Microstructure and solidification behavior of multicomponent CoCrCuxFeMoNi high-entropy alloys

Author’s Accepted Manuscript Microstructure and solidification Behavior of Multicomponent CoCrCuxFeMoNi High-entropy Alloys P.H. Wu, N. Liu, W. Yang, Z.X. Zhu, Y.P. Lu, X.J. Wang www.elsevier.com/locate/msea

PII: DOI: Reference:

S0921-5093(15)30114-3 http://dx.doi.org/10.1016/j.msea.2015.06.061 MSA32499

To appear in: Materials Science & Engineering A Received date: 13 February 2015 Revised date: 11 June 2015 Accepted date: 21 June 2015 Cite this article as: P.H. Wu, N. Liu, W. Yang, Z.X. Zhu, Y.P. Lu and X.J. Wang, Microstructure and solidification Behavior of Multicomponent CoCrCuxFeMoNi High-entropy Alloys, Materials Science & Engineering A, http://dx.doi.org/10.1016/j.msea.2015.06.061 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Microstructure and Solidification Behavior of Multicomponent CoCrCuxFeMoNi High-entropy Alloys P.H. Wu1, N. Liu1*, W. Yang2, Z. X. Zhu1, Y.P. Lu3 X.J. Wang1 1.School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu, 212003, China 2. School of Aeronautical Manufacturing Engineering, Nanchang Hangkong University, Nanchang, Jiangxi 330063, China 3. School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China Abstract: (Fe, Co, Ni) rich dendrites nucleate primarily in CoCrFeMoNi and CoCrCu0.1FeMoNi alloys, followed by peritetic and eutectic reactions. The quasi-peritectic reaction occurs between the primary Mo-rich dendrites and liquids in the CoCrCu0.3FeMoNi melts, and transfers to a eutectic coupled-growth at the edge of the quasi-peritectic structure. Subsequently, eutectic reaction happens in the remnant liquids. Liquid-phase separations have occurred in CoCrCuxFeMoNi alloys when x≥0.5. Meanwhile, some nanoscale precipitates are obtained in the Cu-rich region. Two crystal structures, FCC and BCC, are identified in CoCrCuxFeMoNi high entropy alloys. Amazingly, a pretty high plastic strain (51.6 %) is achieved in CoCrCu0.1FeMoNi alloy when the compressive strength reaches to 3012Mpa. With the increase of Cu content, atomic size difference (ΔR) and electro-negativity difference (ΔX) decrease while valence electron concentration (VEC), mixing enthalpy (ΔH) and mixing entropy (ΔS) increase. Consequently, the valence electron concentration (VEC) values range for the formation of mixture of FCC and BCC structures can be enlarged to 6.87~8.35 based on the study of this paper. It is the positive enthalpies of mixing that causes the liquid-phase separation in CoCrCuxFeMoNi high entropy alloys. Keywords: high-entropy alloy; quasi-peritectic reaction; eutectic reaction; liquid-phase separation; mechanical properties

1. Introduction *

Corresponding author, Tel.: +86-511-84426291 fax: +86-511-84407381 E-mail address：[email protected] (N. Liu) 1

Recently, high entropy alloys

[1]

, or multi-component alloys

[2,3]

with

equiatomic or close-to-equiatomic composition, have become one of the research frontiers in the domain of materials science. High entropy alloys demonstrate excellent properties [4-9], and can be one kind of excellent high-temperature materials, or a coating material with different properties. Among the reported systems, AlCoCrCuFeNi alloys have been investigated extensively, which showed different microstructure and properties

[1, 6, 8-11]

. As Al content increases, the constituent phases

change from FCC at x=0.5 to BCC at x=2.8[6]. Previous researches showed that, Cu element has a tendency to segregate at the grain boundary and is helpful to improve the ductility of high entropy alloys [2,8]. Therefore, Cu may be one of beneficial elements for the plasticity of high entropy alloy. Mo element has been added in AlCoCrFeNi and AlCoCrCuFeNi alloys to improve mechanical properties and the formation of complex structures [12-15]

. A body-centered tetragonal structural σ phase, which is similar to

the crystal structure of the binary intermediate phase CoCr, has been found in AlCoCrFeMo0.5Ni alloy

[13]

.

The alloy strength has been

improved significantly due to the addition of Mo, while the ductility decreases at the same time

[12]

. Additionally, eutectic high-entropy alloys

(EHEAS) have attracted interests in recent years. Lu et al

[16]

have

proposed an idea of EHEAS and designed an AlCoCrFeNi2.1 EHEAS, which 2

shows an unprecedented combination of high tensile ductility and high fracture strength at room temperature. Besides, sunflower-like eutectic colony structure has also been observed in a near-eutectic Al2CrCuFeNi2 high entropy alloy [17]. As mentioned above, microstructures and properties of high-entropy alloys have gained wide interests previously. However, no much attention has been focused on the microstructure formation process of high-entropy alloys. It is known that the solidification process decides the microstructure formation and properties of alloys. So, CoCrCuxFeMoNi system alloys, with different Cu content, have been prepared to study the formation of as-solidified microstructure in this work. Moreover, mixing enthalpy (ΔH), mixing entropy (ΔS), atomic size difference (ΔR), electro-negativity difference (ΔX) and valence electron concentration (VEC) have been calculated to investigate the phase formation in the CoCrCuxFeMoNi alloys. Additionally, the phase constitution and properties of the alloys have also been studied. 2. Experimental procedures By using vacuum arc-melting, CoCrCuxFeMoNi high-entropy alloys with various Cu contents (x=0.1~1.0 in molar ratio) were prepared, a mixture of constituent elements with purity higher than 99.9 wt% in an Ar atmosphere. The materials were melted for at least 3 times to ensure the homogeneity of the melting. The microstructures of the alloys were 3

examined by using scanning electron microscope (SEM, JEOL-5410), equipped with X-ray energy dispersive spectrometry (EDS). The phase constitutions of the alloys were identified by using an X-ray diffractometer (XRD, Rigaku ME510-FM2) at a scanning speed of 6°/min and a scanning range from 30°to 80° by using a copper target with the applied voltage and current of 30KV and 20mA respectively. The thermal behaviors of the alloys were analyzed by a high temperature differential scanning calorimeter (DSC Netzsch STA449F3) in an argon atmosphere at a heating rate of 20K/s. For the compressive test, the samples with diameter of 5mm and length of 10mm were prepared. Room temperature compressive properties were tested on an UTM5205X testing machine with a loading speed of 2mm/min. 3. Results and analyses 3.1 microstructures and solidification process of CoCrCuxFeMoNi alloys 3.1.1 CoCrFeMoNi alloy For Cu free CoCrFeMoNi alloy, a simple structure composed of dendrites and inter-dendrites is observed, Fig.1a and 1b. According to EDS (Table 1), Fe、Co and Ni are rich in the dendrite spines, and Mo segregates into the inter-dendrite region. Especially, lamellar structures, detected to be rich in Cr and Mo, are found in the inter-dendrite region. Based on the Mo-Ni-Cr [18] and Mo-Fe-Cr

[19]

