Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures

Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures Bernd Gludovatz Anton Hohenwarter Keli V.S. Thurston Hongbin Bei Zhenggang Wu E.P. George Robert O. Ritchie

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Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures 2016 Nature Communications 10.1038/ncomms10602 gludovatz2016-exceptional-damage-tolerance-of-a gludovatz2016-exceptional-damage-tolerance-of-a.txt, the project's staged copy 653c39d65ab36a7c8693b75edb4d68ed01508ed7 cc-by engineering

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0 spans located by searching the stored text for the quote's exact words, allowing any whitespace between them the equiatomic three-element CrCoNi medium-entropy alloy, and its strength, ductility and fracture toughness from room temperature to 77 K Quotation withheld because this record is not cleared for redistribution. whether the properties of these alloys come from high configurational entropy itself or from which elements are present Quotation withheld because this record is not cleared for redistribution. a three-element alloy whose damage tolerance exceeds every high-entropy alloy reported, and the argument that element identity matters more than element count Quotation withheld because this record is not cleared for redistribution. existence Quotation withheld because this record is not cleared for redistribution. simultaneous increase of strength, ductility and toughness as temperature falls, against the usual strength-toughness compromise Quotation withheld because this record is not cleared for redistribution. experiment experiment Quotation withheld because this record is not cleared for redistribution. the three-element alloy twins at room temperature where the five-element one deforms by slip alone, and the extra deformation mode arrives before the strength penalty does earlier onset of deformation nano-twinning Quotation withheld because this record is not cleared for redistribution. twinning supplies steady strain hardening, which delays plastic instability by necking, and adds a second way to accommodate strain besides dislocation motion twinning defeats the strength-toughness compromise Quotation withheld because this record is not cleared for redistribution. why this particular combination of elements forms a single phase while others of comparable configurational entropy do not remains unexplained Quotation withheld because this record is not cleared for redistribution. the dislocation glide mechanism is presumed from the five-element alloy rather than observed directly in this one Quotation withheld because this record is not cleared for redistribution. the twinning-induced plasticity mechanism, recognised first in Hadfield manganese steels and copper thin films and applied here to explain an entropy-named alloy Quotation withheld because this record is not cleared for redistribution. the five-element CrMnFeCoNi alloy, tested by the same group over the same temperature range, as the comparison eliminates: a cryogenic toughness attributed to medium-entropy composition when the five-element alloy from the same laboratory over the same range is the thing it must beat · outcome: held Quotation withheld because this record is not cleared for redistribution. that the specimens were in fully plane strain, checked by slicing through the thickness eliminates: a fracture toughness inflated by a specimen that was not in plane strain, which the standard requires and which thickness alone does not guarantee · outcome: held Quotation withheld because this record is not cleared for redistribution. that the alloy is genuinely single-phase, checked by XRD, backscattered electron imaging and the ternary phase diagram eliminates: a second phase supplying the strength that is being attributed to the single-phase solid solution · outcome: held Quotation withheld because this record is not cleared for redistribution. single-phase character at the atomic scale, checked by three-dimensional atom probe tomography - on the FIVE-element alloy, not this one eliminates: fine-scale segregation hidden below the resolution of diffraction - established by atom probe tomography for the FIVE-component alloy, and not for this one · outcome: absent-stated-about-other Quotation withheld because this record is not cleared for redistribution. High-entropy alloys High-entropy alloys Quotation withheld because this record is not cleared for redistribution. medium-entropy alloy medium-entropy alloy Quotation withheld because this record is not cleared for redistribution. configurational entropy configurational entropy Quotation withheld because this record is not cleared for redistribution. Cantor alloy Cantor alloy Quotation withheld because this record is not cleared for redistribution. nano-twinning nano-twinning Quotation withheld because this record is not cleared for redistribution. strain hardening strain hardening Quotation withheld because this record is not cleared for redistribution. solid solution solid solution Quotation withheld because this record is not cleared for redistribution. intermetallic phases intermetallic phases Quotation withheld because this record is not cleared for redistribution. twinning-induced plasticity steels twinning-induced plasticity steels Quotation withheld because this record is not cleared for redistribution. 