High Entropy Bulk Metallic Glass Research Articles

Plasticity enhancement of high-entropy bulk metallic glasses by electroless plating with Ni-P amorphous films

Using chemical plating, Ni-P films were successfully coated on Ti20Zr20Hf20Be20Cu20 high-entropy bulk metallic glasses (HE-BMGs), and presented an enhancive adhesion as well as a higher deposition rate on account of the chemical pretreatment before electroless plating. With the coating, the plastic strain of the HE-BMGs is increased up to 5.7%, which is 3.2 times of 1.8% of the bare pillars. It shows that the adhesive coating with a thickness of 10µm leads to a plasticity enhancement of HE-BMGs via the dispersive impact of coating on the concentrated stress. In addition, the coating leads to more homogeneous regions where shear banding may take place and offers a preventible action for the rapid propagation of shear bands.

High thermal stability and sluggish crystallization kinetics of high-entropy bulk metallic glasses

Metallic glasses are metastable and their thermal stability is critical for practical applications, particularly at elevated temperatures. The conventional bulk metallic glasses (BMGs), though exhibiting high glass-forming ability (GFA), crystallize quickly when being heated to a temperature higher than their glass transition temperature. This problem may potentially be alleviated due to the recent developments of high-entropy (or multi-principle-element) bulk metallic glasses (HE-BMGs). In this work, we demonstrate that typical HE-BMGs, i.e., ZrTiHfCuNiBe and ZrTiCuNiBe, have higher kinetic stability, as compared with the benchmark glass Vitreoy1 (Zr41.2Ti13.8Cu12.5Ni10Be22.5) with a similar chemical composition. The measured activation energy for glass transition and crystallization of the HE-BMGs is nearly twice that of Vitreloy 1. Moreover, the sluggish crystallization region ΔTpl-pf, defined as the temperature span between the last exothermic crystallization peak temperature Tpl and the first crystallization exothermic peak temperature Tpf, of all the HE-BMGs is much wider than that of Vitreloy 1. In addition, high-resolution transmission electron microscopy characterization of the crystallized products at different temperatures and the continuous heating transformation diagram which is proposed to estimate the lifetime at any temperature below the melting point further confirm high thermal stability of the HE-BMGs. Surprisingly, all the HE-BMGs show a small fragility value, which contradicts with their low GFA, suggesting that the underlying diffusion mechanism in the liquid and the solid of HE-BMGs is different.

Insight on Viscoelasticiy of Ti16.7 Zr16.7 Hf16.7 Cu16.7 Ni16.7 Be16.7 High Entropy Bulk Metallic Glass

High entropy bulk metallic glasses show promising mechanical and physical properties. Dynamic mechanical properties of Ti16.7 Zr16.7 Hf16.7 Cu16.7 NU16.7 Be16.7 high entropy bulk metallic glass were investigated by mechanical spectroscopy (or called dynamic mechanical analysis). The main (α) relaxation was observed in the framework of the loss modulus G“, which is related to the dynamic glass transition behaviour for the glassy materials. From physical model point of view, dynamic mechanical properties of the Ti16.7 Zr16.7 Hf16.7 Cu16.7 Ni16.7 Be16.7 high entropy bulk metallic glass show good agreement compared with the quasi-point defects theory.

Nanoindentation mechanical properties of glassy Cu29Zr32Ti15Al5Ni19

Cylindrical high entropy metallic glass Cu29Zr32Ti15Al5Ni19 (φ1mm) was prepared via suction casting into a water-cooled mold. The mechanical properties of glassy Cu29Zr32Ti15Al5Ni19 were valued via nanoindentation with Continuous Stiffness Measurement (CSM) mode. The results show that glassy Cu29Zr32Ti15Al5Ni19 is of good plasticity and homogeneous. The average values of nano-hardness and modulus of high entropy bulk metallic glass Cu29Zr32Ti15Al5Ni19 are 7.45 GPa and 105.4 GPa, respectively. Creep can be observed at room temperature when the alloy is held with a constant load. The average creep degree in holding stage is 52.4%, and the creep rate in steady-state creep is about 0.007% s−1. The creep compliance begins with a constant and then increases with time.

Nonisothermal crystallization kinetics, fragility and thermodynamics of Ti20Zr20Cu20Ni20Be20 high entropy bulk metallic glass

Abstract

Pseudo-quinary Ti20Zr20Hf20Be20(Cu20-xNix) high entropy bulk metallic glasses with large glass forming ability

Abstract A series of pseudo-quinary Ti20Zr20Hf20Be20(Cu20 -xNix) (x = 2.5, 5, 7.5, 10, 12.5, 15, 17.5 and 20 at.%) high entropy bulk metallic glasses (HE-BMGs) with large glass forming ability (GFA) were successfully prepared by copper mold tilt-casing. The critical diameters (Dc) of these HE-BMGs are all above 12 mm. In particular, the developed Ti20Zr20Hf20Be20(Cu7.5Ni12.5) and Ti20Zr20Hf20Be20Ni20 high entropy alloys (HEAs) can be produced in the amorphous state with diameters up to 30 mm and 15 mm, respectively, which are the largest HE-BMG and quinary HE-BMG hitherto. The two HE-BMGs also exhibit high yield strength, together with the plastic strain values of (3.0 ± 1.1) % and (4.0 ± 0.9) %, respectively. With increasing Ni additions in the pseudo-quinary HEAs, the crystallization growth resistance and thermal stability have been improved, which is apparently due to the sluggish diffusion of the atoms in the HEAs.

Soft magnetic Fe25Co25Ni25(B, Si)25 high entropy bulk metallic glasses

New Fe25Co25Ni25(B, Si)25 high entropy bulk metallic glasses (HE-BMGs) with superior soft magnetic and mechanical properties are developed. The HE-BMGs show high glass transition temperature and wide supercooled liquid region (ΔTx). Fully glassy rods with diameters up to 1.5 mm were fabricated for the Fe25Co25Ni25(B0.7Si0.3)25 alloy by copper mold casting method. The HE-BMGs exhibit high yield strength of ∼3624 MPa with large plastic strain of ∼3.1%, which is superior to the pre-developed HE-BMGs. The alloys also possess good soft magnetic properties, i.e., rather high saturation magnetization of ∼0.87 T, low coercive force of ∼1.1 A/m, and high effective permeability at 1 kHz of ∼19,800. This combination of these excellent properties gives the new HE-BMGs good promise for both scientific and engineering applications.

Thermodynamic modeling and composition design for the formation of Zr–Ti–Cu–Ni–Al high entropy bulk metallic glasses

This work explores the idea of predicting metallic glass forming composition in a multi component alloy for which an equilibrium phase diagram is yet to be deciphered. Deep eutectic regions in a quaternary alloy (Zr–Ti–Cu–Ni) have been extrapolated to the quinary Zr–Ti–Cu–Ni–Al system for designing a potential bulk glass forming composition. PHSS parameter which is the product of mixing enthalpy, mismatch entropy and configurational entropy of an alloy, has been utilized for thermodynamic modeling. PHSS values are computed through substitution of Al into the each of the fifteen quaternary eutectics that have been reported in the literature in the Zr–Ti–Cu–Ni system. A good correlation of PHSS range between modeled alloys and established glass formers indicates the subtle efficacy of this method for high entropy amorphous alloy design through a rationale thermodynamic approach.

Crystallization kinetics of TiZrHfCuNiBe high entropy bulk metallic glass

The isochronal and isothermal DSC annealing techniques have been employed to investigate the crystallization behavior of a newly developed Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy bulk metallic glass. In non-isothermal condition, the activation energies for glass transition, onset and the first crystallization process were determined by Kissinger equation, to be 331.8±8.0, 215.3±4.5 and 245.5±6.3kJ/mol, respectively. The isothermal kinetics was modeled by the Johnson–Mehl–Avrami (JMA) equation. During the crystallization process, the isothermal activation energy calculated by the Arrhenius equation changes little with an average value of 259.9kJ/mol. The Avrami exponent is in the range from 1.81 to 2.04, indicating that the crystallization process is mainly dominated by growth of particles with a decreasing nucleation rate.

A quinary Ti–Zr–Hf–Be–Cu high entropy bulk metallic glass with a critical size of 12 mm

A quinary Ti20Zr20Hf20Be20Cu20 high entropy bulk metallic glass (HE-BMG), with a critical diameter (Dc) of 12 mm—the largest size in the reported quinary high entropy alloys (HEAs), has been successfully prepared by copper mold casing. This novel HE-BMG possesses a supercooled liquid region ΔT (=Tx − Tg) of 78 K, indicating a better thermal stability than those of other HE-BMGs. In addition, the HE-BMG exhibits a relatively good compressive plasticity (2.2 ± 0.1%) among the HE-BMGs. The newly developed HE-BMG may offer insights for the indepth understanding of the fundamental issues associated with the glass formation and the unique structure-property relationship when combining the features of HEAs and BMGs together.

