Viscoelastic Damping in Defect-Engineered CoNiCrFeMn High Entropy Alloy by Molecular Dynamics Simulations

High-frequency mechanical vibrations and sound propagation in materials are governed by their viscoelastic behavior. Efficient viscoelastic damping is necessary to enhance the stability, safety, and service life of dynamic systems such as brake discs, shielding devices, high-frequency resonators, etc. Therefore, there is an increasing demand for the design and development of materials with high damping capability. Recently, viscoelastic studies in alloys have attracted a lot of attention as these materials possess simultaneously high stiffness and high loss tangent, thereby resulting in a high loss modulus. The inadequacy of the traditional alloys such as the low working temperature of Cu- based damping alloys, and anti-corrosion treatment of the Fe-based damping alloys have limited their applications. High Entropy Alloys (HEAs) exhibit simple solid solutions and excellent mechanical properties such as high hardness, high strength, good corrosion, and wear resistance and are good candidates for high-frequency damping applications. Moreover, defects such as stacking faults, twin boundaries, interstitials, and vacancies are intrinsic to crystals and have the ability to further enhance damping.<br/>In the present work, three defects namely stacking fault, edge dislocation, and vacancies were introduced in the FCC single-phase solid solution CoNiCrFeMn HEA to investigate its viscoelastic response. A Modified Embedded Atom Method (MEAM) potential was used to describe the interatomic interactions. Non-equilibrium molecular dynamics simulations via oscillatory shear deformation were performed to understand the viscoelastic behavior under a frequency range spanning 3 decades, from GHz to THz. It was noted that each defect exhibited a significant enhancement in damping over the defect-free alloy, while considered individually. However, the coexistence of all three defects dramatically improved the damping performance of the alloy up to 172% more compared to the defect-free structure. Below the peak damping frequency, the loss modulus was fitted successfully by power-law scaling. The enhancement in loss moduli for various defected structures was observed to result from the anharmonic coupling of phonon modes as verified by the mode-dependent Gruneisen parameters. The inclusion of defects also shifted the peak damping frequency to larger values. This work thus demonstrates that HEAs with carefully engineered defects have promising applications in damping high-frequency vibrations.