High Entropy Bulk Metallic Glass Research Articles

Effect of Cr/Mo content on the properties of transition-metal based high entropy bulk metallic glasses

In this work, new Fe20Co20Ni20CrxMo20-xP10B10 (x = 5, 10 and 15 at.%) high-entropy bulk metallic glasses (HE-BMGs) with the maximum diameter of 1.0–2.0 mm were prepared by combining fluxing treatment and J-quenching technique, and the effects of Cr/Mo content on thermal stability, mechanical properties, corrosion and wear resistances were systematically investigated. It is found that the glass transition temperature (Tg) and onset crystallization temperature (Tx) of the present transition-metal based HE-BMGs slightly decrease with the increase/decrease of Cr/Mo content. Compressive test shows that the compressive strength of the present transition-metal based HE-BMGs monotonously decrease from 3124 MPa for x = 5 to 2745 MPa for x = 15, but the compressive plasticity is nearly zero. Electrochemical measurements in 3.5 wt.% NaCl solution show that the corrosion resistance of the present transition-metal based HE-BMGs decrease with the increase/decrease of Cr/Mo content and the alloy with x = 15 exhibit the highest corrosion resistance with a self-corrosion current density of 1.02 × 10−8 A/cm2 among the present transition-metal based HE-BMGs. Wear test shows that, as the Cr/Mo content increases/decrease, the friction coefficient and wear rate of the present transition-based HE-BMGs decrease, i.e., wear resistance increases.

Alloying behavior and characterization of (CoCrFeNiMn)90M10 (M=Al, Hf) high-entropy materials fabricated by mechanical alloying

The alloying behavior and microstructures of the (CoCrFeNiMn)90M10 (M=Al, Hf) high-entropy alloy (HEA) powders fabricated by mechanical alloying were studied. The CoCrFeNiMn)90Al10 powders have duplex solid-solution structures. In contrast, nanocrystalline HfNi3 anchoring in amorphous structures is found in the (CoCrFeNiMn)90Hf10 powders. The (CoCrFeNiMn)90Al10 powders show better ferromagnetic behaviors, mainly explained by the facilitated motion of the magnetic domain induced by the coherent interface between duplex phases. Combined with our previous work, the rules of forming solid-solution and amorphous phase in as-milled HEA powders are preliminarily proposed. It is found that, compared with the as-cast HEA reported previously, the variation range of mixing enthalpy with atomic size difference of the solid-solution formed in as-milled HEA powders is broader. Moreover, the variation ranges between mixing enthalpy and entropy with atomic size difference of the amorphous phase in HEA powder become wider than those of high-entropy bulk metallic glass.

Utilization of high entropy in rare earth-based magnetocaloric metallic glasses

In this study, the magnetic behavior and magnetocaloric effect (MCE) of Dy18Er18Y18Ni26Al20 and Dy13.5Er13.5Y13.5Gd13.5Ni26Al20 high-entropy bulk metallic glasses (BMGs) were systematically investigated, as well as Dy27Er27Ni26Al20 and Dy54Ni26Al20 medium-entropy BMGs. Distinct spin glass-like behavior below the Curie temperature and large MCE at cryogenic temperature were observed in all BMGs. Competitive magnetic entropy change values of 10.6 and 10.2 J kg−1K−1 were obtained for the Dy27Er27Ni26Al20 and Dy18Er18Y18Ni26Al20 BMGs, respectively, under a magnetic field change of 5 T. Accordingly, the effect of configuration entropy on the magnetic response and MCE was discussed. It was found that the magnetic phase transition temperature, magnetic hysteresis and refrigeration capacity can be altered by utilization of configuration entropy, which can be ascribed to the change in random magnetic anisotropy and magnetic interactions. However, no distinct difference in the magnetic entropy change was observed from the ternary Dy54Ni26Al20 to senary Dy13.5Er13.5Y13.5Gd13.5Ni26Al20 BMGs with increasing configuration entropy. The results reveal that the typical cocktail effect of high-entropy alloys is not applicable to magnetic entropy changes in these BMGs. Nevertheless, all BMGs in this study show good glass-forming ability and MCE which make them promising refrigerant candidates at cryogenic temperatures.

