  In this study, we report on face-centered cubic structured CoCrFeNi
high-entropy alloy thin films with finely dispersed nano-oxide particles which
are formed by internal oxidation. Analytical scanning transmission electron
microscopy imaging found that the particles are Cr2O3. The oxide particles
contribute to the hardening of the film increasing its hardness by 14% compared
to that of the film without precipitates, through the Orowan-type strengthening
mechanism. Our novel approach paves the way to design medium- and high-entropy
alloys with high strength by making use of oxide phases.
