High Entropy Bulk Metallic Glass Research Articles

In-depth Analysis of Structural Heterogeneity in High Entropy Bulk Metallic Glasses Using 4D-STEM

In-depth Analysis of Structural Heterogeneity in High Entropy Bulk Metallic Glasses Using 4D-STEM

Dynamic mechanical response and constitutive model of (Ti37.31Zr22.75Be26.39Al4.55Cu9)94Co6 high-entropy bulk metallic glass

In this work, the mechanical response and fracture characteristics of (Ti37.31Zr22.75Be26.39Al4.55Cu9)94Co6 high-entropy bulk metallic glass (HE-BMG) were investigated in detail over a wide range of strain rates (10−4–105 s−1). The HE-BMG exhibited a negative strain rate sensitivity under uniaxial compression, with the strength showing more significant rate dependence under dynamic conditions. The shear band behavior translated from the dominance of multiple shear bands propagations under quasi-static compression to the rapid propagation of a single shear band to form cracks under dynamic compression. Under dynamic loading, the shearing velocity increased along an arc-shaped displacement path, and the local stress state on the shear fracture surface shifted from compressive-shear to tensile-shear, accompanied by changes in fracture morphologies. The spall strength of HE-BMG decreased as flyer impact speed increased, while the long-term dependence of spall strength on strain rate may be positive. With the increase of impact speed, the main microstructural features of the spalling surface translated from flat regions accompanied by dimples to cup-cone structures. Furthermore, the complete parameters of the Johnson–Holmquist II (JH-2) model for HE-BMG were obtained based on experimental data. Numerical simulations of planar impact, penetration, and hypervelocity impact are in good agreement with experimental results, demonstrating the validity of the JH-2 model parameters. The current work has important guiding value for the application of HE-BMG in space debris protection.

Effect of strain rate and temperature on dynamic compressive behavior of HfBeTiZrCuNi high entropy bulk metallic glass

This study investigated the high-temperature dynamic mechanical properties of Hf-based high entropy bulk metallic glass (HE-BMG). Uniaxial dynamic compressive tests of Hf-based HE-BMG were conducted at elevated temperatures (from 298 to 800 K) under a high strain rate (from 1000 to 5000 s−1) by a split Hopkinson pressure bar (SHPB) device with a high-temperature system, and the failed specimens were analyzed in terms of microstructures and fracture modes. The dynamic test results show that the maximum compressive stress and the total strain decrease with increasing strain rate and temperature, exhibiting significant strain rate and temperature sensitivity. Three different fracture modes were observed with increasing strain rates, while heating the temperature could promote the transition process of the fracture modes. When the adiabatic or heating temperature reaches above the crystallization temperature, the embrittlement caused by metallic glass crystallization makes the fracture mode change. The mechanical behavior of Hf-based HE-BMG at high temperatures and high strain rates could be attributed to the combination of adiabatic heating and embrittlement.

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

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

Concurrently achieving strength-ductility combination and robust anti-wear performance in an in-situ high-entropy bulk metallic glass composite

High-entropy bulk metallic glasses (HE-BMGs) with desired thermal stability often exhibit limited plasticity due to the occurrence of shear localization avalanches. The present study reports the fabrication of a novel composite TiZrHfNb0.5Cu0.5Be0.5, consisting of a high entropy crystalline phase (TiZrHfNb) and an amorphous matrix (TiZrHfCuBe). The composite exhibits a distinctive combination of strength and ductility, surpassing that of traditional BMG composites, along with a notable capacity for work-hardening. Furthermore, it demonstrates exceptional wear resistance under varying normal loads or frequencies. The deformation and wear mechanisms are attributed to the solid-solution strengthening and stress-induced β→α" martensitic transformation in the high entropy crystalline phase, as well as the deformation-induced crystallization in HE-BMG matrix. These findings would provide a new strategy for preparing advanced HE-BMGs composite with unique properties.