High-entropy bulk metallic glasses as promising magnetic refrigerants

In this paper, the Ho20Er20Co20Al20RE20 (RE = Gd, Dy, and Tm) high-entropy bulk metallic glasses (HE-BMGs) with good magnetocaloric properties are fabricated successfully. The HE-BMGs exhibit a second-order magnetic phase transition. The peak of magnetic entropy change (ΔSMpk) and refrigerant capacity (RC) reaches 15.0 J kg−1 K−1 and 627 J kg−1 at 5 T, respectively, which is larger than most rare earth based BMGs. The heterogeneous nature of glasses also contributes to the large ΔSMpk and RC. In addition, the magnetic ordering temperature, ΔSMpk and RC can be widely tuned by alloying different rare earth elements. These results suggest that the HE-BMGs are promising magnetic refrigerant at low temperatures.

高エントロピー合金，バルク金属ガラスおよび高エントロピーバルク金属ガラスの合金設計

高エントロピー合金，バルク金属ガラスおよび高エントロピーバルク金属ガラスの合金設計

The magnetocaloric effect of Gd-Tb-Dy-Al-M (M = Fe, Co and Ni) high-entropy bulk metallic glasses

In this article, we report the formation of the high-entropy Gd20Tb20Dy20Al20M20 (M = Fe, Co and Ni) bulk metallic glasses with good magnetocaloric properties. Compared with most of the rare earth based metallic glasses, these alloys are found to have the comparably large maximum magnetic entropy changes (ΔSM), but much broader widths of the ΔSM peaks, and hence larger refrigerant capacity (RC). This can be attributed to the combination of the spin glass behaviors and the complicated compositions in these alloys. Our work show that the high entropy bulk metallic glasses is a promising candidate material as the magnetic refrigerant.

High-Entropy Alloys with a Hexagonal Close-Packed Structure Designed by Equi-Atomic Alloy Strategy and Binary Phase Diagrams

High-entropy alloys (HEAs) with an atomic arrangement of a hexagonal close-packed (hcp) structure were found in YGdTbDyLu and GdTbDyTmLu alloys as a nearly single hcp phase. The equi-atomic alloy design for HEAs assisted by binary phase diagrams started with selecting constituent elements with the hcp structure at room temperature by permitting allotropic transformation at a high temperature. The binary phase diagrams comprising the elements thus selected were carefully examined for the characteristics of miscibility in both liquid and solid phases as well as in both solids due to allotropic transformation. The miscibility in interest was considerably narrow enough to prevent segregation from taking place during casting around the equi-atomic composition. The alloy design eventually gave candidates of quinary equi-atomic alloys comprising heavy lanthanides principally. The XRD analysis revealed that YGdTbDyLu and GdTbDyTmLu alloys thus designed are formed into the hcp structure in a nearly single phase. It was found that these YGdTbDyLu and GdTbDyTmLu HEAs with an hcp structure have delta parameter (δ) values of 1.4 and 1.6, respectively, and mixing enthalpy (ΔH mix) = 0 kJ/mol for both alloys. These alloys were consistently plotted in zone S for disordered HEAs in a δ-ΔH mix diagram reported by Zhang et al. (Adv Eng Mater 10:534, 2008). The value of valence electron concentration of the alloys was evaluated to be 3 as the first report for HEAs with an hcp structure. The finding of HEAs with the hcp structure is significant in that HEAs have been extended to covering all three simple metallic crystalline structures ultimately followed by the body- and face-centered cubic (bcc and fcc) phases and to all four simple solid solutions that contain the glassy phase from high-entropy bulk metallic glasses.

A senary TiZrHfCuNiBe high entropy bulk metallic glass with large glass-forming ability

Most reported bulk metallic glasses (BMGs) contain multiple constituent elements but only one of them is the principal element. Here we report that a senary Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 high entropy bulk metallic glass (HE-BMG) with a critical diameter larger than 15mm has been successfully prepared by copper mold casting. It shows that newly developed HE-BMG possesses large glass-forming ability, together with the supercooled liquid region ΔT (=Tx−Tg), reduced glass transition temperature Trg (=Tg/Tl) and γ parameter (=Tx/(Tg+Tl)) of 70K, 0.619 and 0.422, respectively. The present result indicates that high entropy alloys, even for senary alloys or metal–metal type, could also possess large glass-forming ability. And the present HE-BMG could serve as a model material for studying the fundamental issues both of high entropy alloys and bulk metallic glasses.