ternary phase diagrams,

peritectic reactions occur at 1460 ℃ and 1455 ℃, and eutectic reaction 4

occurs at 1275 ℃

and 1345℃ respectively. Combined with the

as-solidified microstructure, it can be deduced that peritectic reaction is likely to take place in this multi-component CoCrFeMoNi alloy. Primarily, (Fe, Co, Ni) rich dendritic phase nucleates from the melt, and peritectic reaction occurs to form a Mo-rich solid-solution phase. Subsequently, the remnant liquids solidify to form Mo-rich eutectic lamellar structure. 3.1.2 CoCrCu0.1FeMoNi alloy Fig.1c and 1d show the microstructures of CoCrCu0.1FeMoNi alloy. Dendrites rich in Co、Fe and Ni elements are obtained, and the peritectic phase exists at the edge of the primary dendrites. With the addition of Cu element, the volume fraction of Mo-rich eutectic structures increases in the inter-dendrite region. According to the as-solidified microstructure, the solidification process can be explained as follows, the (Fe, Co, Ni) rich dendritic phases nucleate from the melt firstly, and then peritectic reaction takes place, which is replaced by eutectic reaction immediately after a peritectic margin was formed. 3.1.3 CoCrCu0.3FeMoNi alloy Interestingly, three different types of microstructures can be observed in CoCrCu0.3FeMoNi alloy, Fig.1e and 1f. Where zone Q is likely to be the quasi-peritectic microstructure; zone FE means the first eutectic structure, and zone SE refers to the second eutectic structure. With an equation of L + α = β + γ, quasi-peritectic reaction occurs in both Mo-Ni-Cr and 5

Mo-Fe-Cr ternary alloys

[18,

19]

. Therefore, in the investigated

CoCrCuFeMoNi multi-component system, quasi-peritectic reaction probably occurs at certain proper alloy content range. Until now, the solidification process of CoCrCu0.3FeMoNi alloy can be deduced. Originally, Mo-rich phase, white claviform in the region Q, nucleates from the melt, and quasi-peritectic reaction occurs to produce a strip-shaped quasi-peritectic structure, consisting of (Co, Fe, Ni) rich phase and another Mo-rich phase. For the slow diffusion of solute atoms, the quasi-peritectic reaction cannot proceed completely, and is replaced by extended eutectic couple growth to form the island-like eutectic structure, which is defined as the first eutectic microstructure (FE in Fig.1f). Consequently, parts of the primary Mo-rich phases are reserved in the final microstructure. Later, eutectic reaction occurs in the residual liquids, to form a fine layer eutectic structure, which is named as the second eutectic microstructure (SE in Fig.1f). Compared with CoCrCu0.1FeMoNi alloy, the primary phase changes to Mo-rich phase. It indicates that the Cu content of the eutectic point in the alloys system is between x=0.1 and x=0.3. 3.1.4 CoCrCu0.5FeMoNi alloy Surprisingly, some spherical structures, with an average diameter of 173.72 μm, emerge in the microstructure of CoCrCu0.5FeMoNi alloy, in which some white feather-like structures can be observed. Respectively，the matrix of the 6

spheres and feather-like structures are rich in Cu and Cr. The emergence of Cu-rich spheres indicates the occurrence of liquid-phase separation before solidification of CoCrCu0.5FeMoNi alloy, i.e., the original liquids separate into two liquids with different component, Cu-rich and Cu-depleted. Generally, the minor liquid phase nucleates and droplets form before the occurrence of the liquid-solid transformation. Liquid-phase separation occurs in such alloy systems as Mo-Fe-Cu, Cr-Fe-Cu and Cr-Mo-Cu [20-22] according to ternary phase diagrams. As listed in Table 3

[23]

, the mixing enthalpies of Cu and the other

four elements (Co, Cr, Fe and Mo) are large positive, so Cu element is rejected by Co, Cr, Fe and Mo elements in the dendrite during solidification process. It is investigated that the occurrence of phase separation is related to the mixing enthalpies of the alloy system. If a mixed liquid is cooled below the spinodal temperature, the concentration fluctuation is intensified and the decomposition of the mixed liquid into two liquids occurs by nucleation and growth [24]. In the meantime, feather-like structures (labeled as Q) and eutectic structures