Effect of partial substitution of Cr with Co on the properties of Fe35Ni20Cr20-xCoxMo5P12C4B4 high-entropy bulk metallic glasses

Novel Fe35Ni20Cr20-xCoxMo5P12C4B4 (x = 0, 4,8, 12, 16 in at.%, denoted as Cr20-xCoxMo5) high-entropy bulk metallic glasses (HE-BMGs) with excellent comprehensive performance were successfully fabricated using Fluxing and J-quenching methods. The focus was on studying the influences of different Co content on the glass-forming ability (GFA), mechanical performances, magnetic properties, and anti-corrosion performance. It was found that adding an appropriate amount of Co to replace Cr in Cr20-xCoxMo5 alloys can improve GFA. The Cr12Co8Mo5 specimen displays the maximum critical diameter of 3.5 mm and maximum super-cooled liquid phase of 51 K. The compression tests show that the plasticity was enhanced from 0.2 % for the Co-free alloy to 2.5 % for the 12 at.% Co-added alloy. The saturation magnetization (Js) of Cr20-xCoxMo5 alloys gradually increased from 0.04 to 0.68 T with the increase of Co. Electrochemical tests indicate that in 3.5 wt.% NaCl solution at room-temperature (RT), the anti-corrosion performance of Cr20-xCoxMo5 alloys expresses a trend of first increasing and then decreasing with the increase of Co, and all samples show a remarkably higher anti-corrosion performance than 316 L and 304 L stainless steel. The Cr16Co4Mo5 sample exhibits the highest anti-corrosion performance with the self-corrosion current density (Icorr) and the self-corrosion potential (Ecorr) are 9.5 × 10−9 A/cm2 and -0.270 V, respectively. The X-ray photoelectron spectroscopy (XPS) analysis of the Cr16Co4Mo5 shows that there is a higher content of metal kation oxides of Fe2+, Cr3+ and Mo4+ in the passive films compared to Cr20Mo5 and Cr4Co16Mo5. It is indicated that the Cr16Co4Mo5 specimen has the optimal corrosion resistance in this current research. The present HE-BMGs have high GFA, high plastic strain,and excellent anti-corrosion performance, which have potential application value in the engineering field.

Sluggish atomic dynamics in a Y-Sc-Co-Al high entropy bulk metallic glass

We present how 20 at% Sc addition affects the atomic packing and dynamics in a Y-Co-Al metallic glass (MG) and find that it greatly suppresses the dynamics of Co atoms by reducing the atomic packing difference in their surroundings. The Co atoms tending to be mobile or static depend on their nearest neighbors, i.e., possessing more Y/Y+Sc atoms but fewer Co atoms or vice versa. The X-ray absorption fine structure results confirm that Sc addition mainly changes the local environment around Co atoms, forming more Co-Co and Co-Sc pairs but significantly fewer Co-Y pairs than in the ternary counterpart, which can seriously slow the atomic dynamics and stabilize the competing phases. Our findings shed new light on the understanding of strong glass forming ability of the Sc-added Y-based high entropy MG from its local structure and dynamics and will be helpful in developing new bulk MGs.

Critical behavior of the fluctuation heat capacity near the glass transition of metallic glasses

The high-frequency shear modulus of five Zr-, Pd-, Cu-based conventional and two high-entropy bulk metallic glasses was measured in a wide temperature range up to the beginning of crystallization. Using these data and general thermodynamic relations, the “fluctuation” heat capacity ΔCf determined by local structural fluctuations in the defect regions is introduced and calculated. It is found that ΔCf temperature dependence for all metallic glasses has a large peak located slightly below or above the glass transition temperature but clearly lower than the crystallization onset temperature. The form of this peak resembles the characteristic λ-peak typical for order–disorder phase transitions. It is suggested that this ΔCf-peak reflects certain underlying critical phenomenon. The critical temperature T0 (peak temperature) and corresponding critical index α are determined. Averaged over all seven metallic glasses under investigation in the initial and relaxed states, the critical index <α>=0.26. The results obtained indicate that the fluctuations of thermal energy near the glass transition bear the marks of a continuous phase transition. However, the derived critical index is between those corresponding to a second-order phase transition (α≈0.1) and a critical transition characterized by a tricritical point (α≈0.5).

A novel senary Hf-Be-Ti-Zr-Cu-Ni high entropy bulk metallic glasses with high glass forming ability and high density

New high glass-forming ability and high-density Hf20+xBe20-xTi20Zr20Cu7.5Ni12.5 (X = 1,2,3) and Hf22+2yBe18Ti20-yZr20-yCu7.5Ni12.5 (y = 1,2,3,4) high entropy bulk metallic glasses (HE-BMG) were prepared by the copper mold casting method. The effect of partially substituting Be or Zr (Ti) by Hf on the glass-forming ability (GFA) and mechanical properties of HE-BMGs was investigated. The results show Hf24Be18Ti19Zr19Cu7.5Ni12.5 HE-BMG exhibits a relatively high compressive plasticity of 2.1%. Hf28Be18Ti17Zr17Cu7.5Ni12.5 HE-BMG exhibits a large GFA (critical diameter Dc = 15 mm), fracture strength (2013 MPa), and high density (8.56 g/cm3), possessing excellent overall performance. In current alloys, high-entropy effect causes atoms to sluggish diffusion, increased crystallization growth resistance and thermal stability. The partial replacement of Be or Zr (Ti) with appropriate amounts of Hf significantly increases the degree of structural heterogeneity, which results in the improvement of GFA, strength, and plasticity of HE-BMGs.

