Enhanced mechanical properties of a CoCrFeNi high entropy alloy by supercooling method

Enhanced mechanical properties of a CoCrFeNi high entropy alloy by supercooling method

    Enhanced mechanical properties of a CoCrFeNi high entropy alloy by supercooling method Jinshan Li, Wenjuan Jia, Jun Wang, Hongchao Ko...

1MB Sizes 0 Downloads 178 Views

    Enhanced mechanical properties of a CoCrFeNi high entropy alloy by supercooling method Jinshan Li, Wenjuan Jia, Jun Wang, Hongchao Kou, Dong Zhang, Eric Beaugnon PII: DOI: Reference:

S0264-1275(16)30110-1 doi: 10.1016/j.matdes.2016.01.112 JMADE 1313

To appear in: Received date: Revised date: Accepted date:

6 December 2015 21 January 2016 22 January 2016

Please cite this article as: Jinshan Li, Wenjuan Jia, Jun Wang, Hongchao Kou, Dong Zhang, Eric Beaugnon, Enhanced mechanical properties of a CoCrFeNi high entropy alloy by supercooling method, (2016), doi: 10.1016/j.matdes.2016.01.112

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 proof before it is published in its final 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.

ACCEPTED MANUSCRIPT Enhanced mechanical properties of a CoCrFeNi high entropy alloy by supercooling method

State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, Shaanxi

Province, P.R. China

Univ. Grenoble Alpes, CNRS-LNCMI, F-38000 Grenoble, France

NU

b

SC R

a

IP

T

Jinshan Li, a* Wenjuan Jia, a Jun Wang, a Hongchao Kou, a Dong Zhang, a Eric Beaugnon b

*Corresponding author: Tel.:+86 29 88491074; Fax:+86 29 88460294. E-mail addresses:

MA

[email protected]

Abstract

D

A CoCrFeNi high entropy alloy has been solidified with a high undercooling up to 300K

TE

adopting glass fluxing method. Results show that the compressive yield strength of the alloy

CE P

is enhanced about 3 times: from 137MPa for a traditional casting condition to 455MPa for the samples processed at large undercooling. The enhanced mechanical properties are attributed

AC

to both the refined grain size and complex phases obtained through the supercooling method, which appears to be an efficient way to modify the microstructure and improve the properties of high entropy alloys. Keywords: High–entropy alloys; Supercooling; Mechanical properties; Microstructure 1. Introduction The concept of high entropy alloys (HEAs) developed by Yeh et al. [1] has broken the traditional way of designing alloys. This new type of metal material brings researchers many challenges and opportunities in the field of material science and engineering. As a new field _____________________________

1

ACCEPTED MANUSCRIPT of metal materials, high entropy alloys have been reported more and more frequently in the last decade for an amount of outstanding properties such as excellent wear resistance [2-4],

IP

T

good high temperature strength [5], superior low-temperature fracture-resistance [6] and

SC R

irradiation resistance [7]. Traditionally, these alloys mainly consist of solid solution structures [8]rather than complex intermetallic compound: the structures of HEAs are mainly solid solution such as BCC, FCC or a mixture of BCC and FCC. The equimolar systems and

NU

non-equimolar systems [9] containing more than four elements have been frequently studied

MA

so far. However, HEAs with four or less elements have also been studied for the single-phase solid solution structure such as the equiatomic ternary and quaternary alloys based on the

D

elements Fe, Ni, Co, Cr and Mn [6,10-11].

TE

Improving the mechanical properties of the HEAs has been one of the most interesting

CE P

fields for many researchers recently. Until now, many ways were put forward to improve the mechanical properties of HEAs, e.g. thermal treatments [12-16], alloy elements addition

AC

[17-20], thermo-mechanical treatment [21,22] and controlling solidification process [23,24]. Among the solidification treatments, supercooling method is an efficient way to obtain metastable phases and refined grain structure. However, few research has been carried out to investigate the effect of supercooling method on HEAs although this method have been widely used in many alloys, such as Iron-based alloys [25] and Cobalt-based alloys [26]. Further more, Qian M. et al. have investigated more about analytical model for constitutional supercooling-driven grain formation and grain size prediction[27]. In this paper, the supercooling method is adopted to investigate the change of the microstructure and mechanical properties of CoCrFeNi high entropy alloy which contains the main elements of

ACCEPTED MANUSCRIPT many HEAs [28,29]. 2. Material and experimental procedures

IP

T

All alloying elements with high purity (99.9 wt.%) were melted in a vacuum arc melting

SC R

furnace. In order to achieve a good uniformity of the composition of the samples, these materials were melted at least 5 times. The uniformity of the sample was confirmed by SEM and EDX analysis. To achieve solidification with a high undercooling, the sample with mass

NU

about 100g was put in high quality quartz tube together with B2O3 glass and submitted to

MA

cyclic superheating and solidification, which was called the supercooling method. The B2O3 glass was dehydrated at the 1073 K for 2 h at the muffle furnace and then cooled down in

D

order to be used as coating agent in the supercooling experiment. The supercooling

TE

experiment was performed by using the high frequency induction power supply and the

CE P

temperature measurement equipment. The thermal behavior of the sample was monitored by a two-color pyrometer with a relative accuracy of ± 5 K and a response time of 10 ms. The

AC

undercooled solidified specimen were cut and then polished, etched with 30 ml HCl + 10ml HNO3 + 10 ml H2O. The crystalline structure of the as-cast material and supercooled samples was characterized using DX 2700 X-ray diffractometer (XRD). A SUPRA 55 scanning electron microscope (SEM) was used for microstructure observation. The microstructure of the samples was also characterized by a FEI Tecnai G2F30 TEM. Uniaxial compression tests of the as-cast and supercooled samples were carried out by a MTS SANS CMT5105 testing machine under the strain rate of 10-3 s-1. 3. Results and discussions Fig. 1. exhibits the cooling curve of CoCrFeNi high entropy alloy during supercooling

ACCEPTED MANUSCRIPT experiments. During the cooling process, at the nucleation point, Tn = 1387 K, the recalescence measured by a pyrometer is clearly evidenced by a rapid rise of temperature

IP

T

during the release of latent heat. At Tn = 1387 K, a large undercooling ΔT = 300 K below the

SC R

melting temperature (1687 K) is obtained. The bulk sample (about 100 g) shown in the inset of Fig. 1. is very bright with a smooth surface, which is typical characteristic of high

AC

CE P

TE

D

MA

NU

undercooling.

Fig. 1. Solidification curve of CoCrFeNi high entropy alloy with an undercooling of 300 K. Inset is the image of the solidified sample.

The compressive engineering stress–strain curves of the as-cast and supercooled CoCrFeNi high entropy alloy are presented in Fig. 2. Both the samples kept unfractured with plastic strain over 40% at the end of the compression test, indicating a good plasticity of this material. The compressive yield strength of the two samples are quite different, as the strength of supercooled CoCrFeNi high entropy alloy is nearly 3 times higher than that of the as cast sample: increased from 137 MPa for traditional as-cast condition to 455 MPa for the

ACCEPTED MANUSCRIPT

D

MA

NU

SC R

IP

T

sample processed with a large undercooling.

TE

Fig. 2. Engineering compressive stress-strain curves of CoCrFeNi high entropy alloy solidified at as-cast and supercooled conditions.

CE P

The relation between compressive yield strength and the fracture ductility of different alloys based on CoCrFeNi HEA are exhibited in Fig. 3. It can be seen that the as-cast

AC

CoCrFeNi alloy has excellent ductility but very poor yield strength. When more elements, e.g. Al, Cu, Mo are added, their properties evolve. The yield strength of Al0.5CoCrFeNiCu alloy under different state (as cast and heat treated) [30], CoCrFeNiMo0.3 alloy [31] are all increased to a much higher value. However, the fracture strain will be decreased to a much lower value, such as in CoCrFeNiMo0.5 and CoCrFeNiTi0.5 [32]. The CoCrFeNi alloy processed by supercooling technique up to 300K shows a good combination of yield strength and ductility without using more alloying elements or further treatment.

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

TE

Fig. 3. Relationship between compressive yield strength and fracture strain of alloys based on CoCrFeNi HEA. The yield strength of Al0.5CoCrFeNiCu alloy under different state (as cast and heat

CE P

treated) [30], CoCrFeNiMo0.3 alloy [31] and CoCrFeNiTi0.5 [32] is all plotted.