(labeled

as

E)

are

found

in

the

microstructures

of

CoCrCu0.5FeMoNi alloy, (see Fig.2). According to EDS, region B of feather-like eutectic structure is Mo-rich phase, in which Mo content reaches 40.22at.%, region A are rich in Co, Cu, Fe and Ni element, while lamellar eutectic structure (region C in Fig.2c) is rich in Cr and Mo element. Feather-like eutectic structure is considered to be the product of the quasi-peritectic 7

reaction. Like the stalk of a feather, primary Mo-rich phase is retained in the final microstructure. Meanwhile, region B shows a bit faceted character in the coupled-growth of eutectic microstructure. 3.1.5 CoCrCu0.8FeMoNi alloy More spheres are found in the microstructure of CoCrCu0.8FeMoNi alloy, as shown in Fig.3, and the average diameter of the spheres increases as well. Before the liquid-solid phase transformation, many Cu-rich liquid phases emerge in the original liquids of CoCrCu0.8FeMoNi alloy. To decrease the interface energies between the two liquid phases, the Cu-rich liquid phase takes a spherical shape. Then, the two separated liquid phases, Cu-depleted (L1) and Cu-rich (L2), solidify respectively. Similar to the microstructure of CoCrCu0.5FeMoNi alloy, both quasi-peritectic and eutectic structures are obtained in the Cu-depleted region except for the Cu-rich spherical structures. Moreover, many Cu-rich nano-granular precipitates are obtained at the center of Cu-rich spheres (Fig. 3c). 3.1.6 equal molar ratio CoCrCuFeMoNi alloy As shown in Fig.4a, a (Fe, Co, Ni)-rich transition border can be found between the Cu-rich spheres and the Cu-deplete region in CoCrCuFeMoNi alloy. Some white Cr-rich feather-like structures, as well as many Cu-rich nano-scale granules emerge in the matrix of the spheres, Fig.4c. Additionally, petals-shaped dendrites can be observed in some region of the spheres (Fig.4d), which are rich in Co, Fe and Ni elements according to EDS. Similarly, 8

liquid-phase separation occurs in the original melt of CoCrCuFeMoNi alloy before the liquid-solid transformation. With higher melting temperature, the Cu-deplete

liquids

solidify

firstly,

and

similar

microstructures

as

CoCrCu0.3FeMoNi alloy are obtained. While for the Cu-rich liquids, (Co, Fe, Ni)-rich dendrites crystallize and grow in the Cu-rich droplets at the beginning of the liquid-solid transformation. As results, Cr element is rich in the remnant Cu-rich liquids, and it leads to the formation of Cr-rich phase in the Cu-rich region. After that, the remnant liquids solidify to form Cu-rich supersaturated solid solution, and then the superfluous Cu element segregates from the Cu-rich matrix with nano-size during the following cooling process. 3.2 DSC analyses The DSC thermograms showing the heat flow evolution during the heating, melting and cooling process of the alloys are shown in Fig.5. For Cu free alloy, Fig.5a, the first peak in the heating curve corresponds to the melting of eutectic structure, the second and third peaks are associated with the melting of peritectic phase and primary dendrite, respectively. Obviously, two exothermic peaks are observed in the cooling curve, which attribute to the nucleation of primary dendrite and the peritectic reaction. For the small amount of the remnant liquid, there is no apparent exothermic peak indicative of eutectic reaction. According to the DSC curves, Fig.5b, the melting point for CoCrCu0.1FeMoNi alloy is 1625K, the 9

first peak at 1617K during the cooling process is based on the crystallization of the primary dendrite phase, and the second peak at 1573K corresponds to the occurrence of eutectic reaction. There is no peak for the formation of the peritectic phase, which can be ascribed as the little amount of the peritectic phase. As shown in Fig.5c, the first peak at 1589K in the cooling curve of CoCrCu0.3FeMoNi alloy is associated with the formation of the primary dendrite phase, followed by an exothermic peak at 1579K relating to the quasi-peritectic reaction, and there is a larger peak corresponding to the eutectic growth can be observed at 1568K. After that, a smaller event at 1549K attributes to the solidification of remnant liquids. For CoCrCu0.5FeMoNi alloy, Fig.5d, a small exothermic peak at 1618K corresponds to the solidification of primary phase. An obvious peak (1578K) can be observed in the cooling curve, relating to the quasi-peritectic and eutectic reaction in the Cu-depleted liquid phase. But there is no exothermic peak for the solidification of the Cu-rich liquids; it is probably owing to the fact that the volume of the Cu-rich liquids in CoCrCu0.5FeMoNi alloy is too low to show an exothermic peak in the cooling curve. As shown in Figures 5e and 5f, two exothermic peaks at 1580K and 1623K in the curves of the CoCrCu0.8FeMoNi and CoCrCuFeMoNi alloys, are related to the crystallization of the primary dendrite phase in the Cu-depleted liquids. Followed that, the exothermic peaks at 1575K are associated with the quasi-peritectic and eutectic 10

reactions. Respectively, a small endothermic peak can be found in the heating curves of CoCrCu0.5FeMoNi, CoCrCu0.8FeMoNi and CoCrCuFeMoNi alloys at about 1393K, corresponding to the melting of Cu-rich L2 phase. The heat flow data have proved the inference on the solidification process of the investigated alloys. 3.3 Constitute phase and properties of CoCrCuxFeMoNi alloys The crystal structures of CoCrCuxFeMoNi alloys consist of FCC and BCC phases, as shown by XRD patterns in Fig.6. When x≤0.3, FCC1 is similar to that of Ni-Cr-Co-Mo phase with space group of Fm3m (a=b=c=3.608A ̊), while BCC is a Mo-rich phase with space group of I-43m (a=b=c=8.90A ̊). For CoCrCuxFeMoNi (x≥0.5) alloys, another FCC2 Cu-rich phase is detected, with space group of Fm3m and lattice constants of a=b=c=3.615A ̊, which corresponds to the Cu-rich spheres in the microstructure. Different to AlCoCrFeMo0.5Ni alloy system

[12, 13]

, the

multi-element intermediate σ phase has not been found in CoCrCuxFeMoNi alloys. The room-temperature compressive stress-strain curves of as-cast CoCrCuxFeMoNi alloys are plotted in Fig.7. It is shown that the alloy strength is improved at the beginning with the increase of Cu, but then decreases. The largest strength is achieved at CoCrCu0.1FeMoNi alloy, and the alloy strength decreases when x≥0.3. For the alloy ductility, the smallest ductility is obtained at CoCrCu0.3FeMoNi alloy, while the largest 11

one

is

achieved

in

CoCrCu0.1FeMoNi

alloy.

The

ductility

of

CoCrCu0.1FeMoNi alloy is almost 6.5 times to that of CoCrCu0.3FeMoNi alloy. It can be found that, for alloys with higher strength and ductility, the primary phase is FCC solid solution; while for alloys with lower strength and ductility, their primary phase is BCC solid solution. Moreover, the occurrence of liquid-phase separation before solidification can moderate the unfavorable effect of primary BCC at certain degree, and improve the ductility a little. CoCrCu0.1FeMoNi alloy possesses the largest strength (3012Mpa) and ductility (51.6%) simultaneously. It indicates that, to achieve the optimal strength and ductility combination, the microstructure consists of primary FCC dendrite phase, peritectic and eutectic structures. 4. Discussion According to the methods reported by Guo [25] and Zhang et al

[26,27]

,

such parameters as ΔH, ΔS, ΔR, ΔX and VEC can be calculated to predict the phase formation in high entropy alloys. Recently, a new parameter of atomic-size difference has been put forward by Wang et al

[28]

to

determine the solubility of multi-component alloys. Moreover, the effects of electro-negativity on the stability of topologically close-packed phase in high entropy alloys have been studied [29]. In order to form sole simple phases and their mixtures, the following condition have to be satisfied simultaneously: -22 ≤ ΔHmix ≤7kJ/mol, 11 ≤ ΔSmix ≤ 12

