensional crystallization growth with a constant nucleation rate. The diffusion mechanism result proved the theory of sluggish atomic diffusion of HEA at elevated temperature.

Research on nano-scratching behavior of TiZrHfBeCu(Ni) high entropy bulk metallic glasses

Nanoscratch tests have been conducted to study the tribological behavior of TiZrHfBeCu(Ni) high entropy bulk metallic glasses (HE-BMGs). A classic Zr-based BMG, vit-1 alloy, has been selected as a reference. For all the four adopted alloys, the effect of scratch velocity on the nano-scratch behavior is not obvious. It is found that TiZrHfBeCu(Ni) HE-BMGs possess better nanoscratch resistance than that of vit-1 alloy. Moreover, with the Ni content increasing, the glass transition temperature and hardness increase while the free volume content decreases, resulting in a better nanoscratch resistance. The addition of Ni also changes accumulation mode of the removed chips during the scratching process. Based on the variation of coefficient of friction (COF) during the scratching process, all the four alloys exhibit similar scratching mechanisms, which have been explained in detail.

Strong metallic glass: TiZrHfCuNiBe high entropy alloy

The viscosity and fragility of TiZrHfCuNiBe high entropy bulk metallic glass (HE-BMG) in the supercooled liquid region were investigated by the strain-rate jump tests. The Newtonian viscosities of HE-BMG are generally smaller than the conventional MGs due to higher mixing entropy. The fragility parameter was estimated to be 38 and implying that the supercooled liquid of HE-BMG is stronger. The interrelationship between fragility index and glass forming ability is discussed. The defects concentration of HE-BMG is much smaller than the traditional MGs, which enhances the difficulty of atomic rearrangement and further improves the stability of the supercooled liquid.

Septenary Zr–Hf–Ti–Al–Co–Ni–Cu high-entropy bulk metallic glasses with centimeter-scale glass-forming ability

A new Zr35Hf17.5Ti5.5Al12.5Co7.5Ni12Cu10 high-entropy bulk metallic glass with glass-forming ability up to centimeter scale (diameter of 18 mm) and configuration entropy of 1.77R was discovered. This high-entropy bulk metallic glass differs from previous ones because it was designed to possess a non-equiatomic eutectic composition and was free from Be. The high-entropy alloy exhibited excellent glass-forming ability despite its lower reduced glass transition temperature than those of prototypical glasses. Molecular dynamics simulations suggested that the excellent glass-forming ability was caused by the similar magnitude of the decrease in Hamiltonian from amorphous to crystalline phases to that of a reference ternary bulk metallic glass, as well as the sluggish crystallization of the high-entropy bulk metallic glass.

Magnetocaloric effect of Fe25Co25Ni25Mo5P10B10 high-entropy bulk metallic glass

Abstract In this work, Fe25Co25Ni25Mo5P10B10 high-entropy bulk metallic glass (HE-BMG) with a maximum diameter of 1.2 mm is prepared by combining fluxing treatment and J-quenching technique. The magnetocaloric effect and the “high-entropy effect” on the magnetocaloric properties of the present Fe25Co25Ni25Mo5P10B10 HE-BMG have been investigated. The Curie temperature of the present Fe25Co25Ni25Mo5P10B10 HE-BMG is 560 K, the peak value of the magnetic entropy change and the refrigerant capacity are 0.80 J kg−1 K−1 and 135.4 J kg−1 under the applied field of 1.5 T, 1.88 J kg−1 K−1 and 310.2 J kg−1 under the applied field of 5 T, respectively. Compared with other transition metal-based BMGs, the present Fe25Co25Ni25Mo5P10B10 HE-BMG does not exhibit a relatively larger magnetic entropy change but a much wider full width at half maximum temperature of the magnetic entropy change curve, thus a larger refrigerant capacity.

New ferromagnetic (Fe1/3Co1/3Ni1/3)80(P1/2B1/2)20 high entropy bulk metallic glass with superior magnetic and mechanical properties

New ferromagnetic (Fe1/3Co1/3Ni1/3)80(P1/2B1/2)20 high entropy bulk metallic glass (HE-BMG) with the maximum diameter of 2 mm has been prepared by combining fluxing treatment and J-quenching technique. The present HE-BMG exhibits excellent soft magnetic properties with a saturation magnetization of 0.90 T, low coercivity of 1.5 A/m, high permeability of 10172 @ 1 kHz and low hysteresis loss of 21 kJ/mol @ 50 Hz (for the annealed glassy ribbon), and mechanical properties with a compressive yield strength of 3000 MPa and large plastic strain of 4%. The combination of superior glass-forming ability, excellent magnetic and mechanical properties makes the present HE-BMG a future promising application as advanced structural and functional materials.

Identifying the origin of strain rate sensitivity in a high entropy bulk metallic glass

A series of nanoindentation tests were performed on a high entropy bulk metallic glass (HE-BMG). At low peak-loads, high positive strain rate sensitivity was found. But increasing the peak-load, the sensitivity of hardness to strain rate decreased dramatically. At low peak-loads, sluggish diffusion in HE-BMG significantly impedes atomic arrangement in the shear yielding events, whereas at high peak-loads, the shear-band deformation is dominated by the shear front triggered events. The work showed the origin of strain rate sensitivity in HE-BMGs and might help for tailoring the mechanical properties.