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'''''High-entropy alloys (HEAs)''''' are substances that are constructed with equivalent quantities of five or more metals. Research indicates that HEAs are also considerably lighter, with a higher degree of ], ], ] and ] resistance than conventional alloys. Although HEAs have existed since before 2004, it is only recently, since 2014, that the quality has become sufficient to use research resources. For example, two 2014 research endeavors have taken place: one at ], and another as a team, consisting of members from ] Lawrence Berkeley and ]. In the latter study, "Gludovatz et al. explored the properties of a high-entropy alloy made from equal amounts of ], ], ], ], and ]".<ref name=lavine> '''''High-entropy alloys (HEAs)''''' are a new class of multi-component alloys containing 5 or more principal constituent elements with each at a concentration between 5 and 35 at.%.<ref name ="tsai">Tsai, Ming-Hung; Yeh, Jien-Wei (2014). "High-Entropy Alloys: A Critical Review" (Free PDF download). Materials Research Letters 2 (3): 107. doi:10.1080/21663831.2014.912690.</ref> Research indicates that HEAs can be considerably lighter, with a higher degree of ], ] and hardness, ] and ] resistance than conventional alloys as well as have exceptional high-temperature strength and structural stability.<ref name="tsai" /><ref name="zhang">Zhang, Yong; Zuo, TingTing; Tang, Zhi; Gao, M.C.; Dahmen, K.A.; Liaw, P.K.; Lu, Z.P. (1 November 2013). "Microstructure and properties of high-entropy alloys". Progress in Materials Science 61: 1–93. doi:10.1016/j.pmatsci.2013.10.001.</ref> Although HEAs have existed since before 2004<ref>Huang KH, Yeh JW. A study on multicomponent alloy systems containing equal-mole elements . Hsinchu: National Tsing Hua University; 1996.</ref><ref>Yeh JW, Chen SK, Lin SJ, Gan JY, Chin TS, Shun TT, Tsau CH, Chang SY. Nanostructured high-entropy alloys with multiple principal elements: novel alloy design concepts and outcomes. Adv Eng Mater. 2004;6:299–303. doi: 10.1002/adem.200300567</ref>, research interest has been renewed due to research performed in 2014 at ]<ref>Shipman, Matt (10 December 2014). "New 'high-entropy' alloy is as light as aluminum, as strong as titanium alloys". Phys.org. Retrieved 9 January 2015.</ref>, and as a team with members from ] Lawrence Berkeley and ].<ref>Lavine, Marc S. (2014). "A metal alloy that is stronger when cold". Science 345: 1131. Bibcode:2014Sci...345Q1131L. doi:10.1126/science.345.6201.1131-b. Retrieved 9 January 2015.</ref><ref>Lyn (4 September 2014). "A metallic alloy that is tough and ductile at cryogenic temperatures". Berkeley Lab News Center (University of California, Berkeley). Retrieved 9 January 2015.</ref><ref>Gludovatz, B.; Hohenwarter, A.; Catoor, D.; Chang, E. H.; George, E. P.; Ritchie, R. O. (5 September 2014). "A fracture-resistant high-entropy alloy for cryogenic applications" (Free PDF download). Science (AAAS) 345 (6201): 1153–1158. Bibcode:2014Sci...345.1153G.doi:10.1126/science.1254581. PMID 25190791. Retrieved 9 January 2015.</ref>
{{cite journal
|title= A metal alloy that is stronger when cold
|journal= Science
|doi=10.1126/science.345.6201.1131-b
|volume= 345
|page= 1131
|url= http://www.sciencemag.org/content/345/6201/1131.2.full
|accessdate = 9 January 2015|bibcode= 2014Sci...345Q1131L
|author1= Lavine
|first1= Marc S.
|year= 2014
}}</ref><ref name=shipman>
{{cite news
| last = Shipman
| first =Matt
| title =New 'high-entropy' alloy is as light as aluminum, as strong as titanium alloys
| newspaper =Phys.org
| location =
| date =10 December 2014
| url =http://phys.org/news/2014-12-high-entropy-alloy-aluminum-strong-titanium.html
| accessdate =9 January 2015}}</ref><ref name=youseff>
{{cite journal
| title = A Novel Low-Density, High-Hardness, High-entropy Alloy...
| journal =]
| page =1
| url =http://www.tandfonline.com/doi/pdf/10.1080/21663831.2014.985855
| doi = 10.1080/21663831.2014.985855
| format = Free PDF download
| date =9 December 2014
| last1 =Youssef
| first1 =Khaled M.
| last2 =Zaddach
| first2 =Alexander J.
| last3 =Niu
| first3 =Changning
| last4 =Irving
| first4 =Douglas L.
| last5 =Koch
| first5 =Carl C.
}}</ref><ref name=cryogenic>
{{cite news
| last =Yarris
| first = Lyn
| title = A metallic alloy that is tough and ductile at cryogenic temperatures
| newspaper =]
| publisher =]
| date =4 September 2014
| url = http://newscenter.lbl.gov/2014/09/04/a-metallic-alloy-that-is-tough-and-ductile-at-cryogenic-temperatures/
| accessdate =9 January 2015}}</ref><ref name=gludov>
{{cite journal
| title = A fracture-resistant high-entropy alloy for cryogenic applications
| journal = Science
| volume = 345
| issue = 6201
| pages = 1153–1158
| publisher = ]
| format = Free PDF download
| date = 5 September 2014
| url = http://www2.lbl.gov/ritchie/Library/PDF/2014_Gludovatz_Science_AFractureResistant.pdf
| doi = 10.1126/science.1254581
| pmid = 25190791
| accessdate =9 January 2015
| last1 = Gludovatz| first1 = B.| last2 = Hohenwarter| first2 = A.| last3 = Catoor | first3 = D.
| last4 = Chang| first4 =E. H.| last5 = George| first5 = E. P.| last6 = Ritchie| first6 = R. O.
| bibcode = 2014Sci...345.1153G}}</ref>


== High entropy effects ==
HEAs are a new class of multi-component alloy containing essentially equal numbers of unique metal elements, which form into a metallic substance with novel properties. To form the HEA each principal constituent metal has a ] of 20 to 25 percent.<ref name=lavine/><ref name=gludov/>
HEAs are so named because of the high ] exhibited by such ]s. The resultant substance can become a simple solid solution due to its high ]. The higher ] in these alloys facilitates the formation of ] with simple structures (such as ] or ]) and thus reduces the number of phases to one phase at the right temperatures.<ref name ="tsai" /><ref name ="zhang" />
These alloys are currently the focus of significant attention in ] and engineering because they can have desirable properties.<ref name=tsai>
{{cite journal
|title=High-Entropy Alloys: A Critical Review
|journal=Materials Research Letters
|volume=2
|issue=3
|page=107
|doi=10.1080/21663831.2014.912690
|url= http://www.tandfonline.com/doi/pdf/10.1080/21663831.2014.912690
|format= Free PDF download|year=2014
|last1=Tsai
|first1=Ming-Hung
|last2=Yeh
|first2=Jien-Wei
}}</ref>


Further, it has been shown that ] is limited in these systems, allowing for more easily attained supersaturated states and nano-sized precipitates.<ref>Singh S, Wanderka N, Murty BS, Glatzel U, Banhart J. Decomposition in multi-component AlCoCrCuFeNi high-entropy alloy. Acta Mater. 2011;59: 182–190. doi: 10.1016/j.actamat.2010.09.023</ref>
HEAs are so named because of the high ] exhibited by such ]s. The resultant substance becomes a simple solid solution due to its high ]. The higher ] in these alloys facilitates the formation of ] with simple structures and thus reduces the number of phases to one phase at a given temperature. High entropy alloys possess exceptionally high strength/hardness, outstanding wear resistance, exceptional high-temperature strength, good structural stability, good corrosion and oxidation resistance.<ref name=tsai/>

== High entropy effect ==
The high-entropy effect states that the higher ] (mainly configurational) in HEAs lowers the free energy of solid solution phases and facilitates their formation, particularly at higher temperatures. There are nearly 30 elements used in production of over 300 alloys. Typically used metals are ], ], ], ], ], ], ], ], ], and ].