19.5J/(K mol) and ΔR ≤8.5[26,27]. Based on Guo’s conclusion [25], FCC phase is stable at a high value of VEC (>8.0), while BCC phases tends to form when VEC < 6.87, and a value between 6.87 and 8.0 leads to the formation of the mixture of FCC and BCC phases. According to the physiochemical parameters listed in Table 3[21] and Table4[24], the forementioned parameters have been calculated and listed in Table 5(for x=0, 0.1, 0.3, 0.5, 0.8 and 1.0, the alloys are denoted as Cu0, Cu0.1, Cu0.3, Cu0.5, Cu0.8 and Cu1.0, respectively). With the increase of Cu content, ΔR and ΔX decrease while VEC, ΔH and ΔS increase. Especially, the values of ΔH are positive when x≥0.5. The decrease of ΔR (from 4.254 to 3.889) and ΔX (from 0.161 to 0.147) can stabilize solid solution. According to XRD, both FCC and BCC phases are obtained in CoCrCuxFeMoNi alloys, and the calculated values of VEC are between 7.8 and 8.35. It is not coincide with Guo’s conclusion, since VEC values of CoCrCuxFeMoNi alloys have not been calculated in Guo’s work. So the range for the formation of mixture of FCC and BCC phases can at least be enlarged to 6.87~8.35 presently, especially for alloys having a tendency of liquid-phase separation. Furthermore, liquid-phase separation occurs in CoCrCuxFeMoNi (x≥0.5) alloys when the mixing enthalpies are positive. It indicates that it is the positive mixing enthalpies that impel the liquid-phase separation before solidification of CoCrCuxFeMoNi alloys. Therefore, a modification should be put forward on the enthalpy of 13

mixing (ΔHmix) criterion, that is, for CoCrCuxFeMoNi alloys, liquid-phase separation will occur when ΔHmix>0. 5. Conclusions (1) (Fe, Co, Ni)-rich dendritic phase forms originally in CoCrFeMoNi and CoCrCu0.1FeMoNi alloys, and peritectic reaction and eutectic reaction take place

successively.

Quasi-peritectic

reaction

occurs

in

the

CoCrCu0.3FeMoNi melt between the primary Mo-rich dendrites and liquids, and is replaced by the extended eutectic couple growth to form the island-like eutectic structure. Later, the eutectic reaction takes place in the remnant liquids. Liquid-phase separation occurs in CoCrCuxFeMoNi (x≥0.5) alloys before liquid-solid transformation. The increase of Cu element can enhance the quasi-peritectic reaction and eutectic reaction, as well as the occurrence of liquid-phase separation in CoCrCuxFeMoNi alloys. (2) FCC and BCC solid solution structures are identified in CoCrCuxFeMoNi high entropy alloys. The maximum compressive strength and plastic strain, 3012Mpa and 51.6 %, are achieved in CoCrCu0.1FeMoNi alloy simultaneously. (3) ΔR and ΔX decrease, while VEC, ΔH and ΔS increase with the increase of Cu element in CoCrCuxFeMoNi alloys. The upper limit of the VEC qualification for the formation of a mixture of FCC and BCC phase can be enlarged to 8.35 according to the current work. Additionally, the ΔHmix 14

criterion should be amended, i.e., liquid-phase separation can occur before solidification of CoCrCuxFeMoNi alloys when ΔHmix>0. Acknowledgements This work is supported by The National Natural Science Foundation of China Grant Nos. 51201072 and 51461032, and Qinglan Project of Jiangsu Provence. P.H. Wu is grateful to the financial support of Graduate Student Innovation Projects of Jiangsu University of Science and Technology (YSJ14S-15). The authors are grateful to the financial support of the Priority Academic Program Development of Jiangsu Higher Education Institutions. The authors acknowledge the valuable discussions with Professor J.F. Li and Dr. M.Y. Niu. References [1] J.W. Yeh, S.K. Chen, S.J. Lin, J.Y. Gan, T.S. Chin, T.T.Shun, C.H. Tsau, S.Y. Chang, Metall. Mater. Trans. A 35 (2004) 2533-2536. [2] B. Cantor, I.T.H. Chang, P. Knight, A.J.B. Vincent,Mater. Sci. Eng. A 375–377 (2004) 213–218. [3] B. Cantor, High-entropy alloys. In: Buschow KHJ, Cahn RW, Flemings MC, Ilschner B, Kramer EJ, Mahajan S, Veyssière P, editors. Encyclopedia