Enhancing the tribological performance of the TiZrHfCuBe high entropy bulk metallic glass by Sn addition

Inheriting the advantages of bulk metallic glasses (BMGs) and high entropy alloys (HEAs), high entropy bulk metallic glasses (HE-BMGs) have sparked great interest in recent years. In this work, the evolutions of structural heterogeneity, thermal stability and mechanical property of the TiZrHfCuBe HE-BMG with minor Sn addition were characterized, and the corresponding tribological properties under different normal loads and frequencies were investigated. The results showed that minor Sn addition can significantly enhance wear resistance of the HE-BMG by improving its structural heterogeneity and mechanical properties in a rather limited composition range. When excessive Sn is added, plentiful crystal particles are precipitated in the amorphous matrix, and the wear mechanism of the HE-BMG changes from slight abrasive and oxidation wear to severe fatigue and oxidation wear, leading to dramatically declined wear resistance. These findings would provide guidance for the development of advanced HE-BMGs with unique properties.

Designing High Entropy Bulk Metallic Glass (HE-BMG) by Similar Element Substitution/Addition.

In this paper, we report that two newly designed high entropy bulk metallic glasses (HE-BMGs), Ti20Hf20Cu20Ni20Be20 with a critical diameter of 2 mm, and Ti16.7Zr16.7Nb16.7Cu16.7Ni16.7Be16.7 with a critical diameter of 1.5 mm, can be fabricated by copper mold casting method. These newly developed HE-BMGs exhibited a high fracture strength over 2300 MPa. The glass forming ability and atomic size distribution characteristics of the HE-BMGs are discussed in detail. Moreover, a parameter δ′ was proposed to evaluate the atomic size distribution characteristics in different HEAs. It showed that this new parameter is closely related to the degree of lattice distortion and phase selection of high-entropy alloys. Adjusting the value of δ′ parameter by similar element substitution/addition would be beneficial for designing high entropy bulk metallic glasses.

Research progress in Zr-Ti containing high-entropymatellic glasses

<p indent="0mm">High-entropy bulk metallic glasses (HE-BMGs) are alloys that contain five or more principal elements in equal or near-equal atomic ratios. HE-BMGs have the composition of a high-entropy alloy (HEA), structure of a bulk metallic glass, and satisfy the thermodynamic, kinetic, and structural conditions for amorphous formation. They have excellent comprehensive properties and potential as structural and functional materials. This paper summarizes the composition design, crystallization behaviors and the physical, mechanical, and thermal stability properties of Zr-Ti containing HE-BMGs. The phase formation rules for HEAs can be used to determine compositions region for bulk glass formation. However, the developed HE-BMGs have poor glass-forming ability (GFA) compared with other BMGs in the same system. In order to obtain HE-BMGs with high GFA, attempts have been made to design near-equiatomic HE-BMGs. An effective strategy for developing HE-BMGs with high GFA is to replace elements in the HE-BMGs at equal atomic ratios. This strategy has enabled the preparation of a Ti₂₀Zr₂₀Hf₂₀Be(Cu_7.5Ni_12.5) high-entropy amorphous alloy with a critical diameter of <sc>30 mm.</sc> New near-equiatomic HE-BMGs with high GFA can also be obtained by similar element substitution based on selected ternary alloys. Because of the high-entropy effect, the crystallization behaviors of HE-BMGs differ from those of other BMGs in the same/similar alloy systems. The non-isothermal crystallization of Zr-Ti containing HE-BMGs involves multistage crystallization, and the nucleation rate decreases with increasing crystallization degree. Zr-Ti containing HE-BMGs have higher activation energies than Vit-1, which means better thermodynamic stabilities. In addition to having a high-entropy effect, near equatomic Zr-Ti containing HE-BMGs are affected by a single principal element. For example, the nucleation rate of Zr₃₁Ti₂₇Be₂₆Cu₁₀Ni₆ increases gradually during the initial stage of crystallization; this is consistent with the behavior of Zr-based metallic glass. At the next stage, high entropy effect plays the major role. In other words, the effect induced by single principal elements has a stronger influence on the crystallization process of the near equiatomic Zr-Ti containing HE-BMGs. In terms of mechanical properties, a Zr-Ti containing HE-BMG has high strength, i.e., close to the theoretical prediction, high corrosion and wear resistance, and room-temperature brittleness. The room-temperature plasticity of the Zr-Ti containing HE-BMGs can be obviously improved by adjusting the composition, surface coating, cryogenic cycling treatment and cryothermal cycling treatment. Because of the high-entropy effects and sluggish diffusion effect due to the complexity of the ingredients, HE-BMGs have high creep resistance and corrosion resistance and give high thermal oxidation performances. The macroscopic deformation behaviors of the HE-BMGs show significant temperature and strain rate dependence. At the temperature of hot-embossing process, it was found that Zr-Ti containing HE-BMGs possess a relatively poor thermoplastic formability, especially under the reduced mould size to tens micrometers. Ultrasonic loading is an effective measure to conspicuously enhance the thermoplastic formability of Zr-Ti containing HE-BMGs. There are some expected goals that have not been reached in research on Zr-Ti containing HE-BMGs. At present, the alloy design strategies are mainly applicable to single-element, binary and ternary amorphous alloys. Multi-principal-element amorphous alloys have no appropriate measures for design. The compatibility of tensile ductility and high strength of HE-BMGs is still an overarching goal. New techniques such as machine learning and high throughput can be used to identify compositions with excellent properties. With the development and use of new experimental apparatus, the influence of a higher number of elements on the structures and properties of Zr-Ti HE-BMGs will able to be verified more accurately. In terms of hot-embossing process, the problem of the high viscosities of Zr-Ti HE-BMGs at their formation temperature needs to resolve by process optimization.

