Deformation mechanisms of Mo alloyed FeCoCrNi high entropy alloy: In situ neutron diffraction

A FeCoCrNiMo2.3 high entropy alloy was processed by powder metallurgy with two conditions: hot extruded and annealed. In situ neutron Diffraction, together with electron microscopy, was used to study the deformation mechanisms and concomitant microstructural evolution for both conditions. The as-extruded alloy has a single face-centered-cubic structure with a calculated stacking fault energy of ∼19 mJ/m2. When the alloy is tensile deformed, nano-twins and microbands are induced, resulting in an excellent combination of strength and ductility. Annealing at 800 °C for 72 h led to an increase of the strength of the alloy, but a decrease of the ductility. This is due to the decomposition of the alloy after annealing, causing the formation of Mo-rich intermetallic particles and a decrease of the stacking fault probability. These results highlight that combined mechanisms (i.e. solute strengthening and twin/microband induced plasticity) can effectively improve both the strength and ductility of high entropy alloys.