Optimizing dry-wear performance of a Ti-based high entropy bulk metallic glass via isothermal annealing

The evolution of microstructure, thermal stability, mechanical response behavior and tribological properties of the Ti20Zr20Cu20Hf20Be20 high entropy bulk metallic glass (HE-BMG) before and after isothermal annealing were systematically studied. The results demonstrate that isothermal annealing affects the mechanical and tribological properties by modifying the microstructure and the consumption of free volume in the structure. Although the strength/hardness of HE-BMG can be improved after the isothermal annealing before crystallization, the deterioration of shear plastic deformation leads to serious brittle fracture, thus cancelling out the contribution of strength to wear resistance and resulting in negligible variation of wear rates. When the crystallization isothermal annealing is performed, the wear resistance can be dramatically enhanced and the wear mechanism changes to slight abrasive and oxidation wear, which can be mainly attributed to the good co-deformation between the amorphous matrix and precipitated crystalline phases.

Correlation of microstructure and tensile properties in in-situ high-entropy bulk metallic glass composites

To investigate the ‘structure-property’ correlation in the high-entropy bulk metallic glass composites (HE-BMGCs), a series of in-situ dendrites-reinforced Zr28Ti19Hf19Nb9.5Co5.5Be19 HE-BMGCs containing different microstructures are fabricated by varying the cooling rate (R). The underlying correlation between microstructure characteristics of dendrites and tensile properties of HE-BMGCs are elucidated by the postmortem microstructure observation and fracture analysis. The critical investigation shows the volume fraction (Vd), size (δ) and arm diameter (d) of dendrite increase with decreasing R, whereas the interdendritic spacing (λ) decreases correspondingly. The larger d is more beneficial to enhance the back-stress-induced hardening effect of HE-BMGCs, while the strengths of all the HE-BMGCs are negative linear correlation with their Vd (56∼70%). Besides, the finer δ matches the size of ‘plastic zone’ associated with larger λ, which results in higher tensile ductility (∼6.4%). Therefore, the combination of finer δ and appropriate Vd at higher R is favorable for HE-BMGCs to obtain better ductility and higher strength. Our findings provide an important implication for the microstructural optimization of HE-BMGCs with desirable mechanical properties.

Crystallization kinetics of Hf28Be18Ti17Zr17Cu7.5Ni12.5 high-entropy bulk metallic glass

Crystallization kinetics of Hf28Be18Ti17Zr17Cu7.5Ni12.5 high-entropy bulk metallic glass (HE-BMG) in the non-isothermal and isothermal conditions were investigated by differential scanning calorimetry (DSC). In non-isothermal crystallization condition, DSC traces exhibited three crystallization processes. The apparent activation energies of peak crystallization temperatures were calculated by Kissinger methods and found to be Ep1 > Ep2 > Ep3. The dependence of local activation energy on crystallized volume fraction was summarized by the Kissinger-Akahira-Sunose (KAS) method. The non-isothermal crystallization reaction was described mathematically using the Šesták-Berggren model. In the isothermal crystallization condition, with the increase of annealing temperature, the incubation time and crystallization time become shorter and the crystallization peak becomes higher. All Avrami indices were less than 2.5, indicating that crystallization of glassy alloy is dominated by a diffusion-controlled three-dimensional growth with a decreasing nucleation rate.

Mechanical properties and non-isothermal crystallization kinetics of novel Ti-based high-entropy bulk metallic glasses

In this work, five novel Ti- and TiZr-based high entropy bulk metallic glasses (HE-BMGs) with good glass forming ability (GFA) were developed, among which the (Ti37.31Zr22.75Be26.39Al4.55Cu9)94Ni6 alloy possesses the largest critical diameter of 9 mm. All developed HE-BMGs exhibit high yield strength and good compressive plasticity at room temperature. Especially, the (Ti37.31Zr22.75Be26.39Al4.55Cu9)94Co6 alloy with large GFA has suitable density and high specific strength (3.90 × 105 N m/kg), showing great potential in the aerospace sector. Moreover, the activation energies at characteristic temperatures of three HE-BMGs were obtained using the Kissinger method. The local Avrami exponents were calculated to analyze the crystallization mechanism of these HE-BMGs, revealing that the first crystallization process is mostly dominated by diffusion-controlled three-dimensional growth of pre-existing nuclei. In addition, all three HE-BMGs can be classified as “intermediate glasses” according to their fragility index values.

A generative deep learning framework for inverse design of compositionally complex bulk metallic glasses

The design of bulk metallic glasses (BMGs) via machine learning (ML) has been a topic of active research recently. However, the prior ML models were mostly built upon supervised learning algorithms with human inputs to navigate the high dimensional compositional space, which becomes inefficient with the increasing compositional complexity in BMGs. Here, we develop a generative deep-learning framework to directly generate compositionally complex BMGs, such as high entropy BMGs. Our framework is built on the unsupervised Generative Adversarial Network (GAN) algorithm for data generation and the supervised Boosted Trees algorithm for data evaluation. We studied systematically the confounding effect of various data descriptors and the literature data on the effectiveness of our framework both numerically and experimentally. Most importantly, we demonstrate that our generative deep learning framework is capable of producing composition-property mappings, therefore paving the way for the inverse design of BMGs.

Preparation and electrochemical corrosion performances of Zr-Ti-Ni-Cu-Be high-entropy bulk metallic glasses

The high entropy bulk metallic glasses (HE-BMGs) are the mathematical intersection of sets of bulk metallic glasses (BMGs) and high entropy alloys (HEAs). Owing to their unique structural and compositional features, HE-BMGs exhibit peculiar physical, chemical, and mechanical properties. Herein, non-equiatomic alloys ZrxTiNiCuBe (x = 1.5, 2, 2.5, 3, and 3.5 at. %) HE-BMGs were designed according to the atomic size difference (δ), mixing enthalpy (ΔHmix), mixing entropy (ΔSmix), valence electron concentration (VEC) and electronegativity difference (Δχ) parameters. The electrochemical corrosion behaviors in 1 mol/L H2SO4 and 3.5% NaCl solutions were also studied in this paper. The results show that fully glassy rods with diameters of 6 mm were obtained. The designed HE-BMGs show large glass forming ability, a narrow supercooled liquid region and a wide crystallization region compare with the traditional BMGs. In 1 mol/L H2SO4, the designed HE-BMGs show very small corrosion current densities and a typical passivation behavior, and their corrosion resistance is much better than that of 304L stainless steel. In 3.5% NaCl, the prepared HE-BMGs also have much smaller corrosion current densities than 304L stainless steel. As potential increases, the pitting corrosion resistance is not as good as 304L stainless, however, the HE-BMGs all show superior pitting corrosion re-passivation abilities.

Ductilizing Ti19Zr19Hf19Nb19TM5Be19 (TM = Fe, Co, Ni and Cu) high-entropy bulk metallic glass composites via in-situ precipitated refractory high-entropy alloy dendrites

In this work, a series of Ti19Zr19Hf19Nb19TM5Be19 (at.%, TM = Fe, Co, Ni and Cu) high-entropy bulk metallic glass composites (HE-BMGCs) were successfully developed to address the absence of tensile ductility in high-entropy bulk metallic glasses (HE-BMGs). It is shown that the mechanical properties of HE-BMGCs are jointly affected by the two constituent phases of refractory high-entropy alloy (RHEA) dendrites and HE-BMG matrix. The present composites show that the good tensile ductility as well as excellent work-hardening capability at ambient temperature. Based on the post-deformation microstructure and theoretical analyses, cross slips dominate the deformation mechanism of HE-BMGCs, and it is found that the dislocation multiplication mechanism composed of dislocation pinning and double cross-slip is very prevalent in current composites. Therein, the dislocation multiplication of RHEA dendrites facilitates the inhibition and retardation to the propagation of shear bands in the HE-BMG matrix, which is responsible for the good tensile ductility of HE-BMGCs. Additionally, the excellent work-hardening capability of composites is attribute to severe dislocation interactions caused by intrinsic local-regional multicomponent fluctuations and dislocation cross-slips in RHEA dendrites. Our research results not only aid in understanding the underlying deformation mechanism of HE-BMGCs, but also offer a novel perspective for designing the ductile high-entropy dual-phase alloys.

Quasi-static and dynamic deformation behavior of Hf28Be18Ti17Zr17Cu7.5Ni12.5 high-entropy bulk metallic glass

A series of quasi-static and dynamic compression experiments were performed on Hf28Be18Ti17Zr17Cu7.5Ni12.5 high-entropy bulk metallic glass (HE-BMG) at room temperature and at different strain rates. The findings showed that under quasi-static loading, strain rate had no considerable impact on the fracture strength of the HE-BMG. Nevertheless, the plastic strain disappeared with the increasing strain rate. The analysis of the fracture morphology under quasi-static loading revealed the shear fracture mode of HE-BMG and the critical role of the shear bands in the plastic deformation stage. In addition, the dynamic mechanical properties of the HE-BMG were tested at different strain rates. The dynamic deformation behavior of the HE-BMG was also investigated using a split Hopkinson pressure bar. Compared with the quasi-static compression results, a strain-rate softening phenomenon was observed under dynamic loading. With the increasing strain rate, the yield strength of the HE-BMG gradually decreased, and three different failure modes occurred under dynamic loading. The reasons for the different fracture mechanisms were also investigated by examining the unique fracture surface morphology of the HE-BMG specimens in dynamic compression.

Corrosion behavior of TiZrHfBeCu(Ni) high-entropy bulk metallic glasses in 3.5 wt. % NaCl

The corrosion behavior of TiZrHfBeCu(Ni) high-entropy bulk metallic glasses (HE-BMGs) has been investigated. The TiZrHfBeCu(Ni) HE-BMGs exhibited high corrosion resistance in 3.5 wt. % NaCl solution because of accumulation of ZrO2 and TiO2 in the passive film. Ni promoted increases of the ZrO2, TiO2, and HfO2 contents and a decrease of the BeO content, which improved the HE-BMG corrosion behavior. Compared with Zr41.2Ti13.8Ni10Cu12.5Be22.5 BMG, the high-entropy effect of HE-BMGs can significantly reduce the atomic mobility, which inhibits outward migration of Cu, reduces the kinetics of the dissolution reaction, and inhibits inward erosion by Cl−, thereby improving the corrosion performance.

Improved Plasticity of Fe25Co25Ni25(Si0.3B0.7)25 High Entropy Bulk Metallic Glass through the Addition of Cu

This work was focused on enhancement in the plasticity of Fe25Co25Ni25(Si0.3B0.7)25 high entropy bulk metallic glass (HE-BMG) by adding minor Cu (0–1.2, in at.%). It is found that the appropriate addition of Cu can efficiently improve the plasticity of the present HE-BMG while the excessive addition of Cu will deteriorate again the plasticity, and especially, the plastic strain of the present HE-BMG is improved from 0.8% for the Cu-free alloy to 4.7% for the 0.3 at.% Cu-added alloy. The transmission electron microscopy observation shows that there are many α-Fe (Co, Ni) clusters with sizes of less than 5 nm dispersed in the glassy matrix in the 0.3 and 0.6 at.% Cu-added alloys, which may account for the significant improvement in the plasticity of the two alloys, and further increase in Cu content more than 0.9 at.% leads to the precipitation of α-Fe (Co, Ni) and Fe (Co, Ni) B compound grains with diameters of tens of nanometers, in which the plasticity of the present HE-BMGs has deteriorated rapidly.

Structural characterization of a composite joint prepared during laser welding of Ti–22Al–27Nb intermetallic alloy with an interlayer of Cu-Hf-Ni-Ti-Zr high entropy bulk metallic glass

The advent of high entropy alloys (HEAs) has provided scientific solutions to material related problems of grave importance. High-temperature embrittlement (HTE) in the laser welded joint (LWJ) of titanium aluminides is one of the challenges, known to impede the prevalent applications of this novel alloy system. In the current research work, a sandwich-structured composite joint of an intermetallic based alloy (Ti–22Al–27Nb) with a high entropy bulk metallic glass (HE-BMG) composed of Cu, Hf, Ni, Ti and Zr was welded through laser beam. The adulteration of LWJ with HE-BMG resulted into evolution of finite microregions in the fusion zone (FZ) through heterogeneous nucleation. The FZ comprised fine-grained B2 phase with greater fractions of high angle grain boundaries (HAGBs) and lower degree of local area misorientations (LAM). The crystal texture of B2 phase in the FZ abetted the plastic deformation at room as well as high temperature (650 °C), as the Schmid factor “m” for ≥ 99% of {1 1 0} <1 1 1> slip system of B2 remained greater than 0.38. The high-resolution transmission electron microscopy revealed the presence of nano-sized composite regions (NCRs), composed of crystalline/non-crystalline structure. These NCRs remained stable at 650 °C and inhibited the nucleation of O phase along B2 grain boundaries (GBs). The percentage elongation of HE-BMG supplemented LWJ of Ti–22Al–27Nb was improved by 28.19 and 31.34% at room temperature and 650 °C, respectively. The dilution of FZ with HE-BMG contributed a significant increase in tensile ductility at room as well as high temperature.