Viscoelastic damping in defect-engineered CoNiCrFeMn cantor alloy

Since their discovery in 2004, High-Entropy Alloys (HEAs) have shown immense promise in several cutting-edge engineering applications. In this work, Molecular dynamics (MD) simulations were used to study the frequency-dependent viscoelastic damping studies in defect-engineered face centered cubic, single-phase solid solution of CoNiCrFeMn HEA. Through detailed non-equilibrium oscillatory shear simulations in the frequency range spanning three decades (in the GHz to THz range), defect-free and defect-engineered structures demonstrate starkly contrasting mechanisms at disparate frequency regimes. In the high-frequency regime, each defect (vacancy, stacking fault and edge dislocation) contributed significantly to the enhancement in viscoelastic damping, as characterized by the loss modulus. With the most significant, multifold, enhancement observed when all three defects present. A well-defined peak was observed in the high-frequency regime followed by decaying loss moduli for all structures. However, in the low-frequency regime, there exist some special cases where the orientation of dislocations with respect to the shear direction enables facile gliding of dislocations, resulting in exceptionally large damping. Finally, we elucidated detailed damping mechanisms including the harmonic coupling of phonon modes at high frequencies and the evolution of defects, especially dislocations, at lower frequencies. HEAs are thus promising materials that offer precise control for damping applications through defect engineering.