Deformation Mechanisms and Remarkable Strain Hardening in Single-Crystalline High-Entropy-Alloy Micropillars/Nanopillars

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 AlCrFeCo-Ni 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.

Automated summary

Limited studies have been conducted on plastic deformation mechanisms in single-crystalline high-entropy alloys with body-centered cubic phases. Experimental results have shown significant size effects on yield/flow stress and remarkable strain hardening in these HEA micropillars/nanopillars, especially those with<100> orientation. Dislocation slip, reaction, tangling, accumulation, and solid solution effects contribute to the observed size effects on yield/flow stress and strain hardening, but these mechanisms depend on nanopillar orientation.