Optimisation of superplastic processing parameters for a TiZrHfBeCuNi high entropy bulk metallic glass in the supercooled liquid region

In this study, the deformation behavior of Ti20Zr20Hf20Be20(Cu10Ni10) high entropy bulk metallic glass (HE-BMG) in the supercooled liquid region was investigated via uniaxial compression tests. The thermal workability was also investigated to determine the optimal range of processing parameters. The results revealed that the deformation behavior in the supercooled liquid region exhibited two modes: flow deformation and brittle fracture, both of which were significantly affected by temperature and strain rate. The homogeneous flow deformation behavior changed from Newtonian to non-Newtonian with a decrease in temperature and an increase in strain rate. The activation volume of the HE-BMG ranged from 0.146 to 0.304 nm3 based on the transition theory of the free volume model, indicating that the atomic group can migrate (about 12–25 atoms) during high-temperature deformation. The fracture surface analysis of the HE-BMG revealed that the fracture angle increases with increasing deformation temperature, which was primarily due to an increase in cohesive strength. The optimal processing parameters for forming HE-BMG without crystallization were determined by constructing a deformation map based on the deformation behavior and microstructural analysis results.

Effect of Cr/Mo Content on the Properties of Transition-Metal Based High Entropy Bulk Metallic Glasses

Effect of Cr/Mo Content on the Properties of Transition-Metal Based High Entropy Bulk Metallic Glasses

Deformation behavior of Zr33Hf8Ti6Cu32Ni10Co5Al6 high-entropy bulk metallic glass and Cu47Zr47Al6 low-entropy bulk metallic glass at room and high temperatures

Compressive deformation behavior at room temperature and the high temperatures was studied for Zr33Hf8Ti6Cu32Ni10Co5Al6 developed HEBMG and Cu47Zr47Al6 BMG alloys. Compressive strain-stress curves at room temperature showed that with the development of HEBMG, ductility and fracture stress improved by 58% and 5.4%, respectively. The high density of shear bands in the HEBMG compared to the BMG had a significant relationship with their mechanical properties, which indicated that the ductility of HEBMG is higher than BMG. The high temperatures deformation studies were performed at strain rates of 2.5×10−4s−1, 2.5×10−3s−1, and 5.0×10−5s−1 and at temperatures of 710K and 730K. The hot deformation behavior of both alloys was similar, but HEBMG with standed more stresses than BMG (under similar conditions). Considering the free volume theory, for the results obtained from stress-strain curves at high temperatures, the maximum value of activation volume was equal to V = 0.3076 nm3 for HEBMG. Also, viscosity has shown a decreasing trend with increasing strain rate, however HEBMG samples had a higher value of viscosity than BMG samples. Deformation behavior of the HEBMG at high strain rates has been closer to Newtonian flow compared to BMG.

Boson heat capacity peak and its evolution with the enthalpy state and defect concentration in a high entropy bulk metallic glass

We first measured the low temperature heat capacity of a high entropy bulk metallic glass in different enthalpy states created by preannealing. We found a boson heat capacity peak located at a temperature of ≈7 K with the height decreasing upon preannealing. Using the results of specially performed calorimetrical and shear modulus measurements and applying the Interstitialcy theory, we showed that the boson peak (BP) height increases linearly both with the excess enthalpy of glass determined calorimetrically and concentration of interstitial-type defects assumed responsible for the BP. The BP peak height and defect concentration are found smaller as compared with those in conventional metallic glasses based on a single element that is attributed to the high entropy state of the glass under investigation.

