A cuboidal B2 nanoprecipitation-enhanced body-centered-cubic alloy Al0.7CoCrFe2Ni with prominent tensile properties

Abstract

The present work reports a cuboidal B2-coherently-enhanced body-centered-cubic (BCC) alloy Al 0.7 CoCrFe 2 Ni with prominent tensile properties at both room (ultimate tensile strength  b = 1223 MPa and elongation to fracture = 7.9 %) and high temperatures. This multi-principal-element alloy is developed out of a cluster formula [Al-M 14 ]Al 1 issued from the cluster-plus-glue-atom model of a BCC structure. Here, the [Al-M 14 ] cluster is centered by Al, surrounded by fourteen average atoms M = Co 1/5 Cr 1/5 Fe 2/5 Ni 1/5 , and glued with one Al atom. Its excellent mechanical properties are attributed to a superalloy-like microstructure, characterized by cuboidal B2 nanoprecipitates coherently embedded in the BCC matrix.

The BCC/B2 Morphologies in AlxNiCoFeCr High-Entropy Alloys

“…Especially if the shape of the precipitates is closely related to the lattice misfit, ε, between the precipitated phase and the matrix phase [29,[31][32][33][34][35][36][37][38]. Generally speaking, a smaller …”

“…A smaller ε (ε < 0.10%) can produce another morphology of spherical particles coherently precipitated into the matrix. Only a moderate ε can produce cuboidal precipitates, as demonstrated by the fact that the cuboidal B2 nanoprecipitates are coherently embedded into the BCC matrix in the BCC Al 0.57 NiCoFe 2 Cr HEA with a ε = −0.38% [29]. …”

“…The FCC HEAs possess good ductility but lower strength, while the BCC/B2 HEAs have higher strength at the expense of ductility, as demonstrated by the fact that the equimolar AlNiCoFeCr HEA is very brittle with a nearly zero tensile ductility at room temperature due to a weave-like microstructure caused by spinodal decomposition of BCC and B2 phases [19]. However, changing the combination of TMs instead of Al could also make Al 0.7 NiCoFe 2 Cr HEA with a low Al content exhibit a BCC/B2-based structure [29]. More importantly, the unique morphology of the cuboidal B2 phase coherently-embedded into the disordered BCC matrix renders this HEA with both a higher tensile strength (σ UTS = 1223 MPa) and a good ductility of 8% at room temperature.…”

The BCC/B2 Morphologies in AlxNiCoFeCr High-Entropy Alloys

“…Especially, the shape of the precipitates is closely related to the lattice misfit, ε, between the precipitated phase and the matrix phase [28,[30][31][32][33][34][35][36][37]. Generally speaking, a smaller lattice misfit, ε, leads to a spherical shape, and when the misfit becomes larger, it is difficult to control the morphology of the precipitates, and the coherency between them will disappear gradually, resulting in coarse second particles finally.…”

“…The FCC HEAs possess good ductility but lower strength, while the BCC/B2 HEAs have higher strength at the expense of ductility, as exampled by the fact that the equimolar AlNiCoFeCr HEA is very brittle with a nearly zero tensile ductility at room temperature due to a weave-like microstructure caused by spinodal decomposition of BCC and B2 phases [19]. However, that changing the combination of TMs instead of Al could also make the Al0.7NiCoFe2Cr HEA with a low Al content exhibit a BCC/B2-based structure [28]. More importantly, the unique morphology of the cuboidal B2 phase coherentlyembedded into the disordered BCC matrix renders this HEA with both a higher tensile strength (σUTS = 1223 MPa) and a good ductility of 8 % at room temperature.…”