To undercover the enhancing mechanism of the supercooling method, the phases and

AC

microstructure of the samples are examined. Fig. 4. is the XRD pattern of the as-cast and supercooled CoCrFeNi alloy. It is known that CoCrFeNi HEA possesses a single phase FCC structure [28,33]. Different from the as cast sample with solely FCC structure, the sample solidified with a large undercooling of 300K shows a mixture of FCC and BCC phases. All diffraction peaks are much sharper at the large undercooling condition, showing the mean grain size is much smaller after high undercooling. Besides, the peaks of the phases shift to low angles (shown in the inset of Fig. 4.), indicating the severe lattice distortion of the non-equilibrium solidified sample. The lattice parameter of the FCC matrix phase for the as-cast and undercooled samples are calculated as 3.570 Å and 3.576 Å, respectively.

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

TE

Fig. 4. XRD patterns of CoCrFeNi high entropy alloy solidified at as-cast and supercooled conditions.

CE P

Fig. 5. shows the microstructure of CoCrFeNi HEA solidified at as-cast (near-equilibrium) state and non-equilibrium state with the undercooling of 300 K. The

AC

as-cast state possesses a dendritic microstructure. The parameter, S (μm), proposed by Qiao et al. [34] is used to estimate the size of the dendritic. In the as cast alloy, spanning length of the individual dendrite tree is S >400 μm, as shown in Fig. 5(a). The supercooled sample contains rod- and strip-like precipitates which are distributed homogeneously in the matrix (see in Fig. 5(b)). The grain size is hugely refined from over 400 μm to about 5~10 μm. Meantime, rod- and strip-like precipitates with a volume fraction of about 15% appear from the main FCC solid solution matrix. Fig. 5(c) is the TEM image of the supercooled sample and the corresponding selected area electron diffraction (SAED) of the image. Results show that BCC phase exists and that the matrix phase is the FCC solid solution phase which is

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

SC R

IP

T

consistent with the XRD pattern.

Fig. 5. SEM and TEM image of CoCrFeNi high entropy alloy solidified at as-cast and supercooled condition. (a) Dendrites morphology of the as-cast CoCrFeNi alloy; (b) Morphology of the large undercooling condition; (c) TEM image and the corresponding SAED patterns of the matrix and the precipitates of the supercooled condition.

Based on the microstructure analysis shown in Figs. 4 and 5, two factors can be considered to explain this unique strength enhancing behavior. According to the Hall-Petch relation, the yield strength will be increased with smaller grain. Thus, the refined grain size

ACCEPTED MANUSCRIPT by supercooling technique could be a main reason of the enhancement of the yield strength. Another factor is the BCC precipitates in the supercooled sample. As reported before, the

IP

T

BCC structure in high entropy alloys can obviously increase the strength [33]. Combined

SC R

with the above two factors: grain refinement and BCC precipitates, the supercooled sample possesses much higher yield strength than the as cast one. 4. Conclusions

NU

In summary, the CoCrFeNi high entropy alloy has achieved high undercooling of 300 K

MA

through the way of glass fluxing method. The compressive yield strength is enhanced significantly from 137 MPa to 455 MPa when the sample was further solidified with an

D

undercooling of 300K. The microstructure of the supercooled sample was transformed from

TE

dendritic morphology with spanning length of the individual dendrite over 400 μm to

CE P

equiaxed fine grain morphology with grain size about 5-10 μm including many rod- and strip-like BCC precipitates. The grain refinement together with the BCC precipitates are the

AC

main reasons for the enhanced compressive yield strength. Acknowledgments

The authors acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51271151 and 51571161) and the Program of Introducing Talents of Discipline to Universities (Grant No. B08040). References [1] J.W. Yeh, S.K. Chen, S.J. Lin, J.Y. Gan, T.S. Chen, T.T. Shun, C.H. Tasu, S.Y. Chang, Nanostructured high-entropy alloys with multiple principal elements: novel alloy desigh concepts and outcomes, Adv. Eng. Mater. 6 (2004) 299-303.

ACCEPTED MANUSCRIPT [2] M.H. Chuang, M.H. Tsai, W.R. Wang, S.J. Lin, J.W. Yeh, Microstructure and wear behavior of AlxCo1.5CrFeNi1.5Tiy high-entropy alloys, Acta Mater. 59 (2011) 6308-6317.

IP

T

[3] J.M. Wu, S.J. Lin, JW. Yeh, S.K. Chen, Y.S. Huang, H.C. Chen, Adhesive wear behavior of

SC R

AlxCoCrCuFeNi high-entropy alloys as a function of aluminum content, Wear 261 (2006) 513-519.

[4] Y. Yu, W.M. Liu, T.B. Zhang, J.S. Li, J. Wang, H.C. Kou, J. Li, Microstructure and tribological

NU

properties of AlCoCrFeNiTi0.5 high-entropy alloy in hydrogen peroxide solution, Metall. Mater.