== Production == == Production ==
High entropy alloys are mostly produced using two distinct methods. High entropy alloys are mostly produced using distinct methods that depend on the initial phase - starting either from a liquid, solid, or gas state.


* Melting casting or laser cladding coatings * Melt casting
** The component metals (with purities higher than 99.9%) are vacuum arc-melted and cast into billets. ** The component metals (with purities higher than 99.9%) are melted using ] and cast into billets. For elements with a low melting point and are easy to evaporate (e.g. Mg, Zn, and Mn), the arc-melting process may not be the best choice.<ref name ="zhang" />
* Mechanical alloying (high energy ball milling) * Mechanical alloying (high energy ball milling) of solids
** High purity (> 99.5% pure) metallic powders with particle size below 45 microns are mixed in equiatomic composition and milled in a ] for 10 to 100 hours in an inert atmosphere and then sintered by ]. This powder metallurgy technique produces nano-crystalline structure which has superior properties over conventional materials in use. ** High purity (> 99.5% pure) metallic powders with particle size below 45 microns are mixed in equiatomic composition and milled in a ] for 10 to 100 hours in an inert atmosphere and then sintered by ].<ref>Youssef, Khaled M.; Zaddach, Alexander J.; Niu, Changning; Irving, Douglas L.; Koch, Carl C. (9 December 2014). "A Novel Low-Density, High-Hardness, High-entropy Alloy..." (Free PDF download). Materials Research Letters: 1. doi:10.1080/21663831.2014.985855.</ref><ref>Ji, Wei; Wang, Weimin; Wang, Hao; Zhang, Jinyong; Wang, Yucheng; Zhang, Fan; Fu, Zhengyi (January 2015). "Alloying behavior and novel properties of CoCrFeNiMn high-entropy alloy fabricated by mechanical alloying and spark plasma sintering".Intermetallics 56: 24–27. doi:10.1016/j.intermet.2014.08.008.</ref>
* Mixing elements from gas state * Mixing elements from gas state
** sputtering or by molecular beam epitaxy (MBE) to get high entropy films or high entropy ceramics. ** ] or ] (MBE) are used to carefully control different elemental compositions to get high entropy metallic or ceramic films.<ref name ="zhang" />

== Properties and potential uses ==

]


HEAs, because of their high form-ability and strength combined with low density, are expected to replace ]s in energy sectors and aero-space applications. Because HEAs are a cocktail of metallic elements, a wide range of materials can be produced which can serve future requirements at a lower cost with superior mechanical properties.
High entropy alloys mainly have ] (BCC) and/or face-centered cubic (FCC) structure.


Recent research has also indicated that magnetic properties of high entropy alloys could also be promising.<ref>Zhang et.al (Scientific Reports Volume: 3 Published: MAR 15 2013,DOI: 10.1038/srep01455)</ref>
== Uses ==
HEAs, because of their high form-ability and strength combined with low density, are expected to replace ]s in energy sectors and aero-space applications. Because HEAs are the cocktail of metallic elements a wide range of materials can be produced which can serve the future requirements at a lower cost with superior mechanical properties.Zhang et.al (Scientific Reports Volume: 3 Published: MAR 15 2013,DOI: 10.1038/srep01455) reported that magnetic properties of high entropy alloys are also promising.