Alloy Designs of High-Entropy Crystalline and Bulk Glassy Alloys by Evaluating Mixing Enthalpy and Delta Parameter for Quinary to Decimal Equi-Atomic Alloys

The values of mixing enthalpy (¦Hmix) and Delta parameter (¤) were calculated with 73 elements from Miedema’s model for multicomponent equi-atomic alloys to investigate the possibilities of the alloys to be formed into high-entropy (H-E) alloys or high-entropy bulk metallic glasses (HE-BMGs). The equi-atomic alloys from about 15 million (73C5) quinary to 621 billion (73C10) decimal systems were evaluated by referring to a ¦Hmix­¤ diagram for zones S and B’s for H-E alloys with disordered solid solutions and BMGs, respectively, reported by Zhang et al. The results revealed that the number of quinary equi-atomic alloys plotted in zone S is 28405 (30.19% in 73C5), whereas those in zones B1 and B2 for conventional and Cuand Mg-based BMGs, respectively, were 1036385 and 21518 (36.90 and 30.14%), respectively. This kind of statistical approach using ¦Hmix­¤ diagram will lead to finding out unprecedented H-E alloys and HE-BMGs. [doi:10.2320/matertrans.M2013352]

Entropies in Alloy Design for High-Entropy and Bulk Glassy Alloys

High-entropy (H-E) alloys, bulk metallic glasses (BMGs) and high-entropy BMGs (HE-BMGs) were statistically analyzed with the help of a database of ternary amorphous alloys. Thermodynamic quantities corresponding to heat of mixing and atomic size differences were calculated as a function of composition of the multicomponent alloys. Actual calculations were performed for configurational entropy (Sconfig.) in defining the H-E alloys and mismatch entropy (Ss) normalized with Boltzmann constant (kB), together with mixing enthalpy (DHmix) based on Miedema’s empirical model and Delta parameter (d) as a corresponding parameter to Ss/kB. The comparison between DHmix–d and DHmix– diagrams for the ternary amorphous alloys revealed Ss/kB ~ (d /22)2. The zones S, S′ and B’s where H-E alloys with disordered solid solutions, ordered alloys and BMGs are plotted in the DHmix–d diagram are correlated with the areas in the DHmix – Ss /kB diagram. The results provide mutual understandings among H-E alloys, BMGs and HE-BMGs.

In vitro and in vivo studies on biodegradable CaMgZnSrYb high-entropy bulk metallic glass

In order to enhance the corrosion resistance of the Ca65Mg15Zn20 bulk metallic glass, which has too fast a degradation rate for biomedical applications, we fabricated the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass because of the unique properties of high-entropy alloys. Our results showed that the mechanical properties and corrosion behavior were enhanced. The in vitro tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass could stimulate the proliferation and differentiation of cultured osteoblasts. The in vivo animal tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass did not show any obvious degradation after 4weeks of implantation, and they can promote osteogenesis and new bone formation after 2weeks of implantation. The improved mechanical properties and corrosion behavior can be attributed to the different chemical composition as well as the formation of a unique high-entropy atomic structure with a maximum degree of disorder.

High entropy Ti20Zr20Cu20Ni20Be20 bulk metallic glass

In this letter, we report that a new bulk metallic glass (BMG) of Ti20Zr20Cu20Ni20Be20, with a critical diameter of 3mm, has been successfully fabricated using copper mold casting method. Different from most reported BMGs which possess one or two main constituents, this newly developed BMG possesses five elements with equal atomic concentration, which has been defined as high entropy alloy. This high entropy bulk metallic glass (HE-BMG) exhibits high fracture strength of 2315MPa but a brittle behavior. The glass forming ability, mechanical property and phase transformation after annealing of the HE-BMG are discussed in detail. And a way for designing high entropy bulk glassy alloy has been proposed.

Alloy Design for High-Entropy Bulk Glassy Alloys

An efficient alloy design for bulk metallic glasses (BMGs) assisted by a composition–configurational entropy (C-CE) diagram has been proposed by introducing a feature of high-entropy (HE) alloys that are defined by an equi-atomic alloy with five or more elements. The proposed alloy design compensated for a shortcoming in determining the compositions of BMGs and led to success in forming a Pd20Pt20Cu20Ni20P20 HE-BMG with a maximum diameter of 10mm. The C-CE diagram demonstrates the equi-atomicity of alloys, providing candidates for HE-BMGs. The alloy design for HE-BMG will promise opening up the new cutting-edge in both HE alloys and BMGs.