RESUMEN
There have been very limited studies on plastic deformation mechanisms in single-crystalline high-entropy alloys (HEAs) with body-centered cubic (BCC) phases. We performed in situ uniaxial compression on single-crystalline BCC AlCrFeCoNi micropillars/nanopillars with three orientations (including [100], [110], and [111]) and diameters of 270-1583 nm, inside a scanning electron microscope. The experimental results showed the significant size effects on yield/flow stress and the remarkable strain hardening in these HEA micropillars/nanopillars. Especially, HEA micropillars/nanopillars with ⟨100⟩ orientation exhibited higher strain hardening exponents than BCC pure metals and Al0.7CrCoFeNi counterparts. A combination of transmission electron microscopy observations and large-scale atomistic simulations revealed that dislocation slip, reaction, tangling and accumulation, and solid solution effects are responsible for the observed size effects on yield/flow stress and remarkable strain hardening, but these dislocation mechanisms are dependent on nanopillar orientation. Our present study sheds light on the underlying deformation mechanisms in BCC HEA single crystals.
RESUMEN
Precipitation-hardening high-entropy alloys (PH-HEAs) with good strength-ductility balances are a promising candidate for advanced structural applications. However, current HEAs emphasize near-equiatomic initial compositions, which limit the increase of intermetallic precipitates that are closely related to the alloy strength. Here we present a strategy to design ultrastrong HEAs with high-content nanoprecipitates by phase separation, which can generate a near-equiatomic matrix in situ while forming strengthening phases, producing a PH-HEA regardless of the initial atomic ratio. Accordingly, we develop a non-equiatomic alloy that utilizes spinodal decomposition to create a low-misfit coherent nanostructure combining a near-equiatomic disordered face-centered-cubic (FCC) matrix with high-content ductile Ni3Al-type ordered nanoprecipitates. We find that this spinodal order-disorder nanostructure contributes to a strength increase of ~1.5 GPa (>560%) relative to the HEA without precipitation, achieving one of the highest tensile strength (1.9 GPa) among all bulk HEAs reported previously while retaining good ductility (>9%).