==References== ==References==
{{reflist}} {{reflist}}


== Sources == == See also ==
* ]
* {{cite book
* ]
|title=High-Entropy Alloys
* ]
|first1=B.S.|last1=Murty
|first2=Jien-Wei|last2=Yeh
|first3=S.|last3=Ranganathan
|publisher=Butterworth-Heinemann
|year=2014
|isbn=9780128005262
}}
* {{cite journal
|first1=Ming-Hung|last1=Tsai
|first2=Jien-Wei|last2=Yeh
|title=High-Entropy Alloys: A Critical Review
|journal=Materials Research Letters
|date=30 April 2014
|volume=2 |issue=3
|page=107
|doi=10.1080/21663831.2014.912690
}}
* {{cite journal
|first1=Wei|last1=Ji
|first2=Weimin|last2=Wang
|first3=Hao|last3=Wang
|first4=Jinyong|last4=Zhang
|first5=Yucheng|last5=Wang
|first6=Fan|last6=Zhang
|first7=Zhengyi|last7=Fu
|title=Alloying behavior and novel properties of CoCrFeNiMn high-entropy alloy fabricated by mechanical alloying and spark plasma sintering
|journal=Intermetallics
|volume=56
|date=January 2015
|pages=24–27
|doi=10.1016/j.intermet.2014.08.008
}}
* {{cite journal
|first1=P.P.|last1=Bhattacharjee
|first2=G.D.|last2=Sathiaraj
|first3=M.|last3=Zaid
|first4=J.R.|last4=Gatti
|first5=Chi|last5=Lee
|first6=Che-Wei|last6=Tsai
|first7=Jien-Wei|last7=Yeh
|title=Microstructure and texture evolution during annealing of equiatomic CoCrFeMnNi high-entropy alloy
|journal=Journal of Alloys and Compounds
|volume=587
|pages=544–552
|date=25 February 2014
|doi=10.1016/j.jallcom.2013.10.237
}}
* {{cite journal
|first1=Yong|last1=Zhang
|first2=TingTing|last2=Zuo
|first3=Zhi|last3=Tang
|first4=M.C.|last4=Gao
|first5=K.A.|last5=Dahmen
|first6=P.K.|last6=Liaw
|first7=Z.P.|last7=Lu
|title=Microstructure and properties of high-entropy alloys
|journal=Progress in Materials Science
|volume=61
|pages=1–93
|date=1 November 2013
|doi=10.1016/j.pmatsci.2013.10.001
}}
] ]
] ]

Revision as of 00:39, 21 April 2015

This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (January 2015) (Learn how and when to remove this message)

High-entropy alloys (HEAs) are a new class of multi-component alloys containing 5 or more principal constituent elements with each at a concentration between 5 and 35 at.%. Research indicates that HEAs can be considerably lighter, with a higher degree of fracture resistance, tensile strength and hardness, corrosion and oxidation resistance than conventional alloys as well as have exceptional high-temperature strength and structural stability. Although HEAs have existed since before 2004, research interest has been renewed due to research performed in 2014 at North Carolina State University, and as a team with members from DOE's Lawrence Berkeley and Oak Ridge National Laboratories.

High entropy effects

HEAs are so named because of the high configuration entropy exhibited by such alloys. The resultant substance can become a simple solid solution due to its high configurational entropy. The higher entropy of mixing in these alloys facilitates the formation of solid solute phases with simple structures (such as face-centered cubic or body-centered cubic) and thus reduces the number of phases to one phase at the right temperatures.

Further, it has been shown that diffusion is limited in these systems, allowing for more easily attained supersaturated states and nano-sized precipitates.

Production

High entropy alloys are mostly produced using distinct methods that depend on the initial phase - starting either from a liquid, solid, or gas state.

  • Melt casting
    • The component metals (with purities higher than 99.9%) are melted using vacuum arc remelting and cast into billets. For elements with a low melting point and are easy to evaporate (e.g. Mg, Zn, and Mn), the arc-melting process may not be the best choice.
  • Mechanical alloying (high energy ball milling) of solids
    • High purity (> 99.5% pure) metallic powders with particle size below 45 microns are mixed in equiatomic composition and milled in a planetary ball-mill for 10 to 100 hours in an inert atmosphere and then sintered by spark plasma sintering.
  • Mixing elements from gas state

Properties and potential uses

High-entropy alloys (orange) show an exceptional combination of toughness and strength relative to other materials.

HEAs, because of their high form-ability and strength combined with low density, are expected to replace superalloys in energy sectors and aero-space applications. Because HEAs are a cocktail of metallic elements, a wide range of materials can be produced which can serve future requirements at a lower cost with superior mechanical properties.

Recent research has also indicated that magnetic properties of high entropy alloys could also be promising.

References

  1. ^ Tsai, Ming-Hung; Yeh, Jien-Wei (2014). "High-Entropy Alloys: A Critical Review" (Free PDF download). Materials Research Letters 2 (3): 107. doi:10.1080/21663831.2014.912690.
  2. ^ Zhang, Yong; Zuo, TingTing; Tang, Zhi; Gao, M.C.; Dahmen, K.A.; Liaw, P.K.; Lu, Z.P. (1 November 2013). "Microstructure and properties of high-entropy alloys". Progress in Materials Science 61: 1–93. doi:10.1016/j.pmatsci.2013.10.001.
  3. Huang KH, Yeh JW. A study on multicomponent alloy systems containing equal-mole elements . Hsinchu: National Tsing Hua University; 1996.
  4. Yeh JW, Chen SK, Lin SJ, Gan JY, Chin TS, Shun TT, Tsau CH, Chang SY. Nanostructured high-entropy alloys with multiple principal elements: novel alloy design concepts and outcomes. Adv Eng Mater. 2004;6:299–303. doi: 10.1002/adem.200300567
  5. Shipman, Matt (10 December 2014). "New 'high-entropy' alloy is as light as aluminum, as strong as titanium alloys". Phys.org. Retrieved 9 January 2015.
  6. Lavine, Marc S. (2014). "A metal alloy that is stronger when cold". Science 345: 1131. Bibcode:2014Sci...345Q1131L. doi:10.1126/science.345.6201.1131-b. Retrieved 9 January 2015.
  7. Lyn (4 September 2014). "A metallic alloy that is tough and ductile at cryogenic temperatures". Berkeley Lab News Center (University of California, Berkeley). Retrieved 9 January 2015.
  8. Gludovatz, B.; Hohenwarter, A.; Catoor, D.; Chang, E. H.; George, E. P.; Ritchie, R. O. (5 September 2014). "A fracture-resistant high-entropy alloy for cryogenic applications" (Free PDF download). Science (AAAS) 345 (6201): 1153–1158. Bibcode:2014Sci...345.1153G.doi:10.1126/science.1254581. PMID 25190791. Retrieved 9 January 2015.
  9. Singh S, Wanderka N, Murty BS, Glatzel U, Banhart J. Decomposition in multi-component AlCoCrCuFeNi high-entropy alloy. Acta Mater. 2011;59: 182–190. doi: 10.1016/j.actamat.2010.09.023
  10. Youssef, Khaled M.; Zaddach, Alexander J.; Niu, Changning; Irving, Douglas L.; Koch, Carl C. (9 December 2014). "A Novel Low-Density, High-Hardness, High-entropy Alloy..." (Free PDF download). Materials Research Letters: 1. doi:10.1080/21663831.2014.985855.
  11. Ji, Wei; Wang, Weimin; Wang, Hao; Zhang, Jinyong; Wang, Yucheng; Zhang, Fan; Fu, Zhengyi (January 2015). "Alloying behavior and novel properties of CoCrFeNiMn high-entropy alloy fabricated by mechanical alloying and spark plasma sintering".Intermetallics 56: 24–27. doi:10.1016/j.intermet.2014.08.008.
  12. Zhang et.al (Scientific Reports Volume: 3 Published: MAR 15 2013,DOI: 10.1038/srep01455)

See also

Categories: