The ultrahigh charpy impact toughness of forged Al x CoCrFeNi high entropy alloys at room and cryogenic temperatures
DongYue Li,Yong Zhang*
State Key Laboratory for Advanced Metals and Materials,University of Science and Technology Beijing,Xueyuan Road30#,Beijing100083,China
a r t i c l e i n f o
Article history:
Received18August2015 Received in revised form
12November2015
Accepted13November2015 Available online xxx
Keywords:
High-entropy alloys Toughness
Mechanical testing a b s t r a c t
AlxCoCrFeNi high-entropy alloys(HEAs)with different aluminum ,x values in molar ratio, where x¼0.1,0.3)were initially prepared using vacuum magnetic levitation melting and,then,plate samples were prepared by hot forging method.The twofive-element HEAs,Al0.1CoCrFeNi and Al0.3CoCrFeNi,both had a simple face-centered cubic(FCC)structure.The measurements of Charpy impact energy with V-type notch and tensile tests were carried out at different temperatures.It was observed that the tensile strength and elongation increased with decreasing temperatures and reached 1042MPa and81.6%at77K,respectively,for the Al0.1CoCrFeNi alloy.The Charpy impact energy reached a maximum value of420J at room temperature for the Al0.1CoCrFeNi alloy.
©2015Elsevier Ltd.All rights reserved.
1.Introduction
The novel designed high-entropy alloys(HEAs)are attracting increased attention for their exclusive structures and excellent mechanical property performances[1e10].In contrast to the traditional alloy design strategy,which is based on one or two principal metal elements to determine the primary phase and mi-nor alloying elements as their constituents for the enhancement of their definite proper
ties[11](such as iron based,aluminum based, and nickel based super alloys),the HEAs havefive or more principal elements in equal or near-equal molar ratios.These principal ele-ments represent a newfield of metallurgy which is focused on the center of the phase diagrams,rather than merely the corners and edges[1,2,8].The new concept of alloy designing is not only changing alloy composition,but it also clarifies the basic physical problems,such as configurational entropy,free energy,and phase selection,as well as competition[12e14].The effects of the high mixing entropy and sluggish cooperative diffusion serve to enhance the formation of simple solid-solution phases with multi-principal elements,rather than intermetallic compounds[15].These novel compositions bring about an extensive solid solution phase with face-centered cubic(FCC)and body-centered-cubic(BCC)struc-tures,or hexagonal close packing(HCP)structures,as the single or matrix phase at the macroscopical and atomic levels,and in accordance unique properties[6,16e18].The discovery of HEAs has provided a novel alloy concept,and has greatly expanded numerous applicable alloy systems.
Recent study results have shown that the comprehensive properties of the HEAs may not be available in other materials which exactly appeal for certain special environmental applica-tions.For example,the HEAs obtain high thermal stability and wear resistance,great fatigue resistance,and sup
erior high tensile high-temperature elongation,as well as excellent corrosion resistance and magnetic properties[5,19e23].These impressive properties make the HEAs promising engineering materials for use in the turbine blades of aircraft engines,and other machine surface layers. However,a more complete assessment of their potential for structural applications will require the documentation of their damage tolerance.Therefore,the completion of uniaxial tension and impact energy tests with relatively high strain rates are very important to the future applications of HEAs.
Generally speaking,the FCC-based alloys have lower strengths than that of the BCC-based alloys[24].However,most reported applications of the mechanical properties were tested as casting samples.In this study,the HEAs after forging were found to have improved both ductility and in strength,when compared to the cast HEAs.Al x CoCrFeNi[25e30]alloys have been thoroughly studied, and it has been determined that the concentration of Al had an important impact on the modifying phase structures[25,31,32].A single FCC structure was exhibited when the content of Al was less than0.45.In this study,the Al0.1CoCrFeNi and Al0.3CoCrFeNi alloys were chosen which had typical FCC structures,and the damage
婚姻走到尽头*Corresponding author.
E-mail address:drzhangy@skl.ustb.edu(D.
Li).Contents lists available at ScienceDirect Intermetallics
journal homepage:www.elsev ier/locat
e/intermet
/10.1016/j.intermet.2015.11.002
0966-9795/©2015Elsevier Ltd.All rights reserved.
Intermetallics70(2016)24e28
tolerance after forging was comprehensively examined.
In this study,the microstructures of the Al x CoCrFeNi HEA sam-ples were analyzed using X-ray diffraction (XRD),along with scanning electron microscopy (SEM).Tensile and impact toughness tests were also performed.Then,based on these experimental re-sults,the relationship between the temperature and structural damage was discussed,and the possible mechanisms controlling the damage tolerance of the HEAs were provided.
2.Experiment
In this study,alloy ingots with nominal compositions of Alx-CoCrFeNi (x value in a molar ratio,where x ¼0.1and 0.3,denoted by Al 0.1and Al 0.3,respectively)were synthesized with vacuum magnetic levitation melting high-purity elemental starting mate-rials (purity higher than 99.9wt.%)in a high-purity argon atmo-sphere.The ingots were re-melted a minimum of four times in order to obtain a uniformity in the chemical composition.Then,plate samples were prepared with thicknesses of approximately 20mm by a hot forging of 87%,at approximately 1050 C.
The crystal structures were identi fied using an XRD pattern,under radiation conditions of 30kV and 20mA,with a Cu target and a scanning speed of 10 /min.The microstructures and damage fracture surfaces were obtained using a ZEISS SUPRA 55field emission scanning electron microscopy (SEM)
,along with energy-dispersive spectrometry (EDS).The uniaxial tensile tests dumb-bell shaped specimens with a gauge length of 15mm,a width of 3mm,and thickness of 2mm were cut from these HEA sheets using an electrical discharge machine.Then,the specimens were pol-ished,and tensile tests were carried out using an MTS SANS CMT 5000materials testing machine,at room temperature to cryogenic temperature,with a strain rate of 2Â10À4s À1.At this point,the Charpy-impact tests were measured by employing an ASTM stan-dard E À23tester (samples with dimension of 10Â10Â55mm 3,and with a 2mm deep V-notch at the center)within the range of 77K e 298K,by implementing a Tinius Olsen impact tester with a 450J儿子太帅被求出道
capacity.
Fig.1.(a)Ingots HEA plates after forging;(b)XRD patterns of Al 0.1and Al 0.3
alloys.
Fig.2.Microstructures of the (a)Al 0.1and (b)Al 0.3alloys with massive twinning crystals;(c)Al 0.1alloy
with higher magni fication using BSE and SEM.
D.Li,Y.Zhang /Intermetallics 70(2016)24e 2825
3.Results and discussion
The HEAs sheet plates without oxidation or cracks after forging are shown in Fig.1(a),and indicate that deformation by forging is feasible for the HEAs.The XRD patterns of the two alloys after forging are shown in Fig.1(b).All of the peaks can be identified as a FCC phase,and there was little difference found between the Al0.1 and Al0.3alloys.In order to further study the microstructures formed during the hot deformation,the SEM-backscattered elec-tron(BSE)images of the alloys were examined,as shown in Fig.2. There were massive annealing twins commonly observed in the solid solution alloys with relatively low-stacking fault energy,and in the recrystallized FCC alloys[33].The chemical compositions(at. %)of the Al0.1CoCrFeNi and Al0.3CoCrFeNi were analyzed using EDS, and are listed in Table1.Furthermore,one of the most important aspects in the material selection was its mechanical properties. Fig.3illustrates the measured uniaxial stress e strain curves,con-ducted at temperatures and ranging from298K to77K,at an initial strain rate of2Â10À4sÀ1.Surprisingly,the ductility did not show a usual inverse dependence on strength.Instead,with the tempera-ture decreas
ing from298K to77K,the yield strength s y of the Al0.1 alloy increased from250MPa to412MPa,and the ultimate tensile strength s uts increased from635MPa to1042MPa,respectively. Similarly,the tensile ductility after failure increased from58.5%to 81.6%.The s y of the Al0.3alloy increased from220MPa to515MPa, and the s uts increased from620MPa to1010MPa,respectively. Meanwhile,the tensile ductility after failure increased from58.4% to68%.This abnormal phenomenon had a strong possibility of deformation induced twinning at a cryogenic temperature.In a recent study,Otto[34]and Gludovatz[8]examined the influence of temperature on the tensile properties of CrMnFeCoNi.Their research also showed that the yield strength and ductility increased with decreasing temperatures.They observed nanoscale twins when performing HEAs tensile tests at77K,and attributed this to the deformation modes transition from planar-slip dislocations at 298K,to mechanical nano-twinning with the decreasing temper-ature.The deformation of FCC metal always occurs through dislo-cation slips.Also,it is possible for twinning to occur in low stacking fault energy alloys at cryogenic temperatures.
