  The exceptional mechanical strengths of medium and high-entropy alloys have
been attributed to hardening in random solid solutions. Here, we evidence
non-random chemical mixings in CrCoNi alloys, resulting from short range
ordering. A novel data-mining approach of electron nanodiffraction patterns
enabled the study, which is assisted by neutron scattering, atom probe
tomography, and diffraction simulation using first principles theory models.
Results reveal two critical types of short range orders in nanoclusters that
minimize the Cr and Cr nearest neighbors (L11) or segregate Cr on alternating
close-packed planes (L12). The makeup of ordering-strengthened nanoclusters can
be tuned by heat treatments to affect deformation mechanisms. These findings
uncover a mixture of bonding preferences and their control at the nanoscopic
scale in CrCoNi and provide general opportunities for an atomistic-structure
study in concentrated alloys for the design of strong and ductile materials.