Superplastic formability of the developed Zr40Hf10Ti5Al10Cu25Ni10 high entropy bulk metallic glass with enhanced thermal stability

The Zr55Cu30Al10Ni5 BMG as a base alloy was alloyed with Hf and Ti to develop a high entropy bulk metallic glass. The aim of the present work was to investigate the superplastic formability of HE-BMG, which can be used for micro-forming applications. Therefore, thermal stability and crystallization kinetics of the newly developed HE-BMG was first studied and then the results were used for the designed hot deformation experiments. It was demonstrated that HE-BMG has higher thermal stability than the base BMG, supposedly due to the sluggish diffusion and high entropy effect. Hot deformation behavior of the developed HE-BMG was investigated and it was found that at temperature of 753 K and the strain rate of 2 × 10–5 s-1, the alloy shows a good superplastic deformation with a plastic strain of at least 50% at compression stress around 500 MPa that is good enough for near net shape forming.

Thermal behavior of newly developed Zr33Hf8Ti6Cu32Ni10Co5Al6 high-entropy bulk metallic glass

In this study, new non-equiatomic high entropy bulk metallic glass (HEBMG) Zr33Hf8Ti6Cu32Ni10Co5Al6 was developed according to the Cu47Zr47Al6 prototype BMG. Kinetic studies were performed with non-isothermal DSC for the BMG and the HEBMG, and their thermal properties were compared. Calculation of activation energies by different methods indicated that Eg is higher for the HEBMG than the BMG, while Ep is lower for the HEBMG than the BMG, and Ex is similar for both alloys. The values of structural relaxation enthalpy for the BMG and the HEBMG were 4.95 J/g and 8.19 J/g, respectively. Free volume was calculated at room temperature and Tg. By doing so, the direct correlation between fragility, structural relaxation enthalpy, diffusion, and free volume was shown. Using a compression test at room temperature, a 58% improvement in plastic strain was obtained for HEBMG, which confirmed the calculations.

Dynamic mechanical relaxation and thermal creep of high-entropy La30Ce30Ni10Al20Co10 bulk metallic glass

Dynamic mechanical relaxation is a fundamental tool to understand the mechanical and physical properties of viscoelastic materials like glasses. Mechanical spectroscopy shows that the high-entropy bulk metallic glass (La30Ce30Ni10Al20Co10) exhibits a distinct β-relaxation feature. In the present research, dynamic mechanical analysis and thermal creep were performed using this bulk metallic glass material at a temperature domain around the β relaxation. The components of total strain, including ideal elastic strain, anelastic strain, and viscous-plastic strain, were analyzed based on the model of shear transformation zones (STZs). The stochastic activation of STZ contributes to the anelastic strain. When the temperature or external stress is high enough or the timescale is long enough, the interaction between STZs induces viscous-plastic strain. When all the spectrum of STZs is activated, the quasi-steady-state creep is achieved.

Relaxation-Induced Changes in High-Entropy Bulk Metallic Glasses

Relaxation-Induced Changes in High-Entropy Bulk Metallic Glasses

Relaxation behavior of high-entropy bulk metallic glass: Influences of physical aging and cyclic loading

<p indent="0mm">In this study, the correlation among the relaxation behavior, deformation mechanism, and structural heterogeneity of metallic glasses is examined using La₃₀Ce₃₀Ni₁₀Al₂₀Co₁₀ high-entropy bulk metallic glass as the model glass. Dynamic mechanical analysis (DMA) was used to investigate the influences of physical aging and cyclic loading on the dynamic relaxation and deformation mechanism of the model glass. The correlation between the deformation units and the structural heterogeneity was analyzed on the basis of the activation energy spectrum (AES). The results demonstrated that La₃₀Ce₃₀Ni₁₀Al₂₀Co₁₀ high-entropy bulk metallic glass displays an apparent β relaxation. A more stable state can be achieved during physical aging below the glass transition temperature and in cyclic loading because the atomic rearrangements are suppressed during these processes. This structural relaxation during the physical aging process enables the transition from liquid-like regions to an elastic matrix. Further, more time is required to activate the deformation units that are frozen during the transition. The applied stress results in a decrease in the number of liquid-like regions, which suppresses the activation of the deformation units during the cyclic loading process. As a result, the intensity of the β relaxation in the metallic glass decreases. Therefore, the origin of the β relaxation in La₃₀Ce₃₀Ni₁₀Al₂₀Co₁₀ high-entropy bulk metallic glass is ascribed to the liquid-like regions.