There are many parts and tools working during impact loading over long periods of time,especially at low temperatures,and it is important to pay strict attention to the requirements for brittle fractures.In this study,the Charpy impact toughness was carried out at temperatures of298K,200K,and77K.Also,t
he Charpy impact energy of the Al0.1CoCrFeNi alloy was above289J at77K, and even achieved420J at room temperature.The value of the Al0.3CoCrFeNi alloy was approximately328J at77K,andfinally achieved413J at room temperature.This outstanding fracture resistance suggests that these alloys have promising potential ap-plications,especially in extremely cold environments.Fig.4pro-vides a detailed summary of the Charpy V-Notch impact energy at different temperatures.The sizes of the Charpy V-Notch impacts are listed in Table2.The Charpy notch toughness of the HEAs decreased as expected at the cryogenic service temperatures, which was the inverse of the abnormal phenomenon in the tensile tests.A possible reason for this could have been that the Charpy impact test was conducted to measure the toughness and fracture resistance with high speed deformations,and the energy required for the dislocation motion increased with the decreased tempera-tures.As a result,the slip critical shear stress was greater.Cold
Table1
Chemical compositions(in at.%)of the.Al0.1CoCrFeNi and Al0.3CoCrFeNi
Alloy Al Co Cr Fe Ni
Al0.1CoCrFeNi(at.%) 2.2124.9325.9624.3322.56 Al0.3CoCrFeNi(at.%) 6.4423.4724.3423.36
22.40Fig.3.Representative engineering stress/strain curves of the(a)Al0.1and(b)Al0.3 alloys at the three testing
temperatures.
Fig.4.Summary of the Charpy impact energy of materials at the different tempera-tures[35e51].
D.Li,Y.Zhang/Intermetallics70(2016)24e28 26
working environments always lower the resistance to impact at all temperatures.However,the toughness conditions at all of the test temperatures were much higher than many traditional alloys.This can be attributed to the following reasons:the ductility of the HEAs increased due to the improvement of the microstructure homoge-neity,as well as the decrease of the casting defects through hot forging.The cracking usually occurred along the defects or grain interfaces of the samples,and caused relatively low energy absorption.
The dimple-like features are shown in Fig.5(a)and (d)for the Al 0.1and Al 0.3alloys,respectively.These fractures were typically correlated with the relatively high impact energy of 420J and 413J.When compared with the Al 0.1fracture feather,the dimple-like region in Al 0.3comparatively decreased with a further addition of Al.However,both alloys predominantly showed the ductile fracture appearance of a micro-void coalescence when tested at 298K.The FCC phase structures and forging deformations were responsible for the impressive ductility.In regards to foundr
y lacuna,impurity
gathering,and other casting defects,which were unavoidable and particularly susceptible to the fracturing of the specimens,forging was determined to be an effective method for the improvement of the mechanical properties.However,a small amount brittle frac-ture also was observed,and this could have been due to the high degree of shock hardening,which may have caused the brittle fractures in the ductile materials.The tested samples which frac-tured at 200K are presented in Fig.5(b)and (e),and display a combination of dimple-like and brittle fractures.As the tempera-ture decreased,the dimple-like regions gradually reduced,indi-cating that temperature had an in fluence on the impact resistance.Fig.5(c)and (f)show the fracture surfaces of the Al 0.1and Al 0.3alloys which were broken at 77K.Due to the low test temperature,the fracture surfaces contained high-density tear edges,with relatively large and fewer dimples.These features indicated a ten-dency to be quasi-cleavage cracks,which was consistent with the relatively low impact energies of 289J and 328J.
4.Conclusions
The microstructure and mechanical properties of forged Al x-CoCrFeNi (x ¼0.1and 0.3)alloys were studied in the present work.The tensile strength and ductile ability were found to increase with the de
crease of the temperature,which was in contrast to that observed in the traditional metallic alloys with a face-centered cubic structure.In the present HEA alloys,property enhancement is probably due to the fact that mechanical nano-twinning is the
Table 2
Size Alloy
Size Be 55Â10Â2.5Pearlite steel
55Â5Â10Zn 55Â10Â2.514Cr ferritic steel 27Â3Â4Ti
55Â10Â2.5X7055Â10Â7.5DP590
55Â10Â5.5FeAl 45Â10Â10Low alloy steel
55
Â10
Â25
*
55
Â
10Â朱时茂妻子
10
Fig.5.SEM pictures of the fractured surfaces of the Charpy impact specimens:(a),(b),and (c)are the Al 0.1alloy,fractured at 298K,200K,and 77K,respectively;and (d),(e),and (f)are the Al 0.3alloy,fractured at 298K,200K,and 77K,respectively.
D.Li,Y.Zhang /Intermetallics 70(2016)24e 28
27
structuralflow unit instead of planar slip of dislocations.Further studies are needed to shed lights on the microstructural feature/ evolution that governs yielding and fracturing in the materials.The Charpy-impact toughness increases with increasing temperature from77K to298K which is significantly higher than conventional steels and the precise nature also deserves a study in the future.
Acknowledgements
The authors would like to thank the National High Technology Research and Development Program of China(grant no. 2009AA03Z113)and the National Science Foundation of China (grant nos.514710
25and51210105006)for theirfinancial support; 111Project(B07003).
References
[1]Y.Zhang,T.T.Zuo,Z.Tang,et al.,Prog.Mater Sci.61(2014)1e93.
[2]J.W.Yeh,S.K.Chen,S.J.Lin,et al.,Adv.Eng.Mater6(5)(2004)299e303.
[3] B.Cantor,I.T.H.Chang,P.Knight,et al.,Mater Sci.Eng.A375(2004)213e218.
[4]Y.Jien-Wei,E.H.Ann,Chim.Sci.Mat.31(6)(2006)633e648.
[5]O.N.Senkov,G.B.Wilks,J.M.Scott,et al.,Intermetallics19(5)(2011)698e706.
黎明个人资料[6]T.T.Shun,Y.C.Du,J.Alloy Compd.479(1)(2009)157e160.
[7]Y.J.Zhou,Y.Zhang,Y.L.Wang,et al.,Appl.Phys.Lett.90(18)(2007)1904.
[8] B.Gludovatz,A.Hohenwarter,D.Catoor,et al.,Science345(6201)(2014)
1153e1158.
[9] C.J.Tong,Y.L.Chen,J.W.Yeh,et al.,Metall.Mater Trans.A36(4)(2005)
881e893.
[10]Y.Zhang,T.T.Zuo,Y.Q.Cheng,et al.,Sci.Rep.(2013)3.
[11]K.Lu,Science328(5976)(2010)319e320.
[12]W.H.Liu,J.Y.He,H.L.Huang,et al.,Intermetallics60(2015)1e8.
[13]M.R.Chen,S.J.Lin,J.W.Yeh,et al.,Mater Trans.47(5)(2006)1395e1401.
[14]M.R.Chen,S.J.Lin,J.W.Yeh,et al.,Metall.Mater Trans.A37(5)(2006)
1363e1369.
[15]X.Yang,Y.Zhang,Mater Chem.Phys.132(2)(2012)233e238.
[16]M.C.Gao,D.E.Alman,Entropy15(10)(2013)4504e4519.[17]T.Saito,T.Furuta,J.H.Hwang,et al.,Science300(5618)(2003)464e467.
[18]M.Feuerbacher,M.Heidelmann,C.Thomas,Mater Res.Lett.3(1)(2015)1e6.
[19] A.V.Kuznetsov,D.G.Shaysultanov,N.D.Stepanov,et al.,Mater Sci.Eng.A533
(2012)107e118.
[20]M.H.Chuang,M.H.Tsai,W.R.Wang,et al.,Acta Mater59(16)(2011)
6308e6317.
[21] C.Huang,Y.Zhang,J.Shen,et al.,Surf.Coat.Tech.206(6)(2011)1389e1395.
[22]Y.J.Hsu,W.C.Chiang,J.K.Wu,Mater Chem.Phys.92(1)(2005)112e117.
[23]Y.Zhang,X.Yang,P.K.Liaw,JOM64(7)(2012)830e838.
[24] C.J.Tong,M.R.Chen,J.W.Yeh,et al.,Metall.Mater Trans.A36(5)(2005)
1263e1271.
[25] C.Li,J.C.Li,M.Zhao,et al.,J.Alloy Compd.504(2010)S515e S518.
[26]N.Kumar,Q.Ying,X.Nie,et al.,Mater Des.(2015).
[27]W.R.Wang,W.L.Wang,S.C.Wang,et al.,Intermetallics26(2012)44e51.
[28] A.Manzoni,H.Daoud,R.V€o lkl,et al.,Ultramicroscopy132(2013)212e215.
[29]S.G.Ma,S.F.Zhang,M.C.Gao,et al.,JOM65(12)(2013)1751e1758.
[30]S.Wang,Entropy15(12)(2013)5536e5548.
[31]J.Y.He,W.H.Liu,H.Wang,et al.,Acta Mater62(2014)105e113.
[32]K.B.Zhang,Z.Y.Fu,J.Y.Zhang,et al.,Mater Sci.Eng.A508(1)(2009)214e219.
[33]S.Huang,W.Li,S.Lu,et al.,Scripta Mater(2015).
[34] F.Otto,A.Dlouhý,C.Somsen,et al.,Acta Mater61(15)(2013)5743e5755.
[35]R.Kacar,M.Acarer,J.Mater.Process Tech.152(1)(2004)91e96.
[36]ASM Metals Handbook,ninth ed.,vol.2,ASM International,Metals Park,OH,
1992,p.596.
[37]W.Bolton,Engineering Materials Pocket Book,second ed.,Newnes,Oxford,
1996.
[38] A.A.Karimpoor,K.T.Aust,U.Erb,Scr.Mater.56(3)(2007)201e204.
[39]Y.J.Chao,J.D.Ward,R.G.Sands,Mater.Des.28(2)(2007)551e557.
[40]S.Y.Shin,B.Hwang,S.Lee,et al.,Mater.Sci.Eng.A458(1)(2007)281e289.
[41] A.Rossoll,C.Berdin,C.Prioul,Int.J.Fract.115(3)(2002)205e226.
[42] B.Garbarz,F.B.Pickering,Mater.Sci.Tech.4(4)(1988)328e334.
[43]W.Yan,Y.Y.Shan,K.Yang,Metall Mater Trans A37(7)(2006)2147e2158.
经典歌词大全[44] B.Hwang,Y.G.Kim,S.Lee,et al.,Metall.Mater.Trans.A36(8)(2005)
2107e2114.
[45]S.Y.Han,S.Y.Shin,S.Lee,et al.,Metall.Mater.Trans.A41(2)(2010)329e340.
[46]P.J.Maziasz,D.J.Alexander,J.L.Wright,Intermetallics5(7)(1997)547e562.
[47] B.Hwang,C.G.Lee,Mater.Sci.Eng.A527(16)(2010)4341e4346.
[48]Z.Oksiuta,N.Baluc,J.Nucl.Mater.374(1)(2008)178e184.
[49]Y.R.Im,Y.J.Oh,B.J.Lee,et al.,J.Nucl.Mater.297(2)(2001)138e148.
[50]X.L.Yang,Y.B.Xu,X.D.Tan,et al.,Mater.Sci.Eng.A641(2015)96e106.
[51] C.Buirette,J.Huez,N.Gey,et al.,Mater.Sci.Eng.A618(2014)546e557.
D.Li,Y.Zhang/Intermetallics70(2016)24e28 28
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