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Fig.1 SEM images of CoCrCuxFeMoNi alloy, (a) and (b) x=0, (c) and (d) x=0.1, (e) and (f) x=0.3, where zone Q means quasi-peritectic 17

microstructure; zone FE is the first eutectic structure, and zone SE refers to the second eutectic structure. Fig.2 SEM images of CoCrCu0.5FeMoNi alloy Fig.3 as-solidified microstructure of CoCrCu0.8FeMoNi alloy Fig.4 microstructures of equal atomic portion CoCrCuFeMoNi alloy (a) One of the Cu-rich sphere, (b) microstructure of the Cu-depleted region, Cr-rich precipitations (c)and petals-like dendrites (d) in the Cu-rich spheres Fig.5 DSC curves of as-cast CoCrCuxFeMoNi alloys (a) x=0, (b) x=0.1, (c) x=0.3, (d) x=0.5, (e) x=0.8 and (f) x=1.0 Fig.6 the XRD patterns of CoCrCuxFeMoNi alloys with various Cu content Fig.7 compressive stress-strain curves of as-cast CoCrCuxFeMoNi alloys (x=0, 0.1,0.3,0.5,0.8,1.0)

18

19

20

21

22

23

24

25

26

27

28

29

30

Table 1 Component of different region in microstructure of CoCrFeMoNi alloys (at.%) Region Co Cr Fe Mo Ni Nominal 20 20 20 20 20 Dendrite 22.32 11.58 30.27 13.55 22.28 Peritectic 18.39 10.92 20.85 37.73 12.11 Eutectic 12.28 26.43 19.08 43.64 8.57 Table 2 Component of different region in microstructure of CoCrCu0.5FeMoNi alloys (at.%) Region Co Cr Cu Fe Mo Ni Nominal

18.18

18.18

9.09

18.18

18.18

18.18

A

20.86

11.79

9.13

20.92

14.03

23.27

B

19.83

2.48

15.23

40.22

12.60

C

14.34

21.77

13.47

31.48

15.88

3.06

Table 3 The values of ΔHABmix(kJ/mol) by Miedema’s model for atomic pairs between the elements [21] Co Co

Cr

Cu

Fe

Mo

Ni

-4

6

-1

-5

0

12

-1

0

-7

13

19

4

-2

-2

Cr Cu Fe Mo

-7

Ni Table 4 physiochemical properties for elements in CoCrCuxFeMoNi alloys [24] Elements

Atomic radius (pm)

Pauling electro-negativity

VEC

Co

125

1.88

9

Cr

128

1.66

6

Cu

128

1.9

11

Fe

126

1.83

8

Mo

139

2.16

6

Ni

124

1.91

10

Table 5 Calculations of various parameters for CoCrCuxFeMoNi alloys Alloy

ΔR

VEC

Δχ

ΔH (kJ mol-1)

ΔS (J K-1mol-1)

Cu0

4.254

7.8

0.161

-4.64

13.38

Cu0.1

4.216

7.86

0.159

-3.63

13.92

Cu0.3

4.181

7.98

0.157

-1.83

14.44

Cu0.5

4.156

8.09

0.154

0.26

14.7

Cu0.8

4.09

8.23

0.151

1.7

14.86

Cu1.0

3.889

8.35

0.147

2.79

14.91

31

32