Realizing strength-ductility combination of coarse-grained Al0.2Co1.5CrFeNi1.5Ti0.3 alloy via nano-sized, coherent precipitates

A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength

“…The shearing mechanism will be active when a precipitate with small size is coherent, whereas the Orowan bypass mechanism occurs preferentially when the precipitate is incoherent ( 27 , 28 , 35 ). Since γ′ and γ* precipitates are coherent with the γ matrix and γ′ precipitates have an average diameter of ~57 nm, shearing is suspected to be the operative mechanism.…”

“…Excessive amounts of strong phases lead to a notable decrease in ductility or even failure before yielding during mechanical testing ( 25 ). Precipitates are often observed in HEAs when a significantly positive enthalpy of mixing (or significantly negative enthalpy of formation of intermetallic phases) cannot be counteracted by a high entropy of mixing ( 17 , 27 , 28 ). A dispersion of coherent γ′ precipitates in the γ matrix in some Al- and/or Ti-containing HEAs leads to high strength/hardness at room temperature and at high temperatures ( 17 , 27 , 28 , 31 ).…”

“…Precipitates in HEAs usually contain multiple principal elements ( 27 , 28 ). Two interesting questions arise: (i) Can a hierarchical architecture involving nanoprecipitates be formed in HEAs; that is, can some secondary nanoprecipitates form inside these primary nanoprecipitates consisting of multi-principal elements?…”

Engineering heterostructured grains to enhance strength in a single-phase high-entropy alloy with maintained ductility

“…To date, the reported superior mechanical properties of HEAs, have been achieved mostly with multi-phase structures, which are principally attributed to the presence of second phases and phase metastability induced strengthening [2,[4][5][6][7][8][9][10]. Comparing with multi-phase HEAs, it is more difficult to attain a good combination of strength and ductility in single-phase HEAs at room temperature, particularly for single-phase fcc HEAs [2,11].…”

“…In order to provide insight into the mechanical behaviour of the HS single-phase fcc Fe 29 Ni 29 Co 28 Cu 7 Ti 7 HEA, the yield strength versus failure strain and the ultimate tensile strength versus failure strain are plotted in Figure 5 alongside other single-phase fcc HEAs/MEAs and enhanced fcc HEAs/MEAs [7][8][9]11,13,16,17,19,27,28]. It is worth mentioning that the enhanced fcc HEAs/MEAs refer to the alloys using C- [17] and B-doping [8], coherent precipitation strengthening [9,13,28] and brittle intermetallic strengthening [7], as well as grain refinement strategies [19], to strengthen a fcc HEA/MEA matrix. As shown in Figure 5(a), the yield strength of the HS Fe 29 Ni 29 Co 28 Cu 7 Ti 7 HEA, which is comparable with those of some enhanced fcc HEAs/MEAs, is much higher than those of the single-phase fcc HEAs/MEAs.…”