Recent Progress in Alloy Designs for High-Entropy Crystalline and Glassy Alloys

J. Jpn. Soc. Powder Powder Metallurgy Vol. 63, No. 4 209

General Reviews

Akira TAKEUCHI*

Institute for Materials Research, Tohoku University, 2-1-1 Katahira Aoba-ku, Sendai 980-8577, Japan.

Received November 20, 2015; Accepted December 7, 2015

ABSTRACT This paper provides general overviews for the recent progress in alloy designs for high-entropy crystalline and glassy alloys in the following aspects. First, the alloy designs for bulk metallic glasses (BMGs) are briefly reviewed by focusing on atomic size differences, mixing enthalpy and valence electron concentration as well, followed by their extension to the other related alloys including high-entropy alloys (HEAs). Then, the historic backgrounds of the high-entropy bulk metallic glasses (HE-BMGs) are dealt with by pointing out the features of the HE-BMGs. Subsequently, the recently-developed HEAs with hcp structure, which are the new ones to the conventional HEAs with bcc, fcc and their mixture structures, are discussed for their future development. Finally, recent alloy designs utilizing crystallographic data acquired from Pettifor map, Pearson’s Crystal Data and binary phase diagrams are discussed in order to use them for the development of new alloys in near future. KEY WORDS alloy design, bulk metallic glass, high-entropy alloy, high-entropy bulk metallic glass, hcp structure

1 Introduction in 1970s7), together with other factors, such as quasi-stoichiometric

Of a class of multicomponent alloy systems, bulk metallic compositions (A12B, A5B and A3B), eutectic compositions, 2kF 1) glasses (BMGs) with a glassy structure and high-entropy alloys (Fermi vector) ~ qp (the first peak of the structure factor). In (HEAs), which possess bcc, fcc or its mixture crystalline phase2,3), addition, a topological instability (λ) was separately modeled for have grown up as advanced metallic materials in a recent couple binary alloys8), succeeded to the multicomponent systems9). This of decades. The representative alloys and their characteristic are kind of criteria was summarized and simplified as the component not described in the present paper, since they are well-summarized rules in the early 1990s when Inoue et al.10) have focused on these in the books recently published for BMGs4) and HEAs5). The factors leading to achieving high glass-forming ability (GFA) for BMGs are a sub-set of metallic glasses (MGs), which exhibit glass BMGs. In reality, these factors are accompanied by their threshold transition in temperature on cooling or heating, where the sample values, and thus, they have a formula of “empirical rules” or dimensions distinguish BMGs from conventional MGs: BMGs “component rules”10). For instance, it was reported as Fig. 111) that have a sample thickness or diameter of a couple of millimeters or five sorts of advance metallic materials including (I) BMGs can be more. On the other hand, HEAs are defined as the alloys with exact obtained by utilizing component rules where some of HEAs are or near equi-atomic alloys, without principal-element, or with included in a category of (V). Fig. 1 suggests that BMGs and HEAs component of solute elements ranging 5 to 35 at.%3). In general, are in the same class of materials under the same alloy design for BMGs are formed in multicomponent systems with three or more their development. elements, excepting for some of the binary BMGs, such as the ones Followed by the alloy designs for BMGs utilizing component in Cu-Zr system6). On the other hand, in general HEAs are alloys rules, Takeuchi and Inoue12) have tried to extend them to composition with five or more elements. The BMGs and HEAs are family alloy rules by introducing the concept of compositional dependence of in that they have been produced by utilizing the same strategic alloy the factors mentioned above. Here, the composition rules aim to designs including the following factors: the number of elements predict the appropriate compositions for forming BMGs, together (N), atomic size mismatch (difference in atomic size), and heat with the alloy systems that can be selected by the component rules. 12) of mixing (mixing enthalpy, ΔHmix). Here, it should be noted that In reality, Takeuchi and Inoue computed ΔHmix and mismatch these three factors originate from early studies on MGs performed entropy normalized by Boltzmann constant (Sσ/kB) for ternary amorphous alloys. These results were the first statistical data obtained * Corresponding author, E-mail: [email protected] by calculating the thermodynamic and physical quantities from the

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Fig. 1 The relationships between the factors described in the three component rules and the resultant alloys. Reproduced with permission from Ref.11).

