Misplaced Pages

High-entropy alloy

Article snapshot taken from Wikipedia with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.

This is an old revision of this page, as edited by Drzhangyong (talk | contribs) at 17:07, 17 February 2015 (→Production). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Revision as of 17:07, 17 February 2015 by Drzhangyong (talk | contribs) (→Production)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)
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 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 fracture resistance, tensile strength, corrosion and oxidation 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 North Carolina State University, and another as a team, consisting of members from DOE's Lawrence Berkeley and Oak Ridge National Laboratories. In the latter study, "Gludovatz et al. explored the properties of a high-entropy alloy made from equal amounts of chromium, manganese, iron, cobalt, and nickel".

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 concentration of 20 to 25 percent. These alloys are currently the focus of significant attention in materials science and engineering because they can have desirable properties.

HEAs are so named because of the high configuration entropy exhibited by such alloys. The resultant substance becomes 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 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.

High entropy effect

The high-entropy effect states that the higher mixing entropy (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 iron, nickel, copper, aluminium, chromium, cobalt, manganese, titanium, tantalum, and silicon.

Production

High entropy alloys are mostly produced using two distinct methods.

  • Melting casting or laser cladding coatings
    • The component metals (with purities higher than 99.9%) are vacuum arc-melted and cast into billets.
  • Mechanical alloying (high energy ball milling)
    • 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. This powder metallurgy technique produces nano-crystalline structure which has superior properties over conventional materials in use.
  • Mixing elements from gas state
    • sputtering or by molecular beam epitaxy (MBE) to get high entropy films or high entropy ceramics.

High entropy alloys mainly have body-centered cubic (BCC) and/or face-centered cubic (FCC) structure.

Uses

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 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

  1. ^ 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.
  2. 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.
  3. 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.
  4. Yarris, 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.
  5. ^ 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. 345 (6201). AAAS: 1153–1158. Bibcode:2014Sci...345.1153G. doi:10.1126/science.1254581. PMID 25190791. Retrieved 9 January 2015.
  6. ^ 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.

Sources

  • Murty, B.S.; Yeh, Jien-Wei; Ranganathan, S. (2014). High-Entropy Alloys. Butterworth-Heinemann. ISBN 9780128005262.
  • Tsai, Ming-Hung; Yeh, Jien-Wei (30 April 2014). "High-Entropy Alloys: A Critical Review". Materials Research Letters. 2 (3): 107. doi:10.1080/21663831.2014.912690.
  • 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.
  • Bhattacharjee, P.P.; Sathiaraj, G.D.; Zaid, M.; Gatti, J.R.; Lee, Chi; Tsai, Che-Wei; Yeh, Jien-Wei (25 February 2014). "Microstructure and texture evolution during annealing of equiatomic CoCrFeMnNi high-entropy alloy". Journal of Alloys and Compounds. 587: 544–552. doi:10.1016/j.jallcom.2013.10.237.
  • 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.
Categories: