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Amorphous film of high entropy alloy deposited by direct

current magnetron sputtering#

LI Jianchen, ZHU Jianbo* 5

(Department of Materials Science and Engineering, Jilin University, Changchun 130021)

Foundations: NNSFC (Grant No. 50571040); National Foundation of Doctoral Station (Grant No.

20100061110019)

Brief author introduction:Li Jianchen(1957-), Male, Professor,Main research: Metal materials. E-mail:

ljc@jlu.edu.cn

Abstract: In this paper, The amorphous films of AlFeCoNiCuZrV multicomponent high-entropy alloy

were deposited by direct current magnetron sputtering in the mixture atmosphere of Ar and O2. The

results demonstrate that the chemical composition, microstructure, and mechanical properties of the

amorphous films intimately rely on the concentration of O2 in the atmosphere mixture. When O2 flow 10 ratio increases from 0 to 50%, the thickness of the films decreases, whereas the roughness firstly

decreases and then increases. At the O2 flow ratio of 30%, a perfect dense and smooth amorphous

nitride film could be achieved. While the hardness and Youngs modulus of the film reach the maximum values of 12 and 166 GPa, respectively.

Key words: High entropy alloy; amorphous film; properties; magnetron sputtering 15

0 Introduction

The conventional alloys generally consist of one principal element associated with a

substantial amount of other elements to enhance the properties and processing [1], which differ

from the high-entropy alloy (HEA) recently proposed by Yeh et al. [2, 3]. HEA is a novel concept 20

for the alloy system that has multiple principal elements with equimolar or near-equimolar ratios

in the rang of 5-35 at.%. In recent years, HEA films have been widely studied, such as TiVCrZrHf

film [4], AlCrMoTaTiZr film [5, 6], etc. Moreover, HEA films have been proposed for the

potential applications as protective films [7-9], wear-resistant materials [10], corrosion-resistant

materials [11], and coatings in communication devices [12]. That is due to their interesting 25

properties, such as high hardness [13], strength [14, 15], wear resistance [16, 17], and

microstructure stability against heat treatment [18-20].

It is known that the transition metal nitride and oxide coatings are usually much harder, more

chemically inert, but brittler than the original metals or alloys. This has stimulated recent

explorations for improving the mechanical properties of alloys. In previous work [21, 22], we have 30

developed the novel HEA alloys (i.e. FeCoNiCu system) with a single FCC crystalline structure,

which exhibits good plastic properties with the tensile strain up to 18%. Musil et al. reported the

hard and super-hard Zr-Ni-N nanocomposite films with the hardness of 40 GPa [23]. The similar

strengthening effect was also revealed in VN [24]. Moreover, the addition of other element, such

as Al, was found to further improve the thermal stability of the film [25, 26]. Based on the above 35

observations, the multicomponent FeCoNiCuVZrAl film is expected to possess excellent

mechanical properties.

In this contribution, the amorphous films of AlFeCoNiCuZrV HEA are prepared by using

direct current magnetron sputtering system at a low depositing temperature. The amorphization

occurs probably due to the enhanced glass-forming ability for the alloys containing more than 40

three elements [27], as well as the limited diffusion of the elements at the low depositing

temperature [28]. In addition, the composition, microstructure, hardness and Young modulus of

the amorphous film were systematically investigated and discussed.