Calculations of the Fragility of High-Entropy Bulk Metallic Glasses Using the Data on Shear Elasticity Relaxation

Calculations of the Fragility of High-Entropy Bulk Metallic Glasses Using the Data on Shear Elasticity Relaxation

RETRACTED ARTICLE: Effects of Primary Stored Energy on Relaxation Behavior of High Entropy Bulk Metallic Glasses Under Compressive Elastostatic Loading

This paper aims to show the effects of primary stored energy in high entropy bulk metallic glasses (HE-BMGs) on their relaxation behavior after elastostatic loading process. For this purpose, three HE-BMGs with different chemical compositions and primary stored energy were fabricated. Differential scanning calorimetry and nanoindentation tests were carried out to evaluate the relaxation enthalpy and microscopic mechanical characterization of alloys. The results showed that increase in the number of element types in the alloying composition leads to the increment of stored energy and structural heterogeneity in the primary alloys. Moreover, the elastostatic loading rejuvenates the primary alloys; however, an optimum heterogeneity is needed for the maximum structural heterogeneity and stored energy in the glassy alloy. The hardness measurements also indicate that the elastostatic loading intensifies the hardness variations in the alloys, which may be due to the increased structural heterogeneity.

Dynamic mechanical relaxation behavior of Zr35Hf17.5Ti5.5Al12.5Co7.5Ni12Cu10 high entropy bulk metallic glass

Non-equiatomic high entropy bulk metallic glasses were reported recently and show unique mechanical and physical properties. Dynamic mechanical relaxation behavior of Zr35Hf17.5Ti5.5Al12.5Co7.5Ni12Cu10 high entropy bulk metallic glass was investigated by dynamic mechanical analysis (DMA) and the mechanical spectra could be well described by the quasi-point defects (QPD) theory. Compared to typical metallic glasses, the intensity of the β relaxation of Zr35Hf17.5Ti5.5Al12.5Co7.5Ni12Cu10 high entropy bulk metallic glass is lower due to the sluggish diffusion. At the same time, the correlation factor χ is higher than that of conventional metallic glasses and this is ascribed to the high configuration entropy. In parallel, physical aging below the glass transition temperature leads to a decrease of atomic mobility, caused by a decrease of the concentration of defects.

Effects of minor Si addition on structural heterogeneity and glass formation of GdDyErCoAl high-entropy bulk metallic glass

Glass-forming ability (GFA) of the Gd20Dy20Er20Co20Al20 high-entropy bulk metallic glass (HE-BMG) was improved through microalloying Si element. The critical diameter of this rare-earth-based HE-BMG increases from 1.5 to 8.5 mm with 0.5 at.% Si addition without any deterioration of magnetocaloric property. Compared with the Si-free sample, the BMG with 0.5 at.% Si addition exhibits low driving force for crystallization, strong supercooled liquid behavior and sluggish crystallization kinetics, whereas excessive Si addition leads to reverse variations. Furthermore, microalloying Si can enhance nanoscale heterogeneity of elemental distribution, and thus facilitates the formation of local crystal-like structures. The connectivity and competition between icosahedra-like clusters and crystal-like structures promote the formation of stable network structure which frustrates crystallization. As Si content is excessive, icosahedra-like cluster is consumed by the further grown crystal-like structure, leading to the destruction of network and decreasing GFA. This work not only elucidates the underlying mechanism of the GFA enhanced by microalloying, but also sheds light on improving the GFA of HE-BMGs through altering nanoscale elemental distribution and structural heterogeneity.

Crystallization evolution and relaxation behavior of high entropy bulk metallic glasses using microalloying process

The role of the microalloying process in relaxation behavior and crystallization evolution of Zr20Cu20Ni20Ti20Hf20 high entropy bulk metallic glass (HEBMG) was investigated. We selected Al and Nb elements as minor elements, which led to the negative and positive effects on the heat of mixing in the master HEBMG composition, respectively. According to the results, both elements intensified β relaxation in the structure; however, α relaxation remained stable. By using different frequencies in dynamic mechanical analysis, it was revealed that the activation energy of β relaxation for the Nb-added sample was much higher, which was due to the creation of significant structural heterogeneity under the microalloying process. Moreover, it was found that Nb addition led to a diversity in crystallization stages at the supercooled liquid region. It was suggested that the severe structural heterogeneity in the Nb-added sample provided multiple energy-level sites in the structure for enhancing the crystallization stages.