Observation of phonon softening in CrCoNi medium entropy alloy

Medium entropy alloys (MEAs) are a class of single-phase multicomponent alloys with three elements, known for their distinctive mechanical and physical properties. Specifically, face-centered cubic (FCC) CrCoNi MEA exhibits remarkable tensile strength, uniform elongation, and fracture toughness. However, there is limited experimental understanding of the phonon behavior, which plays a vital role in thermal and elastic properties in MEAs. In this study, we measured the phonon density of states and phonon dispersion curves of CrCoNi MEA using inelastic neutron scattering. We have observed signatures of phonon softening near the Brillouin zone boundary, in comparison with phonon dispersions in FCC Ni and binary CoNi-based systems. We will discuss the influence of chemical disorder on the observed softening mode and its implications for the elastic and thermal properties of MEAs.