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1 Experimental methods

The AlFeCoNiCuZrV HEA was melted for at least 5 times by the arc melting-method under a 45

purified argon gas atmosphere. Then, it was shaped into a disc of 60 mm in diameter and 5 mm in

thickness as a target. Table 1 lists the composition of the target and the atomic ratios of each

element measured by energy dispersive spectrometry (EDS). Quartz glass wafers were cleaned

sequentially in de-ionized (DI) water, acetone and DI water, for the following deposition of the

nitride films of AlFeCoNiCuZrV by DC magnetron sputtering. In a mixture atmosphere of Ar and 50

N2, the nitride films with the thickness of about 12 m were deposited under a plasma power of

30 W, a constant working pressure of 0.9 Pa, a substrate bias of 98 V, a deposited time of 2 hours

at room temperature. The distance between the substrate and the target was set as 75 mm. The

nitrogen flow ratio RN = O2/(Ar+O2) was precisely adjusted by varying the O2 flow rate from 0 to

30 sccm with a constant Ar flow rate of 30 sccm. The phase structure analysis of the target and 55

nitride films was performed on Rigaku D/max 2500 X-ray diffractometer at 50 KV and 250 mA

(XRD, D/Max 2500pc) with the scanning angles ranging from 20 to 90 degree at a scanning rate

of 2 degree/min. Both the surface morphology and thickness of the deposited films were observed

by field-emission scanning electron microscopy (FESEM, JEOL JSM 6700F). The chemical

compositions of the films were analyzed by EDS. The hardness and Youngs modulus of the films 60

were measured by a nanoindenter (XP nanomechanical testing system, MTS Corporation), during

which the penetration depth of the indenter was controlled at about 1/10 of the film thickness to

avoid substrate effect.

Table 1 Composition of the AlFeCoNiCuZrV high-entropy alloy target (at.%)

Element Fe Co Ni Cu V Zr Al

Nominal composition 14.28 14.28 14.28 14.28 14.28 14.28 14.28

Composition By EDS 13.96 13.95 13.20 13.83 14.57 15.19 15.31

2 Results and discussion 65

Fig. 1 shows the XRD pattern of the target of AlFeCoNiCuZrV HEA. As indicated, the

crystalline structures are composed of (cubic), (cubic) and (monoclinic) phases with the

space group of Fm3m (225), Im3m (229) and C2/m(12), respectively. Fig. 2 illustrates the XRD

patterns of the films of AlFeCoNiCuZrV alloy deposited under different O2 flow ratios (RN). It can

be clearly seen that all the films exhibit amorphous structure, dramatically different from that of 70

the as-melted HEA target shown in Fig. 1. This phenomenon was also observed in the preparation

of the nitride films of the AlCrSiTiV [29], AlCrMoSiTi [30], and AlMoNbSiTaTiVZr [31], the

oxide films of AlCoCrCu0.5NiFe [32] and AlCrTaTiZr HEA [33].

The formation of the amorphous films during the fabrication is reasonable according to the

rules proposed by Inoue [27] that the glass-forming ability can be strengthened for 75

multicomponent systems. From a thermodynamical point of view, the large glass-forming ability

is obtained under the condition of low Gibbs free energy G (T) for the transformation from liquid

to crystalline phase, where G = Hf - TSf with Hf and Sf being the enthalpy and entropy of

fusion, respectively. According to the above equation, the low G value is obtained in the case of

low Hf and large Sf. The large Sf is expected to be obtained in multicomponent alloy systems, 80

because Sf is proportional to the number of microscopic states. The G at a constant temperature

also decreases in the cases of low chemical potential caused by the low enthalpy, high reduced

glass transition temperature, and large solid/liquid interface energy. Based on these

thermodynamical considerations, it can be concluded that the multicomponent increases the dense

random packing, which is favor of the decrease of Hf and the increase of solid/liquid interface 85

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energy. This is consistent with the result that a larger glass-forming ability has been obtained for

the above multicomponent systems. In conclusion, the low enthalpy, the great difference between

the depositing temperature of films and the glass transition temperature, and the large solid/liquid

interface energy benefit the formation of the amorphous films. From Fig. 2, we can find that the

film without oxygen is also amorphous. Thus, the RN has almost no effect on the amorphous 90

formation. However, the RN has great effects on the chemical compositions, thickness,

morphology, hardness and Young's Modulus of the films, which will be discussed later.

Fig. 1 X-Ray diffraction curve of the AlFeCoNiCuZrV target.

20 40 60 80 1000

100

200

300

400

500

600

700

800

900

1000

Inte

nsi

ty(C

PS

)

0%

10%

30%

50%

95 Fig. 2 X-Ray diffraction curves of the AlFeCoNiCuZrV films deposited under different O2 flow ratios (RN).

Fig. 3 shows the chemical compositions of the multicomponent AlFeCoNiCuZrV films

deposited under different RN. When RN = 0, the concentration (atomic ratio) of each metallic

element in the film is rather close to that in the AlFeCoNiCuZrV target, whose composition is

listed in Table 1. Oxygen concentration in the film rises sharply to 55 at.% when the oxygen flow 100

ratio (R0) is set to 2.5%. Compared with nitride films prepared based on the same alloy, where the

concentration of nitrogen was only 39 at.% at a much higher flow ratio of 9%, it is seen that

oxygen has a much stronger tendency to react with the individual metal atoms than nitrogen does.

This is supported by the significantly larger heat of formation of the metal oxides relative to

corresponding metal nitrides. For example, the heat of formation of TiN is only 338 kJ/mol [34], 105

while that of TiO2 is 944 kJ/mol [35]. When R0 is further increased, concentration of oxygen

also increases and then saturates near 67 at.%.

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0 10 20 30 40 500

10

20

30

40

50

60

70

80

Co

nc

en

tra

tio

n (

at%

)

O2/(O

2/Ar)ratio(%)

Al

V

Fe

Co

Ni

Cu

Zr

O

Fig. 3 Chemical compositions of the AlFeCoNiCuZrV films deposited under different O2 flow ratios (RN).

Table 2 gives the thickness of the AlFeCoNiCuZrV films deposited under different RN. The 110

largest and smallest thicknesses are 2.100 m (RN = 0) and 0.875 m (RN = 50%), respectively. It

is also found that the thicknesses of the films decrease with the increasing RN. This originates from

the formation of the oxide film at the target surface due to the good affinity of all the target

elements with oxygen, which hinders the atoms from sputtering. It is a typical result of target

poisoning [36]. Additionally, oxygen ions are known as less effective as argon ions for sputtering 115

[36]. Therefore, as the two gas species have comparable collision cross-sections for ionization [37],

a greater proportion of the target current will be carried by oxygen ions at higher oxygen partial

pressures, inducing the decrease in the sputtering rate. Moreover, when more O2 are added, more

metallic oxide are formed on the substrate, which enhances the internal stress of the film and

inhibits the growth. Another aspect is probably due to the fact that more metallic oxide is pumped 120

out of deposition chamber along with exhaust gas [32].

Table 2 Thickness of the AlFeCoNiCuZrV films deposited under different O2 flow ratios (RN).

RN 0 10% 30% 50%

Thickness (m) 6.450 3.545 2.432 1.725

Fig. 4 shows the top-view FESEM images of the AlFeCoNiCuZrV films deposited under

different RN, illustrating the evolution of morphology. It can be see that the films are composed of

nanoparticles with different geometric morphology as RN changes. When RN = 0, an amount of 125

nanoparticles with the size of about 10 to 25 nm gather together, as shown in Fig. 4(a). With

increasing RN, the surface of the film becomes smoother and forms a smooth coating [see Fig.

4(b)]. Fig. 4(c) shows a morphology for a perfect dense amorphous AlFeCoNiCuZrV film

obtained at RN = 30%, where the surface is much smoother and cleaner than other films. This

decrease in the roughness at the higher nitrogen flow rate could be attributed to the reduction in 130

the arrival rate of the sputtered species, which can be reflected by the decrease of the film

thickness and corresponds to the structure zone models [38, 39]. There is more energy of per

depositing atom that leads to the formation of denser coatings with reduced surface roughness.

However, when the RN is increased to 50%, the surface become rougher [Fig. 4(d)], and the dense

amorphous coating seems to be destructed. That is because with further increasing RN, the target 135

poisoning is enhanced and the arrival rate of the sputtered species becomes so low that there are

not enough sputtered species arriving at the substrate. Therefore, the film surfaces become looser

and have more micro-holes. Therefore, RN of 30% is the just right ratio to form the smooth and

dense amorphous AlFeCoNiCuZrV film.

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140 (a) (b)

(c) (d)

Fig. 4 FESEM morphology of the AlFeCoNiCuZrV films deposited under different O2 flow ratios (RN): (a) RN = 0;

(b) RN = 10%; (c) RN = 30%; (d) RN = 50%. 145

Fig. 5 plots the hardness and Youngs modulus of the AlFeCoNiCuZrV films as a function of

RN. For the AlFeCoNiCuZrV film without the addition of O2, the hardness and Youngs modulus

are 8.6 and 153 GPa, respectively. They are relatively superior to typical films of pure metals and

alloys, which is mainly caused by the great solid-solution strengthening effect from the addition of

a large amount of different-size atoms. With addition of O2, the hardness and modulus increase 150

and reach maximum values of 12 and 166 GPa for the film deposited at RN = 30%. That might be

due to the perfect dense and smooth amorphous structure. With further increasing RN, the surface

becomes rougher and looser, as shown in Fig. 4(d). Meanwhile the micro-holes among particles

increase in size. Therefore, the hardness and modules decrease.

0 10 20 30 40 508

10

12

14

16

18

20

Hardness

Young's Modulus

O2/(O2+Ar)ratio (%)

Ha

rdn

es

s (

Gp

a)

140

145

150

155

160

165

170

175

180

185

Yo

un

g's M

od

ulu

s

155 Fig. 5 Hardness and Young's Modulus of the AlFeCoNiCuZrV films deposited under different O2 flow ratios (RN).

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3 Conclusion

The films of AlFeCoNiCuZrV high-entropy alloy have been deposited successfully using

direct current magnetron sputtering. All the films exhibit amorphous structure, dramatically

different from the as-melted HEA target. The morphology and mechanical properties of these 160

amorphous films depend on the oxygen flow ratio. The thickness of films decreases with the

increasing O2 flow ratio. The biggest and smallest thicknesses are 2.100 m (RN = 0) and 0.875

m (RN = 50%), respectively. a perfect dense and smooth amorphous film is obtained with the

hardness and Youngs modulus up to the maximum values of 12 and 166 GPa, respectively.

References 165

[1] Handbook Committee. Metals nadbook[Z]. Metals Park, OH: ASM International, 1990.

[2] YEH J W,CHEN S K, LIN S J, GAN J Y, CHIN T S, SHUN T T,TSAU C H, CHANG S Y. Nanosctructured

high entropy alloys with multiple principal elements: novel alloy design concepte and outcomes [J]. 2004, 6:

299-303

[3] HUANG P K, YEH J W, CHEN T T, CHEN S K.Multi-principal-element alooys with improved oxidation and 170 wear resistance for thermal spray coating[J]. Adv. Eng, Mater., 2004, 6: 74-78.

[4] LIANG S C, TSAI D C, CHANG Z C, SUANG H S, LIN Y C, YEH J W, DENG M J, SHIEU F S. Structural

and mechanical properties of multi-element (TiVCrZrHf) coating by reactive magnetron sputtering [J]. Appl, Surf.

Sci., 2011, 258: 399-403.

[5] CHENG K H, LAI C H, LIN S J, YEH J W. Structureal and mechanical properties of multi-element 175 (AlCrMoTaTiZr)Nx coating by reactive magnetron sputtering [J]. Thin Sold Films, 2011, 519: 3185-3190.

[6] LIANG S C, CHANG Z C, TSAI D C, LIN Y C, SUNG H S, DENG M J, SHIEU F S. Effect of substrate

temperature on the structure and mechanical properties of (TiVCrZrHf)N coatings [J]. Appl. Surf. Sci., 2011, 257:

7709-7713.

[7] TSAI M H, YEH J W, GAN J Y.Diddusion barrier properties of AlMoNbSiTaTiVZr high entropy alloy layer 180 between copper and silicon [J]. Thin Solid Films, 516: 5527-5530.

[8] CHEN T K, SHUN T T, YEH J W, WONG M S. Nanosreuctured nitrid films of multi-element high entropy

alloys by reactive DC sputtering [j]. Suf. Coat. Technol., 2004, 188-189: 193-200.

[9] CHANG S Y, CHEN D S. (AlCrTaTiZr)N/(AlCrTaTiZr)N-0.7 bilayer structure of high resistance to the

interdiffusion of Cu and Si at 900 degrees C [J]. Mater. Chem. Phys., 2011, 125: 5-8. 185 [10] REN B, LIU Z X, SHI L, CAI B, WANG M X. Structure and properties of (AlCrMnMoNiZrB0.1)Nx coating

prepared by reactive DC sputtering [J]. Appl. Surf. Sci., 2011, 257: 7172-7178.

[11] CHEN Y Y, DUVAL T, HUNG U D, YEH J W, SHIH H C. Structure and electrochenical properties of high

entropy alloys - a comparison with type-304 stainless steel [J]. Corros. Sci., 2005, 47: 2257-2279.

[12] CHEN H K, LI S H, DUH J G. Structure and soft magnetic properties of Fe-Co-Ni-based multicomponent 190 thin films [J]. J Electron. Mater., 2005, 34: 1480-1483.

[13] ZHOU Y J, ZHANG Y, WANG Y L, CHEN G L. Microstructure and compressive properties of

multicomponent Alx(TiVCrMnFeCoNiCu)100-x high entropy alloys [J]. Mater. Sci. Eng. A, 2007, 454-455:

260-265.

[14] ZHOU Y J, ZHANG Y, WANG Y L, CHEN G L. Solid solution alloys of AlCoCrFeNiTix with excellent 195 room temperature mechanical properties [J]. Appl. Phys. Lett., 2007, 90: 181904

[15] HU Z H, ZHAN Y Z, ZHANG G H, SHE J, LI C H. Effect of rare earth Y addition on the microstructure and

mechanical properties of high entropy AlCoCrNiTi alloys [J]. Mater. Des., 2010, 31: 1599-1602.

[16] HSU C Y, SHEN T S, YEH J W. Effect of iron content on wear behavior of AlCoCrFexMo0.5Ni high

entropy alloys [J]. Wear, 2010, 268: 653-659. 200 [17] HUANG C, ZHANG Y Z, VILAR R, SHEN J Y. Dry sliding wear behavior of laser clad TiVCrAlSi high

entropy alloy coating on Ti-6Al-4V substrate [J]. mATER. dES., 2012, 41: 338-343.

[18] REN B, LIU Z X, CAI B, WANG M X. Aging behavior of CuCr2Fe2NiMn high entropy alloy [J]. Mater.Des.,

2012, 33: 121-216.

[19] TSAI C W, CHEN Y L, TSAI M H, YEH J W, SHUN T T, CHEN S K. Deformation and annealing behavior 205 of high entropy alloy Al0.5CoCrFeNi [J]. J Alloy Compd., 2009, 486: 427-435.

[20] SENKOV N, WILKS G B, MIRACLE D B, CHUANG C P, LIAW P K. Refractory high entropy alloys [J].

Intermetallics, 2010, 18: 1758-1765.

[21] LIU L, ZHU J B, ZHANG C, LI J C, JIANG Q. Microstructure and properties of FeCoCuNiSnx high entropy

allos [J]. Mater. Sci. Eng. A, 2012, 548: 64-68. 210 [22] LIU L, ZHU J B, ZHNAG C, LI J C, JIANG Q. Microstructure and tensile properties of FeMnNiCuCoSnx

high entropy alloys [J]. Mater. Des., 2013, 44: 223-227.

[23] MUSIL J, KARVANKOVA P, KASL J. Ward and superhard Zr-Ni-N nanocomposite films [J]. Surf. Coat.

Technol., 2001, 139: 101-109.

[24] UCHIDA M, NIHIRA N, MITSUO A, TOYODA K. Friction and wear properties of CrAlN and CrVN films 215 deposited by cathodic arc ion plating method [J]. Surf. Coat. Technol., 2004, 177-178: 627-630.

http://www.paper.edu.cn

- 7 -

[25] KIM C W, KIM K H. Anti-oxidation properties of TiAlN film prepared by plasma-assisted chemical vapor

deposition and roles of Al [J]. Thin Solid Films, 1997, 307: 113-119.

[26] LAI C H, LIN S J, YEH J W, CHANG S Y. Prepationg and characterization of AlCrTaTiZr multi-element

nitride coatings [J]. Surf. Coat. Technol., 2006, 201: 3275-3280. 220 [27] INOUE A. High strength bulk amorphous alloys with low cooling rates [J]. Mater. Trans. JIM, 1995, 36:

866-875.

[28] GUO S, LIU C T. Phase stability in high entropy allys: Formation of solid-solution phase or amorphous phase

[J]. Prog. Nat. Sci., 2011, 21: 433-446.

[29] TSAI C W, LAI S W, CHENG K H, TSAI M H, DAVISON A, TSAU C H, YEH J W. Strong amorphization 225 of high entropy AlBCrSiTi nitride film [J]. Thin Solia Films, 2012, 520: 2613-2618.

[30] LIU L, ZHU J B, LI J C, JIANG Q. Dense and smooth amorphous films of multicomponent FeCoNiCuVZrAl

high entropy alloy deposited by direct current magnetron sputtering [J]. Mater. Des., 2013, 46: 675-679.

[31] CHANG H W, HUANG P K, DAVISON A, YEH J W, TSAU C H, YANG C . Nitride films deposited from

an eqimolar Al-Cr-Mo-Si-Ti alloy target by reactive direct current magnetron sputtering [J]. Thin Solid Films, 230 2008, 516: 6402-6408.

[32] HUANG Y S, CHEN L, LUI H W, CAI M H, YEH J W. Microstructure, hardness, resistivity and thermal

stability of sputtered oxide films of AlCoCrCu0.5NiFe high entropy alloy [J]. Mater. Sci. Eng. A, 2007, 457:

77-83.

[33] LIN M I, TSAI M H, SHEN W J, YEH J W. Evolution of structure and properties of multi-component 235 (AlCrTaTiZr)O-x films [J]. Thin Solid Films, 2010, 518: 2732-2737.

[34] PIERSON H O. Handbook of refractory carbides and nitrides[Z]. New Jersey: Noyes Publications, 1996.

[35] DEAN J A. Lange's handbook of chenistry [Z]. New York: Mcgraw Hill, 1999.

[36] MASON R M, PICHILING M. Sputtering in a glow discharge ion source-pressure dependence: theory and

experiment [J]. J Phys. D, 1994, 27: 2363-2371. 240 [37] CHAPMAN B N. Glow discharge processes [Z]. New York: John Wiley & Sons, 1980.

[38] THORNTON J A. The microstructure of sputter-deposited coatings [J]. J Vac. Sci. Technol. A, 1986, 4:

3059-3066.

[39] MESSIER R, VENUGOPAL V C, SUNAL P D. Origin and evolution of aculptured thin films [J]. J Vac. Sci.

Technol. A, 2000, 18: 1538-1545. 245

130021 250 Ar O2 AlFeCoNiCuZrV 0-50% O2 30% 12GPa 166 GPa 255 TG113