'high-entropy alloy' = FIVE OR MORE elements at high concentration, crystallising as a single phase Quotation withheld because this record is not cleared for redistribution. 'medium-entropy alloy' = the same thing with THREE - the two categories differ by an element count and nothing else Quotation withheld because this record is not cleared for redistribution. the same class is called high-entropy alloys, multi-component alloys OR compositionally complex alloys - three names, one referent Quotation withheld because this record is not cleared for redistribution. high configurational entropy BY ITSELF does not suppress intermetallics - a twenty-element equiatomic alloy came out brittle and multi-phase Quotation withheld because this record is not cleared for redistribution. equiatomic composition maximises configurational entropy and does NOT minimise Gibbs free energy - the two come apart Quotation withheld because this record is not cleared for redistribution. contradicts → the premise that maximised configurational entropy is what stabilises a single-phase multi-element solid solution note: the corpus holds gild2016, which rests on that premise. This paper supplies the counterexample - a twenty-element equiatomic alloy that came out brittle and multi-phase - and concludes for element identity over element count Quotation withheld because this record is not cleared for redistribution. extends → the CrMnFeCoNi Cantor alloy and its reported cryogenic damage tolerance note: same group, same tests, two elements removed - and the smaller alloy wins Quotation withheld because this record is not cleared for redistribution. qualifies → the belief that useful new alloys lie near the centres rather than the corners of phase diagrams Quotation withheld because this record is not cleared for redistribution. medium-entropy alloy —distinct-from→ High-entropy alloys medium-entropy alloy High-entropy alloys differs in: the number of principal elements - three against five or more, with no other criterion separating them · strength of the relation: 0.95 Quotation withheld because this record is not cleared for redistribution. nano-twinning —causes→ strain hardening nano-twinning strain hardening direction on the measure: increases · strength of the relation: 0.95 · direction on the measure (stated by the tagger, no quotation): increases Quotation withheld because this record is not cleared for redistribution. the three-element alloy has better fracture toughness than the five-element one, and improves as temperature falls Quotation withheld because this record is not cleared for redistribution. nano-twinning begins at room temperature in the three-element alloy and only at 77 K in the five-element one Quotation withheld because this record is not cleared for redistribution. high configurational entropy alone does not suppress intermetallic formation Quotation withheld because this record is not cleared for redistribution. it is one of the toughest materials in any materials class ever reported Quotation withheld because this record is not cleared for redistribution. High-entropy alloys High-entropy alloys Quotation withheld because this record is not cleared for redistribution. medium-entropy alloy medium-entropy alloy Quotation withheld because this record is not cleared for redistribution. room temperature: tensile strength near 1 GPa, failure strain about 70%, KJIc above 200 MPa m1/2 — None Quotation withheld because this record is not cleared for redistribution. at cryogenic temperature: above 1.3 GPa, failure strain up to 90%, KJIc 275 MPa m1/2 — None Quotation withheld because this record is not cleared for redistribution. crack-growth toughness exceeding 430 MPa m1/2 at liquid-nitrogen temperature — None Quotation withheld because this record is not cleared for redistribution. twenty elements in equal atomic ratios produced a brittle multi-phase microstructure — None Quotation withheld because this record is not cleared for redistribution. the Cantor alloy: tensile strength 763 to 1,280 MPa and ductility 0.5 to 0.7 between room temperature and 77 K — None Quotation withheld because this record is not cleared for redistribution. strain-hardening exponents of the order of 0.4 — None Quotation withheld because this record is not cleared for redistribution. strain-hardening exponent strain-hardening exponent Quotation withheld because this record is not cleared for redistribution. fracture toughness fracture toughness Quotation withheld because this record is not cleared for redistribution. configurational entropy configurational entropy Quotation withheld because this record is not cleared for redistribution.

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