MA

Trans. A 45 (2013) 201-207.

[5] O.N. Senkov, S.V. Senkova, C. Woodward, D.B. Miracle, Low-density, refractory multi-principal

TE

(2013) 1545-1557.

D

element alloys of the Cr-Nb-Ti-V-Zr system: microstructure and phase analysis, Acta Mater. 61

CE P

[6] B. Gludovatz, A. Hohenwarter, D. Catoor, E.H. Chang, E.P. George, R.O. Ritchie, A fracture-resistant high-entropy alloy for cryogenic applications, Science 345 (2014) 1153-1158.

AC

[7] T. Egami, W. Guo, P.D. Rack, T. Nagase, Irradiation resistance of multicomponent alloys, Metall. Mater. Trans. A 45 (2013) 180-183. [8] Y. Zhang, T.T. Zuo, Z. Tang, M.C. Gao, K.A. Dahmen, P.K. Liaw, Z.P. Lu, Microstructures and properties of high-entropy alloys, Prog. Mater. Sci. 61 (2014) 1-93. [9] M.J. Yao, K.G. Pradeep, C.C. Tasan, D. Raabe, A novel, single phase, non-equiatomic FeMnNiCoCr high-entropy alloy with exceptional phase stability and tensile ductility, Scr. Mater. 5 (2014) 72-73. [10] Z. Wu, H. Bei, G.M. Pharr, E.P. George, Temperature dependence of the mechanical properties of equiatomic solid solution alloys with face-centered cubic crystal structures, Acta Mater. 81 (2014)

ACCEPTED MANUSCRIPT 428-441. [11] C. Niu, A.J. Zaddach, A.A. Oni, X. Sang, JW. Hurt, III, J.M. LeBeau, C.C. Koch, D.L. Irving,

IP

T

Spin-driven ordering of Cr in the equiatomic high entropy alloy NiFeCrCo, Appl. Phys. Lett. 106

SC R

(2015) 161906.

[12] T.T. Shun, L.Y. Chang, M.H. Shiu, Age-hardening of the CoCrFeNiMo0.85 high-entropy alloy, Mater. Charact. 81 (2013) 92-96.

MA

alloy, Mater. Des. 33 (2012) 121-126.

NU

[13] B. Ren, Z.X. Liu, B. Cai, M.X. Wang, L. Shi, Aging behavior of a CuCr2Fe2NiMn high-entropy

[14] L.C. Tsao, C.S. Chen, C.P. Chu, Age hardening reaction of the Al0.3CrFe1.5MnNi0.5 high entropy

D

alloy, Mater. Des. 36 (2012) 854-858.

TE

[15] Y.D. Wu, Y.H. Cai, X.H. Chen, T. Wang, J.J. Si, L. Wang, Y.D. Wang, X.D. Hui, Phase

CE P

composition and solid solution strengthening effect in TiZrNbMoV high-entropy alloys, Mater. Des. 83 (2015) 651-660

AC

[16] Y. Dong, L. Jiang, H. Jiang, Y.P. Lu, T.M. Wang, T.J. Li, Effects of annealing treatment on microstructure and hardness of bulk AlCrFeNiMo0.2 eutectic high-entropy alloy, Mater. Des. 82 (2015) 91-97

[17] J.Y. He, W.H. Liu, H. Wang, Y. Wu, X.J. Liu, T.G. Nieh, Z.P. Lu, Effects of Al addition on structural evolution and tensile properties of the FeCoNiCrMn high-entropy alloy system, Acta Mater. 65 (2014) 105-113. [18] Y. Dong, K. Zhou, Y. Lu, X. Gao, T. Wang, T. Li, Effect of vanadium addition on the microstructure and properties of AlCoCrFeNi high entropy alloy, Mater. Des. 57 (2014) 67-72. [19] Z. Hu, Y. Zhan, G. Zhang, J. She, C. Li, Effect of rare earth Y addition on the microstructure and

ACCEPTED MANUSCRIPT mechanical properties of high entropy AlCoCrCuNiTi alloys, Mater. Des. 31 (2010) 1599-1602. [20] J. Chen a, P.Y. Niu, Y.Z. Liu, Y.K. Lu, X.H. Wang, Y.L. Peng, J.N. Liu, Effect of Zr content on

IP

T

microstructure and mechanical properties of AlCoCrFeNi high entropy alloy, Mater. Des. 94

SC R

(2016) 39-44

[21] A.V. Kuznetsov, D.G. Shaysultanov, N.D. Stepanov, G.A. Salishchev, O.N. Senkov, Tensile properties of an AlCrCuNiFeCo high-entropy alloy in as-cast and wrought conditions, Mater. Sci.

NU

Eng. A 533 (2012) 107-118.

MA

[22] A.V. Kuznetsov, D.G. Shaysultanov, N.D. Stepanov, G.A. Salishchev, O.N. Senkov, Superplasticity of AlCoCrCuFeNi high entropy alloy, Mater. Sci. Forum 735 (2013) 146-151.

D

[23] S.G. Ma, S.F. Zhang, M.C. Gao, P.K. Liaw, Y. Zhang, A successful synthesis of the

TE

CoCrFeNiAl0.3 single-Crystal, high-entropy alloy by bridgman solidification, Jom 65 (2013)

CE P

1751-1758.

[24] F.J. Wang, Y. Zhang, G.L. Chen, H.A. Davies, Cooling rate and size effect on the microstructure

AC

and mechanical properties of AlCoCrFeNi high entropy alloy, J. Eng. Mater. Technol. 131 (2009) 034501.

[25] H.L. Yi, S.K. Ghosh, W.J. Liu, K.Y. Lee, H.K.D.H. Bhadeshia, Non-equilibrium solidification and ferrite in δ-TRIP steel, Mater. Sci. Technol. 26 (2010) 817-823. [26] P.R. Ohodnicki, Y.L. Qin, D.E. Laughlin, M.E. McHenry, M. Kodzuka, T. Ohkubo, K. Hono, M.A. Willard, Composition and non-equilibrium crystallization in partially devitrified Co-rich soft magnetic nanocomposite alloys, Acta Mater. 57 (2009) 87-96. [27] M. Qian, P. Cao, M.A. Easton, S.D. McDonald, D.H. StJohn, An analytical model for constitutional supercooling-driven grain formation and grain size prediction, Acta Mater. 58

ACCEPTED MANUSCRIPT (2010) 3262-3270. [28] G.A. Salishchev, M.A. Tikhonovsky, D.G. Shaysultanov, N.D. Stepanov, A.V. Kuznetsov, I.V.

IP

T

Kolodiy, A.S. Tortika, O.N. Senkov, Effect of Mn and V on structure and mechanical properties

SC R

of high-entropy alloys based on CoCrFeNi system, J. Alloys Compd. 591 (2014) 11-21. [29] Y. Brif, M. Thomas, I. Todd, The use of high-entropy alloys in additive manufacturing, Scr. Mater. 99 (2015) 93-96.

NU

[30] H.F. Sheng, M. Gong, L.M. Peng, Microstructural characterization and mechanical properties of

MA

an Al0.5CoCrFeCuNi high-entropy alloy in as-cast and heat-treated/quenched conditions, Mater. Sci. Eng. A 567 (2013) 14-20.

D

[31] T.T. Shun, L.Y. Chang, M.H. Shiu, Microstructure and mechanical properties of multiprincipal

TE

component CoCrFeNiMox alloys, Mater. Charact. 70 (2012) 63-67.

CE P

[32] T.T. Shun, L.Y. Chang, M.H. Shiu, Microstructures and mechanical properties of multiprincipal component CoCrFeNiTix alloys, Mater. Sci. Eng. A 556 (2012) 170-174.

AC

[33] W.R. Wang, W.L. Wang, J.W. Yeh, Phases, Microstructure and mechanical properties of AlxCoCrFeNi high-entropy alloys at elevated temperatures, J. Alloys Compd. 589 (2014) 143-152.

[34] J.W. Qiao, P. Feng, Y. Zhang, Q.M. Zhang, G.L. Chen, Quasi-static and dynamic deformation behaviors of Zr-based bulk metallic glass composites fabricated by the bridgman solidification, J. Alloys Compd. 486 (2009) 527-531.

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

SC R

IP

T

Graphical abstract

ACCEPTED MANUSCRIPT Highlights 1.

The CoCrFeNi high entropy alloy has been solidified with a high undercooling up to

IP

The compressive yield strength of the alloy is enhanced about 3 times after the samples processed at large undercooling.

The enhanced mechanical properties are attributed to the supercooling method which was

CE P

TE

D

MA

NU

applied to the CoCrFeNi high entropy alloy.

AC

3.

SC R

2.

T

300K adopting glass fluxing method.