Micromechanics reveal strain rate dependent transition between dislocation mechanisms in a dual phase high entropy alloy

An equimolar NiCoFeCrGa high entropy alloy having dual-phase composition was studied, where the constituent phases exhibit distinct mechanical properties. Micropillars with various diameters were created from two differently heat treated samples, then they were compressed at slow strain rates, that revealed the material's limited sensitivity to size. On the other hand, increased strain rate sensitivity at high deformation speeds was observed, that differs substantially depending on the phase composition of the specimen. Dislocations within the two phases were studied by high resolution transmission electron microscopy and high angular resolution electron backscatter diffraction. The performed chemical analysis confirmed that slow cooling during casting create Cr-rich precipitates, that, contrary to traditional alloys, cause significant softening of the material.