17) 18) Table 1 HE-BMGs found to date, critical diameter (dc) for forming glassy alloy . Furthermore, a Zr20Ti20Cu20Ni20Be20 and Ti16.7Zr16.7Hf16.7 phase and year published. 19) Cu16.7Ni16.7Be16.7 alloys have very recently been reported where

No HE-BMG dc/mm Year published Reference the latter exhibits critical diameter (dc) in the centimeter as well as 16) 13) Pd20Pt20Cu20Ni20P20 alloy . Furthermore, the authors have recently 1 Ti20Zr20Hf20Cu20Ni20 1.5 2002 15) 2 Zn20Ca20Sr20Yb20(Li0.55Mg0.45)20 3 2011 reported Fe25Co25Ni25(B, Si)25 alloys as the first ferromagnetic HE- 16) 3 Pd20Pt20Cu20Ni20P20 10 2011 BMGs under a definition of HEAs regarding the concentration of 2 17) 3) 4 Sr20Ca20Yb20Mg20Zn20 2 × 5 mm * 2011 the solute elements ranging 5 to 35 at.% . 17) 5 Sr20Ca20Yb20Mg20Zn10Cu10 5 2011 17) Table 1 implies that some of the HE-BMGs possess prototypical 6 Er20Tb20Dy20Ni20Al20 2 2011 18) BMGs. For instance, the Pd20Pt20Cu20Ni20P20 HE-BMG originates 7 Zr20Ti20Cu20Ni20Be20 3 2013 20) 19) from a Pd40Ni40P20 BMG , whereas the Zr20Ti20Cu20Ni20Be20 8 Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7 15 2014 49) 9 Fe25Co25Ni25(B, Si)25 1.5 2015 HE-BMG has the same components and close composition to a 21) * sheet sample Zr41.2Ti9Cu12.5Ni10.0 Be22.5 BMG . In this sense, the HE-BMGs are not exactly the newly-created alloys independent of BMGs, factors computed as a function of composition of the multicomponent but rather modified ones for their compositions to meet the equi- systems. There still remains shortcoming in using this sort of atomicity in HE-BMGs. However, Sr-containing HE-BMGs listed approach for fining out new BMGs, but this approach has played an in Table 1 are the exceptions, and they are the original ones to important role as a prototype of the alloy design for BMGs when BMGs. In general, GFAs of the HE-BMGs are inferior to that considering that every criterion gives a necessary condition only. of BMGs, which is in part due to the fact that HE-BMGs are In addition to BMGs and HEAs, there exists another new type not optimized in composition due to the equi-atomic strategy. of BMGs with a compositional characteristic of HEAs. These new Furthermore, there are some peculiar discrepancies between the alloy are called as high-entropy bulk metallic glasses (HE-BMGs), HE-BMGs and BMGs for GFA parameters where the number which are the BMGs with exact or near equi-atomic compositions. of them reported to date are amounted to be 124), such as the

At present, several HE-BMGs have been found in sequence, reduced glass transition temperature (Tg/Tl) defined by glass 13) since the first report in 2002 in a Ti20Zr20Hf20Cu20Ni20 alloy . The transition temperature (Tg) normalized by liquidus temperature (Tl), representative HE-BMGs found to date are summarized in Table 1. supercooled liquid range (ΔTx) defined by the temperature interval

The Ti20Zr20Hf20Cu20Ni20 HE-BMG is the first one fabricated by between the crystallization temperature (Tx) and Tg, and dc. For 14) 16) referring to “confusion principle” proposed by Greer in 1993 , but instance, it was reported that the Pd20Pt20Cu20Ni20P20 HE-BMG 13) no description in HEA was written in the literature . After about exhibits the highest Tg/Tl of 0.71, but the resultant dc = 10 mm is 20) one decade, the subsequent HE-BMGs have suddenly been found smaller than the Pd40Ni40P20 BMG with dc = 25 mm. In addition, 15) in sequence in 2011 in a Zn20Ca20Sr20Yb20(Li0.55Mg0.45)20 alloy the equi-atomicity inherent to HE-BMGs disagrees to the presence 16) 4) and a Pd20Pt20Cu20Ni20P20 alloy , and Sr20Ca20Yb20Mg20Zn20 and of preference of GFA parameters , indicating that validity of the 15) Sr20Ca20Yb20Mg20Zn10Cu10 alloys , and an Er20Tb20Dy20Ni20Al20 GFA parameters depends on the principal elements. In other word,

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different GFA parameters were able to give a strong correlation for different alloy system. For instance, Zr-based BMGs have considerably weak correlations between dc and Tg/Tl, but Co-based BMGs exhibit good correlations4). At present, there are no effective solutions to explain these discrepancies between BMGs and HE- BMGs. However, the appearance of the HE-BMGs will contribute to understanding the nature of glass-transition that is inherent to MGs and BMGs in near future by performing fundamental researches step by step. This can be the significance of the HE- BMGs that appear historically after the BMGs and HEAs.

2 Alloy Designs for HEAs, BMGs and HE-BMGs Based on δ–ΔH diagram and VEC Analysis mix 23) Fig. 2 (a) The δ–ΔHmix diagram , in which disordered and ordered HEAs By nature, alloy designs should literally be used for predicting are plotted in the trapezoid shaped zones S and S', respectively, and the unprecedentedly new alloys, but they are occasionally used for BMGs are in zone B (B1 for the conventional and B2 for the Cu- and evaluating the features of the alloys of interest found to date by Mg-based BMGs). The plots of YGdTbDyLu and GdTbDyTmLu alloys are also shown for comparison. (b) An insert of the δ–ΔHmix utilizing statistical analysis. In practice, the prediction of HEAs diagram magnified near the origin. advances to those of BMGs as well as MGs and HE-BMGs, since the equi-atomicity inherent to HEAs greatly helps to decide the composition of the candidates. The component rules mentioned literature24). In short, it is understood that HEAs have values of δ in Section 1 have an ability to provide candidates for BMGs in and ΔHmix nearly zero, since they tend to be plotted near origin in terms of alloy components (alloy systems), but no information is the δ–ΔHmix diagram. The resultant values of δ and ΔHmix of HEAs available for compositions. This can be regarded as shortcoming are considerably smaller in their magnitude than those of BMGs of the component rules, and thus, one has no way, but do searching plotted in the δ–ΔHmix diagram (zone B1) with a shape of ellipsoid . –1 alloy compositions for forming BMGs by trial and errors by with δ ranging 5–19 and ΔHmix in the range of –25 to –37 kJ mol , . –1 referring to supplemental data from phase diagrams and so forth. with its center at δ ~ 12 and ΔHmix ~ –31 kJ mol . This indicates In short, the alloy searching for BMGs is considerably difficult that HEAs are formed into solid solutions by keeping their best by nature because of the lacks of necessary information, although atomic size differences to hold simple crystalline structures, such some reports claim that BMGs can be predicted pinpoint for a as fcc and bcc. However, there still remains uncertainty about certain alloy system6,22). At least, it can be regarded that there exists the types of structures of HEAs. The experimental data revealed no effective alloy design for BMGs to predict completely new alloy that the HEAs with fcc, bcc or their mixture phases appear for a compositions. Thus, the following introduces the current status of certain case and those with other phases appear for the other cases. the alloy design for HEAs mainly. For instance, Cantor et al.25) examined the formation of single A successful result has been reported23) as an alloy design for solid solutions for several multicomponent equi-atomic alloys HEAs based on the statistical analysis based on Delta parameter (δ) mainly composed of late transition metals, resulting in finding 23) and ΔHmix. The diagram provided is a δ–ΔHmix diagram , in which an Fe20Cr20Mn20Ni20Co20 HEA only formed into a single fcc solid disordered and ordered HEAs are plotted in the trapezoid shaped solution. A similar select-ability of the constituent elements for zones S and S', respectively. In the δ–ΔHmix diagram, the BMGs are forming solid solution also takes place for HE-BMGs, although also plotted in Zones B (B1 for the conventional and B2 for the Cu- they are solidified into a non-equilibrium state. For instance, the 16) and Mg-based BMGs). Fig. 2 demonstrates the δ–ΔHmix diagram, Pd20Pt20Cu20Ni20P20 HE-BMG is obtained from the alloy series together with the plots of the HEAs with hcp structures that will denoted by Pd20Pt20TM120TM220P20 as a case TM1 = Cu and TM2 = be explained in the next Section. The δ–ΔHmix diagram is the Ni, but the other combinations of TM1 and TM2 resulted into most successful diagram for alloy designing HEAs and it clearly forming crystalline phases only as shown in Fig. 3. indicates that the roles of the atomic differences denoted by the The δ–ΔHmix diagram cannot deal with crystallization structures value of parameter δ and the magnitude of ΔHmix are considerably of HEAs, but they are rather well-summarized based on the analysis 26) smaller than those of the BMGs. The δ–ΔHmix diagram originates of VEC (valence electron concentration) : VEC < 6.87 (bcc), 12) from ΔHmix–Sσ/kB diagram , which has been proposed to 6.87 ≤ VEC < 8.0 (bcc + fcc) and 8 ≤ VEC (fcc) where it should be summarize the characteristics of BMGs for ΔHmix and the effect noted that Al is regarded as VEC = 3 as a constituent element. An of atomic size differences. The relationships between the δ–ΔHmix explanation of VEC(Al) = 3 results from empirical data that Al is 27) and ΔHmix–Sσ/kB diagrams were reported in the authors’ previous a bcc former in the HEAs. For instance, AlxCoCrCuFeNi HEAs

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Fig. 3 XRD profiles of Pd20Pt20TM120TM220P20 cylindrical alloys cast into diameters of 3 and 5 mm46).

Fig. 4 XRD patterns of the YGdTbDyLu and GdTbDyTmLu HEAs with exhibits interesting features in terms of their phase transitions hcp structure. Reproduced with permission from Ref.28). in that phases of their HEAs change from bcc, bcc + fcc and fcc with decreasing Al content. The authors’ recent report regarding the HEAs with hcp structure28) firstly defined the VEC for hcp alloys with N ≥ 5 had not been reported until 2013. This situation structure as 3, which is the supplemental data to the results of VEC was broken by the first report shown in Fig. 4 by Takeuchi et mentioned above for HEAs with fcc and bcc structures. al.28) for YGdTbDyLu and GdTbDyTmLu alloys comprising heavy-lanthanide elements mainly, followed by Feuerbacher et 3 HEAs with HCP Structure al. for a HoDyYGdTb alloy31). It should be noted that the success It has long been a mystery that HEAs with hcp structure was in forming HEAs with hcp structure for the YGdTbDyLu and not reported until recent year. Needless to say, there were some GdTbDyTmLu alloys has been achieved by procedures from reports about the formation of hcp structure for the equi-atomic computational selections of candidates in a statistical process, alloys, such as a ternary OsReRu29) and a quinary MoRuRhPd30) followed by the careful examinations of the constituent binary alloys. However, the HEAs with hcp structure for equi-atomic phase diagrams shown in Fig. 5. The former statistical process

Fig. 5 Binary phase diagrams47) of constituent elements from Gd-Tb-Dy-Tm-Lu and Y-Gd-Tb-Dy-Lu alloys. Reproduced with permission from Ref.33).

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has been proposed initially as the alloy design for BMGs32) by but they again provide predictions only and no experimental data utilizing the relationships of forward- and reverse-mappings in the are accompanied by the theoretical and computational data. In 38) following two physical spaces: alloy compositions and ΔHmix–Sσ/kB strong contrast, the authors have very recently reported that diagrams. The supplemental explanations of this procedure are a ScYLaTiZrHf alloy can be formed into a dual hcp structures also given in literature33). The actual procedure performed was (Fig. 6). The ScYLaTiZrHf alloy with dual hcp structure is significant as follows. First, the candidates were selected from 73 elements in that main constituent elements are from transition metals that cannot that can be dealt with Miedema’s model34) for the quinary equi- be achieved by the YGdTbDyLu, GdTbDyTmLu and HoDyYGdTb atomic alloys. The total number of the initial candidates were HEAs. However, the ScYLaTiZrHf alloy can be regarded as a amounted to be over 15 million (15020334) that is the number of multi-principal-element alloy instead of a HEA due to the difference the combinations taken 5 from 73 at the same time (73C5). Then, in chemical compositions between the immiscible phases from secondary candidates were squeezed form 73C5 by focusing on the the alloy composition considerably. As described in this Section, alloys with δ and ΔHmix that are plotted in zone S in the δ–ΔHmix it appears that there are some room for improving the selections (Fig. 2). In secondary selection, the authors utilized the authors’ of constituents elements for the achievement of HEAs with hcp 35) previous data of ΔHmix’s computed for 2628 (73C2) atomic pairs structures. from 73 elements. The total number of the candidates decreased from 73C5 to 28405 as a result of the secondary selection. Then, 4 Alloy Designs for HEAs Utilizing Crystallographic Data the listing up the 28405 candidates helped to find out a tendency Acquired from Pettifor Map, Pearson’s Crystal Data that lanthanide elements were included in the list. Subsequently, and Binary Phase Diagrams the authors paid especial attention to the allotropic transformations The authors have recently reported a new alloy designs for from bcc to hcp structures with decreasing temperature inherent HEAs by utilizing crystallographic data acquired from Pettifor to lanthanide elements and IVA transition metals (Ti, Zr and map39) and Pearson’s Crystal Data40). A significance of these alloy Hf). The significant aspect is finding out the constituent binary designs is that crystallographic data of structure of stoichiometries systems that have a narrow temperature range of bcc structure to of alloys are used instead of those of the pure elements for the exist at higher temperatures. Fig. 5 indicates that at A50B50 at.% development of HEAs. This is an extension of the concept of HEAs composition, all the constituent binary systems from the Gd-Tb- in terms of equi-atomicity to equi-mole. Specifically, recent results 41) Dy-Tm-Lu and Y-Gd-Tb-Dy-Lu systems exhibit bcc phase stable in the report indicate that a Cu2Ag2GdTbDyY HEA with a CsCl only a temperature range ~ 100 or smaller or absence where the structure has been designed from constituent binary alloys with absence indicates the direct solidification from liquid (L) to hcp, the CsCl structures. In an actual alloy design, crystallographic data 39) as represented by Fig. 5 (d) in Gd-Lu system at Gd50Lu50 at.%. The summarized as Pettifor map with binary stoichiometry of 1:1 were findings of HEAs with hcp structure are separately predicted by utilized for selecting candidate by computations. In this selecting Zhang et al.36) for lanthanide elements before the reports mentioned the candidates, the Pearson’s Crystal Data40) was also utilized as above, but predictions do not refer to the heavy lanthanide elements supplemental data to compensate for the lacks of the information in in details. After the first report on HEAs with hcp structure, the Pettifor map. An advantageous aspect of these alloy designs for further predictions on HEAs with hcp structure are given by Gao HEAs is to focus on the majority of the crystallographic structure et al. through computational approach based on CALPHAD37), of interest in the constituent binary alloys while the others are

Fig. 6 Element mappings by EDX of the ScYLaTiZrHf alloy with dual hcp structure38) where (Y,La) and (Ti,Zr,Hf) tend to immiscible with Sc homogeneously distributed in both phases. Reproduced with permission from Ref.38).

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Table 2 Crystallographic information of the constituent binary equi-atomic compositions from Pettifor map with 1:1 stoichiometry for the representative quinary and senary HEAs. The data of AgDyGdTbY and CuDyGdTbY alloys are also shown for comparison. The symbols “X”, “\” and “/” indicate the absence of compounds, which were acquired from literature39) regarding Pettifor map.

Str. A B C D E F AB AC AD AE AF BC BD BE BF CD CE CF DE DF EF Ref.

dual 38) ScYLaTiZrHf hcp Ti Zr Hf Sc Y La NbTaTiZrHf bcc Ti Zr Hf Nb Ta 42)

HfNbTiVZr bcc Hf Nb Ti V Zr rQ 43)

MoNbTaVW bcc Mo Nb Ta V W 44)

CoCrFeMnNi fcc Co Cr Fe Mn Ni w4 rv p3 p3 25,45)

DyGdLuTbTm hcp Dy Gd Lu Tb Tm 28)

DyGdLuTbY hcp Dy Gd Lu Tb Y 28)] w4 CuDyGdTbY Mix Cu Dy Gd Tb Y w4 w4 w4 41) kU AgDyGdTbY — Ag Dy Gd Tb Y w4 w4 w4 w4 41)

rv (three-environment type): Cr3Si structure, Cr3S,cP8 Pm3n (223), Frank-Kasper phase p3 (single-environment type): AuCu structure, CuAu, tP2, P4/mmm (123) rQ (two-environment type) TiNi2 structure, Ti2Ni, cF96, Fd 3m O2 (227) kU (two-environment type) BFe structure, FeB-b, oP8, Pnma (62)

Fig. 7 Relationships among the constituent binary alloys. (a) Graph exhibiting the presence of complete bcc solid solution (Edge I: single-layered thick solid line) and bcc as well as hcp complete solid solutions (Edge II: bi-layered thick solid line), while the thin broken and dotted lines indicate −1 the immiscible relationships (Edges III and IV). The values on the edges are the mixing enthalpy (ΔHmix) of liquid phase in the unit of kJ·mol at equi-atomic binary alloy, whereas those at the vertices near the atomic symbols correspond to the atomic radius48). (b–p) Constituent binary phase diagrams47). In Fig. 7 (c) for Y–La binary system47), La is considered to possess a hcp structure, but in reality it exhibits double hcp structure with ABAC ... sequence compared to regular hcp (ABAB ...). Reproduced with permission from Ref.38). ideally the cases without specific structures due to the presence leads to the crystallographic structure of the alloy affected by that 41) of complete solid solutions . Table 2 provides examples of the from the pure elements. In another case of the Cu2Ag2GdTbDyY above mentioned strategy for HEAs25,28,38,41-45), indicating that the HEA41), the CsCl structure is major in the constituent binary alloys, ScYLaTiZrHf38) and NbTaTiZrHf42) equi-atomic alloys do not leading to the CsCl structure when alloyed. On the other hand, the possess any 1:1 compounds in the constituent binary systems. This CoCrFeMnNi HEA with fcc structure possesses the mixture of

「粉体および粉末冶金」第 63 巻第 4 号 Recent Progress in Alloy Designs for High-Entropy Crystalline and Glassy Alloys 215

intermetallic compounds at 1:1 binary constituent alloys, which 5) B. S. Murty, J.-W. Yeh, R. S.: High-Entropy Alloys, may act as a confusion principle14). The absence of 1:1 intermetallic Butterworth-Heinemann (2014). compounds in the constituent binary systems for the ScYLaTiZrHf 6) D. Wang, Y. Li, B. B. Sun, M. L. Sui, K. Lu, E. Ma: “Bulk alloy can be confirmed by Fig. 7. The significance of the Pettifor metallic glass formation in the binary Cu-Zr system”, Appl map for utilizing it as alloy design is that the crystallographic Phys Lett, 84 (2004) 4029-4031. data are summarized into symbols, which in turn, can be easily 7) H. S. Chen: “Glassy Metals”, Reports on Progress in Physics, to be deal with computationally. As described in this Section, it is 43 (1980) 353-432. expected that HEAs and other relevant alloys can be designed by 8) T. Egami, Y. Waseda: “Atomic Size Effect on the Formability utilizing the features of lacks of intermetallic compounds at A50B50 of Metallic Glasses”, J Non-Cryst Solids, 64 (1984) 113-134. by referring to Pettifor map computationally. Thus, Pettifor map, 9) C. S. Kiminami, R. D. S. Lisboa, M. F. de Oliveira, C. Bolfarini, Pearson’s crystal data and binary phase diagrams are the powerful W. J. Botta: “Topological instability as a criterion for design tool for the further development of HEAs. and selection of easy glass-former compositions in Cu-Zr based systems”, Mater Trans, 48 (2007) 1739-1742. 5 Summary 10) A. Inoue: “Stabilization of metallic supercooled liquid and Alloy designs for high-entropy crystalline and glassy alloys bulk amorphous alloys”, Acta Mater, 48 (2000) 279-306. based on atomic size differences and mixing enthalpy have been 11) A. Inoue, A. Takeuchi: “Bulk Nonequilibrium Alloys by used as the guiding principle with demonstrating the features Stabilization of Supercooled Liquid: Fabrication and Functional of HEAs in the form of δ–ΔHmix diagram. The lacks of the Properties”, Proceedings of 3rd International Symposium on crystallographic features of HEAs can be supplemented in valence Slow Dynamicsin Complex Systems, (2004) 547-558. electron concentrations. The finding of HE-BMGs with enough 12) A. Takeuchi, A. Inoue: “Calculations of mixing enthalpy and glass-forming ability and critical diameters in the centimeter, mismatch entropy for ternary amorphous alloys”, Mater T such as Pd20Pt20Cu20Ni20P20 and Ti16.7Zr16.7Hf16.7Cu16.7Ni16.7Be16.7, Jim, 41 (2000) 1372-1378. will bridge the HEAs and BMGs for their future researches. It is 13) L. Q. Ma, L. M. Wang, T. Zhang, A. Inoue: “Bulk glass expected that HEAs with hcp structure contribute to solving the formation of Ti-Zr-Hf-Cu-M (M = Fe, Co, Ni) alloys”, Mater uncertainties of the formations of solid solution in HEAs. It is also Trans, 43 (2002) 277-280. anticipated that recent alloy designs by utilizing Pettifor map and 14) A. L. Greer: “Materials Science - Confusion by Design”, Pearson’s Crystal Data combined with constituent binary phase Nature, 366 (1993) 303-304. diagrams have ability to finding out new types of HEAs. 15) K. Zhao, X. X. Xia, H. Y. Bai, D. Q. Zhao, W. H. Wang: “Room temperature homogeneous flow in a bulk metallic glass with Acknowledgement low glass transition temperature”, Appl Phys Lett, 98 (2011) The researches were performed by a Grant-in-Aid for Scientific 141913. Research from the Japan Society for the Promotion of Science 16) A. Takeuchi, N. Chen, T. Wada, Y. Yokoyama, H. Kato, A.

(JSPS): Grant Program of Scientific Research (B) with program Inoue, J. W. Yeh: “Pd20Pt20Cu20Ni20P20 high-entropy alloy as a title of “Fabrication of High-Entropy Bulk Metallic Glasses based bulk metallic glass in the centimeter”, Intermetallics, 19 (2011) on Confusion Principle, Clarification of their Properties and their 1546-1554. Application” (grant number 24360284). 17) X. Q. Gao, K. Zhao, H. B. Ke, D. W. Ding, W. H. Wang, H. Y. Bai: “High mixing entropy bulk metallic glasses”, J Non- References Cryst Solids, 357 (2011) 3557-3560.

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